MANUAL OF LITHOLOGY: 
 
 TREATING OF 
 
 THE PRINCIPLES OF THE SCIENCE 
 
 WITH SPECIAL REFERENCE TO 
 
 MEGASCOPIC ANALYSIS, 
 
 BY 
 
 EDWARD H. WILLIAMS, JR., E.M., F.G.S.A., 
 
 Professor of Mining Engineering and Geology, 
 Lehigh University, South Bethlehem, Pa. 
 
 WITH SIX PLATES 
 
 SECOND EDITION. 
 FIRST THOUSAND. 
 
 NEW YORK : 
 
 JOHN WILEY & SONS. 
 LONDON CHAPMAN & HALL, LIMITED 
 1899. 
 
COPYRIGHT, 1895, 
 
 BY 
 
 EDWARD H. WILLIAMS, Ji 
 
 \AT 
 
 
 A 
 
 firaunworth, Mnnn ^f Barber, 
 
 Priuters and Bookbinders, 
 
 16 Nassau Street, Brooklyn, N. Y. 
 
PREFACE TO THE SECOND EDITION, 
 
 THE microscope has forced lithology and petrography 
 so widely apart that the layman is often at a loss to recog- 
 nize old acquaintances under new names. This edition of 
 Lithology is written on the same basis as the last for the 
 beginner in the subject who wishes a thorough knowledge 
 in the megascopic presentation of the subject, in a fuller and 
 more compact arrangement than can be obtained in geologi- 
 cal text-books. It is also designed for the engineer who 
 wishes to understand the valuation of rocks for economic 
 purposes. The arrangement is such that those who wish 
 to continue the work in the microscopic analysis of rock- 
 forming minerals, as taught in petrography, will have 
 nothing to unlearn. The reader is supposed to have a 
 practical acquaintance with megascopic crystallography 
 and mineralogy, the use of the blowpipe, and the ordinary 
 methods of chemical analysis, so that these subjects are 
 merely touched upon in the description of the more com- 
 mon megascopic rock-forming minerals. An addition has 
 been made in the line of the economic value of rocks, and 
 the body of the book has been entirely rewritten, and is 
 from five to six times the size of the former edition, so rap- 
 idly has the subject grown. Credit has been given for data 
 taken from other authorities. 
 
 E. H. W., JR. 
 LEHIGH UNIVERSITY, July 22, 1895. 
 
TABLE OF CONTENTS. 
 
 PAGE 
 
 INTRODUCTION, . , - . . . '.... . . i 
 
 PRELIMINARY DESCRIPTION, . . . . . . . . . 6 
 
 ROCK-FORMING MINERALS, . . ... . . . , . . . 14 
 
 GENERAL DEFINITIONS, . ; . . . . ... . ., 55 
 
 THE ROCKS, . . . ... . . x ' . . . 92 
 
 Primary Rocks, . . . . . . . . .' . 97 
 
 Acid Division Mica Rocks, . . % . . .... 107 
 
 Rhyolite-granite Series, . . . . . . . , 107 
 
 Intermediate Division Amphibole Rocks, . . . . . 144 
 
 Trachyte-syenite Series, . ...... 145 
 
 Phonolite-elaeolite-syenite Series, . e . . . 158 
 
 Mica-trap Series, ,. . . . . . . 174 
 
 Porphyrite Series, . - . . . . . . 178 
 
 Andesite-diorite Series, 182 
 
 Basic Division Pyroxene Rocks, . '. . . . . .213 
 
 Nephelinite-iolite Series, . . . . . . . . 214 
 
 Feldspathoid basalts, . . . . . , . . . 217 
 
 Tephrite-basanite-theralite Series, . . . ... 221 
 
 Basalt-gabbro Series, . . ^ . . . . , . 225 
 
 Extrusives, . " . . ... . . . 225 
 
 Plagioclase Group, , J . . , . . , . 226 
 
 Olivine Group, ' . . . . . . ., 233 
 
 Pyroxene Group, . . . , i . . ; 234 
 
 Intrusives, .. ,. . . . ,. . 234 
 
 Plagioclase Group, . , , " . . . 235 
 
 Olivine Group, . -. . , * .,' . . 249 
 
 Pyroxene Group, . . . . . . . , . 252 
 
 Magnetite Group, . . . '" . . . 252 
 
 Secondary Rocks, . . . 255 
 
 Debris Division, . . . . . . . . . . 259 
 
 Sedimentary Division, . . . . t 265 
 
 Metamorphic Division, ........ 324 
 
 Contact Series, ^30 
 
 Acid Series, .-.... 330 
 
 Basic Series, . . . . . . . . nee 
 
 Minerals as Rocks, ........ 371 
 
 SCHEME FOR DETERMINING THE PRINCIPAL ROCKS, . . . 382 
 
 ECONOMIC VALUE OF ROCKS, 39<2 
 
 INDEX OF AUTHORITIES, .... 401 
 
 GENERAL INDEX 4O5 
 
 v 
 
MANUAL OF LITHOLOGY. 
 
 INTRODUCTION. 
 
 THE tendency of modern rock analysis is toward a 
 simplification of the subject, and the discarding of useless 
 and misleading divisions and names. At present there 
 seems to be a reaction against separating dike-forms of 
 rocks from their massive states, the attempting to dis- 
 tinguish rocks on account of geological age, and the basing 
 a rock name on a chemical bulk analysis. The tendency in 
 metamorphism is backward to the old theories of primary 
 origin, and " eruptive " gneiss is no longer a misnomer to 
 many. It seems necessary to faintly outline the present 
 state of belief of petrographers on some of the above sub- 
 jects, so that the reason for the arrangement chosen in this 
 book can be understood, and the first subject will be in 
 regard to dike-rocks. This state is produced whenever an 
 eruptive is forced into or through a fissure whose walls are 
 approximately parallel to one another. Depending on the 
 depth of the fissure below the surface, its walls will be of 
 varying temperatures, and the fluid mass will be cooled 
 correspondingly rapidly or slowly ; but, whether slowly or 
 rapidly, the bulk of the intruded mass will be slight when 
 taken transverse to the cooling surfaces, and the crystal- 
 lization, at best, will not reach the development that obtains 
 in larger masses that cool more slowly ; so that dike-cooling 
 
2 MANUAL OF LITHOLOGY. 
 
 will give smaller sized grains. If the cooling is slow and 
 the walls heated, there may be a uniformity of grain across 
 the fissure ; but the fact that the mass has been cooled before 
 becoming stagnant at the point of consolidation will only 
 allow a uniformly small grain to form. This even grain has 
 been taken as a dike-facies when it depends on the heating 
 of the dike-walls to a degree corresponding to the temper- 
 ature of the intruded mass; and that is caused by the fissure 
 being deep-seated enough to be within the heated abysses, 
 or by so long a passage of the hot magma through the 
 fissure that the country-rock has been heated to a great 
 distance. This presupposes an escape of the magma at the 
 surface readily during the first part of the flow ; or tne in- 
 fluence of the walls would have cooled the mass and plugged 
 the fissure. We need, therefore, a hot liquid lava and a free 
 escape at the surface for the first portions of a flow resulting 
 in a final stagnation that crystallizes evenly across the dike. 
 It is seen at once that all dike-flows cannot follow this 
 sequence, owing to narrowness of fissure or coolness of 
 lava ; so that only some dikes have this facies. We find a 
 similar facies along the peripheries of bosses and large lac- 
 coliths; so that it is not due to the shape of the cooling 
 magma, but to the rapidity of cooling. 
 
 A late eminent authority objected to claiming so great 
 a metamorphic power for dikes, and especially for dike- 
 granite. He stated that the great effect of metamorphism 
 shown in the country of the dike-walls was not due to the 
 granite (which was probably a trachyte when intruded), but 
 to a subsequent regional metamorphism that affected both 
 dike and walls, altering the former to granite, and the latter 
 to its present condition. It would be sufficient to quote the 
 words of Dr. Barrois that regional metamorphism and con- 
 tact metamorphism are much the same thing ; but in this 
 case there is a misapprehension that will extend to others 
 
IN TROD UCTION. 3 
 
 and create a wrong impression. In answer it may be said 
 that it is more probable to imagine the extent of the 
 metamorphism due not to the fact that the granite is in 
 the dike form, but to the fact that dike-walls are some- 
 times heated, as above described ; that this heating from 
 passing hot fluid produces the metamorphism, and the 
 stagnant fluid crystallizes uniformly and sharply up to the 
 dike-walls. Against the argument of a metamorphosed 
 trachyte may be advanced the statement that the latter 
 supposition would not account for the sharpness of the 
 dike-walls, as regional metamorphism of a nature that 
 would produce the necessary mineral zones in the aureola 
 would more or less obliterate the walls, or cause a shading 
 from the granite facies to that of the metamorphosed walls, 
 and such changes are not found. It may also be advanced 
 that it does not require a greater amount of heat to meta- 
 morphose the walls in the one case than in the other, and 
 that it is as easy to suppose the walls heated before the 
 stoppage of the flow, either by the length of time during 
 which the flow passed, or from the fact that the whole 
 region was heated to a point just below metamorphism (by 
 orogenic or other causes) before the fracture and intrusion 
 took place, and that the intrusive supplied the needed 
 increment for metamorphism. It is also difficult to see how 
 regional metamorphism would produce an aureola and 
 zones about a cold dike of trachytic habit, and not extend 
 generally through the mass. 
 
 The attempt to separate dike-rocks from those filling 
 plugs is still more 'hard to understand, as both begin and end 
 alike, differ only in shape, and contain similar fillings. Dike- 
 rocks are generally accepted as fillings of fissures which 
 may have reached the surface and through which extrusives 
 passed. Lapse of time has allowed those surface states to 
 be denuded, and we have only the filled vent. 
 
4 MANUAL OF LITHOLOG Y. 
 
 The credit of destroying the idea that rocks can be 
 separated according to geological age belongs in a high 
 degree to American geologists. If we take the mixture of 
 mica, quartz, and feldspar which forms the rhyolite-granite 
 series, we are asked to believe that the quartz-porphyries 
 .are the extrusives of the granite in the past, and the rhyo- 
 lites in the present. We find quartz-porphyries as late as 
 the Eocene (in Elba); and the late G. H. Williams found in 
 the Archaean area of the South Mountain along the border- 
 line of Pennsylvania and Maryland pre-Cambrian rhyolites 
 devitrified and altered, but retaining lithophysas and flow 
 structure. These two examples, which demolish the hypo- 
 thesis in this group, are parallelled in other groups, so that 
 the American and English authorities do not allow group- 
 ings according to fancied geological ages. 
 
 Bulk analyses of rocks are given in the books on the 
 subject, and rock groups created from chemical differences. 
 The researches of Lang conclusively show that nothing can 
 ;be thus based, as the same rock will show a varying bulk 
 analysis when fresh and weathered, and the same mineral 
 group will vary widely in the components of a bulk analysis ; 
 while rocks of varying mineral composition will agree 
 closely in bulk analyses. The rock groups of the future 
 must, therefore, depend more on mineral than chemical 
 composition. While the majority of authorities define an 
 *' acid " rock as one whose bulk analysis shows a certain 
 percentage of silica, Lessing says that it is one that carries 
 a surplus of silica after saturating the bases, no matter how 
 great or small that may be. The terms " acid " and " basic " 
 .are indefinite terms, and bulk analyses are misleading. 
 
 .Sorby's theory of differentiation of magmas is rapidly 
 pushing its way to the front as a new basis for dividing 
 rocks, though how that is to be done is not yet sufficiently 
 plain. The theory as modified by Iddings is finding quite 
 
IN TROD UCTION. 5 
 
 general acceptance, and the work of the future may be 
 devoted to the study of Judd's " petrographic provinces.'" 
 It is possible that differentiation will finally take the subject 
 out of the hands of the average student, and that it will be 
 understood only by the expert with a microscope. It is a 
 matter of congratulation that the familiar rock names have 
 been left in the majority of cases, so that there is little to be 
 unlearned as the science progresses. In general it may be 
 said that modern progress has been towards simplicity of 
 arrangement. 
 
 In the following pages many rocks based entirely on 
 microscopic distinctions have been given for the purpose of 
 making this a complete book ; but in every case there is a 
 distinction between what can be seen by the eye (with a 
 lens) and by the microscope. The symbol (M) will be used 
 for whatever can be seen by the eye, and will be equivalent 
 to " megascopic," " by the eye," etc., while the lower-case 
 (m) will be equivalent to " microscopic," " by the micro- 
 scope," etc. In rock definitions these symbols will be freely 
 used, as well as in the discussion of states and varieties of 
 rocks and forms of minerals. 
 
PRELIMINARY DESCRIPTION. 
 
 Geology is the discussion of the history of the earth, and 
 of its life, from the earliest times. Geognosy, or structural 
 geology, is that branch which deals with the components of 
 the earth, their arrangement to form its structure, and the 
 development of the latter. The materials can be separated 
 into the envelope (air and water) and the litho sphere. It is 
 with the latter, principally, that structural geology has to 
 do, and this solid portion can be considered in two ways: 
 (i) as formed of individual rocks ; (2) as arranged in masses 
 or beds to form terranes (as used by J. D. Dana ; terrain of 
 C. D'Orbigny). Lithology is that division of geognosy which 
 treats of the rocks of the lithosphere as mineral aggregates, 
 under all conditions of hardness, and all states of aggregation 
 and consolidation. Aggregates totally lacking consolidation 
 are included ; so that loose bodies (as sand, clay), viscoids 
 (as asphalt, ice), organic bodies (as peat, guano), hard bodies 
 (as granite, trap) all are rocks. According to Lang, a rock 
 is an individual product of an uninterrupted rock-forming 
 process. An eruptive rock is formed at a single earth-throe ; 
 a secondary rock is formed from an eruptive by an uninter- 
 rupted action of natural forces. To fully understand rock 
 origin it will be necessary to include some definitions of 
 terrane structure, as well as some theories of the constitution 
 of the earth's interior. In distinction to lithology, there is 
 a second method of studying rocks by the microscope. This 
 is more of a mineral analysis than lithology, and bears to it 
 exactly the same relation that chemical analysis and blow- 
 
PRELIMINARY DESCRIPTION. 7 
 
 pipe reactions do. It investigates the origin of the rock as 
 well as its composition, and is, therefore, a higher branch of 
 the subject, called petrography. 
 
 Rocks are mineral aggregates, and may be simple, when 
 formed necessarily of one mineral, or composite, when made 
 up of two or more different ones. Rock definitions should 
 contain only the necessary and essential components, and all 
 accessory minerals should be placed in the following dis- 
 cussion. Necessary ingredients give the name to rock classes : 
 " A granite is composed of quartz and feldspar." Essential 
 ingredients mark rock species ; as the addition of hornblende 
 to the above makes hornblende granite ; the addition of augite, 
 augite-gramte. Accessory ingredients are local in their oc- 
 currence, or inconsiderable in amount ; but, when more than 
 usually abundant, may form rock subspecies ; as the presence 
 of considerable hypersthene in augite granite makes hyper- 
 f^^-augite-granite ; or an abundance of garnets in mica- 
 schist makes garnetiferous mica-schist. Necessary and es- 
 sential ingredients may be further defined by saying that a 
 change in the former would throw the rock into another 
 class, and in the latter into another species. A rock may 
 have the same mineral as necessary and accessory, or as 
 -essential and accessory ; as quart '^-schist must necessarily 
 have quartz ; but veins of quartz traversing such a schist 
 are but the filling of a fracture that may run into adjoining 
 rocks of a different composition, and are, therefore, only 
 in the slightest degree accessory. In the resolution of 
 pyroclasts, or a partly solidified magma at depths in the 
 arth, there may be mineral components more resisting 
 than the bulk of the mass, and these will float in the 
 magma and be etched (corroded) by it ; or in the case of an 
 intratelluric crystallization before differentiation, or the 
 eruption of magmas of different composition through the 
 same vent and at the same time, there may be a similar 
 
8 MANUAL OF LITHOLOGY. 
 
 placing of the intratelluric phenocrysts in a bath differing 
 from the one in which they formed, and a similar etching 
 will result. M-Levy and Fouque apply the term allogenic 
 to all crystals formed at such different periods as would cover 
 the first supposition ; but the term will not apply to those 
 similar ones formed through corrosion in a differentiated 
 portion of the same mass. Minerals may also be classed as 
 primary and secondary. The former are crystallizations from 
 the original magma before solidification ; the latter, due to 
 causes acting after solidification. These causes may be : 
 
 (a) Growths about the original grains or crystals, by 
 which fetsites have been devitrified and changed to quartz- 
 porphyries ; sandstones have been altered to quartzites, as 
 at Bethlehem, Pa., in this case the growths are of the 
 same mineral material. 
 
 (b) Growths of different mineral matter about crystals to 
 form paramorphs. 
 
 (c) Infiltrations from the country-rock, or from the interior 
 of the rock itself, which crystallize in the openings of the 
 rock (vesicles, pores, cavities, fissures, cracks, joint planes, 
 etc.) to form amygdaloids, druses, geodes, nests, strings, etc., 
 as agate, zeolites. 
 
 (d) Replacements of mineral matter without changing the 
 form of the original mineral, as pseudomorphs, as in the 
 pyritiferous porphyry of Leadville, where pyrite forms 
 pseudomorphs after hornblende and biotite. 
 
 The following definitions and classifications are based on 
 work with the unaided eye (megascopic analysis), though an 
 appeal to the microscope will be taken in the discussion of 
 the theories of rock-formation ; but before entering upon 
 them it is necessary to touch upon that branch of lithology 
 which treats of the individual components of rocks, mineral- 
 ogy, as far as the description of the species common to rocks, 
 and called rock-formers, and the manner in which they occur 
 
PRELIMINARY DESCRIPTION. 9 
 
 in rocks. The student in mineralogy pays attention to the 
 crystallographic, optical, physical, and chemical characters 
 of the mineral as an individual, crystallizing with freedom, 
 and uninfluenced by association with others in process of 
 formation. If exceptions occur, they are noted as foreign 
 to the usual habit. Mineralogy from a lithological stand- 
 point is another study, as all of the minerals which are rock- 
 formers must of necessity mutually influence one another ; 
 so that the first thing to be noted is the shape in which the 
 mineral will be found in rock masses. The next thing of 
 importance is a method of isolating mineral species for 
 inspection or analysis. The only method of inspection here 
 treated is by the pocket lens. The blowpipe and chemical 
 tests are the same as in mineralogy. It is well to note that 
 the rapidity of response to the latter depends on the ratio of 
 the extent of surface exposed to the volume of the mineral. 
 This increases with the extent of comminution; so that 
 powdered forms are most quickly acted upon by solvents. 
 In crushing specimens for chemical tests the powder should 
 be fine enough to ensure definite and rapid reaction ; for 
 physical tests the product must retain as sharp an outline 
 and as great freedom from dust as possible. A rough crushing 
 through rolls frequently separates the component minerals 
 in grains of various sizes, and these can be separated by 
 classification through screens. Woven wire can be procured 
 with a mesh of I-.2 mm., and bolting-cloth of various grades 
 to still finer sizes. Screens need not exceed 2^-3 inches in 
 diameter. A tinsmith can make a series of screen-frames for 
 a field outfit that can be readily renewed at any time, though 
 the wear is insignificant. Make a template by turning one 
 end of a piece of oak two inches square and six inches long 
 to form a cylinder two inches in diameter, and a scant half 
 inch long, and have the tinsmith solder half-inch wide strips 
 of light tin so as to exactly fit the cylinder. Make the same 
 
IO MANUAL OF LITHOLOGY. 
 
 number of small cylinders, of the same length and \-^ inch 
 greater diameter. Place a smaller ring on the template, and 
 cut from the screen material a circle four inches in diameter. 
 If it be of bolting-cloth, lay it centrally over the ring, and 
 slip over cloth and ring one of the larger rings, and drive 
 down with a few taps of a light hammer. The cloth will be 
 stretched and retained between the two rings, and when 
 worn out can be replaced by a new piece. In the case of 
 the wire cloth the edges must first be bent over the template 
 with the fingers, and then placed as above described. This 
 series of screens can be arranged from coarse to fine above 
 one another by procuring tin cylindroids (slightly conical) 
 two inches long, with the larger end fitted to the outside of 
 the screens, and the smaller end to the inside of the same. 
 Any number of screens can thus be arranged in a set, and 
 the ends of the top and bottom ones closed by caps, so that 
 no dust will escape on shaking a mixture placed in the upper 
 and larger screen. On separating the screens each will hold 
 the next larger class, and these may be sorted in any one of 
 the many varieties of laboratory sorters with ascending 
 currents. The most common way is to use a solution of 
 some salt which gives a definite and high specific gravity. 
 The requirements of such a solution are that it shall be as 
 harmless as possible ; that it shall be stable under ordinary 
 conditions of temperature ; that it shall have no effect on the 
 minerals separated ; that they, in turn, shall not react upon 
 it ; that diluting it will not alter its composition ; and that 
 evaporation will bring it back to its condition before dilution. 
 D. Klein, in 1881, proposed a solution that now bears his 
 name, which fulfils the above conditions, and can be diluted 
 with water. There are other solutions of different sp. grs.; 
 but they require some other diluent, are less stable, or are 
 noxious. Kleins solution is formed by dissolving a very 
 
PRELIMINARY DESCRIPTION. II 
 
 soluble borotungstate of cadmium in slightly less than ten 
 per cent, of its weight of water at 22 C. At 15 C. it has a 
 sp. gr. of 3.28 ; but by evaporating over a water bath till 
 oli vine floats in the warm solution it has, on cooling, a sp. 
 gr. of 3.6. By adding water the gravity can be reduced to 
 any required figure, and evaporating will restore it again. 
 In using this or any other solution that can be changed by 
 dilution, and when a certain sp. gr. is to be obtained, we 
 place on the surface a considerable fragment of a mineral 
 with density slightly greater than that desired, and dilute 
 by single drops till the mineral sinks. It must be kept in 
 mind that a number of circumstances may affect the result, 
 and that the sorts may not be exactly what we think them 
 to be , as (i) the buoyant effect of a liquid increases quite 
 rapidly with fineness of crushing, as is well known in ore- 
 dressing ; (2) the buoyant effect is greater in highly cleavable 
 minerals (micas) than in others of the same density that 
 break in other forms ; (3) minerals frequently hold other 
 minerals as inclusions ; (4) the fragments may be mixtures 
 of widely varying minerals, so arranged as to have a medium 
 density ; (5) incipient weathering, metachemism, etc., may 
 have set in. Minerals with magnetic properties can be re- 
 moved from the rock powder by a magnet (magnetite, 
 pyrrhotite, etc.). 
 
 The value of chemical analyses depends on how they are 
 made whether " bulk analyses," where the sum of the ele- 
 ments or their oxides for the whole rock is obtained ; or each 
 mineral is isolated as far as possible and its composition 
 learned. It has been long known that there was too much 
 variation in the silica and other ingredients of rocks, granite, 
 for example, to allow a " type analysis " to be adopted, 
 and lately the majority of authorities have abandoned the 
 attempt to reconstruct the mineral character of a rock from 
 
12 MANUAL OF LITHOLOGY. 
 
 its chemical bulk analysis, as many rocks of greatly varying 
 mineral composition have nearly the same bulk analysis. 
 Iddings is quoted as saying that the variations in the rapidity 
 of cooling the fluid mass cause the variations in mineral 
 composition, independent of the pressure exerted. Bulk 
 analyses, therefore, should be used with caution, and as 
 checks, or for purposes -of comparison ; as a fresh and 
 weathered fragment of the same rock, and taken from places 
 adjacent to one another, will give greatly varying bulk an- 
 alyses, and might throw the specimens into different species 
 were they to be taken alone. 
 
 The examination of mineral powder of varying coarseness 
 can best be made on paper, using a color strongly contrast- 
 ing with that of the powder unless specimens of it are to be 
 preserved, and those can be mounted on glass slides with 
 Canada balsam. Microchemical tests can be made in the 
 field with a good lens and glass slides, and, following the 
 suggestion of Bolton, a bottle of finely powdered citric acid 
 should be carried for acid tests (carbonic acid), which can be 
 applied to the streak of the rock, or its powder placed on 
 glass and both wet. A solution of rock powder in acid will 
 leave behind all insoluble residue, which can be examined 
 by the lens. The two oxides of iron can be detected in a 
 similar way by the use of HCi and cyanide salts of potash. 
 This list can be further extended ; but it is sufficient to say 
 that the expert in qualitative analysis can devise similar tests 
 on slides that will give under the lens a good idea of the 
 composition of the rock in case it be non-crystalline or com- 
 pact. Boricky suggests the action of pure hydrofluosilicic 
 acid on silicates in minute fragments, as follows : fix a minute 
 particle on a glass plate with balsam and moisten with a drop 
 of acid ; place under a bell glass near a vessel with water 
 and stand for twenty-four hours ; then dry by placing over 
 calcium chloride, and examine with a lens, when fluosilicate 
 
PRELIMINARY DESCRIPTION. 13 
 
 of potassium will show as cubes ; of sodium as hexagonal 
 prisms. Nepheline compounds when powdered and touched 
 with HC1 will, on drying, show chloride of sodium crystals. 
 Klemert and Renard's work on microchemistry (Brussels, 
 1886) covers the subject fully. It is needless to add that the 
 .blowpipe set should always be on hand for mineral analysis. 
 In studying the shape of an " aureola " of contact meta- 
 morphism in the field, it may be well to bear in mind that 
 heat transmission in slate and ordinary shales is four times as 
 rapid with the bedding planes as across them. We can find 
 the values of heat transmission in any rock in the laboratory 
 by covering with wax one side of moderately thin sections, 
 made at various angles with the bedding-planes, or along 
 sections where the rock seems to show variations in struc- 
 ture or density, and drilling through the middle of each a 
 hole of sufficient size to pass a platinum wire, which will be 
 heated by an electric current. The heat will be transmitted 
 more rapidly in a thin than a thick section with a given size 
 -of wire, and the relative rates of transmsision will be marked 
 by the shape of the melting wax. If the platinum wire be no 
 longer than the thickness of the section, there will be no 
 heating of the wax by radiation. The record can be kept by 
 photographing the specimen, or dusting upon the melted 
 wax a powder of a different color. A series made at vary- 
 ing angles will give the heat values for that rock, and their 
 comparison with similar ones of the same species from an- 
 other locality may show differences due to moisture, density, 
 etc., as heat travels faster in wet than in dry rocks : in dense 
 than in loose. 
 
ROCK-FORMING MINERALS. 
 
 Minerals can be divided into two classes : those which 
 are the most abundant, arid those which are the most com- 
 mon. The most abundant minerals are generally grouped 
 in a few species ; the most common minerals may never be 
 visible to the eye in the majority of cases ; may exist always 
 in a minute proportion, and yet be always present. Under 
 the modern theory of crystallization from a perfectly fluid 
 magma in the hot abysses of the earth's crust it is decided 
 that the most basic combinations are first to form, so that 
 they are frequently included within those forming later. If 
 we take into consideration the minerals of common occur- 
 rence, as iar as that term stands for generality of occurrence, 
 we shall find that our list contains species not readily seen 
 with the eye or lens, as magnetite, titanite, specular hematite, 
 apatite, allanite, zircon, and olivine. These are among the 
 first to form in the fluid magmas. If we arrange the min- 
 erals in the order of their prominence as rock-formers, we 
 shall find that the ( M) species of common occurrence are 
 quartz, feldspars, micas, amphiboles, pyroxenes, calcite, and 
 dolomite ; those of frequent occurrence, nepheline, leucite, 
 melilite, sodalite, haiiyne, olivine, chlorite, talc, serpentine, 
 hydromicas, garnet, apatite, epidote, magnetite, ilmenite, 
 zircon, and tourmaline ; those occurring as rocks of large 
 extent, by themselves, calcite, dolomite, magnesite, cryolite, 
 asphalt, coal, iron ores, salt, bauxite, sulphur, and a few 
 sulphides. 
 
 14 
 
ROCK-FORMING MINERALS. 1 5 
 
 I. Quartz. Rhombohedral. It occurs (i) phenocrystal- 
 line : 
 
 (a) As an independent rock in veins, beds, and masses of 
 primary or metamorphic origin ; 
 
 (b) As a necessary component in many primary rocks, and 
 especially in the metamorphic schists, e.g., granite, gneiss. ; 
 
 (c) As an essential element in many rocks to form species 
 of an otherwise quartzless class, as quartz-basalt, quartz- 
 diorite ; and 
 
 (d) As principal ingredient in many clastic rocks (sand- 
 stones, conglomerates), and as sand and gravel. 
 
 It occurs (2) cryptocrystalline and amorphous : 
 
 (a) As agate, which is a variegated combination of alternate 
 layers of common quartz (amethyst, or chalcedony) with 
 jasper, carnelian, etc., formed usually in the amygdaloidal 
 cavities of eruptive rocks, as geodes, or in metallic veins. 
 The extensive establishment for manufacturing articles from 
 agate at Oberstein long since exhausted the local deposit, 
 and for many years the supply has come from the volcanic 
 rocks of Uruguay. Agate is also found in the similar rocks 
 of Iceland, the Faroe Islands, and (from the decomposition of 
 the rocks) in the sands of Lake Superior and the northern 
 part of the Mississippi River. Moss agates are not banded. 
 
 (b) As jasper (bright red), flint (grayish blue to black from 
 carbon), and chert, or hornstone (gray, yellow, green, red, 
 brown, black). Jasper is generally associated with iron ores, 
 as it obtains its color from anhydrous sesquioxide of iron, 
 and can be traced by regular gradations from a slightly fer- 
 rated cryptocrystalline form of quartz to a slightly siliceous 
 hematite, as the ferric solutions have more and more re- 
 placed silica by metachemism. It occurs under the same 
 conditions as hornstone, as concretions and layers in rocks. 
 Flint occurs as concretions in calcareous sediments, which, 
 in some cases, have been formed from the spiculas of sih- 
 
l6 MANUAL OF LITHOLOGY. 
 
 ceous sponges. The principal locations are the Chalk of 
 northern Europe, and the Upper Jurassic of Bavaria. 
 Hornstone is not so tough as flint, and breaks with a more 
 splintery fracture. It is abundant in the Siluro-Cambrian 
 limestone of the eastern part of Pennsylvania, and is the 
 form of quartz frequently met with in petrified wood. 
 Basanite is a black jasper. 
 
 H. 7 ; Gr. 2.5-2.8, average 2.6. Colorless and limpid, or 
 variously colored. Comp. SiO,. Luster vitreous, sometimes 
 resinous or waxy, especially on the surface of fractures. 
 
 Bp. Crystalline variety : alone, unaltered ; with soda dis- 
 solves with effervescence ; untouched by microcosmic salt ; 
 cryptocrystalline variety : with borax dissolves to a clear 
 glass. Chem. Crystalline : soluble in HF alone ; cryptocrys- 
 talline : slightly acted upon by caustic alkali. 
 
 Weathering. Crystalline : unchanged, though crystals 
 have been found with corroded edges ; cryptocrystalline : 
 forms a white crust, as in flints. 
 
 Associated with almost every other mineral except 
 ieucite, nepheline, and melilite ; but it is more commonly 
 found with orthoclase and the acid silicates. It frequently 
 occurs with tourmaline, rutile, cassiterite, and topaz. It is 
 found more frequently with hornblende than pyroxene, with 
 muscovite than biotite, and seldom with olivine. 
 
 2. Tridymite. Hexagonal. Tabular crystals, grains. 
 H. 7 ; Gr. 2.28-2.33. Colorless. Luster of fracture, vitreous ; 
 of face, pearly. Fracture conchoidal. Comp. SiO 2 . 
 
 Bp. Infusible ; with soda fuses with effervescence to a 
 colorless glass. Chem. Pure silica, soluble in a boiling 
 solution of sodium carbonate. 
 
 Weathering. Gradually changes from colorless to white. 
 
 Tridymite occurs generally in acid extrusive rocks in 
 thin minute glassy hexagonal crystals. It has been found in 
 the massive states of these rocks and in volcanic ash ; also 
 
ROCK-FORMING MINERALS. I/ 
 
 as enclosures in opal and quartz. It is a frequent com- 
 ponent of rhyolites, andesites, and trachytes. 
 
 3. Opal. Massive, amorphous. 
 
 H. 5.5-6.5 ; Gr. 1.9-2.3. Variously colored, colorless, or 
 characterized by a rich play of colors that is termed " opal- 
 escent." Transparent to opaque. Luster usually waxy or 
 greasy, sometimes resinous and vitreous. 
 
 Bp. Most varieties decrepitate on heating, and yield 
 water in the matrass ; infusible; become opaque, except the 
 yellowish varieties, which contain hydrated sesquioxide of 
 iron and turn red ; there is no change of color. Chem. 
 Amorphous silica combined with non,essential water, which 
 may vary from 2-20 per cent, but usually varies from 3-9, 
 and a small amount of coloring matter. It differs from 
 quartz in being soluble in a solution of caustic potash, 
 from which it can be precipitated by sufficient ammonium 
 chloride, and in being more soluble in heated alkaline 
 waters. 
 
 Weathering. Forms a colorless crust on the earthy and 
 porous solid forms which are colored. Is dissolved by alka- 
 line waters and disappears when in the form of ooze. 
 
 Opal occurs (i) as metachemic exfiltrations in eruptive 
 rocks, (a), as precious opal, which fills vesicular cavities or 
 clefts in trachytic rocks, as in Hungary and Mexico, and 
 sometimes in basalt ; (), as hyalite, a transparent and color- 
 less form which is found under similar conditions in basaltic 
 rocks, and with a globular, reniform, botryoidal, or stalac- 
 titic structure. 
 
 It occurs (2) in metamorphic rocks, as in some slates and 
 crystalline rocks. The " Guinea quartz " of the rocks 
 associated with the iron ores of central Virginia is said to 
 be opal. 
 
 It occurs (3) in petrifactions where the cellulose of wood 
 has been replaced by this soluble silica. 
 
18 MANUAL OF LITHOLOGY. 
 
 It occurs (4) from the decomposition of siliceous minerals 
 of volcanic rocks to form fiorite, which is similar to hyalite. 
 
 It occurs (5) in concretionary deposits about the Iceland 
 and Yellowstone geysers under the name of geyserite. This 
 is soft when first formed, but hardens on exposure ; color 
 white or grayish ; stalactitic, massive (compact and scaly), 
 usually opaque, sometimes crumbly on drying. 
 
 It occurs (6) in organic aggregates, as the skeletons of 
 hexactinellid sponges ; the shells of radiolarians and diatoms, 
 to form tripoli or randanite and through the agency of con- 
 fervid algas to form geyserite. 
 
 THE FELDSPARS. 
 
 After quartz this series is the most important of rock- 
 formers, and especially in eruptives, of which the larger 
 proportion is a feldspar. Crystallographically it is divided 
 into two groups, the monoclinic, or (from the principal type) 
 the orthoclases, and triclinic, which is further divided into the 
 anorthoclases and the plagioclases. 
 
 In the orthoclases the angle measured over the two most 
 perfect cleavage planes is 90 ; in the anorthoclases it is 
 slightly, and in the plagioclases considerably, less than that 
 angle. All feldspars tend to form twins, and in some cases 
 the duplication is marked. 
 
 THE ORTHOCLASES. 
 
 These are orthoclase and sanidine. The former occurs 
 usually in the rocks of the Archaean and in the intrusives, 
 the latter in the extrusives. Orthoclase even when fresh 
 never has the glassy habit of sanidine, and approaches it 
 most nearly in orthophyric porphyries. 
 
 4. Orthoclase (Potash Feldspar). Monoclinic. 
 
 H. 6 ; G. 2.5-2.56. Transparent-translucent. Colorless, 
 more frequently greenish white or flesh-red. Luster vitreous, 
 sometimes pearly on cleavages. Comp. KAlSi 3 O 8 . 
 
ROCK-FORMING MINERALS. 19 
 
 Bp. Fus. 5 on thin edges to a dull porous glass ; with 
 microcosmic salt, soluble with difficulty, leaving a skeleton 
 of silica ; with cobalt, fused edges are colored blue. Chem, 
 Untouched by acids, except HF, which completely decom- 
 poses it ; decomposed by fusion with alkaline carbonates. 
 
 Weathering. Decomposes with comparative rapidity by 
 removal of the alkali, and changes to kaolin more readily than 
 albite ; but less so than labradorite, anorthite, and oligoclase, 
 
 It is always more or less crystal in porphyries and por- 
 phyritic schists. In massives it loses its crystal form with 
 the increasing granularity of the mass, and never holds it in 
 non-porphyritic schists. The crystals are frequently broken 
 in massives from movement of the magma, and in schists 
 from orogenic movements ; but in the latter case the edges 
 alone suffer. It twins most commonly after the Carlsbad 
 law, less commonly after that of Baveno, least so after that 
 of Manebach. It can be separated from the lime-soda feld- 
 spars by classification and sorting when the classification 
 ratio is small. It can, further, be distinguished from them 
 by the absence of striations, which generally exist in the 
 plagioclases from their peculiar (albitic) twinning ; but the 
 flesh-red variety (or rather mixture) perthite, from Perth 
 (Upper Canada), Egypt, etc., shows what seem to be stri- 
 ations, from the intercrystallization of parallel laminae of 
 orthoclase and albite. Orthoclase in quartzose eruptives is 
 associated with hornblende rather than pyroxene. Potash 
 feldspar and potash mica are commonly associated. In the 
 older eruptives it occurs with nepheline more frequently 
 than do the plagioclases. 
 
 5. Sanidine (Potash-soda Feldspar). Monoclinic. Tab- 
 ular crystals, grains. 
 
 It behaves like orthoclase with the exception of showing 
 more soda. Luster vitreous. Color grayish, yellowish white. 
 
 It occurs in extrusive rocks, as phonolite, trachyte, 
 
2O MANUAL OF LITHOLOGY. 
 
 pitchstone, etc. ; has a fissured appearance due to the flow 
 subsequent to crystallization ; is found with quartz, plagio- 
 clase, nepheline, leucite, haiiyne, and the black bisilicates. 
 
 THE ANORTHOCLASES (Parorthodases, Zirkel). 
 
 These are all triclinic, but with slight deviation from a 
 monoclinic habit, and their cleavage angle differs so little 
 from that of orthoclase that they cannot be placed with the 
 plagioclases. Some authorities hold that they are ortho- 
 clases deformed by slight pressure ; as orthoclase under 
 pressure assumes the microstructure of microcline, and the 
 others of the group are monoclinic on heating. Zirkel 
 rightly objects to the prefix an-, as it indicates a divergence, 
 not a great similarity, and suggests par orthoclase. 
 
 6. Microcline (Potash Feldspar.) Triclinic. Never in 
 perfectly bounded crystals ; usually in irregular grains ; 
 twinned to form polysynthetic masses with both albite and 
 pericline, which (masses) twin according to the three laws 
 as with orthoclase. 
 
 H. 6-6.5 5 Gr. 2.54-2.57. Fracture uneven. Brittle. 
 Luster vitreous, sometimes pearly. Color white to yellowish, 
 red, green ; by transmitted light colorless. Transparent- 
 translucent. Comp. KAlSi 3 O 8 , like orthoclase, but carrying 
 soda up to 5$, and lime to \%. Bp. and chem. like orthoclase. 
 
 Microcline can only be safely distinguished from ortho- 
 clase by the microscope, as it occurs with it, and under 
 similar conditions, so that it frequently replaces it. It is 
 generally the feldspar in graphic granite (pegmatite) ; is 
 common to granites, gneisses, syenites, and elaeolite-syenites ; 
 less common in porphyries, and then only in the intratelluric 
 crystals ; almost wanting in the groundmass. It does not 
 replace sanidine in the extrusives. Some authorities doubt 
 the alteration of orthoclase to microcline by pressure, as it 
 is found in cavities in rocks. 
 
ROCK-FORMING MINERALS. 21 
 
 7 and 8. Anorthoclase and Cryptoperthite. Two 
 
 species have thus far been agreed upon in the potash-soda 
 mixtures, and a variety of names have been given them. 
 Following Brogger, they are a potash-soda variety, cryptoper- 
 thite, and a soda-potash variety, microperthite (anorthoclase of 
 Rosenbusch, parorthoclase of Zirkel). They are usually (m), 
 though Fouque" reports anorthoclase crystals from Fayal 
 5 mm. long and 2 mm. thick. 
 
 Cryptoperthite (potash-soda variety) is assumed to be an 
 interlamination of plates of orthoclase (or microcline) and 
 albite of such minuteness as to be invisible under the 
 microscope, and to act as a homogeneous body. The 
 characteristics are similar to those of microcline. Anortho- 
 clase (soda-potash variety), according to Fouqu, has Gr. 
 2.547-2.620 the heavier specimen coming from an olivine- 
 andesite. The average is 2.580, that of microcline being 
 2.560. They twin polysynthetically, and the mass thus 
 formed twins according to the three laws as with orthoclase. 
 They are found in augite- and hornblende-andesites, augite- 
 syenites, trachytes, rhyolites, and peculiar rocks of the 
 island of Pantelleria called pantellerites. 
 
 THE PLAGIOCLASES. 
 
 The members of this group occur crystal, granular, 
 and cryptocrystalline to compact. They are mixtures of a 
 typical albite (L) and anorthite (N), as follows : 
 
 L=NaAlSi s O 8 
 N=CaAl 2 Si,0 8 
 
 Cleavage Angle. 
 
 Albite varies from L,N to L 8 N t 86 24' 
 
 Oligoclase " I^N, " I^N, 86 08' 
 
 Andesine " L 3 N, " L.N, 86 14' 
 
 Labradorite " L t N, " L,N 2 86 04' 
 
 Anorthite " L t N. " L.N, 85 50' 
 
MANUAL OF L1THOLOGY. 
 
 On a fresh fracture, when the light falls somewhat ob- 
 liquely on the basal (cleavage) plane, a striation generally 
 .appears, which is due to polysynthetic twinning of thin 
 laminas. While this is an indication of the group, its 
 absence is not an indication of another group, as it is not 
 quite universal. The crystals are never so large as the 
 large orthoclases ; but they show the same fractures. The 
 microscope has shown that Breithaupt's laws of paragenesis 
 are not universal ; yet it can be noted that, as far as the un- 
 aided eye is concerned, the more acid plagioclases are the 
 more usually found with orthoclase and quartz ; while the 
 more basic, as labradorite and anorthite, are generally absent 
 under similar circumstances. The decomposition of rocks 
 and resulting metachemic formation of secondary minerals 
 frequently allows a determination of the ingredients of com- 
 pact eruptives with a high degree of certainty, as shown by 
 the microscope, or by following the ,mass to its centre 
 where the crystals are large enough to be readily recog- 
 nized. In some cases the materials for the secondary 
 minerals have been leached from the country rock of the in- 
 jected eruptive, and some authorities would extend this to 
 all cases ; but the fact that certain secondary minerals seem 
 to favor rocks of definite mineralogical and chemical com- 
 position points to an origin within the rock. It is generally 
 the case that an abundance of calcite or calcareous zeolites 
 (chabazite, phillipsite, stilbite, etc.), in a compact basic erup- 
 tive enclosed in non-calcareous walls, is due to the decom- 
 position of the minerals in the rock itself, and generally 
 indicates the presence of a lime feldspar. 
 
 Association will frequently enable us to detect an obscure 
 Jorm of this group, as we find together frequently orthoclase 
 .-and oligoclase, or orthoclase, oligoclase, and hornblende ; 
 Jabradorite and pyroxene or hypersthene ; while we less 
 seldom find together labradorite or anorthite and quartz, 
 
ROCK-FORMING MINERALS. 2$ 
 
 or orthoclase and leucite, oligoclase and leucite or nephe- 
 line, etc. According to rapidity of weathering, the feld- 
 spars can be arranged in the following order, beginning 
 with the most readily decomposed : labradorite, oligoclase, 
 orthoclase, albite. If there be two feldspars in a rock and 
 one be weathered, it may be possible to determine it by the 
 unweathered one, from the general habit of association, to- 
 gether with the density of the rock. 
 
 9. Albite (Soda Feldspar). 
 
 H. 6-6.5 ; Gr. 2.62-2.65. Luster pearly on cleavages, 
 otherwise vitreous. Color generally white, sometimes 
 bluish, gray, reddish, greenish, green, but colorless by 
 transmitted light when thin, as is the case of all the group. 
 Transparent-subtranslucent. Fracture uneven. Brittle. 
 
 Bp. Fus. at 4 to a colorless glass and gives a strong 
 flame reaction for Na. Chem. Untouched by acids. 
 
 It is found in granites and gneisses and the crystalline 
 -schists ; in contact zones of diabase ; in trachytes, andesites, 
 phonolites, granular limestones, etc. Untwinned crystals are 
 rare. Not weathered easily. 
 
 10. Oligoclase (Soda-lime Feldspar). 
 
 H. 6-7 ; Gr. 2.65-2.67. Luster vitreo-pearly or waxy to 
 vitreous. Color usually white tinged with shades of grayish 
 green, gray, green, and red. Transparent-subtranslucent. 
 Fracture conchoidal, uneven. 
 
 Bp. Fus. 3.5 to clear enamel-like glass. Chem. Scarcely 
 affected by acids. 
 
 It is necessary in diorite, trachyte, and andesite ; is found 
 with orthoclase in granite and syenite ; is seldom found with 
 leucite and nepheline. Occurs in massive grains and crys- 
 tals, and twins according to the Carlsbad, albite, and peri- 
 <:line laws. 
 
 Weathers more readily than orthoclase and albite to 
 kaolin and light-colored mica. 
 
24 MANUAL OF LITHOLOGY. 
 
 11. Andesine (Soda-lime Feldspar). 
 
 H. 5-6; Gr. 2.68-2.69. Color and luster similar to 
 oligoclase. 
 
 Bp. Fus. 5 on thin splinters ; with borax forms a clear 
 glass. Chem. Soluble in HF; partially in the other acids. 
 It occurs similarly to oligoclase in the eruptives and 
 gneisses; weathers easily to kaolin, and twins like 
 oligoclase. 
 
 12. Labradorite (Lime-soda Feldspar). Rarely crystal ; 
 lath-shaped ; generally massive-granular; sometimes crypto- 
 crystalline. 
 
 H. 6: Gr. 2.70-2.72. Luster pearly on basal cleavage; 
 otherwise vitreous-subresinous. Color gray, brown, green- 
 ish, rarely white. Usually a play of colors on cleavage 
 faces. Translucent-subtranslucent. 
 
 Bp. Fus. 3 to colorless glass. Chem. When fresh is 
 with difficulty soluble in HC1, and leaves residue ; when 
 powdered is easily soluble in hot HC1. 
 
 Weathers like anorthite. It is confined to the basic 
 eruptives and schists, is necessary to basalt and dolerite, 
 abundantly developed in the Archaean rocks of Canada, and 
 occurs chiefly in quartzless rocks, and seldom in those carry- 
 ing nepheline and leucite. 
 
 13. Anorthite (Lime Feldspar). Generally non-crystal, 
 and in lath-shaped, granular, and spathic forms. 
 
 H. 6-7 ; Gr. 2.66-2.78. Luster somewhat like labradorite. 
 Color white, grayish, reddish. Transparent-translucent. 
 Fracture conchoidal. Brittle. 
 
 Bp. Fus. 4.5-5 to colorless glass. Chem. Decomposed 
 by HC1 with separation of gelatinous silica. 
 
 It is found in a few diorites (corsite) ; in diabase, gabbro, 
 norite, and basic schists that have probably been metamor- 
 phosed from gabbros. In Vesuvian lavas it occurs in greasy 
 
ROCK-FORMING MINERALS. 2$ 
 
 crystals when in the mass, but in limpid and vitreous ones 
 when in druses. It weathers easily. 
 
 THE MICAS. 
 
 The members of this group are monoclinic, but are 
 peculiar in having a hexagonal or orthorhombic habit in 
 their crystals and physical characteristics. They generally 
 form folia in rocks with exact hexagonal outline when 
 crystal, and frequently they have considerable thickness ; 
 but the usual habit is the basal plane with irregular 
 boundaries. These folia can be distinguished from those 
 of the chlorite group by their elasticity, the latter being 
 perfectly flexible, and the elasticity increases with the 
 acidity of the mica, while brittleness increases with the 
 basicity. They can thus be arranged, according to amount 
 of silica, lepidomelane (laminae brittle and little elastic), 
 biotite, phlogopite, lepidolite, muscovite, the last being very 
 tough and elastic. Frequently the mica will be a mixture 
 of muscovite and biotite, and always following the law that 
 the muscovite is external, whether as the rim of a single 
 plate or as the outside plates of a crystal series. This 
 mixture cannot be detected by the eye, and only chemically 
 when the mass is large. 
 
 The Acid Micas. 
 
 14. Muscovite (Potash Mica). 
 
 H. 2-2.5 ; Gr. 2.83-2.9. Luster vitreous-pearly. Thin 
 laminae flexible and elastic. Color white, gray, brown, green, 
 yellow, violet, rarely red ; by transmitted light, light 
 shades of yellow and green. Transparent-translucent. 
 Comp. H 2 KAl 3 Si 3 O 12 . 
 
 Bp. In closed tube gives water that frequently reacts 
 for fluorine ; whitens and fus. 5.7 to a gray or yellow glass ; 
 with fluxes reacts for iron ; sometimes Mn, rarely Cr ; 
 
26 MANUAL OF LITHOLOGY. 
 
 decomposed by fusion with alkaline carbonates. Chem t 
 Slightly attacked by acids. 
 
 It is an essential in granite and gneiss, and is found in a 
 few quartz-porphyries; never in eruptives other than above 
 given. We find muscovite associated with quartz and potash 
 feldspar in granitoid rocks. It is not commonly found in 
 porphyries. 
 
 Weathers to steatite and serpentine, and is itself an alter- 
 ation product of other minerals. Among its varieties are : 
 
 I4a. Damourite (Hydromica). 
 
 A variety of muscovite that is extended to include 
 (Dana) most hydromicas, margarodite, sericite, etc. They 
 may give off more water in the closed tube than does 
 muscovite ; but they do not contain any more chemically 
 combined. Folia less elastic. Luster pearly or silky. Feel 
 like talc (formerly much hydromica schist was called talc- 
 schist until distinguished by Dewey). Its difference is shown 
 by the action of the two with cobalt solution and HF. 
 
 I4b. Agalmatolite (Pagoda Stone). Compact, amor- 
 phous. 
 
 Luster feeble, waxy. Color grayish, greenish, yellowish. 
 Like a compact muscovite, and produced from the altera- 
 tion of iolite, spodumene, scapolite, and similar minerals. 
 The Chinese variety has H. 2-2.5 ; Gr. 2.78-2.81. Part of 
 the Chinese agalmatolite is pinite, which is a similar altera- 
 tion product, but with less silica; part is compact pyro- 
 phyllite, and part is steatite. It is used for carving miniature 
 images, etc. 
 
 15. Paragonite (Soda Mica). 
 
 H. 2.5-3 5 Gr. 2.78-2.90. Luster pearly. Color yellowish, 
 grayish, greenish ; colorless by transmitted light. Translu- 
 cent, and smaller scales transparent. Comp. H a NaAl 3 Si 3 O 12 . 
 
 Bp. Fusible with difficulty; some varieties whiten on edges 
 and exfoliate. Occurs in crystalline schists and phyllites, 
 
ROCK-FORMING MINERALS. 2? 
 
 in irregularly bounded plates and fine scaly aggregates 
 looking like talc ; never in massives. 
 
 16. Lepidolite (Lithia Mica). Commonly massive, scaly, 
 .granular. 
 
 H. 2.5-4; Gr. 2.8-2.9. Luster pearly. Color peach- 
 blow red, rose-red, violet gray, yellowish, greenish, 
 white ; colorless by transmitted light. Translucent. Comp. 
 Al(SiO 4 ) 3 Al 2 KLiH + Al(Si 3 B ) 3 K 3 Li 3 (AlF 2 ) 3 . 
 
 Bp. In closed tube gives water and reaction for F. 
 Fus. 2-2.5 with intumescence to a whitish .or grayish glass, 
 and sometimes gives the lithia-flame reaction ; with fluxes 
 &ome varieties react for Fe and Mn. Chem. Only partially 
 decomposed by acids before fusion ; after, it gelatinizes with 
 HC1. Occurs in granite, gneiss, and pegmatitic secretions 
 from them. 
 
 17. Zinnwaldite, Lithionite (Lithia-iron Mica). 
 
 H. 2.5-3 GT. 2.82-3.21. Luster often pearly. Color like 
 lepidolite with brown shades and darker gray ; by trans- 
 mitted light dark brown to light yellow and grayish white. 
 Fine wrinkling on cleavage plane from twinning. 
 
 Bp. Similar to lepidolite, but fuses more easily and 
 :gives F reaction. Comp. (K,Li) 3 FeAl 3 Si 6 O 16 (OH,F). Occurs 
 in tin-bearing granites in Germany, France, Cornwall, etc., 
 .and in pegmatitic secretions in granite and gneiss ; necessary 
 in greisen. 
 
 18. Biotite (Magnesia-iron Mica). 
 
 H. 2.3-3 ; Gr. 2.7-3.1. Luster splendent-pearly on cleav- 
 ages, black kinds submetallic ; lateral surfaces vitreous. 
 Color green-black ; deep black in thick crystals ; by trans- 
 mitted light brown in Archaean rocks; frequently green 
 with hornblende of similar color, but not in massive por- 
 phyries, and rare in granites. Transparent-opaque. Comp. 
 
 <HK).(Mg,Fe).(Al,Fe),SiAr 
 
 Bp. Water in closed tube ; in open tube reaction for F 
 
28 MANUAL OF LITHOLOGY. 
 
 and for Fe ; with fluxes varies greatly in different varieties ; 
 whitens on thin edges and fuses. Chem. Completely 
 decomp. by H,SO 4 with separation of silica in thin scales. 
 
 Occurs in massives and Archaean rocks not in crystals, 
 but as flakes and plates with irregular boundaries. In 
 granites it is intergrown with muscovite, as has been 
 described on p. 25. It is one of the first generations in 
 porphyritic rocks, and is generally absent from the second 
 generations in the groundmass ; is one of the most common 
 results of contact metamorphism, and is often an alteration 
 product of chlorite. It is more abundant in acid than basic 
 rocks. 
 
 (a) Rubellan is an altered ferruginous biotite found in 
 some basalts. 
 
 19. Phlogopite (Magnesia Mica). In crystals and plates. 
 H. 2.5-3 ; Gr. 2.78-2.85. Thin laminae are tough and 
 
 elastic. Luster pearly, often submetallic on cleavages. Color 
 yellowish brown, brownish red with copper-like reflections; 
 also pale brownish yellow, green, white, colorless. A small 
 candle flame viewed through thin plates shows commonly a 
 six-rayed star due to acicular inclusions. Transparent-trans- 
 lucent. Comp. H 6 K 2 Mg 7 Al a (SiO 4 ) 7 , so that it may be called 
 a biotite lacking iron. 
 
 Bp. In closed tube gives little water; frequently in open 
 tube a small amount of F; with fluxes little or no iron; 
 whitens and fuses on thin edges. Chem. Like biotite ; alters 
 to talc. Occurs mostly in Archaean granular limestone ; also 
 in serpentine. 
 
 20. Lepidomelane (Iron-magnesia Mica). Tabular, mas- 
 sive. 
 
 H. 3 ; Gr. 3-3.2. Luster adamantine-vitreous or pearly. 
 Color black with greenish reflection. Streak grayish green. 
 Translucent in thin laminae, otherwise opaque. Somewhat 
 
ROCK-FORMING MINERALS. 29 
 
 brittle. Comp. (H,K) a Fe 3 (Fe,Al)4(SiO 4 ) 6 . This is a ferric 
 biotite. 
 
 Bp. At red heat turns brown and fuses to a black mag- 
 netic globule. Chem. Most easily of all micas decomposed 
 by acids, and by HC1 readily with separation of silica scales. 
 Occurs more restrictedly than biotite in granite, etc. 
 
 Brittle Micas. 
 
 21. Margarite (Pearl Mica). Tabular, scaly, massive. 
 
 H. 3.5-4.5 ; Gr. 2.99-3.08. Brittle. Luster of base pearly. 
 Color grayish, reddish, yellowish, white. Transparent-sub- 
 translucent. Comp. H 2 CaAl 4 Si 2 O 13 . 
 
 Bp. Water in closed tube ; whitens and fuses on edges. 
 Chem. Slowly and imperfectly decomposed by boiling 
 H 2 SO 4 . Commonly associated with corundum in contact 
 formations. 
 
 (a) Ottrelite and phyllite belong here, and are found only 
 in crystalline schists. 
 
 CHLORITES. 
 
 The color of these green minerals is due to ferrous iron 
 and gives them their name. They are sometimes red or 
 brown ; of low hardness and with flexible laminas tough 
 and not elastic. They are all monoclinic in habit, though 
 they simulate hexagonal shapes, as the angles about the basal 
 plane are 120. Chem. the}' are (ferrous) iron-magnesian 
 silicates of aluminum with chemically combined water and 
 no alkalies, and seem to be altered from rich iron-magnesia 
 silicates (hornblende, pyroxene, biotite, phlogopite, etc.). 
 They occur generally in flat or bent laminas, and are at- 
 tacked by acids. 
 
 22 Clinochlore (Magnesia-iron Chlorite). Crystal, coarse 
 scaly, granular, earthy, massive. 
 
 H. 2-2.5 ; Gr. 2.65-2.78. Luster pearly on cleavages. 
 Color deep grass-green-olive green, pale green-yellowish, 
 white, also rose and red (chromium variety) by transmitted 
 
30 MANUAL OF LITHOLOGY. 
 
 light green or yellow-brown. Transparent-translucent 
 Comp. H 8 Mg 6 Al a Si,0 18 . 
 
 Bp. Gives water ; whitens and fuses with difficulty on 
 thin edges of small pieces to a grayish-black glass ; with 
 borax reacts for Fe (sometimes Cr) ; some kinds exfoliate. 
 Chem. Wholly decomposed by H 2 SO 4 . 
 
 23. Penninite (Magnesia-iron Chlorite). Flat or bent lam* 
 inae, massive, compact cryptocrystalline. 
 
 H. same as 22 ; Gr. 2.6-2.85. Luster, etc., like 22. 
 
 Bp. Water in closed tube ; exfoliates slightly and fuses 
 with difficulty ; reacts for Fe (and Cr in many cases). Chem. 
 Like 22, and also partly decomposed by HC1. 
 
 24. Prochlorite (Iron-magnesia Chlorite). Massive, fol- 
 iated, granular. 
 
 H. i. -2.; Gr. 2.78-2.96. Luster of cleavages feebly pearly. 
 Color darker shades of green ; by transmitted light green 
 (sometimes red). Streak more generally uncolored than that 
 of the others. Opaque-transparent only in thin folia. Comp. 
 
 H 4 (Mg,Fe) s SiA- 
 
 Bp. same as 22. 
 
 The chlorites are most widely distributed and give to 
 many eruptives their green color. They also occur in the 
 basic schists. Prochlorite occurs most frequently in erup- 
 tives, the other two in the schists. The cromium varie- 
 ties are found in olivine-bearing schists. 
 
 THE PYROXENES 
 
 These are widely distributed eruptive and schistose 
 rock-formers, which crystallize in orthorhombic, mono-, or 
 triclinic forms ; but agree in having an angle of 87 and 93 
 to the fundamental prism, and a more or less distinct cleav- 
 age parallel to it. 
 
 Orthorhombic Section. 
 
 25. Enstatite. Rarely crystal, usually massive, fibrous, 
 lamellar. 
 
ROCK-FORMING MINERALS. 3* 
 
 H. 5.5 ; Gr. 3.1-3.3. Luster on cleavages subpearly-vitre- 
 ous (metalloidal in bronzite). Color grayish, yellowish, or 
 greenish white, olive-green, brown ; by transmitted light 
 enstatite is grayish-yellowish white, and bronzite yellowish,, 
 greenish. Streak uncolored-grayish. Translucent-nearly 
 opaque. 
 
 Bp. Fus. 6. Chem. Insoluble in HC1. 
 
 (a) Enstatite. Comp. MgSiO 3 ; color white with shades 
 of yellow, green, and gray. Luster vitreo-pearly. Gr. 3.10- 
 
 3-13- 
 
 (b) Bronzite. (Magnesia - iron. Enstatite). Comp. 
 (Mg,Fe)SiO 3 . Color grayish or olive-green, brown. Luster 
 of cleavages adamantine-pearly (the stibmetallic or bronzy 
 luster that gives it its name is not essential, as it is the result 
 of alteration). It is intermediate between enstatite and 
 hypersthene, and has Gr. up to 3.3. 
 
 The enstatites are found massive in gabbro, norite, granu- 
 lar peridotites, and the derived serpentine. Crystals are 
 rare and found in porphyritic rocks with monoclinic pyrox- 
 ene ; also in trachytes and andesites, and in schists. They 
 alter to talc, serpentine, and, 
 
 Bastite (Schiller Spar). H. 3.5-4; Gr. 2.5-2.7. This 
 comes mostly from bronzite and shows highly its peculiar 
 luster (schiller). It occurs in granular eruptives and is com- 
 pletely decomposed by H 2 SO 4 . 
 
 26. Hypersthene. (Iron-magnesia Enstatite.) Some- 
 times tabular, usually foliated, massive, crystals rare, some- 
 times in thin prisms. 
 
 H. 5-6; Gr. 3.40-3.50. Luster subpearly on cleavages, 
 frequently metalloidal. Color darker shades of the enstatite 
 colors, brownish green, grayish black, greenish black ; by 
 transmitted light, light red, brown-red. Translucent-nearly 
 opaque ; streak grayish, brownish gray. Comp. (Fe.Mg)SiO, 
 
32 MANUAL OF LITHOLOGY. 
 
 and sometimes with A1 2 O 3 , so that it approximates to 
 the aluminous species of this group. 
 
 Bp. Fuses to a black enamel, and gives on charcoal a 
 magnetic mass. Chem. Partially decomposed by HC1. 
 
 Occurs in masses in gabbro, norite ; in prisms in por- 
 phyrites, trachytes, andesites, and lavas ; not found in true 
 Archaean rocks, except when it is metachemized ; alters to 
 limonite, hornblende, actinolite, bastite, etc. 
 
 Comparison of enstatite (a), bronzite (), and hypersthene 
 (c) : (a) and (b) have their best cleavage parallel to the 
 rhombic prism ; have generally lighter colors and lower 
 specific gravity ; are almost infusible Bp. and untouched 
 by HC1. (c) has the best cleavage parallel to brachy- 
 pinacoid ; has darker colors ; is fusible and partially de- 
 composed by HC1. (a) and (b) are often fibrous, (c) not so. 
 
 'Monoclinic Section. 
 
 27. Pyroxene. Crystal, lamellar, granular, rarely fibrous 
 or columnar. A (m) form in magmas rich in alkalies is that 
 of an hourglass. 
 
 H. 5-6 ; Gr. 3.2-3.6 (as a rock-former never less than 3.3). 
 Luster vitreous-resinous, sometimes pearly. Color colorless 
 through greenish or yellowish shades to brown and black. 
 Streak white-gray or grayish green. Transparent-opaque. 
 Pyro-electric ; comp. RSiO 3 , R being commonly protoxides 
 of Ca, Mg, and Fe ; less commonly Mn and Zn ; rarely K 
 and Na, and in small per cent ; sometimes also sesquioxides 
 of Fe, Mn, and Al. Chem. Generally untouched by acids. 
 The varieties are : 
 
 NON-ALUMINOUS. 
 
 (a) Diopside (Malacolite). Slender prismatic crystals, 
 columnar masses. Gr. 3.2-3.38. Color white with light 
 shades of yellow, gray, and green ; also dark green to black 
 (in ferrous varieties) ; sometimes transparent and colorless ; 
 
ROCK-FORMING MINERALS. 33 
 
 by transmitted light colorless to light greenish ; sometimes 
 brown. Comp. Ca,Mg(SiO 6 ). 
 
 Bp. Fus. 3.75. Occurs sparingly in eruptives (augite- 
 granite, diabase, quartz-prophyry, minette, kersantite), but 
 widely disseminated in Archaean rocks and granular lime- 
 stones. 
 
 (b) Diallage. Massive lamellar, thin foliated, generally 
 not crystal, but crystalline, also fibrous, and interlaminated 
 with an orthorhombic pyroxene. 
 
 H. 4 ; Gr. 3.2-3.35. Luster pearly, sometimes metalloidal. 
 Color greenish shades and brown ; like diopside by trans- 
 mitted light. Comp. also like it, but with A1 2 O 3 , which 
 makes it approach augite. Bp. and chem. like diopside. 
 
 Necessary in gabbro and derivatives ; essential in some 
 peridotites and serpentines ; sparingly in basaltic and ande- 
 sitic extrusions in prisms ; infrequent in Archasan rocks, and 
 confined to olivine-bearing massives and schists and their 
 derivatives ; metachemized to serpentine and chlorite ; 
 metamorphosed to amphibole on gabbro-phyllite contacts. 
 
 ALUMINOUS. 
 
 (c) Augite. (CaMgSi a O e ) with (Mg,Fe)(Al,Fe) s SiO.. 
 Usually short prismatic crystals; also in irregular columns 
 and grains. 
 
 H. and Gr. as first given. Color greenish or brownish 
 black to black; by transmitted light green, brown, rarely 
 yellow, red, or violet. 
 
 Bp. Fus. 3 ; in general the ferruginous varieties of py- 
 roxene give a magnetic globule on charcoal, and the 
 greenish and yellowish kinds become reddish brown by 
 heating on platinum foil from the formation of ferric oxide. 
 
 This is one of the commonest components of crystalline 
 rocks. In the extrusives it is more commonly crystal; in 
 the granitoid massives it occurs in irregular columns ; not 
 
34 MANUAL OF LITHOLOGY. 
 
 found in the crystalline schists unless the greenish mono- 
 clinic pyroxenes in them are augite instead of a dark diop- 
 side. The light green variety, omphacite, is found in ec- 
 logites in rounded grains or short columnar aggregates. 
 
 Pyroxene is necessary in the basalt-gabbro series, and 
 essential in many rocks. Diallage is necessary in gabbro. 
 Pyroxene alters to chlorite and thence to carbonates, 
 limonite, clay, and quartz ; by uralitization to hornblende,, 
 to talc, serpentine, epidote, glauconite, mica. According 
 to Rosenbusch, the pyroxenes in acid and alkaline rocks 
 are green, in basic extrusives brown, in crystalline schists 
 colorless to greenish. 
 
 28. Acmite. (^Egerite.) (Lime-soda Pyroxene.) Long 
 prisms. 
 
 H. 6-6.5 ; Gr. 3.50-3.55. Luster vitreous-resinous. Streak 
 pale yellowish gray. Color brownish or reddish brown, 
 green ; by transmitted light green, brown to violet. Sub- 
 transparent-opaque. Comp. Na a (Fe 2 )Si 4 O 12 . 
 
 Bp. Fus. 2 to lustrous black magnetic globule, coloring 
 the flame deeply yellow ; with fluxes reacts for Fe and Mn. 
 Chem. Slightly acted on by acids. 
 
 Occurs in elseolite-syenite and augite-syenite of Canada, 
 New Jersey, and Norway ; in sodalite-granite of Greenland, 
 at Ditro ; in acid lavas of San Miguel, Azores ; in alkaline 
 granites rich in soda, acmite- trachyte, etc. 
 
 Triclinic Section. 
 
 29. Hiortdahlite. Crystals tabular and vertically elon- 
 gated. 
 
 H. 5-5.6; Gr. 3.267. Luster vitreous on crystal faces, 
 greasy on fractures. Color light shades of straw-, sulphur-, 
 to honey-yellow ; less often yellowish brown. Comp. nearly 
 4Ca(Si,Zr)O 3 .Na 2 ZrO,F 2 . Bp. Fus. easily to yellowish white 
 enamel. Chem. Gelat. with acids. The crystals are 5-10 mm. 
 
ROCK-FORMING MINERALS. 35 
 
 iong and 2-3 mm. broad, and resemble wohlerite ; but gr. is 
 lower, bp. fuses more easily. Occurs in elaeolite-syenite in 
 Norway. 
 
 THE AMPHIBOLES. 
 
 These dark-colored bisilicates rank next to the pyroxenes 
 in wideness of diffusion, and like them are grouped in the 
 same crystallographic systems. There are fewer species 
 than in the former group ; but these show close parallels 
 with similar pyroxenes. The prismatic angles are 56 and 
 124 ; the other differences will be discussed later. 
 
 Orthorhombic Section. 
 
 30. Anthophyllite. Crystals rare, unterminated prisms, 
 commonly lamellar and without definite boundaries, fibrous 
 massive, with slender fibers^ in prismatic aggregates like 
 actinolite. 
 
 H. 5.5-6; Gr. 3.15-3.24. Luster vitreo-pearly on cleav- 
 ages. Color grayish, yellowish, and greenish brown, 
 emerald-green, sometimes metalloidal. Streak uncolored or 
 grayish. Transparent-translucent. Comp. (Mg,Fe)SiO 8 , or 
 like the enstatite-hypersthenes. 
 
 Bp. Fusible with difficulty to a black magnetic enamel ; 
 reacts for Fe with fluxes. Chem. Untouched by acids. 
 Varieties : 
 
 (a) Anthophyllite (Mg-Fe- Anthophyllite). Prismatic angle 
 54 23' ; corresponds to enstatite. 
 
 (&) Gedrite (Al-Fe-Mg-Anthophyllite). Prismatic angle 
 54 40' ; corresponds to hypersthene. 
 
 These are generally restricted to the hornblende gneisses 
 and schists among unaltered rocks ; occurs abundantly in 
 olivine serpentines. Alteration products unknown. 
 
3 MANUAL OF LITHOLOGY. 
 
 Monoclinic Section. 
 
 31. Amphibole. Prismatic, columnar, fibrous, rarely la- 
 mellar, granular-massive. 
 
 H. 5-6; Gr. 2.9-3.4. Fracture subconchoidal, uneven. 
 Brittle. Luster vitreous. Color from black to white 
 through shades of green and brown, rarely reddish, 
 yellowish. Sometimes transparent, usually translucent. 
 Varieties : 
 
 SLIGHTLY OR NON-ALUMINOUS. 
 
 (a) Tremolite (Ca-Mg-Amphibole). Crystals long-bladed 
 and short and stout, thin columnar, fibrous, compact granu- 
 lar massive. 
 
 H. 5-6; Gr. 2.9-3.16. Color white to dark gray; color- 
 less by transmitted light. Occurs in Archaean granular lime- 
 stone, in altered olivine rocks and serpentines. Alters to 
 talc. 
 
 (b) Actinolite (Ca-Mg-Fe-Amphibole). Prismatic individu- 
 als, columnar and fibrous aggregates, granular-massive. 
 
 Gr. 3-3.2. Sometimes transparent. According to thick- 
 ness and arrangement of fibers it is glassy, asbestiform, and 
 radiated ; color green from ferrous iron, and same by trans- 
 mitted light. Occurs principally in Archasan basic schists ; 
 necessary in actinolite-schist ; also in metachemized diabase 
 and gabbro. The Smaragdite in saussurite-gabbro is a 
 slightly aluminous actinolite. 
 
 {c) Asbestus is a finely fibrous tremolite, actinolite, or 
 other slightly or non-aluminous amphibole. 
 
 (d) Uralite is a paramorph of hornblende after pyroxene, 
 in which the crystals have the habit of the latter and the 
 cleavage, gr., and optical characteristics of the former. Oc- 
 curs in diabase, diabase-porphy rites interbedded with 
 schists, augite-diorite, augite-syenite, etc. 
 
ROCK-FORMING MINERALS. 37 
 
 (e) Nephrite (Jade) is a compact and fine-grained tremo- 
 lite or actinolite. H. 6-6.5 5 Gr. 2.96-3.1. Fracture splin- 
 tery. Luster glistening. Occurs in eastern Siberia and 
 New Zealand. 
 
 ALUMINOUS. 
 
 32. Hornblende (Pargasite) (Al-Fe-Mg-Ca-Amphibole). 
 Crystals, prismatic individuals. The lighter green kinds are 
 sometimes called pargasite and the darker ones hornblende ; 
 but E. S. Dana says that no line can be drawn between them 
 from this or any other characteristic. Gr. 3.05-3.47. Color 
 green, bluish green, greenish black, black. Varieties : 
 
 (a) Ordinary hornblende with color generally green, 
 sometimes deep brown and brownish red. Occurs in por- 
 phyritic states of granite, syenite, and diorite ; granular 
 massives of the Archaean. Alters to chlorite, thence to 
 clay, carbonates, limonite, and quartz. 
 
 (b) Basaltic hornblende with color black ; by trans- 
 mitted light brown in all directions. Always in crystals. 
 Becomes greenish on altering. Occurs only in porphyritic 
 extrusives. The bp. and chem. tests are as in pyroxene. 
 
 33. Arfvedsonite (Al-Na-Amphibole). Imperfect crys- 
 tals and massive. 
 
 H. 5.5-6 ; Gr. 3.44. Luster vitreous. Color pure black, 
 in thin scales deep green or brown. Streak grayish green. 
 Opaque, except in thin splinters. Fracture subconchoidal. 
 
 Bp. Fuses at 2 with intumescence to a black magnetic 
 globule ; colors the flame yellow (soda), and reacts with 
 fluxes for Fe and Mn. Chem. Not touched by acids. 
 Comp. about 4Na 2 O,3CaO,i4 2 FeO,(Al,Fe) 3 O 3 ,2iSiO 2 . Oc- 
 curs in elseolite-syenites and other rocks poor in silica and 
 rich in soda. 
 
 34. Glaucophane (Al-Na-Amphibole). Commonly mass- 
 ive fibrous, or columnar to granular. 
 
38 MANUAL OF LITHOLOGY. 
 
 H. 6-6.5; Gr- 3.103-3.044. Luster vitreous to pearly. 
 Color azure-blue, lavender-blue, bluish black, grayish. 
 Streak grayish blue. Translucent. Fracture conchoidal 
 to uneven. Brittle. Comp. NaAl(SiO 3 ) 2 (Fe,Mg)SiO 3 . Pris- 
 matic cleavage angle 58 16'. Recognized by its blue color. 
 Occurs in glaucophane-schist ; less frequently in mica- 
 schist, gneiss, eclogite ; altered from diallage. 
 
 35. Riebeckite (Fe-Na-Amphibole). Unterminated pris- 
 matic crystalloids. 
 
 H. 5-6; Gr. 3.3. Luster vitreous. Color black. Comp. 
 2Na 2 Fe(SiO 3 ) 2 .FeSiO 3 , corresponding closely to acmite (28). 
 Prismatic cleavage 56 perfect. Occurs in keratophyre, 
 quartz-keratophyre, and minette, gneiss, soda granite. 
 
 36. iEnigmatite (Cossyrite). Prismatic crystals ; angle 
 66. 
 
 H. 5-6 ; Gr. 3.80 (^Enig.), 3.74 (Coss.). Luster vitreous. 
 Color black ; brownish black by transmitted light. Streak 
 reddish brown. Translucent to opaque. Comp. titano-sili- 
 cate of ferrous iron and sodium, with sesquioxides of iron 
 and alumina. 
 
 Bp. Fusible easily to brownish-black glass. Chem. 
 Partly decomposed by acids. ^Enigmatite occurs in large 
 crystals in the elseolite-syenite of Norway ; cossyrite in 
 small crystals in the rhyolite lavas of the island of Pantel- 
 leria. 
 
 COMPARISON OF THE PYROXENE AND AMPHIBOLE GROUPS. 
 
 Prismatic angle with pyroxene 87 and 93 ; with amphi- 
 bole 56 and 124. Prismatic cleavage more distinct in am- 
 phibole. Crystals in pyroxene stouter, and the massive kinds 
 lamellar and granular; in amphibole they are long, pris- 
 matic, and fibrous. In corresponding kinds the gr. is one 
 tenth higher in pyroxene. Pyroxene has more lime ; amphi- 
 bole more magnesia and alkalies. Of the rock-makers the gr. 
 
ROCK-FORMING MINERALS. 39 
 
 of pyroxene is never less than 3.3 ; that of amphibole al- 
 ways so. Amphibole is associated with the more acid rocks, 
 soda and potash feldspars, potash mica, and pyrite ; pyr- 
 oxene with basic rocks, leucite, olivine, and labradorite. 
 That they are closely isomorphous is shown by the fact that 
 of twinned forms one is frequently pyroxene and the other 
 amphibole. 
 
 THE EPIDOTES. 
 
 37. Zoisite (Ca Al-Epidote). Orthorhombic, crystal, 
 prismatic aggregates, massive, compact. 
 
 H. 6-6.5 ;Gr. 3- 2 5-3-37- Luster vitreous and pearly on 
 most perfect cleavage. Color grayish white, gray, yellowish 
 brown, greenish gray, apple-green ; also shades of light 
 red ; by transmitted light colorless, gray, greenish gray. 
 Comp. HCa 2 Al 3 Si 3 O 13 . It graduates into epidote by the 
 addition of iron. 
 
 Bp. Fusible at 3.5 with intumescence to a white blebby 
 mass and gives much water. Chem. Undecomposed by acids 
 unless previously heated to redness, and then gelatinizes 
 with HC1. Occurs in the crystalline hornblende-schists. 
 The variety 
 
 (a) Saussurite is compact and tough with splintery 
 fracture. H. 6.5-7; Gr. 3-3.4. Color white to gray with 
 greenish shades. Translucent to opaque. Not homoge- 
 neous, but the result of dynamo-metamorphism of a plagio- 
 clase. With smaragdite forms euphotide ; also present in 
 saussurite-gabbro. 
 
 This name has also been applied to forms of garnet, 
 meionite, labradorite. Many European authorities place it 
 under labradorite ; J. D. Dana, from its high gr., and Sterry 
 Hunt, from its chem. comp., put it as above. They are fol- 
 lowed by Zirkel, who names authorities of the same opinion ; 
 Rosenbusch puts it under epidote. 
 
4O MANUAL OF LITHOLOGY. 
 
 38. Epidote (Ca-Al-Fe-Epidote). Monoclinic, seldom 
 sharply defined crystals, usually fibrous-granular-massive. 
 
 H. 6-7; Gr. 3.25-3.5. Luster vitreous, but pearly to resin- 
 ous on the orthopinacoid. Color shades of green to black ; 
 also red, yellowish, gray ; by transmitted light colorless, 
 pale yellow, rarely yellowish brown, pale green, seldom 
 red. Comp. HCa a (Al,Fe 3 )Si 3 O 13 . The greater density over 
 zoisite is due to iron. 
 
 Bp. Water in closed tube on strong heating ; fusible at 
 3-3.5 with intumescence to dark brown or black mass ; mag- 
 netic in the darker shades ; gives iron with the fluxes. 
 Chem. Decomp. by fus. with alkaline carbonates, and by HC1 
 with gelatinization after heating to redness ; otherwise un- 
 touched by acids. 
 
 The commonest of metachemic minerals, and seldom, if 
 ever, occurs as an original component in rocks. (Keyes 
 thinks that the occurrence of epidote with allanite in the 
 Maryland granite shows it to be a primary mineral.) 
 Occurs in crystalline massives and schists as an alteration of 
 the iron-amphiboles, as granite, syenite, mica- and horn- 
 blende-schists, serpentine, etc. Alters with difficulty, as all 
 the elements have peroxidized. Variety : 
 
 (a) Piedmontite (Mn-Epidote). Gr. 3.404. Bp. Fusible 
 at 3.5 to a lustrous glass ; otherwise like epidote. Common 
 in the crystalline schists of Japan and altered pre-Cambrian 
 rhyolites of Pennsylvania and Maryland. 
 
 39. Allanite (Cerium, etc., Epidote). Tabular crystals, 
 massive, granular. 
 
 H. 5.5-6; Gr. 3.5-4.2. Brittle. Fracture uneven. Luster 
 submetallic, pitchy, resinous. Color dark brown to black 
 with shades of green and yellow ; by transmitted light 
 reddish brown, greenish brown. Subtranslucent to opaque. 
 Comp. like epidote, but with partial substitution of Fe for 
 Ca, and Ce, La, Di, Y, and Er for AL 
 
ROCK-FORMING MINERALS. 4 1 
 
 Bp. More or less water on strong heating in closed tube; 
 fus. 2.5 with results like epidote ; reacts for Fe with fluxes. 
 Chem. Unlike epidote and zoisite,as it gelatinizes with HC1 
 only before ignition ; untouched after. Occurs in gneiss, 
 granite, granite-porphyry, quartz-porphyry, diorite-porphy- 
 rite, andesite, rhyolite, dacite. Alters with yellow crust, 
 but generally fresh in rocks. 
 
 LEUCITE-NEPHELINE-SODALITE GRO UP. 
 
 These are silicates more or less common to eruptives. 
 containing the black bisilicates. They are found with, and 
 more or less replace, the plagioclases in them. All have 
 H. 5-6 ; Gr. 2.14-2.6. 
 
 40. Leucite. Tetragonal at ordinary temperatures, but 
 isometric at 500 C. commonly crystal, in disseminated 
 grains, rarely massive. 
 
 H. 5.5-6; Gr. 2.45-2.50. Luster vitreous. Color white, 
 grayish. Translucent to opaque. Comp. KAl(Si a O 6 ). 
 
 Bp. Infusible ; gives blue of Al with cobalt solution. 
 Chem. Slightly attacked by HC1 in the solid, but decomp. 
 without gelat. when powdered. Occurs in Tertiary and 
 post-Tertiary extrusives ; in older rocks metachemized to 
 allied forms; found in leucite-basalts, leucite rock, phonolite,. 
 etc.; is not found with free quartz. Alters to feldspar, 
 nepheline, and kaolin. 
 
 41. Nepheline (Elseolite). Hexagonal, stout, prismatic, 
 thin-columnar, granular-massive, compact. 
 
 H. 5.5-6; Gr. 2.55-2.65. Fracture subconchoidal. Brit- 
 tle. Luster vitreous to greasy. Color colorless, yellowish 
 (nepheline), and when massive greenish and reddish shades 
 (elaeolite). Comp. K 2 Na 2 Al a Si 2 O 8 . 
 
 Bp. Fus. 3.5 quietly to a clear glass. Chem. Gelatinizes 
 with acids. 
 
 Nepheline bears the same relation to elseolite that sani- 
 
4 2 MANUAL OF LITHOLOGY. 
 
 dine does to orthoclase, and both are found under similar 
 conditions. 
 
 (a) Nepheline is the glassy crystalline form found in the 
 younger effusives, and with Gr. 2.56. Occurs in phonolites, 
 nepheline-basalts, and with sanidine. 
 
 (b) Elceolite is the coarser crystalline and generally mas- 
 sive form, variously colored, that occurs in older intrusive 
 rocks, and frequently associated with orthoclase. Gr. 2.59- 
 2.65. Occurs in elaeolite-syenite, miascite, ditroite, augite 
 syenite. 
 
 Both alter to thomsonite, analcite, sodalite, natrolite, 
 pinite, and kaolin. 
 
 42. Cancrinite. Hexagonal, usually massive. 
 
 H. 5-6 ; Gr. 2.42-2.5. Color white to gray, yellow, green, 
 blue, reddish ; by transmitted light colorless. Luster sub- 
 vitreous with pearly or greasy film. Transparent to trans- 
 lucent. Comp. 4Na a O,4Al 2 O 3 ,9SiO 2 + 2CaO,CO 2 + sH a O. 
 
 Bp. Water in closed tube ; fuses at 2 with intumescence 
 and loss of color to a white blebby glass (being thus distin- 
 guished from nepheline). Chem. Effervesces with HC1, and 
 after heating forms a jelly. Occurs in elseolite-syenite. 
 Alters to natrolite. 
 
 43. Sodalite. Isometric, prisms, grains, massive. 
 
 H. 5.5-6; Gr. 2.14-2.30. Luster vitreous-greasy. Color 
 white and light shades of green, blue, yellow, and red ; shows 
 the same by transmitted light and colorless. Comp. 
 Na 4 (AlCl)Al,Si 3 O ia . 
 
 Bp. In closed tube the blue kinds become white and 
 opaque ; fuses at 3.5-4 with intumescence to a colorless glass, 
 and with microcosmic salt and oxide of copper gives bluish 
 flame-coloration due to chlorine. Chem. Decomp. by 
 HC1 with separation of gelatinous silica. Occurs as es- 
 sential in elaeolite-syenite ; crystallizes in rocks after augite 
 
ROCK-FORMING MINERALS. 43 
 
 and before nepheline and the feldspars ; alters to thomsonite, 
 muscovite, natrolite, and kaolin. 
 
 44. Haiiyne. Isometric, rounded grains. 
 
 H. 5.5-6; Gr. 2.4-2.5. Fracture flat-conchoidal. Brittle. 
 Luster vitreous-greasy (like sodalite and nepheline). Color 
 bright shades of blue and green, red, yellow ; by trans- 
 mitted light the same and colorless. Subtransparent-trans- 
 lucent. Comp. 2(Na 3 O,Al 9 O 2 ,2SiO 2 ) + Na 2 O,SO 3 , with Na 
 partly replaced with Ca. There are two varieties : 
 
 (a) Haiiyne with considerable Ca. Bp. Retains its color 
 in closed tube, and is thus distinguished from sodalite ; 
 fuses at 4.5 to white glass ; gives sulphur reaction with soda 
 on charcoal. Chem. Decomposed by HC1 with separation 
 of gelatinous silica. 
 
 (b) Nosean (Soda Haiiyne). 
 
 H. 5.5 ; Gr. 2.25-2.4. Color grayish, bluish, brownish, 
 black. Translucent-opaque. Otherwise like haiiyne, except 
 that hauyne gives H 3 S on heating with H a SO 4 , and has the 
 stronger blue color; but nosean takes a bright blue on heat- 
 ing, owing to a change in the sodium sulphide. The red 
 color of hauyne is due to ferric scales. Occurs in basalt, 
 phonolite, and extrusives poor in quartz and alkali. 
 
 45. Melilite. Tetragonal, usually in short square prisms, 
 also in irregular grains. 
 
 H. 5 ; Gr. 2-3.10. Luster vitreous. Color white, shades 
 of yellow and brown. Translucent to opaque. Comp. 
 (Ca,M g ) s (Al,Fe) a Si.0 19 . 
 
 Bp. Fuses at 3 to a yellowish greenish glass ; gives Fe 
 with fluxes. Chem. Gelatinizes with HC1. Occurs in the 
 extrusives and abundant in leucite and nepheline rocks, and 
 often replaces the feldspars so as to be necessary to the 
 species. 
 
 46. Olivine (Chrysolite, Peridot). Orthorhombic, usu- 
 
44 MANUAL OF LITHOLOGY. 
 
 ally in imbedded grains, massive and compact or granular;. 
 The precious form (chrysolite) is not a rock-former 
 
 H. 6.5-7; Gr. 3.3-3.45. Luster vitreous. Color commonly 
 olive-green and changing to yellowish brown or red on 
 oxidation of the iron ingredients ; by transmitted light 
 colorless to greenish white. Comp. (Mg,Fe) 2 SiO 4 . 
 
 Bp. Whitens, but is infusible ; reacts for iron with fluxes. 
 Chem. Decomposed by HC1 and H,SO 4 with separation of 
 gelatinous silica. Alters to carbonates, silicates, serpentine, 
 limonite, and in Archaean rocks to amphiboles. Occurs in 
 basic granular eruptives and basic crystalline schists ; some- 
 times accessory and sometimes essential and necessary. 
 Varieties : 
 
 (a) Hyalosiderite (Ferruginous Olivine). Gr. 3.57. Bp. 
 Fuses to a black magnetic globule ; otherwise like olivine. 
 
 (b) Fayalite (I ro n-oli v i ne). Gr. 4-4.14. Luster metalloidal. 
 Color light yellow to black through shades of brown due to- 
 oxidation. Comp. Fe 2 SiO 4 . Bp. Fuses easily to a magnetic 
 globule ; otherwise like olivine. Occurs in extrusives, 
 among them rhyolite from Yellowstone Park. 
 
 Olivine is distinguished from quartz by its yielding to- 
 acids, fusibility, and Fe reaction with borax. 
 
 SERPENTINE-TALC GROUP. 
 
 47. Serpentine. Monoclinic, in pseudomorphs, some- 
 times foliated and fibrous, usually amorphous. 
 
 H. 2.5-4 (rarely 5.5); Gr. 2.50-2.65. Luster feebly greasy, 
 waxy. Color shades of green and brownish yellow, some- 
 times nearly white ; by transmitted light transparent with 
 shades of green and yellow. Translucent-opaque. Comp, 
 
 H ( Mg s Si,0.. 
 
 Bp. gives water ; fus. 6 on edges ; reacts for Fe. Chem. 
 Decomposed by HC1 and H 3 SO 4 , and more vigorously in 
 proportion to the heat of the acids. Widely distributed 
 
ROCK-FORMING MINERALS. 45 
 
 .and frequently in large masses, and results from the altera- 
 tion of peridotite and other rocks. 
 
 Serpentine is distinguished from pyrophyllite and talc 
 by its complete decomp. by H a SO 4 , pyrophyllite being only 
 partially decomp., talc not at all. Talc gives a red color 
 (Mg) with cobalt solution on heating, while pyrophyllite 
 gives blue (Al). 
 
 48. Talc. Orthorhombic or monoclinic, usually foliated, 
 massive, also granular-massive. 
 
 H. 1-1.5; Gr. 2.7-2.8. Sectile. Thin laminae, not elastic. 
 Luster pearly. Color shades of green from white to blackish. 
 Comp. H,Mg 3 Si 4 12 . 
 
 Bp. gives water generally after hard heating ; whitens, 
 exfoliates; fuses at 5.5 on thin edges to a white enamel; red 
 color (Mg) on heating with cobalt solution, and is thus dis- 
 tinguished from muscovite. Chem. Not decomposed by 
 acids ; important in crystalline and metamorphic schists. 
 
 49. Pyrophyllite. Monoclinic, foliated, granular-com- 
 pact or cryptocrystalline. 
 
 H. 1-2 ; Gr. 2.28-2.9. Color rather more yellowish than 
 talc. Comp. H 2 Al a Si 4 O 12 (an aluminous talc). 
 
 Bp. Water at high temperature; whitens and fuses at 6 
 on thin edges ; radiated variety exfoliates ; gives blue color 
 (Al) with cobalt solution. Chem. Partly decomposed by 
 H 2 SO 4 and completely by fusion with alkaline carbonates. 
 Occurs in crystalline schists. 
 
 The two following minerals are found generally in erup- 
 tives in microscopic proportions, and are among the first to 
 crystallize. Their crystals are therefore included in those 
 formed later. They also occur of macroscopic proportions. 
 
 50. Zircon. Tetragonal, crystal, never massive. 
 
 H. 7.5; Gr. 4.68-4.70. Luster adamantine. Color color- 
 less to brownish shades of yellow; by transmitted light, 
 
46 MANUAL OF LITHOLOG Y. 
 
 light yellow, pink, and violet. Transparent-opaque. Comp. 
 ZrSiO 4 . 
 
 Bp. Infusible; not acted on by microcosmic salt; de- 
 composed when powdered and fused with soda on a plat- 
 inum wire, and gives with turmeric paper the orange color 
 for Zr when treated with HC1. Chem. When powdered is 
 decomposed by hot H 3 SO 4 ; otherwise not attacked ; de- 
 comp. by fusion with alkaline carbonates and bisulphates. 
 Occurs in almost all eruptives and Archaean rocks in the 
 former it is one of the first intratelluric crystals ; abundant 
 in granite, syenite, and gabbro ; necessary in zircon-syenite. 
 
 51. Apatite. Hexagonal, columnar in eruptives, usually 
 slender, but infrequently short and stout, granular, in crys- 
 talline schists massive. 
 
 H. 4.5 (massive), otherwise 5 ; Gr. 3.17-3.23. Luster 
 vitreous-subvitreous. Color usually shades of green, some- 
 times variously colored ; usually colorless by transmitted 
 light. Transparent-opaque. Comp. 3Ca 3 P 2 O 8 + Ca(F,Cl) a . 
 Rosenbusch says that all rocks contain apatite ; more abun- 
 dant in the granular eruptives and feldspathic crystalline 
 schists of acid types. 
 
 THE ZEOLITES. 
 
 These form amygdaloids in the vesicular cavities of 
 effusives, and replace other minerals in compact states by 
 metachemism. They are, therefore, all secondary minerals 
 and of little importance as rock-formers. Analcime is the 
 only one that gives its name to a rock. In some cases they 
 furnish by their composition an idea of the components 
 (chemical) of a compact rock. They are all hydrous silicates 
 of alumina with alkalies and alkaline earths, and can be 
 divided into : 
 
 (a) Lime zeolites : Heulandite, epistilbite, laumontite 
 (all monoclinic). 
 
ROCK-FORMING MINERALS. 47 
 
 (&) Lime-soda zeolites : Stilbite (monoclinic) and chaba- 
 zite (rhombohedral). 
 
 (V) Lime-potash zeolite : Phillipsite (monoclinic). 
 
 (d) Barium-potash zeolite : Harmotome (monoclinic). 
 
 (e) Soda zeolites : Analcite (isometric) and natrolite 
 (orthorhombic). 
 
 Analcite generally shows the presence of nepheline or 
 leucite, as it is altered from them. 
 
 The following species are found mostly in metamorphic 
 rocks and crystalline schists. Some are found sparingly in 
 eruptives ; others never occur there. They are grouped 
 according to their chemical composition. 
 
 SILICATES. 
 
 52. Scapolite (Wernerite). Irregular grains, fibrous, lath- 
 shaped aggregates. 
 
 H. 5.5 ; Gr. 2.569-2.735. Luster vitreous-pearly to res- 
 inous. Color white gray bluish, greenish, reddish, all in 
 light shades, but colorless and transparent when fresh. 
 Fracture subconchoidal. Brittle. 
 
 Bp. Fus. easily with intumescence to a white blebby 
 glass. Chem. Imperfectly decomposed by HC1. Occurs 
 in metamorphic, but not primary, rocks. 
 
 53. lolite (Cordierite). Orthorhombic, crystal, irregular 
 grains. 
 
 H- 7-7.5 ; Gr. 2.60-2.66. Luster vitreous. Color shades 
 of blue ; colorless by transmitted light, rarely yellowish, 
 blue, violet. Transparent-translucent. Comp. H 2 (Mg,Fe) 4 - 
 Al 8 Si IO O,,. 
 
 Bp. Loses transparency and fusible 5-5.5. Chem. Par- 
 tially decomposed by acids ; decomposed by fusion with al- 
 kaline carbonates. Occurs most commonly in gneiss and 
 the crystalline schists ; less commonly in granite, quartz- 
 porphyry, andesites. 
 
4 MANUAL OF LITHOLOGY. 
 
 54. Garnet Isometric, crystal, granular-massive. 
 
 H, 6.9-7.5; Gr. 3.15-4.3. Luster vitreous to resinous. 
 Color white to black through red, brown, yellow, green. 
 Transparent to subtranslucent. Comp. an orthosilicate 
 with interchangeable bivalent (Ca,Mg,Fe,Mn) and trivalent 
 (Al,Fe,Cr,Ti) elements, as follows : 
 
 (a) Grossularite (Ca-Al-Garnet) (Cinnamon Stone). 
 
 Gr. 3.55-3.66. White, yellow, brown, red, green ; color- 
 less by transmitted light. Occurs in Archaean granular lime- 
 stone and lime-silicate-hornstones. 
 
 (b} Pyrope (Mg-Al-Garnet) (Bohemiam Garnet). 
 
 Gr. 3.70-3.75. Red to nearly black ; blood-red by trans- 
 mitted light. Transparent and a gem. Occurs in peridotites 
 and their derivatives. 
 
 (c) Almandite (Fe-Al-Garnet) (Oriental Garnet). 
 
 Gr. 3.9-4.2. Color red in precious garnet, black in the 
 common variety; red by transmitted light. Occurs in granite 
 rocks, andesites ; most abundant in gneiss and Archaean rocks 
 without feldspar. 
 
 (d) Spessartite (Mn-Al-Garnet). 
 
 Gr. 4-4.3. Color dark red, brownish red ; by transmitted 
 light blood-red, yellowish red, and colorless,. Occurs in 
 rhyolite. 
 
 (e) Andradite (Ca-Fe-Garnet) (Common Garnet, Black 
 Garnet). 
 
 Gr. 3.8-3.9. Variously colored, but not white ; brown by 
 transmitted light. Occurs generally in metamorphic schists. 
 
 (/) Uvarovite (Ca-Cr-Garnet). 
 
 H. 7.5 ; Gr. 3.41-3.52. Color emerald-green. From the 
 Ural Mountains, etc. 
 
 Bp. Fusible generally to a light-brown to black glass at 
 3 in (a), (c), (d), 3.5 in (b), and 6 in (/) ; most kinds react for 
 Fe. Chem. All partially decomposed by acids ; all, except 
 (/), decomp. by HC1 after ignition, and generally with sep- 
 
ROCK-FORMING MINERALS. 49 
 
 aration of gelatinous silica ; decomposed by fusion with 
 alkaline carbonates. Plentiful in eruptives, but most com- 
 mon in metamorphic schists of all kinds, in serpentine, 
 granular and crystalline limestones. 
 
 55. Vesuvianite. Tetragonal, in irregular shapes and 
 prismatic aggregates, crystal only in granular limestone. 
 
 H. 6.5; Gr. 3.35-3.45. Luster vitreous to resinous. Color 
 brown, green, seldom yellow ; colorless by transmitted light, 
 yellowish, reddish, seldom brown. Subtransparent to sub- 
 translucent. Comp. a basic Ca-Al-silicate. 
 
 Bp. Fusible at 3 with intumescence to a greenish brown- 
 ish glass ; Fe with fluxes. Chem. Partly decomposed by 
 HC1 and completely after ignition. Occurs principally in 
 metamorphic rocks ; most common in limestones and silicate- 
 hornstones in contact formations, less common in gneiss . 
 
 56. Topaz. Orthorhombic, crystal, rarely in grains or 
 masses. 
 
 H. 8 ; 0^3.4-3.65. Luster vitreous. Color yellowish, 
 white, grayish, greenish, bluish, reddish. Transparent to 
 subtranslucent. Comp. 5(Al 3 )SiO 5 + (Al,)SiF 10 . 
 
 Bp. Infusible ; in closed tube with previously fused micro- 
 cosmic salt fuses and etches the glass for HF; blue on heat- 
 ing with cobalt solution. Chem. Partly attacked by HSO. 
 Occurs in talc and mica-schists, tin-bearing granites and 
 greisen. Alters to muscovite, steatite, kaolin. 
 
 57. Andalusite (Chiastolite). Orthorhombic, always crys- 
 tal, seldom in grains, never massive. 
 
 H. 7.5; Gr. 3.16-3.20. Luster vitreous, often weak. 
 Color red, gray, brown, green ; by transmitted light usually 
 colorless. Transparent to opaque, usually subtranslucent. 
 Comp/Al 2 SiO 5 . 
 
 Bp. Infus.; gives blue (Al) on heating with cobalt 
 solution. Chem. Undecomposed by acids, but decomposed 
 by fusion with caustic alkalies and carbonates. Occurs in 
 
SO MANUAL OF LITHOLOGY. 
 
 metamorphic rocks and some contact formations; some 
 forms are like sillimanite, and can only be distinguished by 
 optical differences. Alters to mica, cyanite, kaolin. 
 
 58. Sillimanite (Fibrolite). Orthorhombic, long thin pris- 
 matic crystals. , 
 
 H. 6-7 ; Gr. 3.25-3.34. Luster vitreous. Color brown, 
 green, grayish white. Transparent to translucent. Comp.. 
 like andalusite ; also bp. Occurs in gneiss, mica-schist, and 
 related crystalline rocks. 
 
 59. Cyanite (Disthene). Triclinic, columnar and parallel 
 aggregates. 
 
 H. 5-7.25; Gr. 3.56-3.67 (the blue varieties are heavier 
 than the white). Luster vitreous to pearly. Color white, 
 blue (blue along the center of the blades and white on 
 margins. Transparent to translucent. Comp. and bp. like 
 last two. At high temperatures in the furnace is altered to 
 sillimanite. Occurs in metamorphic and crystalline schists, 
 almost universally with garnet. Alters to talc and steatite. 
 
 60. Tourmaline. Hemimorphic, rhombohedral, colum- 
 nar crystal, rarely granular-massive. 
 
 H. 7-7.5 ; Gr. 2.98-3.20. Some varieties pyro-electric. 
 Luster vitreous to resinous. Color black, blue, green, never 
 white or colorless as a rock-former ; by transmitted light 
 always colored. Transparent to opaque. Comp. a silicate 
 of Al, Bo, and either Fe, Mg, Na, or K. 
 
 Bp. Variously fusible, those with Mg easily so to a 
 white blebby glass ; with increase of Fe less easily so, and 
 to a slag that darkens with the increased percentage of Fe ; 
 lithia varieties infusible; some react for Fe and Mn; give 
 boric acid with bisulphate of potash and fluorite. Chem. 
 Not decomposed by acids till after fusion, and then by 
 H a SO 4 , and gelatinizes with HC1. Occurs in older granular 
 and acid eruptives, rarely in later eruptives ; alters to lepid- 
 olite, steatite, etc. 
 
ROCK-FORMING MINERAL^. 5 1 
 
 61. Staurolite. Orthorhombic, cruciform twins, pris- 
 matic crystals. 
 
 H. 7-7.5 ; Gr. 3.66-3.75. Luster subvitreous to resinous. 
 Color shades on brown and black ; by transmitted light yel- 
 lowish-brown. Translucent-opaque. Comp. HFeAl 5 Si 2 O 13 . 
 
 Bp. Infusible (Mg varieties fuse easily to black magnetic 
 glass) ; reacts for Fe and sometimes Mn. Chem. Imper- 
 fectly decomposed by H 2 SO 4 ; perfectly so by HF. Occurs 
 in crystalline schists and in contact formations, never in 
 eruptives. Alters to steatite. 
 
 PHOSPHATE. 
 
 62. Monazite. Monoclinic, small crystals. 
 
 H. 5-5.5 ; Gr. 4.9-5.3. Luster resinous. Color shades of 
 red and brown. Subtransparent to subtranslucent. Comp. 
 (Ce,La,Di)PO 4 , with some Th. Bp. Infusible, turns gray 
 and gives bluish-green color to the flame when moistened 
 with HSO ; with borax gives a bead yellow when hot and 
 colorless when cool. Chem. Soluble with difficulty in HC1 
 with white residue. Abundant in gneiss in Brazil, North 
 Carolina ; in large crystals in pegmatite dikes in Scandinavia 
 and Finland. 
 
 OXIDES. 
 
 63. Corundum. Rhombohedral, also massive and gran- 
 ular. 
 
 H. 9; Gr. 3.9-4.16. Luster vitreous, sometimes pearly 
 on basal planes ; and sometimes showing a six-rayed opales- 
 cent star in the direction of the axis. Color black, blue, red, 
 yellow, brown, gray, and nearly white. Streak uncolored. 
 Transparent-translucent. Fracture conchoidal to uneven 
 anu splintery. When compact exceedingly tough. Comp. 
 A1 2 O 3 . Occurs in three principal varieties : 
 
 (a) Sapphire, which is the general name for all pure 
 
$2 MANUAL OF LITHOLOGY. 
 
 transparent to translucent states which are valuable as gems, 
 and, according to color, are called red (true of oriental 
 rub} 7 ), yellow (oriental topaz), green (oriental emerald), 
 purple (oriental amethyst). 
 
 (ft) Corundum, which includes the non-transparent and 
 dark- or dull-colored states. It is ground and used as an 
 abrasive and polisher. 
 
 (c) Emery, which includes the granular states of corun- 
 dum which are black or dark-colored. It is an impure 
 variety, as it is intimately mixed with magnetite and hema- 
 tite, and is used for the same purposes as the last. 
 
 Bp. Unaltered ; slowly dissolves in borax and salt of 
 phosphorus to a clear glass, which is colorless when free 
 from iron, but not changed by fusion with soda ; a fine blue 
 is given to the fine powder by heating with cobalt solution. 
 Chem. Insoluble in acids; after fusion with potassium bi- 
 sulphate or the similar soda salt is soluble, associated with 
 metamorphic crystalline rocks, as crystalline limestones and 
 schists, metagranite, etc. It is electric by friction. 
 
 64. Magnetite. Isometric, commonly in the octahedron 
 and dodecahedron; one of the first-formed minerals in rocks. 
 
 H. 5.5-6.5 ; Gr. 4.9-5.2. Luster metallic-submetallic. 
 Color iron-black. Streak black, except in some ores that 
 are probably mixtures with hematite, and where there is the 
 magnetic reaction with a more or less reddish streak. 
 Opaque when in mass, but subtransparent when in folia of 
 mica. Fracture subconchoidal. Brittle. Strongly mag- 
 netic ; separated from pulverized rock mass by a weak 
 magnet. 
 
 Bp. Fus. with diff.; in O.F. becomes non-magnetic; with 
 fluxes is like hematite. Chem. Untouched by HF; easily sol. 
 in HC1. As a rock it seems to be a varying mixture of 
 protoxides and sesquioxides of iron, and its color and streak 
 vary accordingly. 
 
ROCK-FORMING MINERALS. 53 
 
 Weathering. Shows crust of earthy limonite with color 
 yellowish brown. 
 
 It is the most widely distributed mineral in rocks, but 
 occurs generally in small proportion and so minute as to be 
 detected only by the magnet in rock powder ; as an ore it 
 exists in lenticular beds. 
 
 65. Chromite. Isometric, in octahedrons, generally mass- 
 ive. 
 
 H. 5.5 ; Gr. 4.32-4.8. Luster submetallic. Streak brown. 
 Iron-black to brownish black; by transmitted light gray, 
 lilac-gray. Opaque in mass. Fracture uneven. Brittle. 
 Sometimes magnetic. 
 
 Bp. Inf. in O.F.; slightly rounded on edges in R.F. and 
 becomes magnetic ; with fluxes shows iron reaction when 
 hot, but chrome-green when cold. Chem. Slightly touched 
 by acids, but decomposed after fusion with alkali bisul- 
 phates. 
 
 Occurs in serpentine and in meteorites; never as an es- 
 sential component of rocks. 
 
 CARBONATES. 
 
 66. Calcite. Rhombohedral, never in crystals; in irregular 
 grains and plates. 
 
 H. 3 ; Gr. 2.71. Luster vitreous, subvitreous, resinous. 
 Color white and variously colored. Transparent-opaque. 
 Comp. CaCO 3 . 
 
 Bp. Infus. and glows with reddish-yellow flame. Chem. 
 Effervesces with cold HC1. 
 
 Occurs most extensively, after quartz, of all the minerals, 
 as limestones, which will be treated later ; also occurs in 
 basic rocks as a filling of cracks, cavities, and amygdaloidal 
 openings, and replaces silicates with pseudomorphs after 
 them ; also infiltrates from the country rocks of the mass. 
 When limestone is metamorphosed it becomes " marble." 
 
54 MANUAL OF LITHOLOGY. 
 
 67. Dolomite. Rhombohedral, crystals saccharoidal with 
 curved faces, grains. 
 
 H. 3.5-4 ; Gr. 2.8-2.9. Luster vitreo-pearly. Color white 
 to black through reds, browns, greens, and grays. Trans- 
 parent to translucent. Comp. (Ca,Mg)CO 3 . 
 
 Bp. Generally like calcite, but does not, like it, give a 
 clear mass with soda on platinum foil. Chem. Cold HC1 
 acts slowly on fragments. 
 
 It occurs in sedimentary strata, which are sometimes 
 altered from limestone through Mg solutions ; also occurs 
 locally in metamorphosed clay slates and phyllites ; more 
 frequently associated with magnesia rocks and minerals than 
 calcite. 
 
 (The other minerals occurring as rocks will be treated 
 later as economic products.) 
 
 The following are decomposition products: 
 
 Viridite is a greenish translucent form of matter in minute 
 scales and fibres, which results from the decomposition of 
 hornblende, pyroxene, and olivine. 
 
 Ferrite. Amorphous yellow, brown, or red earthy matter, 
 frequently pseudomorphous after minerals containing iron. 
 Chemically it is anhydrous or hydrated sesquioxide of 'iron, 
 and forms the coloring matter of porphyries and weathered 
 porphyrites. 
 
 Opacite. A term applied to black opaque amorphous 
 matter in granules, patches, or scales, which occurs in rocks 
 containing magnetite, and which some authorities state to 
 be composed of it. 
 
GENERAL DEFINITIONS. 
 
 Minerals occur in rocks in various (M) forms, as shown 
 in the preceding pages. From them we see that two general 
 forms occur in mineral matter individualized, when it is 
 bounded by surfaces that can be readily distinguished (M) 
 or (;), and unindividualized, when it forms an amorphous 
 mass or occurs in patches between individualized matter. 
 
 Individualized forms are : 
 
 (a) More or less perfect crystals, the failure in perfecting 
 the shape being due to want of material or stoppage of 
 crystallization, rather than to interference from other 
 forces, as : 
 
 1. Perfect crystals with regular terminations. 
 
 2. Prismatic shapes with unterminated ends, which may 
 be solid, fibrous, lath-shaped, columnar, or a mere shell filled 
 with other minerals. 
 
 3. Solid pyramidal heads with prismatic faces mo?e or 
 less complete, or merely sketched by a few fibres, like the 
 teeth of a comb. 
 
 4. What may be styled the unterminated skeletons of 
 crystals, with only portions of the prismatic faces devel- 
 oped in irregular patches, and of the most minute thinness, 
 which disappear entirely in places and leave only a tendency 
 to break from the enclosing body along those (missing) 
 faces. 
 
 (b) Crystalline grains which have an internal crystalloid 
 structure (as shown by polarized light), but whose exterior 
 presents irregular shapes due to interferences in crystalliza- 
 tion, or to fracture or abrasion. 
 
 55 
 
$6 MANUAL OF LITHOLOGY.\ 
 
 Unindividualized forms are : 
 
 (a) Vitreous particles or masses due to fusion and sudden 
 cooling. 
 
 (b) Colloid masses, lithoid, stony. 
 
 (c) Aggregations of indefinite form, belonging to none of 
 the above, and occurring in streaks, stains, tufts, etc. 
 
 Lithologyvn a megascopic basis requires that classifications 
 and definitions conform closely to observations with the eye 
 and lens ; and the microscope must be left for theories of 
 rock-formation. In the following pages association in nature 
 (geological), mineral and physical states will be employed in 
 forming divisions and groups, and bulk analyses used only as 
 checks. The physical states are used in definitions of texture 
 and structure. 
 
 TEXTURE. 
 
 This refers to the size, shape, state, and mode of union of 
 the individual particles of a rock, whether they be single 
 minerals, aggregates of minerals, or fragments of an older 
 rock. In each case the texture definition must give the ex- 
 ternal and internal condition of those particles. These con- 
 ditions are characteristic or irregular. The former are pecul- 
 iar to free crystallization in a saturated solution ; the latter 
 to any other mode of formation, as (a) crystallization under 
 other conditions than those above given, or (b) to organic 
 or other mode of aggregation. 
 
 The divisions of texture are : 
 
 (A) When some (hypophaneromeric) or <z//0/"(phaneromeric) 
 the particles can be distinguished by the eye or the lens. The 
 varieties are : 
 
 1. Crystal, when both internal and external arrangement 
 are characteristic. This is the " automorph " of Rohrbach, 
 and the " idiomorph " of Rosenbusch. The latter, though 
 the later, term is the better, as it means " characteristic," 
 while the former is " natural." The converse of this is the 
 
GENERAL DEFINITIONS. 57 
 
 " xenomorph " of Rohrbach, and u allotriomorph" of Rosen- 
 busch, and here the latter term is again the better, as the 
 former is ''foreign," while the latter is "peculiar to an- 
 other," and the crystallization of many minerals simultan- 
 eously imposes on each forms peculiar to the bounding 
 planes of those adjacent. Rocks cannot be formed wholly 
 of crystals, and the term " holocrystalline " of Rosenbusch 
 means " wholly crystalline-granular," and will be so used 
 hereafter; but it might be forced from this sense to mean 
 " wholly crystal (M\" where a rock has sufficient base to 
 form an exceedingly fine-grained porphyry of its ground- 
 mass. There must, therefore, be a cementing medium when 
 minerals occur crystal, and they so occur in three forms : 
 
 (a) Individual crystals (" phenocrysts " of Iddings), or frag- 
 ments of crystals scattered through a groundmass to form 
 a porphyroid texture or a porphyry. According to J. D. Dana 
 the rock is " quartzophyric," " plagiophyric," " leucito- 
 phyric," etc, as the phenocrysts are quartz, etc. The ground- 
 mass may be divided (Iddings) into : 
 
 1. Anisotropic, or not of uniform constitution, when it is a 
 holocrystalline mixture with particles of different sizes, 
 which is Vogelsang's granophyre (if microscopic) ; or a mix- 
 ture of phenocrysts in an isotropic base. 
 
 2. Isotropic, or the reverse of the former, when the micro- 
 scope shows only amorphous matter, which is Vogelsang's 
 felsophyre (when felsitic) and vitrophyre (when glass;. 
 
 The late Dr. G. H. Williams divides the holocrystalline 
 groundmass into one : 
 
 (a) Wholly composed of individual crystalline grains, or 
 microgran itic. 
 
 (ft] Where two minerals crystallized simultaneously and 
 with equal rapidity, so that they became equidimensional 
 and mutually interpenetrant, or micropegmatitic (see " Impli- 
 cation Structure"). 
 
$8 MANUAL OF LITHOLOGY. 
 
 (y) Where a single large crystal or one of the two com- 
 ponents of the groundmass may be filled with smaller and 
 irregular grains or crystals of the latter, he suggests the 
 term poikilitic, and, when microscopic, micropoikilitic. 
 
 Rosenbusch calls all crystals formed in the fluid magma 
 in the hot abysses intratelluric, and many authorities state 
 that the porphyroid texture is peculiar to such a crystal- 
 lization, while Judd, Van Hise, and others have shown that 
 some have been caused by secondary growths about crys- 
 tals after solidification. 
 
 (/>) As phenocrysts distributed through a crystalline- 
 granular foliated mass, as in the metamorphic schists, to form 
 porphyritic states of those rocks. 
 
 (c) As the result of " crystallinic metamorphism " (J. D. 
 Dana), where crystals have been built up by infiltrating so- 
 lutions, as just described. 
 
 II. Granular, when either internal or external arrange- 
 ment, or both, are not characteristic. We can distinguish 
 two varieties of internal arrangement characteristic, or crys- 
 talloid, as in crystals (and apparent by polarized light), and 
 amorphous, as in organic formations ; guano, shells, etc. 
 
 We can also distinguish three varieties in external form : 
 
 (a) Crystalline, where the internal arrangement is crystal- 
 loid, but the external form is irregular, owing to an inter- 
 ference in the crystallizing of the components through their 
 mutually constricting the areas in which they formed, as 
 where crystallization is simultaneous in a solution of two or 
 more minerals, and the particles are bounded by irregular 
 and few faces whose shapes depend, not on the character 
 of the mineral, but on the shape of the area in which it 
 formed. This variety is found in massive and highly meta- 
 morphic rocks, and is usually preceded by an adjective to 
 give the size of the components, as phanerocrystalline, where 
 they can be detected by the eye, and cryptocrystalline, when 
 
GENERAL DEFINITIONS. 59 
 
 th^y cannot be resolved even by the highest power of the 
 microscope, but where the glistening of the minute cleav- 
 age faces in incident light shows a crystalline texture. 
 Under phanerocrystalline we distinguish coarse-, medium-, 
 fine-, and micro-crystalline. The last cannot be resolved by 
 the lens, but exhibits the glistening noted under crypto- 
 crystalline. Medium-crystalline is so peculiar to granites 
 that it called granitoid, and, if the rock is drusy, miarolitic. 
 The form of crystalline grains can be readily seen by wash- 
 ing a thoroughly kaolinized granite till the quartz is clean. 
 As quartz is the last to crystallize in granite, it is forced to 
 .accommodate itself to the interstices between the already 
 formed feldspar and mica, and most highly shows the pe- 
 culiar outline called " crystalline." Holocrystalline rocks, 
 therefore, have their components crystallized into one an- 
 other without the aid of a cementing medium. 
 
 (b] Clastic (Greek, " broken in pieces"), where the inter- 
 nal arrangement of the particles may be crystalloid or amor- 
 phous, but where the external form whether in indi- 
 vidual minerals or pieces of older rocks is produced by 
 fractured surfaces, or by faces (crystal or irregular) more 
 or less worn by mechanical or chemical agents. Naumann 
 called classes larger than a hazel nut psephites, sand sizes, 
 J>sammites, and slime sizes, pelites. Clastics are always 
 secondary and derivative, and their components may have 
 an angular or a rounded outline the former being the result 
 of fracture ; the latter, the modified form after transporta- 
 tion and weathering. Angular particles are called sharp, as 
 a "sharp sand," which, when solidified, forms a rock of 
 rough feel and is called a grit. Angular particles become 
 rounded by mechanical agents, as moving water (rolled) 
 or moving ice (glaciated) ; by chemical agents in weather- 
 ing (etched). On breaking elastics there is not that showing 
 of cleavage faces as in crystalline rocks, even if the grains 
 
60 MANUAL OF LITHOLOGY. 
 
 are crystalloid, as the particles are not crystallized into 
 one another. They are, on the contrary, more or less 
 dull on the surface, and are cemented together so loosely 
 that the fracture extends around the particles instead of across 
 them, and the surface exhibits only the combined dull surfaces 
 of the particles in a very characteristic manner. When the 
 cementing medium is of the same mineral as the rock, incip- 
 ient metamorphism may produce something like the crys- 
 talline fracture. Similar comparatives are prefixed to clastic 
 as to crystalline to denote the sizes of the grains microclas- 
 tic, for example. " Pyroclastic " is applied to fragments of 
 the walls of dikes or volcanic vents which have been broken 
 by the earth-throes, or by the abrasion of the intruding fluid. 
 Psephites are called agglomerates when the fragments are 
 huge and heaped together disorderly, as by the caving in 
 of the top of a cavern in a limestone formation, or the filling 
 of the vent of a volcano by the fallen sides ; breccias when 
 all the fragments are angular. Through variations in the 
 cementing medium we distinguish pyroclastic-breccias, where 
 fragments of the country rock have been cemented by the 
 erupted mass ; oroclastic-breccias, where the grinding of the 
 walls of the fissure on one another has filled it with their 
 fragments, which have been cemented by intruding so- 
 lutions of vein material; or, as in the Siluro-Cambrian lime- 
 stone of eastern Pennsylvania, orogenic forces have exten- 
 sively crushed the formation, but not displaced it, and in- 
 filtrating waters have cemented its fragments in almost their 
 original positions. To this formation the term brecciated is 
 applied, and ordinary breccias, where cliffs have scaled from 
 aerial changes, and their fragments have been cemented. 
 When the fragments are a mixture of angular and rolled 
 shapes, it is called brecciated conglomerate, and when entirely 
 rolled, a conglomerate. If some rolled portions of greater size 
 than the average are scattered through the mass, the rock 
 
GENERAL DEFINITIONS. 6 1 
 
 becomes a pudding-stone. These terms alone do not form suf- 
 ficient distinction for rocks, so that we must call them after 
 the rocks from which they originated, as " quartz-breccia," 
 " quartz-conglomerate," " diorite-conglomerate," " clay-slate- 
 diorite-breccia." Very coarse conglomerate is called shingle 
 when the fragments are larger than a man's fist, and have 
 been formed by the grinding action of water on hard 
 crystalline rocks. There is a class of formations that in- 
 cludes all sizes from the finest silt to blocks as large as a 
 house, and which occur in generally unstratified aggregates, 
 to form till, moraine-stuff, bowlder-clay, etc. These are due 
 to glaciers with or without the concurrent action of moving 
 water, and will be more fully defined later. The varieties 
 of psam mites and pelites will be similarly explained. 
 
 (c) Irregular, where both internal and external arrange- 
 ment are amorphous, as in peat, guano, and similar rocks of 
 organic origin. The phosphate rocks may consist of coral- 
 line limestones underlying guano beds, and into which the 
 aerial waters have carried the soluble portions of the guano. 
 This metachemized rock is also called " guano." Or, in the 
 Tertiary aggregates of bones of land and marine animals, 
 common to the coast regions of the southern Atlantic States, 
 we have a peculiar formation, also found in the floor de- 
 posits of some caverns, and called bone-breccia. 
 
 (R) Cryptomeric, when none of the particles can be distin- 
 guished. There are two varieties of this : 
 
 i. When they are fused together in an amorphous mass; 
 it is vitreous or glassy, when it has a texture and luster like 
 .glass, as in obsidian ; resinous, when, with similar texture, 
 the luster is like resin, as in pitchstone ; horny, flinty, when 
 homogeneous, cryptocrystalline, and with waxy luster, as in 
 jasper and flint ; lithoidor stony, with similar texture and want- 
 ing luster. This commonly is the result of " devitrification/* 
 or the conversion of a vitreous into a crystalline texture. 
 
62 MANUAL OF LITHOLOGY. 
 
 2. When they adhere loosely without fusion, it is com- 
 pact, when dull, firm, and homogeneous ; earthy, when com- 
 posed of loose, friable particles ; plastic, common to the 
 pelites, capable of being moulded, formed, or modelled ; 
 pulverulent, when the compound is so fine and loosely ce- 
 mented that it can be converted to dust by pressing between 
 the fingers ; incoherent, when it is still more loosely held to- 
 gether, and loses its shape by a slight shock or a puff of air. 
 
 Devitrification. This is a changing of a vitreous to a 
 crystalline texture by means not well known. It is seen in 
 the case of pitchstone dikes whose centres are glass while 
 the selvages are quartz-porphyry. The felsites of Wales are 
 shown to be pitchstones devitrified on an enormous scale, 
 and similar widespread changes have taken place in the 
 ancient rhyolites of the South Mountain on the borders of 
 Pennsylvania and Maryland. Devitrification is shown by 
 the formation of microliths, crystalline granules, or crystals 
 which finally produce felsitic textures, so that the fluxion 
 structures, lithophysae, etc., are all that remain to testify to 
 its original state. Some authorities go so far as to say that 
 the quartz-porphyries, felsites, etc., are only devitrified forms 
 of old extrusive glasses. 
 
 STRUCTURE. 
 
 This refers to the form external or internal in which 
 the rock is massed. Internal structure generally has no- 
 effect on the external shape. Some structures can be seen 
 only in terranes, others are exhibited in hand specimens, 
 while a third class are revealed only by the microscope. 
 Before describing them some of their causes will be briefly 
 outlined, such as pressure, cooling, drying, solution, weather- 
 ing, sedimentation, abrasion, impregnation, secretion, and 
 convergence. 
 
GENERAL DEFINITIONS. 63 
 
 Causes of Structural Variations. 
 
 Pressure. The effects of pressure depend on whether it 
 be applied to a homogeneous and equally resisting mass, or 
 to one with portions varying in resistance to deformation, 
 whether the mass be plastic or solid, and whether the mass 
 may be displaced as a whole by the pressure or not. Tyn- 
 dall has shown that pressure applied to a homogeneous 
 mass without power of motion along the direction of the 
 force will produce a tendency to split into parallel plates 
 whose planes are at right angles to the direction of pressure. 
 These planes are called cleavage-planes in fine-grained masses, 
 and some varieties of foliations result in coarser masses from 
 the same source. In case the mass be solid and the pressure 
 produces a warping or torsion, a series of fractures relatively 
 parallel to one another occur, and these are crossed by a 
 second series making slight variations from a right angle 
 with the first set. These are joints. With unequal resistance 
 to deformation certain portions of the mass move through 
 greater distances than adjacent portions, and shears result. 
 The fractures thus formed may be slight or of vast di- 
 mensions. In a sedimentary mass the gradual weighting of 
 the overlying portions exerts an increasing pressure on the 
 lower parts, and if these are locally of varying degrees of 
 resistance, the stronger parts will retain their form and pro- 
 ject into the softer overlying parts, that sink around them, 
 as shown by Marsh in the case of stylolites. With a greater 
 solidity to the mass the grinding of the sides of the fracture 
 on each other will produce groovings and polishing. In the 
 gneiss of the South Mountain, in Pennsylvania, an abundance 
 of minute slickensides occur from this cause where the rela- 
 tive area of fracture is but a few square inches. Pressure 
 applied to the edges of a mass that has freedom for bending 
 w r ill produce two series of fractures at right angles to one 
 
64 MANUAL OF LITHOLOGY. 
 
 another. The first series are parallel to the axis of the 
 cylinder or cylindroid formed by the mass, and radial, and 
 are caused by the stretching of the upper layers of the mass. 
 The second series are caused by inequality in resistance to 
 the pressure, as above stated, and the shears produce 
 fractures parallel to the direction of pressure. The latter is 
 the ordinary cause vi faults, with extensive movement of the 
 walls up and down, as shown in slickensides of great areas. 
 The two series of fractures can be beautifully seen in the 
 hard slate partings of the sharply flexed beds of anthracite 
 in this State. 
 
 Cooling. On cooling a molten mass against a plane sur- 
 face strains are developed that cause symmetrical fractures 
 to extend normal to that surface, and divide the mass into 
 prisms with polygonal section. In a dike the walls are 
 cooling surfaces, and the prisms run across the dike-open- 
 ing ; in a surface sheet the prisms are vertical ; in either case 
 the axis of the prisms is normal to the plane of flow. Owing 
 to the quicker cooling of the part near the walls, secondary 
 fractures are caused parallel to them, so that the prisms are 
 divided by planes parallel to the base. (See further under 
 "Weathering.") 
 
 Drying. In sands and muds a variety of structures are 
 produced by surface and internal drying. Surface drying 
 produces two series of cracks at right angles to one another. 
 The former are due to the shrinkage of the mass, and extend 
 into it normally to the drying surface, as can be seen in any 
 mud flat exposed to the sun and air, in the form of polygonal 
 prisms, much like those caused by cooling, but irregular in 
 outline ; the latter are due to the more rapid drying of the 
 upper layer of the mass, and a corresponding shear, that 
 separates that layer from the next and causes it to curl up- 
 wards where this fracture meets the prisms. This latter 
 form is seen in the greater readiness of masses of plaster of 
 Paris or artificial stone solidified in uncovered boxes to 
 
GENERAL DEFINITIOA^S. 65 
 
 fracture parallel to the drying surface more readily than 
 across it. 
 
 Internal drying takes place in pelitic masses that are ex- 
 posed to loss of moisture on several sides. The exterior on 
 drying becomes rigid, and the moisture of the interior passes 
 through it without influencing the shape ; but the loss of 
 moisture makes the enclosed portion shrink away from the 
 dry shell. The new surface of the latter may dry in a similar 
 manner, and have a second shell formed. The so-called 
 " rattle-stones " in clay are formed in this way. A second 
 type of centripetal drying forms the concentric rings of 
 staining (J. D. Dana) seen in breaking sedimentary masses. 
 
 Solution. The passage of waters through the earth's 
 crust, with or without acids in solution, dissolves portions 
 of the crust along the lines of flow, and etches the surfaces 
 over which they pass, or excavates caverns of varying di- 
 mensions. Limestones are the best examples of rocks thus 
 affected, and the great caves of the world are in this rock. 
 (See further under the next topic.) 
 
 Weathering. The weathering of rocks depends on their 
 mineralogical composition and mode of aggregation, and 
 comprises those changes in shape and character due to 
 exposure to the " weather," i.e., to the atmospheric agents, 
 taken in their most extended sense. These are the mechan- 
 ical and chemical effects of the air (wind, rain, humidity, 
 variations in temperature, frost, and the chemical solvents) 
 and the humic forces (mechanical effects of growing vegeta- 
 tion and the acids of the soil). The result is the reduction 
 of solids to a friable, sectile, or plastic state by the removal 
 of soluble ingredients ; or the formation of carbonates, oxides, 
 or haloids. Under the first case a granite becomes a crumbly 
 mass of quartz fragments imbedded in kaolin, which may be 
 white, or stained with iron from whatever ferruginous 
 bisilicate formed the essential mineral ; a trachytic porphyry 
 kaolinizes to a compact and sectile tuff, and a clay slate 
 
66 MANUAL OF LITHOLOGY. 
 
 turns to a bed of clay. Under the second case an outcrop 
 of argentiferous galena changes to carbonate, or to horn 
 silver; while the well known " iron hat" forms on a pyri- 
 tiferous lode. A rock can frequently be determined by 
 weathering alone when there is a great and well-marked 
 difference between the fresh and weathered states especially 
 if it be a non-fossiliferous part of a generally fossiliferous 
 formation. The rolled cobbles of Oriskany sandstone in 
 eastern Pennsylvania take a high polish and a deep red, the 
 latter from the oxidation of the minute portions of iron in 
 the mass, which give the fresh rock a slight tinge, as can be 
 seen on breaking a bowlder, whose interior is whitish and 
 gritty. Ferruginous rocks highly oxidized on the surface 
 are bleached when covered by peat bogs, while, on the con- 
 trary, white quartz pebbles are deeply and irregularly stained 
 by immersion in ferruginous muds, as are the pebbles of 
 Potsdam quartzite in Triassic conglomerate in eastern Penn- 
 sylvania. A limestone that appears compact and non-fos- 
 siliferous on a fresh fracture may be found to be highly 
 fossiliferous if we examine the etched fragments in the 
 weathered talus, where the less soluble fossils stand in high 
 relief. Weathering, therefore, affects the hardness, color, 
 and composition of a rock, or all of them, and the student 
 should become familiar with the various states. Some rocks 
 are exceptions and harden on weathering, as do sinters, some 
 sandstones, and the shell aggregate of Florida, called coquina, 
 owing to the hardening of the cementing medium through 
 drying. Weathering acts more rapidly along than across 
 bedding planes, and frequently reveals the bedding in an 
 apparently unstratified mass. Weathering also shapes masses 
 by removing more rapidly the sharp angles, and reducing 
 the mass to a spheroid (spheroidal weathering). The fracture 
 of a spheroid discloses a series of concentric shells that 
 approximate in composition from the fresh nucleus to the 
 highly oxidized exterior. Spheroidal weathering also takes 
 
GENERAL DEFINITIONS. 6/ 
 
 place in rocks with no soluble ingredients, as in the Potsdam 
 quartzite of eastern Pennsylvania. Here it is due to sudden 
 alterations in temperature from rain-squalls on a hot day. 
 The effects of sudden cooling can best be studied on the 
 sea-shore in the northern part of the temperate zone during" 
 the summer, where there is an abundance of bowlders of 
 eruptive rocks. These become intensely heated during low 
 tide, and give low cracking sounds when first struck by the 
 returning waves. Cold showers have a slighter effect. 
 This is accompanied by alteration of the minerals through 
 the changes mentioned above. This variety of weathering 
 seems to be greater in a composition of highly basic aniso- 
 metric minerals, owing, perhaps, to the inequality of strain 
 in the heated part, and the sudden and unequal contraction 
 in cooling, which, in many cases, produces flaking, and may 
 be the cause of the decay of the Egyptian obelisks since 
 their removal from that country, as they remained there 
 intact for centuries, whether in the air, or half buried in the 
 bitter brines with which the soil is saturated, but have 
 deteriorated when removed from a climate of uniform tem- 
 perature to those of great and sudden variation. Joints, 
 fractures, cleavages, and bedding planes aid weathering, and 
 the depth of weathering depends on the relative progress 
 of formation and removal of the decomposed part, and varies 
 with latitude and location. Weathering, finally, is a variety 
 of metachemism. 
 
 Sedimentation. This is the deposit by and under water of 
 the worn material from weathered rocks. If the deposition 
 is continuous and the material uniform in size, there will be 
 formed a mass of uniform character when viewed on a section 
 made in any direction. Moving water has a sorting power, 
 and Hopkins has shown that this varies with the sixth power 
 of the velocity. During the spring and fall freshets the rivers 
 are carrying a burden of larger sizes than during the low 
 waters of summer and winter. Sediments thus formed will 
 
68 MANUAL OF LITHOLOGY. 
 
 show coarser and finer layers intermixed. Leconte has 
 .summed the conditions for this intermixing of layers, called 
 stratification, as follows : for stratification in still water (a 
 lake or the ocean) there must be a heterogeneous supply and 
 an intermittent cause, while for running water there must be 
 in addition a variable current. If the strata are formed of 
 different compositions, as sand, clay, calcareous mud, etc., they 
 are called beds of sand, clay, etc. Sedimentary formations 
 are called bedded, and the planes or surfaces that separate 
 adjacent beds are bedding planes, etc. A section of stratified 
 rocks generally shows a variation in size, kind, or color of 
 material, or all of them, and such rocks tend to split more 
 readily along than across the bedding planes, while penetrat- 
 ing solutions enter more easily along than across the same, 
 even though the mass be fine grained, as in the pelites, and 
 the stratification planes are not apparent. The variations in 
 .structures will be noted later. 
 
 Abrasion is a rounding of the surfaces of rocks by contact 
 with other rocks moved by air or water. The winds carry 
 fine sands, and sculpture and polish the rock faces exposed 
 to their action, as is seen in the Western States, in Egypt, and 
 along sea-coasts. From a study of the etched windows along 
 the New Jersey coast the " sand-blast " was devised, by which 
 stones of any hardness are cut to any shape required, pierced, 
 and otherwise worked. The prime motor in abrasion is water, 
 .liquid or frozen. Rocks in river bottoms are rounded by 
 nvhat is dragged over them. Rapidly moving water in tor- 
 Tents or waves rolls fragments together as in a barrel and 
 rounds them by mutual attrition. Glaciers round the sur- 
 iaces of hard rocks over which they flow and form " sheep- 
 tbacks," " whale-backs," etc., while the fragments that do the 
 work are themselves more or less rounded. Water-rounding 
 by strong currents is called rolling, ice action, glaciation. 
 
 Impregnation. This is due to thermal waters or vapors 
 
GENERAL DEFINITIONS. 69 
 
 acting along certain planes in a mass, and introducing foreign 
 elements to form new mineral combinations. The first case 
 is where a solid porous rock is fractured, and along the frac- 
 ture comes thermal water or vapor to penetrate the pores 
 for a limited distance from the fracture, and leave therein 
 the substances held by the solution or vapor. The second 
 case is where the same agents are injected into a fluid mass, 
 or, with such a mass, into a fissure, and produce the given 
 effect on a limited portion of the same, as boric and fluoric 
 acids are thought to have produced the veins of greisen in 
 granite. Geikie and other authorities call these last segre- 
 gations. 
 
 Secretion. This is a leaching of portions of a mass by 
 penetrating waters or vapors. The simplest case is when 
 carbonated waters dissolve portions of limestone in passing 
 through, and are forced to deposit the same, whenever they 
 lose their free acid, as stalagmite, stalactite, travertine, etc. 
 In the case of thermal waters they dissolve silica, if alkaline, 
 and deposit the same on cooling or drying, to form sinter. 
 Thermal waters or vapors are thought to be agents in the 
 formation of some " veins," by secreting portions from the 
 country rocks, and depositing them in fissures or cavities in 
 the same. Geodes, amygdaloids, etc., are similarly formed. 
 
 Convergence. There are a number of more or less similar 
 rock structures that are due to the convergence of similar 
 molecular compounds ; but what initiates the convergence, 
 or whence and why the molecules converge, is unknown. 
 On assembling the structures it is found that they can be 
 grouped according to whether the convergence was free or 
 restrained. The molecular compounds may exist in solu- 
 tion, in a fused magma, or in vapor. 
 
 (a) Free Convergence. This is shown in all forms of crys- 
 tallization where there was freedom of growth in one or 
 more directions, as : 
 
70 MANUAL OF LIT HO LOG Y. 
 
 1. Crystallization from a solution or fluid magma, where 
 the forms would be characteristic. 
 
 2. Segregation, or crystallization in non-vesicular open- 
 ings in solid rock, as in veins and geodes, and from solutions 
 or vapors. 
 
 3. Vesicular crystallization, in states of extrusive rocks in 
 such proximity to the surface that the occluded steam could 
 expand, but not escape. This occurs in rocks of the highest 
 acidity (rhyolites) as lithophysce, and in basic rocks under 
 two forms with acid solutions, as calcite, zeolites, etc. ; with 
 alkaline solutions, as crystalline quartz in geodes, or colloid 
 agate or chalcedony. 
 
 4. Sedimentary crystallization, when single crystals or 
 crystal aggregates form in fine sediments, from the intrusion 
 of saturated solutions, accompanied by some unknown force, 
 as pyrite in clay, and in shales of the coal region, and pos- 
 sibly both are due to the same cause. In the latter case it 
 is the reducing action of the organic aggregate. Fontaine- 
 bleau limestone is another example of this class; also den- 
 dritic magnetite, etc. 
 
 (b) Restrained Convergence. This is commonly known as 
 concretion. The texture of concretions may be crystalline or 
 colloid ; the force may act towards or from the centre, and 
 the form will vary with the amount ot restraint opposed by 
 the mass in which the concretion forms to the entry of the 
 molecular compounds. If the restraint is equal in all direc- 
 tions, the concretion is isometric ; if unequal, as in sediments 
 (especially if of varying strata), anisometric. Under this we 
 find : 
 
 1. Crystallizations from a pasty magma, or simultaneous 
 crystallization of varying compounds, to produce fibrous, 
 columnar, lath-shaped aggregates. 
 
 2. The aggregation of mineral matter in non-crystalline 
 
GENERAL DEFINITIONS. 7 1 
 
 form in an otherwise crystalline mass, as the nodules of 
 mica in some granites and gneisses. 
 
 3. The same aggregation in a suddenly cooled mass to 
 form spherulites, axiolites, etc. 
 
 4. The results of devitrification, as microliths, etc., 
 perlitic structure, etc. 
 
 5. Ordinary concretions, which may be spherical, len- 
 ticular, botryoidal, tuberous, pipe-formed, etc. 
 
 External Structure. 
 
 This may be symmetrical to an axis, as columnar, stalac- 
 titic, filiform ; to a plane, as jointed, stalagmitic ; centric, 
 as spheroidal ; and irregular, as etched, rolled, glaciated, 
 concretionary. The last two may have any or all of the 
 symmetrical forms. 
 
 Columnar. This is peculiar to dike and sheet effusions, 
 and is due to cooling (see ante). A slight columnar struc- 
 ture is also caused in pelites by drying (see ante). In both 
 cases the columns are normal to the cooling or drying sur- 
 face. Basalt shows the structure more commonly than 
 other effusives, though it is seen in phonolite and obsidian 
 with distinctness. This is called " jointing" by some 
 authorities, and distinguished from the ordinary kind by the 
 adjective " basaltic." In some cases only one series of frac- 
 tures is developed, so that the masses are tabular. In other 
 cases the opposite holds, and so great a number of cracks 
 are formed that the columns are roughly cylindrical. These 
 are generally divided by the fracture parallel to the walls, 
 before described, into rhomboidal, cuboidal, or prismatic 
 pieces in case the fracture be plane; but, if irregular, it 
 causes them to break in pieces with " ball and socket " form, 
 and frequently with spheroidal form. 
 
 Stylolitic. O. C. Marsh has shown that these are due to 
 pressure, from the " slickensided " appearance of their sur- 
 
?2 MANUAL OF LITHOLOGY 
 
 faces. They are columnar or cylindrical bodies varying- 
 from a fraction of an inch in length and breadth up to four 
 inches in length and two inches in diameter, and are found 
 at right angles to the bedding of the mass (limestone or 
 marl), and are composed of the same material. 
 
 Cone in Cone. The same author suggests a similar origin 
 for these structures which extend through thin beds of 
 limestone or calcareous shale in the form of cones. They 
 may have been formed by pressure on concretions in process 
 of formation (see ante under " Pressure.") 
 
 Stalaciitic. Solutions formed by percolating waters 
 usually find certain lines of flow less obstructed than others, 
 and the streams or drops fall more frequently where these 
 lines meet the surfaces of cavities in the mass, and deposit 
 there portions of the material in solution ; so that in tin.e 
 a formation similar to an icicle extends from the roof, and 
 may become many inches, or even tens of feet, in length. 
 Stalactites are common in limestone caves, under arches of 
 masonry (from the stone, or even the mortar), under troughs 
 through which mineral waters flow, and may consist of cal- 
 cite, fluorite, limonite, or other soluble mineral. They are 
 variously colored and frequently show a colored banding on 
 a transverse fracture. 
 
 Filiform. This is seen when glass tubing is heated and 
 pulled apart, or when artificial mineral wool is formed 
 by forcing air through slag. It occurs in nature under 
 similar conditions when highly fluid lava is drawn out by 
 being blown into the air, or drawn out by wind, to form 
 what the Hawaiians call " Pele's hair." Pele was the god- 
 dess of the nether world. 
 
 Jointed. This is a tendency to separate into massive 
 sheets with parallel bounding planes, and is generally due 
 to warping or torsion (see ante under " Pressure "). A 
 columnar structure is commonly formed by the intersection 
 
GENERAL DEFINITIONS. 73 
 
 of two sets of joint planes ; but the columns can be told 
 from those formed from cooling or drying by the fact that 
 joint columns are four-sided and frequently square on a sec- 
 tion, while the others are polygonal. While jointing is 
 usually on a large scale and forms the external shape of 
 masses, it is frequently so minute as to become internal, 
 and so frequently repeated as to resemble cleavage. Joint- 
 ing is not always apparent in fresh states of rock, but shows 
 only on weathering. This variety is called blind jointing by 
 miners, and is used by them in " breaking down " masses. 
 Jointing is also called cleat, and frequently, as in some coals 
 and ores, when there are two systems of joints at right 
 angles to one another, the system that is more developed,, 
 and allows the mass to separate more readily, is called the 
 face of the ore, while the other system is the end. Workings 
 are driven against the cleat or face. A good example of 
 jointing in metamorphic rock is seen in the gneiss of Port 
 Deposit, Md., where the mass is divided into layers of great 
 evenness, and varying from a few inches to many feet in 
 thickness. Where there are two systems of joints in strati- 
 fied rock, one is generally parallel to the dip (dip-joint) and 
 the other to the strike (strike-joint). 
 
 Spheroidal. Under " Weathering " it was shown how 
 angular masses lost their sharp corners and acquired a 
 rounded outline. This is spheroidal weathering. The same 
 shape is seen in fresh volcanic products when the explosive 
 action throws portions of the molten mass into the air with 
 a rotary motion, and they solidify under this condition, to 
 form volcanic bombs. The beginning of spheroidal weather- 
 ing produces a subangular shape. 
 
 Etched. The surface of soluble rocks is rounded by the 
 passage of solutions over them, and this is most commonly 
 shown by the action of water in flowing through jointed 
 
74 MANUAL OF LITHOLOGY. 
 
 limestone, as the angular masses are rounded and the joints 
 widened into fissures and caverns. 
 
 Rolled. We can distinguish current- and wave-rolling. 
 Current-rolling takes place in rivers that have periodic 
 currents of great depth and velocity, and intercalated 
 periods of low water and weak currents. During the for- 
 mer the burden of trash is dragged over all stones too large 
 to be moved, and smaller sizes roll along. The small stones 
 and sand are whirled over the bottom so as to reach all 
 sides of the fixed stones, and the hollows are as finely 
 polished as the projections, the sharp contours only being 
 rounded off in hard rocks. The smaller stones take a shape 
 dependent on their hardness and habit of fracture. During 
 the low waters and weak currents, which prevail during the 
 greater part of the year, all sorts lie on the river bottom and 
 weather, so that river pebbles vary in character, being most 
 rounded and polished in torrential streams, and furthest 
 distributed from their original bed. In sluggish streams 
 with no rapid currents there is little distribution and angu- 
 lar material : the river bed representing the adjacent rocks, 
 while the average river pebbles have a rough and pitted 
 surface. Wave-rolling is seen on steep beaches, where, in a 
 storm, the grinding of the shingle under wave action fur- 
 nishes a large component of the noise. Under this intense 
 attrition the friable rocks fall to sand, and only the hardest 
 remain to be finely polished. The wrecking of a Phil- 
 adelphia collier off Nantasket Beach, some years ago, fur- 
 nished a supply of anthracite coal in shingle and sand, but 
 it wore away to powder in a few months. 
 
 Glaciated. The abrasion is entirely between the exposed 
 surface and material carried by the ice. Surface glaciation 
 takes shapes dependent upon the kind of rock and the man- 
 ner of fracturing. In a hard rock that exhibits jointing the 
 surface is rounded to form the " sheep-backs " and " whale- 
 
GENERAL DEFINITIONS. 75 
 
 backs " shown in works on the subject. This is after 
 the old surface soil due to the long period of weathering 
 that preceded the ice advance had been removed, and the 
 .solid interiors of the masses between joint planes came 
 under the planing action of the glacier, and resisted it better 
 than did the less solid portions along those planes. Softer 
 shales are cut down to a flat surface if the material in the 
 ice is of uniform size ; but larger and harder fragments show 
 their presence by deep striations. The ice advance over a 
 non-glaciated region has neither hard rock surface to act 
 upon nor hard material to drag along, so that there may be 
 planing at a distance back from the ice front, but no stri- 
 ation. The material carried by the ice is rounded only on 
 those sides exposed to abrasion against the surface ; other 
 sides retain their angularity. The masses carried over a 
 hard bottom show scratches arranged in sets of parallel 
 lines, depending on the variety of ways they were held by 
 the ice. 
 
 Glacial aggregation. This can generally be distinguished 
 from sedimentation by the absence of stratification in the 
 mass, and by the heterogeneous mixture of the finest clays 
 with bowlders of the largest size without the slightest trace 
 -of sorting. Where the glacier dams a valley and forms a 
 lake a peculiar form of sedimentation occurs the peculi- 
 arity being due to floating ice. In the still water the finest 
 sediments are distributed to form a more or less sandy clay, 
 and, from the continuity of deposition and uniformity of 
 deposit, there is no stratification. This would not be very 
 noticeable were it not for the bergs " calved " from the ice 
 front, which sail out into the lake bearing their burden of 
 angular and glaciated material, which is dropped on melting 
 and falls to the bottom, to become imbedded in the clay. 
 The rounded pieces drop in straight lines, but the flat and 
 unequiaxial pieces fall along lines of least resistance from 
 
? MANUAL OF LITHOLOGY. 
 
 the water and enter the mud at all angles. In case the de- 
 posit were formed by ice alone on a glaciated surface, the 
 pressure would arrange these with longer axes parallel to 
 the movement. An unstratified clay carrying angular and 
 striated or glaciated material arranged in an irregular 
 manner through it has been formed in slack water, and the 
 large burden has been distributed by ice. In the event of 
 the second advance of ice over a previous glacial deposit,, 
 there is sometimes a pushing and distortion of the old sur- 
 face, and not its entire removal. 
 
 Concretionary. The structures under this head have a 
 common convergent origin, but take a variety of shapes,, 
 which depend on the ease of access of the solution to the 
 origin of the concretion, and growth to or from that origin^ 
 Following J. D. Dana, we can divide concretions into cen- 
 tripetal and centrifugal ; and as the origin is a point, a line, or 
 a plane, the structure may be centric, axial, flat, or irregular 
 (if it be wholly anisometric). The texture may be crystal- 
 line, colloid, or earthy. The growth may be continuous or 
 intermittent ; of considerable size, so as to separate masses,. 
 or so minute as to fall under internal structure. We can- 
 distinguish concretions 
 
 (a) From a solution. These are centrifugal, and are due 
 to the grouping of molecules from the solution about some 
 nucleus. They are seen under process of formation in the 
 waters from the Carlsbad springs. A section shows a small 
 grain of sand or speck of some foreign body as a nucleus r 
 which was rolled about gently by the waters and coated 
 concentrically with " sprudelstein." When a mass is built 
 up of minute spherules, its structure is oolitic, and when the 
 spherules are as large as a pea, pisolitic. 
 
 (b) From an intrusion of a solution into a loose mass. The 
 masses are usually alluvial clays, marls, chalk, and even 
 loam. As these are sediments and usually stratified, there 
 
GENERAL DEFINITIONS. 77 
 
 will be a greater freedom of motion of the solution along 
 bedding planes than across them, and the growth will be 
 greater parallel to the bedding than across it, so that flat 
 concretions will form. An irregular variation in porosity 
 will cause an irregular shape. Structures under this class 
 will be spherical, lenticular, botryoidal, mammillary, reni- 
 form, tuberous, flat, and irregular. In clay we find clay- 
 stones, eye-stones, spectacle-stones, imatra-stones, fairy- 
 stones, where the solution bears calcite ; nodules about 
 pebbles, leaves, fish, etc., in the clays of the Carboniferous, 
 where the solution contained both calcic and ferrous car- 
 bonates ; amorphous nodules of pyrite in coal shales, where 
 the ferrous sulphate in the solution was reduced by the 
 organic matter in the clay, to form what miners call " bells," 
 and which run from minute to large dimensions. In chalk 
 we find flint nodules from the dissolved silica of sponges 
 which has formed around other sponges or other siliceous 
 formations. In loam we find calcite nodules which, in 
 India, are called " kunkurs" (" nodules "), and which form 
 in openings left by roots, or around small bodies, and furnish 
 limestone in sufficient abundance for mortar. In guano and 
 bone beds similar concretions of calcic phosphate are found. 
 It sometimes happens that the concretionary mass has 
 formed centripetally, and that the soft interior has shrunk 
 away from the shell and cracked from drying. The open 
 spaces are then filled with some mineral, usually calcite, and 
 form septaria. If not so filled, they form rattle-stones. In 
 highly ochreous clay the hydrated sesquioxide of iron takes 
 various forms, and is called "bean ore " when of small size, 
 " ore pots " when larger and hollow, " pipe ore " when in 
 axial shapes. Limonite concretions form rapidly, as is 
 shown by the finding of discarded spikes from the track 
 in the center of concretions which, have formed at their 
 expense. 
 
7% MANUAL OF LITHOLOGY. 
 
 (c) From a similar intrusion into a rock after its solidifi- 
 cation. These can be distinguished from the former by the 
 continuity of the bedding planes through the concretion. 
 They are found in sandstones and shales from intrusions of 
 solutions given above, and appear to be formed partly by the 
 concretionary power of the solution, and partly by its dry- 
 ing, as stated under that topic. 
 
 Internal Structures. 
 
 These may be uniform and varied. The only uniform 
 structure is called massive, the uniformity being local. It is 
 possessed by primary rocks, and shows no divisions into 
 strata (layers, beds). Primary rocks are frequently called 
 massives. The varied structures may be regular and irreg- 
 ular. The latter are : 
 
 Damascened (Rutley), as in some obsidians, where the 
 threads of glass are contorted in a confused manner like 
 the markings on Damascus sword-blades. 
 
 Porous, where the rock is penetrated by irregular and 
 often angular cavities, due to the removal of some of the 
 minerals, or to the interstices left during the rock-formation ; 
 not due to gas. If the openings are large, it is cavernous. 
 
 Regularly Varied Structures. These may be (a) bounded 
 by spherical surfaces, or (b) repetitions symmetrical to a 
 plane, warped surface, straight or wavy line. The former 
 will be called spherical, the latter parallel, structures. 
 
 (a) Spherical Structures. 
 
 Cellular. This term is applied to rocks containing 
 cavities more or less rounded from the expansion of gas 
 during effusion. They are generally quite spherical if 
 the motion of the mass had stopped before it became so 
 pasty as to resist the expanding force ; if the contrary 
 state existed, the structure will be described later. The 
 
GENERAL DEFINITIONS. 79 
 
 structure is most commonly met with in surface portions 
 of compact effusives. If the cells are few and isolated, 
 the state is called vesicular; if they occupy an equal space 
 with the solid part, it is styled scoriaceous, or slaglike ; if the 
 cavities predominate, pumiceous, or foamlike. When the 
 cavities become filled with agate, calcice,or zeolites leached 
 from the walls, the state is amygdaloidal. In obsidians sim- 
 ilar cavities, called lithophysce(\. Richthofen), are thought by 
 J. D. Dana to have been filled with an aqueo-igneous or 
 jelly like secretion, which, by alternate crystallization and 
 drying, forms a series of concentric crystalline spheroids of 
 solid or spongy character. The minute crystals are of 
 quartz, tridymite, feldspar, topaz, and garnet. 
 
 Geodic, when cavities of any shape are lined with crys- 
 tals, but not completely filled. In some cases layers of 
 chalcedony occur under the crystalline layer. If the crys- 
 tals are minute, the structure is drusy. 
 
 Spherulitic, GlobuliferouSj and SpJierophyric (J. D. Dana). 
 This is a concretionary structure found in eruptives, and is 
 formed during the plasticity of the mass, as shown by the 
 elongation of spherules by its motion. It occurs megascopic 
 from concretions of mica, or feldspar and mica ; or micro- 
 scopic from the formation of spherulites which are radially 
 crystalline. A not very common form of spherules is caused 
 by the fusion of pyroclastic fragments of the country rock 
 in the intrusive fluid. A good example is seen in the spheres 
 of willemite in the dikes cutting the ore body in the New 
 Jersey zinc mines. 
 
 Perlitic. This is characteristic of perlite, but is found in 
 other vitreous rocks. During cooling the mass is fissured 
 by minute cracks that form spheroids and ellipsoids, whose 
 section shows concentric coats. This is held by some 
 authors to be similar to the spheroidal jointing shown on a 
 greater scale by basalt, etc. 
 
SO MANUAL OF LITHOLOGY. 
 
 (V) Parallel Structures. 
 
 Those symmetrical to planes and warped surfaces will 
 be called flat parallel; those symmetrical to lines, linear 
 parallel. 
 
 The flat-parallel structures are : 
 
 Bedded, Stratified. Stratification has been already de- 
 scribed. We distinguish seams, or thin layers differing in 
 character from those above or below ; beds, as thick seams ; 
 bedded masses, when the horizontal dimensions are inconsid- 
 erable in comparison with the thickness ; lenticular masses, 
 when beds thin out and appear to be isolated in a stratified 
 deposit. The varieties of bedding are : 
 
 Massive, when of great thickness, and not divisible into 
 layers. 
 
 Straticulate (J. D. Dana), when made up of even and thin 
 layers, separate or not, as in clay, stalagmite, agate, etc. It 
 is also called banded. 
 
 False bedding {K. Geikie) includes all kinds that are formed 
 otherwise than by distribution in still water, as : 
 
 (a) Current-bedding, where the stream pushes the detritus 
 along irregularly, so that the front has a slope of 2O-35, 
 and the successive deposits are parallel to this slope. In an 
 estuary the alternating slack waters deposit horizontal layers, 
 so that regular and cross-bedded layers are intercalated. 
 
 (b) Flow-and-plunge structure exhibits a curved cross- 
 bedding that is without intercalated regular bedding. It 
 occurs where waves work over a supply of sand and fine 
 gravel, and is seen on shores and sometimes in sub-glacial 
 deposits. 
 
 (c) Beach structure is a similar case, but exhibits a varia- 
 tion in angle of bedding at the level of high tide. Above 
 that the beach has a slight slope ; below, a steeper one. 
 
 (d) Wind-drift structure is composed of Straticulate 
 
GENERAL DEFINITIONS. 8 1 
 
 layers in positions oblique to one another. It is caused by 
 variations in wind direction in a sandy region. 
 
 Trough-bedding (Ger. Muldenformig), when sediment is 
 deposited in a depression, and takes the shape of the same ; 
 but, owing to the slipping of the sediment down the slopes, 
 the layers are thicker in the trough than on the sides, and, 
 eventually, the depression is filled, and the overlying layers 
 become horizontal. A good example is seen in the Mesozoic 
 coal basins in Virginia, where the deposit is in hollows in 
 the Archaean rocks. 
 
 Cloaklike Bedding (Ger. Mantelformig), where a sinking 
 of the surface causes a lake or ocean, and the hills and 
 smaller elevations are gradually submerged or " cloaked " 
 by the by the sediment. This is seen on a large scale in 
 the bottom of Lake Bonneville, Lake Lehontan, etc. Here 
 the strata dip in all directions from the submerged mass. 
 This and trough-bedding must not be confounded with 
 synclinals and anteclinals, which are caused by flexing beds 
 originally horizontal and parallel, while the above were 
 never horizontal, and always thicker at their lower than 
 their upper parts. 
 
 Veined. A vein is a parallel and " comblike " arrange- 
 ment of crystalline matter in an open fracture in older rocks. 
 The crystals usually have their longer axes especially in 
 the vein matter normal to the walls of the fracture. 
 Alternations in the solutions cause variations in the minerals, 
 and the layers are deposited on one another till they meet 
 in the centre of the fracture. The parallel arrangement of 
 vein matter is not like the similar arrangement of stratified 
 matter, as in the first there is a repetition of the order of 
 succession of the deposits on either side of the middle of 
 the vein, while there is generally no symmetry in the 
 stratification of a bed. The vein, also, is crystalline ; the 
 bed, clastic. The varieties of veins and their origin belong 
 to economic geology. One of the most common vein- 
 
82 MANUAL OF LITHOLOG Y. 
 
 formers is quartz, and it fills the small cracks in sandstones 
 with material more dense than the rock, so that weathering 
 brings them into relief. 
 
 Fissured, Fractured, where rocks have been deformed 
 and crushed. In case the walls of the fissure have been 
 moved on one another, the grinding forms slickensides. 
 These may be grooved or plane. The soft shales of the 
 coal frequently have been grooved; but their softness would 
 have allowed the evidence to be lost were it not for the 
 filling of the fissure with quartz, which has preserved a cast 
 of the same with the minute groovings. In case the rocks 
 are pyritiferous, the movement produces a plane surface 
 with a mirror-like polish ; but weathering blackens the same 
 without entirely destroying the lustre. In erogenic move- 
 ments the rocks are sometimes finely crushed, and Bonney 
 claims this as preliminary to one form of schistocity. 
 
 Fissile. This is a general term for a tendency in rocks to 
 split more or less readily. We can distinguish 
 
 (a) Shaly (Laminated}, where there is an arrangement 
 in layers, relatively parallel, and a tendency to split along 
 the layers. This is also called stratified, and fine layers are 
 straticulate or laminated. The texture is generally fine, as 
 in pelites. 
 
 (b) Schistose (Foliated), with the layers wavy through the 
 somewhat parallel arrangement of unequiaxial minerals, or 
 those that are eminently cleavable in one direction, as mica, 
 talc, chlorite, hornblende, etc. The thin flakes are called 
 folia. The texture of schists is crystalline, and coarser 
 than the clastic, or crystalline-clastic texture of shales. 
 
 (c) Slaty (Cleaved), with a tendenc}^ to split in thin, 
 sheets parallel to a given plane, and with a fine and homo- 
 geneous texture. It is produced by pressure, as before 
 stated (p. 63), and is known, in coarse-grained rocks, as a 
 species of jointing. 
 
 We distinguish the varieties of cleavage as follows : (i) 
 
GENERAL DEFINITIONS. 83 
 
 If parallel to the bedding, and in fine texture, it is generally 
 shaly lamination ; if in a coarse texture, flagstone- QV flagband- 
 cleavage. (2) If at an angle to the bedding, and in a fine 
 texture, slaty-cleavage. 
 
 Streaked, Fluxion Structure (A. Geikie), Banded (Rutley), 
 Fluidal (J. D. Dana). The term " streaked " is indefinite ; 
 " banded " is applied to other structures, as in agate, onyx, 
 etc. ; and neither affords information regarding the origin of 
 the structure, which is peculiar to igneous rocks. Geikie 
 defines it as " having some or all of the component minerals 
 arranged in streaky lines, either parallel or convergent, and 
 often undulating." (This last would include Rutley 's 
 " damascened "). He further states that it is found less 
 marked in crystalline rocks, as diorite and dolerite. Dana 
 defines it as " having the material of the rock or of portions 
 of it in parallel lines or bands and looking as if due to the 
 flow of the rock while melted." He further speaks of the 
 " thin laminated structure " of trachytic and andesitic lavas 
 as due to successive action in the supply of lava to the point 
 of outflow, and refers to Iddings. There are a number of 
 structures thus referred to " flow": (i) a banding of the rock 
 in laminae, as in the lavas above mentioned, and in " slaty " 
 porphyry this structure causes the rock to break a little 
 more readily along than across the laminae ; (2) a stretching 
 of the rock by the flow so as to show a structure like that 
 in pulled molasses candy ; (3) a stretching of vesicles in the 
 line of flow, so that they are no longer spherical, but pear- 
 shaped or elongated ; (4) a fissuring or fracturing of pheno- 
 crysts by movements of a pasty matrix. The experiments 
 of Tresca on " flow " in solids have been improved upon by 
 Townsend, whose exhibits show on polished and etched 
 sections the particles arranged along " fluxion " lines, as in 
 the states of rocks just noted. While, therefore, it may be 
 possible for this structure to be formed in solidified rocks, 
 
84 MANUAL OF LITHOLOGY. 
 
 it is generally exhibited in movements during a pasty state, 
 though the fissured phenocrysts show that motion followed 
 initial crystallization. 
 
 Linear-parallel structures : 
 
 The second and third varieties of the last structure are 
 linear parallel, but cannot be well separated from the others. 
 Also: 
 
 Fibrous, where some of the mineral components are com- 
 posed of distinct fibres, as in gypsum, satin-spar, chrysotile, 
 amianthus, asbestus, etc. Some concretions are fibrous, but 
 they do not fall here, as they are convergent. 
 
 Lathy, where some or all of the components are in flat 
 or twisted lath-shaped forms, as in some diabases, cyanite 
 rock, etc. 
 
 Implication Structure, where there has been a peculiar and 
 regular infolding of one another by two synchronously 
 formed ingredients of a rock (Zirkel), as by the quartz and 
 feldspar in pegmatite, where the quartz is systematically 
 arranged on certain of the cleavage planes of the feldspar 
 so as to produce characters that have been likened to 
 Hebrew, Assyrian, etc., and the rock called graphic granite -, 
 The structure is also called pegmatitic. 
 
 A number of (m) structures are omitted here. 
 
 Fulgurite. The effect of lightning on the earth's surface 
 is to fuse the rocks to varying depths and produce a 
 natural glass therefrom, which is called fulgurite. In solid 
 rocks this may be only a surface fusing, but in sands there 
 is sometimes a tube of considerable length (up to ten feet) 
 thus formed. Fulgurites are indicated by glassy patches, 
 drops, or tubes on rocks, and are found most frequently 
 on the tops of high peaks. In sand the tubes may be three 
 inches across. This form of glass is distinguished by the 
 absence of microlites, thus showing its sudden cooling. 
 
GENERAL DEFINITIONS. 8$ 
 
 COMPOSITION. 
 
 This refers to the average constitution of the rock, and 
 the terms used are derived from chemical, mineral, or 
 structural peculiarities, as : 
 
 Calcareous, containing carbonate of lime. 
 
 Felsitic (Felsophyric, J. D. Dana), having feldspar as a 
 principal ingredient. 
 
 Arenaceous, composed of sandlike grains. 
 
 Argillaceous, consisting of clayey matter. 
 
 Ferruginous, cemented by or containing oxide or car- 
 bonate of iron. The last is sometimes called, in waters, 
 chalybeated. 
 
 Siliceous, Quartzose, containing silica the former in a 
 colloid, the latter in a crystalline, form. The converse of 
 the latter is quartzless, and refers only to the absence of the 
 crystalline mineral, and not to the absence or poverty of 
 the chemical compound, as in basic. 
 
 Acid, containing siliceous acid in chemical composition 
 to such an extent that it forms the larger portion of the 
 rock constitution. The converse is basic. (See p. 4.) 
 
 HARDNESS. 
 
 This refers to the original state of the rock, and not to 
 the hardness after weathering. This change increases the 
 hardness of some sandstones, limestones, and all sinters ; but 
 reduces that of felsophyres. The scale of Mohs is uni- 
 versally used. 
 
 FRACTURE. 
 
 This depends on texture and structure, with slight 
 variations between fresh and weathered states, such as: 
 
 Conchoidal, when the broken surface exhibits shell-like 
 forms, convex or concave, as in the glassy states of rocks 
 and artificial products. 
 
86 MANUAL OF LITHOLOGY. 
 
 Splintery, when the surface is covered with partially 
 separated splinters in irregular fibers. 
 
 Smooth, when, without being plane, the surface presents 
 no irregularities. 
 
 Tabular, when the mineral forms the greater portion of 
 the rock, and possesses a highly developed cleavage, as in 
 some hyperites. 
 
 Crumbly, when the surface is slightly loose and sandy, 
 as in protogine-granite. 
 
 Foliated, Laminated, Slaty, can be inferred from previous 
 definitions. 
 
 Irregular, when the surface exhibits none of the above 
 regular fractures. 
 
 COLOR. 
 
 The color given in each case is that of the fresh fracture 
 of a rock, as many rocks change the color on weathering or 
 even exposure to the air for a few seconds, in the same way 
 as the colors on buried wall-paintings or statues that are 
 uncovered after lying for centuries fade quickly on exposure 
 to air and light. When certain colors are characteristic of 
 fresh, and others of weathered, states of the same rock, the 
 variation is one means of identification, as in phonolite. In 
 general, it can be stated that 
 
 White shows an absence of iron or other heavy metallic 
 oxides, either in the original composition of the rock or 
 owing to subsequent change ; but, if they occur, they have 
 usually been reduced to the pyritiferous form by organic 
 components of the rock, and are returned to the oxide form 
 by weathering. Rocks containing no oxides are marble, 
 .gypsum, white kaolin, fire-clay, etc.; under rocks weathered 
 white are some basic eruptives, especially when under peat 
 swamps. 
 
 Black indicates carbon, magnetite, or a heavy bisilicate 
 
GENERAL DEFINITIONS. 87 
 
 {hornblende, pyroxene, etc.). In the Wyoming (northern) 
 anthracite basin the surface is highly cultivated, and the 
 spring and fall ploughings show the outcrops of the various 
 beds marked by bands of blacker soil. The writer has seen 
 strings of magnetite rotted soft in a drift-face driven to 
 strike a hoped-for ore body. 
 
 Yellow, Dull yellow in a volcanic region may be due 
 to sulphur, but, in general, it indicates iron ocher; bright 
 yellow is due to pyrites. The ochers come from the oxida- 
 tion of ferruginous compounds to form limonite. They are 
 seen lining the ditches through which waters from coal 
 mines flow, or from springs in pyritiferous rocks, and 
 therefore indicate pyrite or marcasite at depths. 
 
 Brown indicates lignite, or hydrated iron or manganese, 
 and the umbers are allied to the ochers in origin. 
 
 Red is due to anhydrous ferric oxide. It is a transition 
 state in the process of complete oxidation, and is common to 
 weathered pyritiferous lodes. In fresh rock it is seen to 
 advantage in jasper; in weathered rock it forms the "iron 
 hat " of the miners, and gives rise to the well-known proverb 
 in all tongues, that may be freely translated : 
 
 " No gangue so good as that 
 Which wears an ' iron hat.' " 
 
 J. D. Dana says that the red color of many sandstones is 
 -due to a small amount of heat that the rocks have received 
 during consolidation, as shown by the reddening of light- 
 colored sandstones bp., and that the color of the Triassic 
 rocks on the Atlantic border of the United States is due to 
 the heating of the rocks and waters by trap effusions, so that 
 high oxides of iron were distributed. 
 
 Green is found in rocks poor in silica and free quartz. If 
 schistose, the color is due to talc, chlorite, serpentine, etc.; 
 if massive and crystalline, to chlorites. Some intrusive 
 
88 MANUAL OF LITHOLOGY. 
 
 rocks were named " greenstones " from this characteristic. 
 Decomposed copper ores sometimes make green crusts or 
 stains ; but these are on the surface only, and are not seen 
 on fresh fractures, except in malachite. 
 
 Lustre, feel, smell, specific gravity, and other properties of 
 rocks and minerals are used as in mineralogy. 
 
 Replacement is a term used to denote the seemingly 
 gradual withdrawal of one mineral from the rock and the 
 taking of its place by another. A dolerite is composed of 
 pyroxene and labradorite. We find associated with dolerites 
 a rock with little or no labradorite, but a great deal of nephe- 
 line, and we call it nepheline-dolerite, and say that the 
 nepheline has replaced the labradorite. The replacement has 
 taken place at the formation of the rock, by some influence 
 that caused nepheline to crystallize, rather than labradorite. 
 A comparison of the analyses of feldspar-basalt and nephe- 
 line-basalt shows a difference of .009 in silica, .01 in lime, 
 and .0004 in soda, while the other ingredients vary, in the 
 two rocks analyzed, as greatly as in two specimens of the 
 same rock from different localities. The " replacement " 
 of mica by hornblende or augite makes the varieties of 
 hornblende and augite-granite. " Replacement " is used in 
 the definitions of varieties of the same rock. 
 
 SUDDEN AND LOCAL CHANGES IN ROCKS. 
 
 In the faces of some granite quarries there are " segre- 
 gations " of the same rock with the crystals of enormous 
 size, called "giant granite," or streaks of " greisen," which 
 are limited in extent. These are due to changes in the 
 rapidity of cooling, or to impregnations during the fused 
 state. In the same fissure two massive rocks run parallel 
 to one another for a short distance; but within slight 
 distances each may be the envelope of the other. As both 
 are fresh, the change must have originated by differentia- 
 
GENERAL DEFINITIONS. 89 
 
 tion in a common magma during eruption. The changes 
 from " contact metamorphism " have been already noted, 
 and can be recognized by the study of the region. In 
 the case of sedimentary rocks the variations are frequent 
 and of limited extent. They may be due to a number of 
 causes : 
 
 To a system of currents of greater intensity over parts of 
 the area of deposit. J. F. Blandy was the first to map the 
 river systems during the Carbonic era by the erosions of the 
 beds during deposit and the filling of the basins with the 
 material of the top rock. Such a case is seen when the bed 
 thins rapidly by the coming down of the top rock for a short 
 distance, and its sudden rising again. 
 
 To a sudden change in the conditions of deposition, as pelites 
 are indications of deep water or feeble currents, or both ; 
 while gravels are indications of currents of considerable 
 force. The writer has seen in the middle of a coal seam 
 (twelvefeet thick) a " parting" of fine-grained shale, averaging 
 seven inches in thickness, that held a lenticular seam of coarse 
 conglomerate two inches thick, and a few feet in length and 
 width. The examination of the same parting throughout 
 the mine, and throughout the region, failed to show a paral- 
 lel instance. E. Orton reports in the coal of northeastern 
 Ohio, two feet below the top of the bed, an angular frag- 
 ment of quartz vein-stuff, as fresh as if just broken from the 
 parent mass. The coal adhered to it on all sides, and had 
 evidently accumulated about it, as it was undisturbed. 
 
 To a variation in conditions subsequent to rock-formation. 
 Quarry faces, as in the Siluro-Cambrian of Pennsylvania, 
 sometimes show that variations in porosity, or other causes, 
 have allowed magnesia solutions to penetrate to different 
 depths in limestone beds, so that thecalcite has been irregu- 
 larly turned to dolomite, and the same hand specimen will 
 
90 MANUAL OF LITHOLOGY. 
 
 consist of both, with the line of separation running across 
 bedding lines. 
 
 The age of rocks can be relatively determined as follows : 
 A rock is always older than tJiat which is deposited on it. 
 In case no subsequent movement has taken place it will show 
 that the upper rock is the younger of the two. The excep- 
 tions are : 
 
 (a) When a fracture has occurred along a bedding plane, 
 and a fluid sheet has been intruded into the fracture, or 
 when the fracture has been filled by vein material. While 
 the sheet or vein is younger than the overlying rock, its 
 recency can be shown by its containing fragments of the 
 same as " breccia " in the first case, and as " horses " in the 
 second. 
 
 (b) When the whole formation has been overturned. In 
 this case the oldest beds are brought on top, and the study 
 of a limited area might mislead the observer, were it not 
 that, in certain cases, the top and bottom rocks of a bed are 
 plainly marked, as in coal, by the former containing the 
 trunks and foliage of the vegetation, and the latter the roots. 
 Top sandstones near a bed carry the trunks and branches of 
 vegetation ; bottom sandstones in similar conditions carry 
 nothing, but frequently become more argillaceous. In the 
 case of a conglomerate we can usually tell an overturn by 
 finding the argillaceous partings that frequently occur in it 
 or bounding it, and noting on which side the greatest 
 amount of ferruginous staining occurs : that will be the 
 side that was uppermost during deposition, as in gravel the 
 percolating waters leach the iron from the mass and carry 
 it downwards till stopped by the impervious strata, and de- 
 posit it therein or in the last few inches or feet of the porous 
 portion depending on the amount of the gravel bed. 
 After solidification that remains as a witness of the position 
 during deposition. 
 
GENERAL DEFINITIONS. 9 1 
 
 A rock is always older than one that has disturbed it. The 
 case of an intruding sheet or vein has been just described. 
 In the case of veins or apophyses intersecting one another, 
 the younger cuts the older. If two igneous sheets, or two 
 veins, lie parallel to one another in the same fissure, and have 
 been formed at different times, the younger will contain 
 fragments of the older, as above stated. The exceptions 
 are : 
 
 (a) When a cloak bedding (p. 81) has been so removed 
 by erosion that the underlying rock is exposed, it seems to 
 have been projected from below and to have raised the 
 overlying strata. 
 
 (b) When a soluble bed has been dissolved and the over- 
 lying strata have been fractured in the resulting settling, 
 as in the case of caverns in salt or limestone. 
 
 The relative level of two rock-formations is no criterion 
 of their age, as the oldest rocks may be shoved upward by 
 orogenic movements, or left by erosion. In eastern Penn- 
 sylvania the Potsdam sandstone and overlying limestone 
 have been carried in patches upward with the Archaean mass 
 to form the South Mountain, and thus rise hundreds of feet 
 above the much younger Mesozoic rocks to the south and 
 the slates to the north. The Oriskany and Medina forma- 
 tions make parallel ridges in the same region that remain 
 intact, while the Marcellus (older than the former) and 
 Lower Helderberg (older than the latter) form deep valleys 
 on their northern flanks. 
 
THE ROCKS. 
 
 We are acquainted with the components of the crust at 
 limited depths by the deformation of some portions and 
 their exposure through denudation. It has been observed 
 that each portion of the crust maintains a temperature de- 
 pendent on the local annual mean at its surface, but that 
 there is an increase on going towards the centre. With a 
 constant pressure at all depths there would finally be 
 reached, even at the lowest rate of increase, a depth whose 
 temperature would suffice to fuse all known substances, 
 without the aid of moisture, which lowers the temperature 
 of fusion. Volcanic extrusions prove that such tempera- 
 tures exist at depths, and with an abundance of moisture, as 
 the accompanying gases, which cause the explosive effects 
 of eruption, contain 99$ of water. Astronomically the earth 
 acts as a rigid body, so that geologists agree that it is prac- 
 tically solid, and that whatever portion exists of sufficient 
 temperature to be fluid at ordinary pressures must consist 
 of an interstratum, between the centre and crust, so strongly 
 compressed as to act as a solid, but which may become lo- 
 cally fluid by crustal adjustments which abate the pressure. 
 The portion thus liquefied may have been formerly at or 
 near the surface as a solid rock, or an aggregate of sedi- 
 ments with its interstitial water. In either case an absolute 
 fluidity would destroy all traces of original structure and 
 allow a rearrangement of molecules. A cooling of this 
 
 92 
 
THE ROCKS. 93 
 
 magma would produce a rock which, as far as structure or 
 texture is concerned, might have been formed in the earliest 
 geological period ; but, as far as origin is considered, may be 
 a complete metamorphism of an aggregate of later sedi- 
 ments. All rocks formed from a state of fluidity such that 
 absolute freedom of motion existed among the molecules 
 will be called primary eruptive, or massive ; the terms massives 
 and eruptives will also be applied. 
 
 In a fluid magma of one element there would be no 
 tendency to disassociation, and no crystallization till the tem- 
 perature approached the point of saturation. In nature the 
 magma contains a large number of elements of varying af- 
 finities and gravities, and capable of forming bodies of widely 
 varying fusibility. Sorby was the first to propose a theory 
 of segregation of magmas into strata of varying densities or 
 fusibilities, and this was modified by v. Richthofen to account 
 for an order of effusions in a given district. Iddings has 
 lately formulated a law that the effusions from a magma are 
 primarily of its average composition, but are subsequently 
 differentiated so that later outpourings become nearer the 
 extremes of acidity and basicity with the lapse of time, and 
 the final ones reach those extremes. In studying the extru- 
 sions of a region that are of nearly the same age, and in the 
 examination of a specimen under the microscope, it is found 
 that differentiation takes place before and after extrusion, so 
 that from a magma of mean composition there may be dif- 
 ferentiated two outflows, which show their origin by their 
 intimate association, as an acid aplite and a basic minette 
 from a granitic magma, a camptonite and bostonite from 
 gabbro. The two outflows are found frequently in the 
 same fissure, and, locally, each as the envelope of the other. 
 It has been abundantly proven that the most basic rocks 
 are of the lowest fusibility, and first to crystallize ; that the 
 mineral components of a given rock form in the order of 
 
94 MANUAL OF LITHOLOGY. 
 
 their acidity ; and that the bath becomes more acid after 
 each crystallization, so that quartz, the most acid, if pres- 
 ent, fills the residual interstices. It has also been frequently 
 shown that the crystals sink in the bath. Zirkel notes 
 instances in granite apophyses where the intruding rock lost 
 first its basic content of phenocrysts (mica), next the feldspar,, 
 so that the ends contained granular quartz only ; and in ex- 
 trusions of obsidian Becker notes that the upper portions are 
 frequently free from crystals, and are most acid, while the 
 crystals are accumulated at the bottom of the flow. Zirkel 
 has compiled a multitude of rock analyses to show that 
 the groundmass of a rock is more acid than the rock 
 average. 
 
 Rosenbusch calls the period of original crystallization in. 
 the hot abysses intratelluric. With a slow rate of cooling 
 the intratelluric crystals would continue to grow as long as- 
 the bath maintained its fluidity, and was sufficiently 
 saturated with the necessary molecules; or until the arrival 
 of a period when other compounds began to crystallize ; or,, 
 again, until the temperature of the bath fell below the point 
 of fluidity. As the bath became crowded with crystals the 
 interstitial spaces would become constricted, and those 
 minerals subsequently formed would be obliged to modify 
 their shape unless they could push aside the enclosing 
 members of former crops, until the mass became solid from 
 the closing of these irregular and gradually diminishing in- 
 terstices by those last to crystallize. The first to form do 
 not always attract all of the molecular compound in the bath, 
 as the second generations frequently show repetitions of the 
 intratelluric forms in the groundmass. If an eruption should 
 take place during the formation of the intratelluric crystals,, 
 they would be dashed against the walls of the fracture,, 
 through which the mass would be forced, and eroded, frac- 
 tured, or fissured by the impact ; or would be drawn out,. 
 
THE ROCKS. 95 
 
 twisted, or otherwise deformed if the bath were pasty. All 
 of these conditions are found in the phenocrysts of por- 
 phyritic rocks, and show that they were formed under the 
 above conditions. 
 
 Primary rocks are also called eruptive, as they are the 
 result of a continuous process from the original earth-throe 
 to their solidification in circumscribed areas into which they 
 have been forced. The variations in texture, structure, and, 
 according to Wadsworth and Iddings, mineral composition 
 depend on the rate of cooling. The two authorities named 
 do not lay much stress on the influence of pressure, though 
 others do so to a great extent, and divide rocks into " plu- 
 tonic" (abyssal, abysmal, etc.) and "volcanic," or those 
 formed at depths and at the surface. All porphyritic states 
 can no longer be taken as evidences of intratelluric crystal- 
 lization before effusion, as the researches of Judd, Van Hise, 
 and others show that crystal-building progresses after solid- 
 ification, either through devitrification or through out- 
 growths about crystals or grains, as some quartz-porphyries 
 are found to be devitrified pitchstones. It will require the 
 microscope to distinguish between original and secondary 
 porphyritic states. Chemical bulk analyses can no longer 
 be depended upon for separation of species, owing to the 
 great variation in the values of the elements of the same 
 mineralogical combination, and the high agreement between 
 bulk analyses of widely varying mineralogical compounds. 
 Some of the states formed under different conditions have 
 been already described, but they can be grouped under two 
 main heads, dependent on whether they reached the surface 
 or not. They may be said to have a uniform abyssal ori- 
 gin, but we know them as eruptives. If they were forced 
 towards the surface, but failed to reach it, they were intru- 
 sives ; if they reached it and were effused upon it, they be- 
 came extrusives. The former are distinguished by few or no 
 
g MANUAL OF LITHOLOGY. 
 
 gas-pores (and this is considered a result of pressure), but 
 possessing miarolitic structures (which are thought to be of 
 similar origin) ; the latter are rich in vesicular states, and 
 other evidences of a release of pressure, and a consequent 
 escape of the included vapors. Secondary rocks will be 
 discussed later. 
 
PRIMARY ROCKS. 
 
 It has been conclusively proved by the finding of rhyontes 
 extending from the present to pre-Cambrian times, and 
 quartz-porphyries forming as late as the Eocene, that in all 
 geological times the extrusions have been of the same char- 
 acter ; so that no division can be made in rocks on account 
 of geological age. Studies in Scotland, where high moun- 
 tains allow the same mass to be studied at different eleva- 
 tions, and where the conditions of consolidation were dif- 
 ferent, have shown us deep-seated rocks running into what 
 were once thought to be different forms that were found 
 only at the surface. The cutting of the Comstock lode by 
 the Sutro tunnel showed the same on a grander scale ; so 
 that the old terms " plutonic " and " volcanic " are not so far 
 apart as some would think. In the present treatise the old 
 terms are put aside, as all extrusives are not of volcanic 
 origin, for the greater bulk of surface flows came from dikes. 
 The terms plutonic and abyssal do not lay enough stress on 
 the fact of motion in the body, as most of the rocks have 
 been moved from their places of liquefaction, and are either 
 thrust into or through openings in the crust, and solidify at 
 various depths or at the surface. They are, as before stated, 
 either intrusive or extrusive, and the later statements of Id- 
 dings allow us to be careless of the depth at which rocks 
 solidified, as that had little to do with their mineral com- 
 position, which depending on the rate of cooling. In fine, all 
 rocks are closely related together, and in the following 
 
98 MANUAL OF LITHOLOGY. 
 
 pages instances will be quoted where they have been seen 
 shading from one species to another, or from one state to 
 another. The mineralogical composition of rocks is taken 
 as the basis of division, and of these minerals only those 
 which are necessary for the rock species are meant. These 
 necessary minerals can be divided into six groups, as fol- 
 lows : 
 
 (a) The black bisilicates (pyroxenes, amphiboles, micas), 
 which are found as essential ingredients in all the modern 
 rock systems. 
 
 (b) Quartz. 
 
 (c) Alkali feldspars. 
 
 (d) Plagioclases. 
 
 (e) Feldspathoids (nepheline, leucite, haiiyne, melilite). 
 (/) Olivine. 
 
 The first of these is the basis for classification, and the 
 various rocks will be divided as they contain one of these 
 groups or the minerals commonly associated with them ; 
 thus, granite is a combination of mica with quartz and an 
 alkali feldspar. Other occurrences of mica are with pre- 
 dominant pyroxenes or amphiboles. In the granite group 
 mica js predominant ; but the term " granite " is extended 
 to include eruptives of predominant quartz with a small 
 content of tourmaline, or predominant feldspar with little 
 quartz or mica. In the same way, in the pyroxene group, 
 gabbro consists of pyroxene, plagioclase, olivine, and mag- 
 netite. Segregations along the selvages of such dikes 
 show rocks that are little more than aggregations of mag- 
 netite ; and some authorities class this mineral as a variety 
 of gabbro. On this basis the mica rocks are found to be 
 the most acid, and the mica varieties of other rock groups 
 carry the highest silica contents ; the amphibole rocks are 
 intermediate in both mineralogical and chemical constitu- 
 ents ; and the pyroxene rocks are the most basic. Olivine is 
 
PRIMARY ROCKS. 99 
 
 the antithesis of quartz, and each is important where the 
 other is rare. We arrange the rocks as : 
 
 1. Acid (mica, alkali feldspar, and quartz). 
 II. Intermediate (amphibole, feldspar subordinate 
 quartz, mica, pyroxene, feldspathoids, and olivine). 
 
 III. Basic (pyroxenes, plagioclases, feldspathoids, and 
 olivine). 
 
 For the purpose of general description rocks can be 
 divided into various combinations of the above minerals, no 
 matter whether those were formed in masses, apophyses, 
 dikes, or extruded sheets. The conditions found in dikes 
 are simulated in the selvages of masses, while wide dikes 
 show the same differentiations in texture that obtain in 
 masses ; and as many of the distinctions between dike and 
 other intrusive states depend on the microscope, these 
 states will be included under the typical combination, with 
 a statement that they are otherwise classed by some author- 
 ities. 
 
 The acid rocks will have above 66$ of silica, and the ultra- 
 acid a great content of free quartz ; their color is generally 
 light, and their texture frequently compact-vitreous, but 
 seldom amygdaloidal in structure. The intermediate rocks 
 are generally darker in color than the acid, with higher 
 specific gravity, a greater tendency to amygdaloidal states, 
 and with fewer examples of vitreous-compact textures. 
 The basic rocks are dark, with high specific gravity, few 
 vitreous, but abundant vesicular and amygdaloidal states. 
 In general, the specific gravity and percentages of soluble 
 matter in rocks are inversely proportionate to the silica con- 
 tent. Acid rocks are more generally distributed over the 
 globe, and form the axes of the great mountain ranges and 
 systems ; while basic rocks are local, and form the effusions 
 of isolated volcanoes, or the eruptions through fissures of 
 varying extent. 
 
100 MANUAL OF LITHOLOG Y. 
 
 Recurring to the two main divisions of extrusive and 
 intrusive rocks, we can distinguish intrusive rocks as more 
 crystalline, extrusive as more compact ; intrusives as lack- 
 ing vesicular states, extrusives as abounding in them ; 
 intrusives as exhibiting more porphyries, extrusives more 
 porphyritic states ; intrusives as cooled under great press- 
 ure and sometimes with great slowness, extrusives as cooled 
 more or less rapidly and under little pressure. 
 
 As an example of the association of rocks in a group, the 
 rhyolite-granite group will be briefly described to show 
 the method followed in this book. Granite is a coarse crys- 
 talline-granular (granitoid) rock (intrusive), which is found 
 in large bosses which are frequently fringed by apophyses 
 into the surrounding country-rocks. The cooling effect of 
 the country increases as the apophyses narrow, so that the 
 granitic filling of the fissure shows a gradual diminution in 
 the size of the crystals till a compact texture is reached, and 
 this changes from stony to vitreous as the fissure-end is ap- 
 proached. These crystalline, stony, or vitreous states may 
 or may not contain phenocrysts, and thus form porphyritic 
 states, or porphyries. We thus find " granite " in the crys- 
 talline state ; " granite-porphyry," if microcrystalline with 
 phenocrysts ; " felsite," if stony; " quartz-porphyry," if quartz- 
 ophyric; " pitchstone," if a vitrophyre; and " pitchstone-por- 
 phyry," if with phenocrysts. These would have an average 
 chemical composition and be formed under pressure, but they 
 would vary in rapidity of cooling. If a dike ran from this 
 granitic magma to the surface, and through this a flow of fluid 
 rock were forced during along period, and sufficient to thor- 
 oughly heat the dike-walls, and if this flow should cease, 
 leaving the fissure filled with molten material, and we could 
 follow it from below to the surface, we should find the filling 
 to be granite at such depths that the original heat supple- 
 mented by that received through the flow had been sufficient 
 
PRIMARY ROCKS. IOI 
 
 to heat the dike-walls to, or nearly to, the temperature of the 
 fluid filling, so that cooling could proceed slowly. Passing- 
 upward through the depths, we should arrive at points where 
 the dike-walls were less heated, and the quicker cooling 
 would form, with gradual losses of heat, granite- and quartz- 
 porphyries or felsite, while the portions thrust into fissures 
 radiating from the dike, and formed at the time of the orig- 
 inal fracture, would form the vitrophyres. These would all 
 be at points so far below the surface that the hydrostatic 
 head of the fluid would act against the expanding gases 
 sufficiently to obliterate vesicular states, or (?) the gases 
 might escape into the porous dike-walls. As the surface 
 was neared and the pressure lessened, the vesicular states 
 would become more prominent ; and if the dike-walls were 
 sufficiently hot, or if the flow at the surface were sufficiently 
 thick, crystallization would take place under conditions of 
 great slowness ; but the greatly lessened if not almost want 
 of pressure would allow the crystals to form with a 
 trachytic facies, and include between them microscopic 
 blow-holes. A more rapid rate would cause the mass to 
 solidify with a rhyolitic facies ; while the portions forced 
 into crevices near the surface would become trachytic pitch- 
 stones, rhyolitic pitchstones, etc., according to their facies, 
 and the surface of the flow would show states of perlite and 
 obsidian. Under this theory all members of the granite 
 group may have been formed at, or nearly at, the same 
 time and from the same magma, by variations in cooling 
 and pressure, and all of the group are equally eruptive. 
 According to their depth from the surface, they can be 
 separated into : 
 A. The intrusive states. 
 
 C. The crystalline textures. 
 
 P. The microcystalline to compact textures, with or with- 
 out phenocrysts, and non-vitreous. 
 
IO2 MANUAL OF LITHOLOG Y. 
 
 V. The compact-vitreous textures, with or without 
 phenocrysts. 
 E. The extrusive states. 
 
 C., P., and V. As above. 
 
 AC. Granite, porphyritic-granite. 
 
 AP. Granite-porphyry, quartz-porphyry, felsite. 
 
 AV. Pitchstone, pitchstone-porphyry. 
 
 EC. Rhyolite. 
 
 EP. Porphyritic states. 
 
 EV. Perlite, obsidian, pumice. 
 
 As the extrusive states are more common and more 
 readily accessible, they will be first treated ; but the groups 
 will be named after both extrusive and intrusive states for 
 readiness of correlation in the field thus, the above group 
 will be styled the rhyolite-granite group. 
 
 It may be well to again call attention to the fact that, 
 in general, the vitreous states of a given rock group are 
 more acid than the crystalline states, especially if an in- 
 tratelluric crystallization began in the magma before erup- 
 tion, as the more basic minerals crystallize first, and the 
 magma thus becomes more and more acid with each sue- 
 
 c> 
 
 ceeding addition to the phenocrysts ; so that a sudden cool- 
 ing would show a vitreous state more acid than the original 
 magma. In general, the extent of the development of the 
 vitreous states of a rock is proportional to its acidity, and 
 in the ultra-acid rocks large masses have a glassy habit, 
 as the obsidian cliff in the Yellowstone National Park. In 
 basic rocks the extent of the vitreous development is con- 
 tracted, till it is limited, in the ultra-base rocks, to a thin 
 lining of vesicular cavities, thin selvages in contact with 
 the country rock through which the eruptive was forced, 
 thin crusts on the surface of sheets or streams, or, finally, 
 narrow dikes of a few inches, or minute apophyses. There 
 are very few rock groups that do not show glassy states 
 
PRIMARY ROCKS. 1 03 
 
 under both intrusive and extrusive conditions ; the syenites 
 alone have not been found with them. Many of these vitre- 
 ous states are characteristic and quite readily distinguished ; 
 but in the majority of cases they cannot be determined by 
 the naked eye, and even chemical and microscopical analyses 
 fail to separate certain basic forms, when separated from 
 the accompanying crystalline states. The intrusive vitro- 
 phyres can generally be distinguished from their extrusive 
 neighbors by their lower density, and the general absence 
 of vesicular structure. In general, the acid varieties are 
 of lighter color than the basic ; but in the same extrusive 
 acid state, if the rock be compact, the more rapid the cool- 
 ing the darker the color, as is seen in the case of furnace 
 slags, which vary from a blackish gray highly vitreous 
 rock to a grayish white feebly lustrous state. Many vitro- 
 phyres have lost their lustre through devitrification 
 {see p. 61). 
 
 Extrusive rocks are found as lava streams with amygda- 
 loidal, vesicular, scoriaceous, columnar, fluidal, and other 
 structures. These may have issued from a central vent in 
 recurrent streams, as in a volcano, or through an extended 
 fissure in a single outpouring which, by cooling, closed the 
 fissure permanentlv, as in a sheet eruption. Subsequent 
 erosion removed the scoriaceous surface and reveals the fill- 
 ing of the volcanic vent as a neck or plug, and of the sheet 
 as a ridge which may have a breadth measured by inches 
 or rods, and a length up to hundreds of miles. The name 
 dike is given to this denuded filling (from its shape), and 
 thence to the whole filling, and many authorities have sepa- 
 rated dike and volcanic extrusions on the score that ve- 
 sicular states were wanting in dikes, forgetting that the 
 lapse of time has allowed these to be removed, with the 
 original surface, by denudation, so that we see only the 
 filling of the fissure at depths. Extrusions through dikes 
 
IO4 MANUAL OF LITHOLOGY. 
 
 and plugs are therefore old ones. The rocks of this class 
 melt at varying temperatures, of easy, medium, and difficult 
 fusibility, which, according to Barus, are : 
 
 2250 F. for basalt and the basic rocks ; 
 
 2520 F. " andesite and the intermediate rocks ; and 
 
 3100 F. " trachyte and the acid rocks. 
 
 It has been found that basic extrusions are very fluid ; 
 spread over the country in thin sheets, and form mountains 
 of low angle ; while the acid types swell into lofty and cir- 
 cumscribed hills (puys, mamelons) or form cones of con- 
 siderable angle. Deformations of the earth's crust accom- 
 panied by intruded masses produce fractures of varying 
 sizes and dimensions. These fractures may have 
 
 (a) Three dimensions of considerable and comparable 
 extent, and may run 
 
 1. Across stratification planes without unduly forcing 
 apart the strata ; 
 
 2. Along stratification planes on either side of a fissure 
 from the side or below, and, by uplifting the overlying beds, 
 form an arch that may be ten thousand feet in height, and 
 of comparatively limited area along the stratification 
 planes ; or 
 
 (b] One small and two large dimensions. Fractures of 
 this kind generally ramify from those of the first class, and 
 their walls may : 
 
 3. Rapidly approach one another to form a root or 
 wedge-shaped opening; or 
 
 4. Extend parallel to one another indefinitely, and across 
 or parallel to bedding planes. 
 
 The material injected into these will form in 
 
 1. An irregular body that, if large, will cool slowly and, 
 if abyssal and under pressure, as in granite, gabbro, etc., will 
 form a boss. 
 
 2. A similar body that will of necessity cool under some- 
 
PRIMARY ROCKS. IOJ> 
 
 what less pressure, to form a laccolite (Gilbert), or the modi- 
 fied term laccolith (]. D. Dana). 
 
 3. A body of limited extent, which is generally considered 
 in connection with the body from which it is an offshoot. 
 These bodies are variously named ; but the fact of the 
 association just given makes the term apophysis (plural 
 apophyses, from Greek " an offshoot ") most applicable, as 
 " vein " is better confined to fillings of fissures crystallized 
 from aqueous solutions. 
 
 4. A sheetlike body, which is best termed a sheet. If it 
 runs across the strata and appears at the surface as a con- 
 siderable outflow, the surface part is called an extrusive 
 sheet ; but if narrow, a lava stream, as in the case of a vol- 
 cano. The intrusive part below the surface is variously 
 named ; if nearly vertical and across the strata, it forms a 
 dike ; all portions parallel to the strata form intruded or 
 bedded sheets or sills ; and where the filled fissure runs alter- 
 nately with and across the strata, it is said to be stepped. 
 Some authorities restrict the term " sheet" to surface flows, 
 and call underground portions " dikes " or " interbedded 
 sheets," as they happen to cut across or run with the 
 strata. 
 
 Owing to the greater extent of bounding surface to a 
 given bulk of injected matter in forms of the third and 
 fourth kind, the cooling is more rapid and the size of crystals 
 smaller. When sheets extend from deep-seated bosses to 
 the surface, they show all varieties of structure between in- 
 trusive and extrusive rocks in the same mass. The boss 
 shows the largest crystals towards its centre, and these di- 
 minish in size towards the walls, but not to a great extent 
 if those walls were so deeply seated as to be within a region 
 of great heat, or if the eruptive material had been forced 
 through the cavity and its fissures long enough to heat the 
 walls to a great depth. The cooler the walls the more 
 
106 MANUAL OF LITHOLOGY. 
 
 rapid the crystallization, until, with sudden cooling 1 , a com- 
 pact mass is formed that will show phenocrysts, in case 
 crystallization began before eruption, and will be called a 
 porphyry. Where pressure began to disappear, the in- 
 cluded gases expanded to form vesicles, and the propor- 
 tion of these increased with nearness to the surface where 
 the lava was blown up to form a foamy, slaggy mass. 
 
 The primary rocks, as just stated, are grouped in three 
 divisions, as they have mica, hornblende, or pyroxene as a 
 characteristic component. < This does not presuppose that 
 they are necessary components of all the varieties of the di- 
 vision to which they belong ; it indicates that the minerals 
 grouped with it are found more frequently combined with it 
 than with either of the other two black bisilicate groups. 
 Each division is composed of rock series, and these are subdi- 
 vided into groups which may have in combination but one of 
 the necessary minerals of the division, as the gabbro series with 
 necessary plagioclase, feldspathoids, pyroxene, olivine, and 
 magnetite embraces groups which have but one of the 
 above as a necessary component, as plagioclase for the 
 anorthosites, olivine for the so-called peridotites, etc. 
 
 The following skeleton will show the method of arrange- 
 ment of the rocks : 
 
 ACID DIVISION. 
 
 MICA : Quartz, alkali feldspar, plagioclase, amphibole, pyroxene, 
 magnetite, feldspathoids, olivine. 
 
 Extrusive, Rhyolite ; Intrusive, Granite. 
 INTERMEDIATE DIVISION. 
 
 AMPHIBOLE: Feldspar, quartz, mica, pyroxene, feldspathoids, mag- 
 netite, olivine. 
 
 Extrusives, Trachyte, Phonolite, Andesite. 
 Intrusives, Syenite, Elseolite- syenite, Diorite. 
 BASIC DIVISION. 
 
 PYROXENE : Plagioclase, feldspathoids, olivine, magnetite, amphibole, 
 mica, orthoclase, quartz. 
 
PRIMARY ROCKS. IO/ 
 
 The intermediate and basic divisions will be fully ar- 
 ranged before the rocks they comprise; the acid division is 
 a simple one and fully arranged above. In the following 
 definitions the signs (M) and (m) will be used as stated in 
 the introduction ; (M) referring to the megascopic appear- 
 ance of a rock, or the manner of its appearance as viewed 
 with the eye or a lens, and (m) to the same as seen with a 
 microscope, or of such a size that it can be seen only with 
 that instrument. 
 
 ACID DIVISION MICA ROCKS. 
 
 This is the most widely spread over the earth's surface, 
 and in the greatest abundance ; and it has been the longest 
 stadied of all the divisions. It comprises but one series 
 that of rhyolite-granite ; but that is greater in bulk than 
 all of the others combined. As the extrusives are the sur- 
 face forms, they will be treated first. 
 
 GROUP I. RHYOLITE-GRANITE. 
 
 ACID EXTRUSIVES. 
 (Necessary minerals : Quartz and an acid feldspar.) 
 
 I. Rhyolite. 
 II. Rhyolite Glass. 
 
IO8 MANUAL OF LITHOLOGY 
 
 I. RHYOLITE. 
 
 RHYOLITE (v. Richthofen), Liparite (J. Roth),. 
 
 Quartz-trachyte (J. Roth). 
 
 A compact (sometimes cavernous or drusy) groundmass 
 containing crystals or crystalline grains of sanidine 
 and quartz. The latter is usually (M), but invariably 
 (m). As (M) essentials tridymite and magnesia-mica 
 and (m) magnetite are frequent, and both (Mm) plagio- 
 clase, muscovite, hornblende (in prisms), bronzite, hy- 
 persthene, and augite are infrequent or rare. As (M) 
 accessories red garnet and cordierite appear in the 
 mixture, and topaz, spessartite, and fayalite in druses. 
 Silica 75-82 ; Gr. 2.4-2.6; H. 5.5-6. 
 
 Rhyolite is not known as the lava of an active volcano, 
 but it is abundant in beds and sheets, and in plugs and 
 dikes. It is extensively developed in central, southern, and 
 southeastern Europe, Great Britain, Iceland, East Indies, 
 New Zealand, South America, and extensively in the west- 
 ern part of North America, and especially of the United 
 States. A great development of devitrified pre-Cambrian 
 rhyolite occurs along the South Mountain, across the border- 
 line of Pennsylvania and Maryland. (See later under 
 " Aporhyolite.") 
 
 The groundmass when compact is felsitic (as in quartz- 
 porphyries), like claystone, hornstone, porcelain, and 
 crockery-ware. The fracture is flinty, splintery, conchoidaL 
 When cavernous, the cells or cavities are sometimes round, 
 sometimes narrow and parallel, sometimes large and ir- 
 regular. The cavities are sometimes filled with chalcedonic 
 material, hornstone, or jasper; sometimes with quartz and 
 amethyst, as well as the minerals noted in the definition. 
 The structure is sometimes plane-parallel (schistose) and 
 sometimes fluidal, with such minute divisions that each is no 
 
PRIMARY ROCKS. 
 
 thicker than a sheet of paper. The colors are white, yel- 
 lowish white, greenish white, pearl-gray, reddish white, ash- 
 gray, reddish yellow, greenish yellow, pink, and brick-red. 
 The feel is usually smooth, but sometimes rough and harsh 
 in the porous states. The luster is usually shining and semi- 
 vitreous, but frequently dull and earthy. The sanidine is 
 sometimes 5 cm. long, but in the United States has not been 
 reported larger than 3 mm. The much-fissured and frac- 
 tured crystals frequently show Carlsbad twinning. The 
 plagioclases are of frequent appearance, but of small pro- 
 portion in the mixture, and they are usually more or less 
 completely kaolinized, so that chemical analyses are neces- 
 sary to distinguish them. The quartz occurs in crystals 
 and rounded grains, or fragments of grains, in sharp con- 
 trast to the groundmass. The color is clear smoke-gray to 
 black, and in size up to a hazel-nut. It is distinguished (Zir- 
 kel) from that of granite by glass inclusions, that are some- 
 times i mm. thick, and by the absence of fluid inclusions. 
 The quartz of quartz-porphyry is distinguished from the 
 two by containing both. Many rhyolites show no (M) 
 quartz, and it seldom appears alone. The magnesia-mica 
 is biotite and frequently occurs in small quantities, and in 
 many rhyolites it is the most conspicuous mineral, and gen- 
 erally abundant in American types. It is sometimes chlori- 
 tized. The black bisilicates are seldom plentiful, and only 
 in scattered cases (M}. Hornblende is the most common, 
 with augite and rhombic pyroxene much less prominent 
 either (M) or (m). Tridymite is abundant in the rocks of 
 the United States, and frequently (M) in druses and cavities, 
 but not in the mixture. Of the accessories, garnet i mm., 
 cordierite 1-3 mm., topaz 3-10 mm., spessartite 2.5 mm. 
 to i cm., and fayalite i mm., occur. In some cases the 
 groundmass is full of spherulites, which cause the rock to 
 -appear perlitic. They are sometimes 5 mm. in diameter. 
 
IIO MANUAL OF LITHOLOGY. 
 
 (a) Lithoidite (v. Richthofen). A compact felsitic ground- 
 mass with hornstone fracture; hardness of feldspar and habit 
 like clay stone; generally light-colored; no (M) quartz, and 
 almost none (m), so that its greater proportion of silica alone 
 separates it from trachyte. The fresh groundmass is 
 porcelain-like with conchoidal-splintery fracture ; luster 
 waxy, with few minerals showing. 
 
 (b) Millstone-porphyry (popular name in Hungary). A 
 felsitic groundmass, like claystone, of dark grayish, yellow- 
 ish shades, or brick-red, full of cells or cavities filled with 
 chalcedony, hornstone, jasper, quartz, and amethyst. It con- 
 tains 70$ of silica. 
 
 (c) Nevadite (v. Richthofen), Granitoid Rhyolite. A dif- 
 ference of opinion exists as to the existence of. a ground- 
 mass. Rosenbusch describes the rock as lacking one, but 
 Zirkel calls attention to the fact that v. Richthofen noted a 
 small proportion in his definition. There are thus types 
 called nevadite with and without a groundmass, which, at 
 best, is of small proportion. Nevadite is a crystalline ag- 
 gregate of quartz, feldspar, biotite, and hornblende in a 
 limited groundmass of similar composition with a micro- 
 scopic or amorphous texture. Hague and Iddings report 
 that the original nevadite of v. Richthofen is a dacite, but 
 they found in the Great Basin a rock of the above descrip- 
 tion, and Cross found the same at Leadville. 
 
 (d) Liparite. A felsitic and porphyritic rhyolite with a 
 stony groundmass, and bearing to rhyolite the same relation 
 that felsite-porphyry does to felsite. Rosenbusch distin- 
 guishes sanidine and albite liparites, but the word is used 
 more in the sense of rhyolite. 
 
 (e) Soda-rhyolite. From Berkeley Hills, Cal. Silica 
 75.46 ; Gr. 2.42. 
 
 (/) Aporhyolite (Bascom). A name given by Miss Bascom 
 to devitrified rhyolite. It occurs in extensive masses in the 
 
PRIMARY ROCKS. Ill 
 
 South Mountain of Pennsylvania and Maryland, and has 
 been completely recrystallized to form a mosaic. These 
 rocks were distinguished by the late G. H. Williams. They 
 are pink, and retain fluxion structures and lithophysse of 
 large (M) dimensions. Subsequent action has sheared them 
 so that slaty cleavage has developed. 
 
 The rhyolites can be told from the quartz-porphyries by 
 the greater luster of the groundmass, and by the fewer pheno- 
 crysts ; and nevadite can be distinguished from granite by 
 the presence of a groundmass, and by the rock being por- 
 phyritic, and not crystalline. 
 
 II. RHYOLITE AND TRACHYTE GLASS. 
 
 The vitreous states of the rhyolites cannot very well be 
 distinguished by the microscope from similar states of the 
 trachytes (Group 2, with necessary alkali feldspar and one 
 of the black bisilicates, but with a high degree of acidity) in 
 hand specimens. Their occurrence is by far more prevalent 
 with the more acid rhyolites than with the trachytes, but, 
 owing to the similarity of the states of these rocks, they will 
 be described together, as chemical analyses are necessary to 
 distinguish between them. We unite, therefore, 
 
 Group I. Rhyolite-granite (necessary minerals quartz 
 and an alkali feldspar) ; 
 
 Group 2. Trachyte-syenite (necessary minerals an al- 
 kali feldspar and hornblende). 
 
 PERLITE, Pearlstone. 
 
 A matrix, sometimes glassy, more frequently enamel-like, 
 pearly, or greasy on a fresh fracture, containing many 
 round grains of a concentric or shaly structure. 
 
 Silica 70-82; water 0-4; Gr. 2.3-2.4; of the 
 spheroids, 2.37-2.54. 
 
 The color is mostly pale gray, lavender-blue, and dark 
 
112 MANUAL OF LITHOLOG Y. 
 
 gray, though sometimes yellowish brown. The spherules 
 vary in size from i mm. to an inch in diameter. They 
 are probably caused by contraction in the cooling mass, as 
 in some basalts. They are sometimes shelly ; sometimes com- 
 pact, and sometimes radially striped. Their composition is 
 felsitic. The rock frequently contains nests and cracks 
 which are lined or filled with fire-opal, precious opal, jasper, 
 and semi-opal. 
 
 (a) Porphyritic Perlite, showing, with the spherules, abun- 
 dant phenocrysts of sanidine and plagioclase (with sometimes 
 anorthoclase), black mica in sharply defined lustrous folia, 
 and sometimes pyroxene and hornblende. Quartz now and 
 then occurs, and in one or two instances hypersthene and 
 bronzite. Occasionally red garnets are found. 
 
 (b) Obsidian-perlite. This is a state when the dense mass 
 preponderates and the spherules are not abundant. 
 
 (c) Vesicular Perlite. Here the mass is more or less ve- 
 sicular, and the color grows lighter with the percentage of 
 pores till it becomes snow-white. In this mass the spherules 
 are sporadic. 
 
 (d) Tr achy tic Perlite. A perlitic glass colored from light 
 to dark or greenish gray, with sanidine, plagioclase, and 
 biotite at times hornblende and augite. This occurs with 
 trachyte at Cervetri, near Sasso, Italy, and elsewhere. The 
 majority of the perlites are states of rhyolite. 
 
 These rocks are found with the rhyolites abundantly in 
 the Lipari Islands, in Hungary, New Zealand, Mexico, and 
 the western part of the United States. They occur in thick 
 lava-streams and in dikes. A variety is 
 
 Marekanite (Herter). A velvet-black mass from Mare- 
 kanka, Siberia, with abundant small glass spherules of 
 smoke-gray to orange-brown color, and great transparency. 
 
PRIMARY ROCKS. 113 
 
 RHYOLITIC PITCHSTONE. 
 
 A vitreous or semivitreous compact rhyolitic glass of 
 high acidity and varying color, with greasy or pitchy 
 luster, and invariably containing chemically combined 
 water. 
 
 Silica 66-80; water 3-10; Gr. 2.2-2.4; H. 5-6.5. 
 
 Both rhyolite and trachyte are accompanied by pitch- 
 stones, but, as the greater number occur with rhyolite, the 
 assembled specimens are placed under the name of the former. 
 They bear to them the same relation that the felsite pitch- 
 stones do to the quartz- and felsite-porphyries. They are 
 found at Hlinik, Hungary, in Italy, the Hebrides, Iceland, 
 Nevada, Utah, Mexico, and South America. They are 
 mainly of a dirty green, dark-brown, or black color, and 
 conchoidal fracture. Though they may have the same luster 
 as obsidian, they can be distinguished from it by their con- 
 tent of water, as obsidian does not carry above one per cent. 
 They commonly show (m) phenocrysts of white or colorless 
 feldspar (sanidine or plagioclase), and sometimes augite and 
 quartz. Rarely and in inconsiderable amounts they show 
 {m) garnet, biotite, what seems to be anorthoclase, pyrite, 
 pyrrhotite, and gold. They melt with more or less difficulty 
 to a frothy glass or a grayish-greenish enamel, and give 
 water in the closed tube. They are untouched by acids. 
 
 (a) Trachytic Pitchstone-porphyry. At Eigg, Hebrides. A 
 velvet- to violet-black, very slightly lustrous rock, rich in 
 sanidine and single plagioclases of large size, prisms and 
 grains of augite, and particles of magnetite ; also pyrite 
 (Italy) and olivine (Gough's Island). Silica 61-71. 
 
 (b) Perlitic Pitchstone. From Massai Land, South Africa. 
 A glass carrying perlitic spherules with (M) quartz, bluish 
 grains of arfvedsonite, and (m) sporadic brown hornblende 
 and feldspar. 
 
114 MANUAL OF LITHOLOGY. 
 
 (c) Pumiceous Pitchstone. All pitchstones of this group- 
 show (m) an abundance of minute vesicles from the expand- 
 ing steam. These are usually drawn out from the flow of 
 the mass, and occasionally they are so expanded and so 
 abundant as to form a pumice. 
 
 RHYOLITIC OBSIDIAN, Volcanic Glass. 
 A compact glass of varying color and luster, of high 
 acidity, and with content of chemically combined 
 water never more than one per cent. 
 
 Silica 70-77 ; Gr. 2.35-2.45 (average 2.4) ; H. 6-7. 
 
 Obsidian is a volcanic glass and forms the surface of 
 quickly cooled acid lava-streams. In general, the thickness of 
 the glassy state is inconsiderable ; rarely as at Obsidian 
 Clifi, Yellowstone Park it forms a rock of extensive dimen- 
 sions which is entirely of this state. It is found less fre- 
 quently with trachytic than rhyolitic effusions. In the 
 western part of the United States it is extensively developed, 
 also in Mexico, and the natives used it for knives, heads for 
 spears and arrows, axes, etc., some of which have been found 
 east of the Mississippi. In its compact state the steam 
 vesicles are not abundant (m) in the average specimens ; 
 but whenever found they are egg-shaped or drawn out to 
 threadlike openings, with the longer axes parallel to the 
 line of flow. Fluxion -structures are common. The color 
 in the transparent varieties is generally uniform, but streaks 
 and parallel banded varieties are common. The shades are 
 light or dark gray, green, grayish blue, and yellowish brown. 
 It is sometimes almost colorless, and sometimes so black as 
 to be translucent only on thin edges. It fuses on the edges of 
 thin splinters, but gives no water in the closed tube. Its 
 hardness is greater than that of basalt glass. 
 
 (a) Typical Obsidian. A clear, transparent glass, free from 
 crystals or inclusions of any kind. It is found on the edges 
 
PRIMARY ROCKS. 11$ 
 
 of streams as thin crusts, in Siberia, Iceland, and New 
 Zealand, and also occurs in large masses as above stated. 
 
 (b) Porpliyritic Obsidian. An obsidian mass carrying (M) 
 phenocrysts of sanidine, plagioclase, laminae of biotite, augite, 
 and quartz, or some of them. This is common in certain 
 parts of the mass. 
 
 (c) Spherophyric Obsidian, when the glassy mass carries 
 colorless, grayish white, yellowish, bluish waxy spherulites 
 of more or less radial structure, which sometimes have a 
 parallel arrangement. 
 
 (d) Lithophysic Obsidian, when the spherulites are con- 
 centric and form lithophysas (p. 78). They are generally 
 rich in (in) minerals, sometimes visible with the lens, as 
 olivine, fayalite, quartz, tridymite, etc. 
 
 (e) Vesicular Obsidian, when the mass contains a large 
 proportion of vesicles, so as to make a slaggy structure, 
 with stretched and parallel arrangement. This is transitional 
 to pumice. 
 
 (/) Trachytic Obsidian. This is found on the surfaces of 
 trachytic lavas in Italy, the Azores, and elsewhere. It is a 
 yellowish, greenish, brownish, or pitch-black transparent 
 glass with feldspar, biotite, and much augite. Contains 
 silica 60-63 ; Gr. 2.44. It occurs in porphyritic, pitchstone- 
 like, and vesicular states. 
 
 (g) Bottlestone (Ger. "Bouleillenstein") Pseudochrysolite, 
 Moldauite. From near Moldauthein, Bohemia, and else- 
 where. This is held by varying authorities to be natural 
 and highly siliceous glass, and, on the other hand, to be an 
 artificial product. Rutley says that it is the former. It 
 occurs in large grains and spheres of transparent glass one 
 inch thick, with irregularly distributed steam vesicles, in 
 sand near the above place, also in tuffs. Contains silica 
 82.70. Similar glasses have been described from other 
 localities, with silica 76-81, and Gr. 2.17-2.35. The break- 
 
Il6 MANUAL OF LITffOLOGY. 
 
 ing of the surface vesicles produces a pitted, corrugated, 
 and wrinkled surface. 
 
 (h) Obsidian Bombs. Clear glass without phenocrysts in 
 shape of bombs, from Australia, and with Gr. 2.41-2.52. 
 
 PUMICE. 
 
 A highly porous and frothy state of rhyolitic obsidian, 
 of light colors, whitish, grayish, yellowish, greenish, 
 but seldom blackish. 
 Silica 73 ; Gr. 2.37. 
 
 This is the surface state of a rhyolitic-trachytic effusion, 
 and occurs especially developed in the Azores, Lipari Isl- 
 ands, Iceland, Mexico, and South America, and in some of the 
 western States of the Union. To a smaller extent it is found 
 on all surface flows of undenuded condition. The pores are 
 sometimes caused by a trachytic structure of the magma, 
 but more commonly by the steam vesicles. It fuses more 
 readily than obsidian before the blowpipe. 
 
 (a) Obsidian-pumice. This is the pumice of commerce, 
 free from phenocrysts, of extremely light colors, approach- 
 ing white, and is extensively found in the Lipari Islands 
 and Iceland. 
 
 (U) Perlitic Pumice. In this rock the tendency to spheru- 
 litic structure was stopped by extrusion to the surface. The 
 vesicles are extremely stretched and parallel, so as to form 
 only threadlike openings, and among them are minute per- 
 litic spheres, as well as phenocrysts of sanidine, biotite, and 
 quartz. This is quite common in Hungary. 
 
 (c) Porphyritic Pumice. In the Eureka district in Nevada, 
 and elsewhere, the foamy mass carries (M) and (m) pheno- 
 crysts of sanidine, plagioclase, biotite, augite, quartz, mag- 
 netite, and sometimes red garnet. In some cases the pores 
 are filled with opal. 
 
 (d) Trachytic Pumice. A vitreous foamy mass, coarse, 
 
PRIMARY ROCKS. II 7 
 
 fibrous, and felty, a cross between a typical pumice and a 
 crystalline magma. This is a transition between obsidian 
 pumice and the porphyritic state. 
 
 (e) Trachyte-pumice. A dark-colored foamy state of 
 trachyte-obsidian, greenish brown, brown, or black, with 62 
 per cent of silica. It occurs in Italy, the Azores, New Zea- 
 land, Philippine Islands, Hungary, and in small exposures 
 in many other localities. 
 
 GROUP II. GRANITE (OESALPINUS). 
 
 ACID INTRUSIVES. 
 
 (Necessary minerals: Quartz and an alkali feldspar.) 
 This group is compounded of the above necessary min- 
 erals, associated with the more acid of the plagioclases ; 
 sparingly of the amphiboles, and still more sparingly of 
 the pyroxenes. With these are combined a large number 
 of accessories. The group is characterized by a variety of 
 states, dependent on varying conditions of solidification, 
 and, as granite is one of the most extensive and well-known 
 rocks, each of these states has been distinguished by a spe- 
 cial name. There is no region of the globe without granite, 
 and in each it is similarly situated with regard to other for- 
 mations, as a foundation, where seen, upon which they have 
 been deposited. It forms the axes of extensive mountain 
 systems, as bosses and laccoliths intruded into later rocks, 
 and as dikes and apophyses which penetrate other rocks 
 even older granites. They afford evidences of their heated 
 state during intrusion by the extensive metamorphism of 
 their enveloping country-rocks, which will be more fully 
 treated Under " Metamorphic Rocks." Some authorities 
 class metamorphic granites with gneisses, and others place 
 the gneisses formed from squeezed granites with them as 
 original states. In this work all rocks that have lost traces 
 
Il8 MANUAL OF LITHOLOGY. 
 
 of secondary origin will be treated as primary. The English 
 authorities are more disposed to treat all granites as erup- 
 tive, while a large number of American authorities place 
 them as the result of complete metamorphism ; but they 
 have been thrust into cracks and cavities, so that they ex- 
 hibit all the apophyses, etc., of eruptive granite, and cannot 
 be told from it in hand specimens. As solidifying under 
 pressure, there are neither vesicular nor amygdaloidal states, 
 though some authorities think that miarolitic structures 
 represent the former. It occurs usually massive, and with 
 thick tabular-jointed structure, and weathers spheroidally to 
 form a kaolin, more or less colored by the iron from the 
 black bisilicates, which contains as angular grains the quartz 
 content of the original rock ; or, in certain loosely cemented 
 and porous varieties, the grains separate to form sand that 
 may be metamorphosed to form arkose, or granitic sandstone. 
 It has already been stated that crystallization in the orig- 
 inal magma originated either with the most basic of the min- 
 eralogical components or, when one composition was greatly 
 in excess, with the predominant compound. In acid gran- 
 ites the quartz is one of the first crystallizations, as shown 
 in quartz-porphyry (unless this state is formed from a sub- 
 sequent devitrification and crystallization of pitchstone, as 
 Judd and others have shown that crystallization can take 
 place in solid rocks). In the average granites the feldspar is 
 greatly in excess and forms the idiomorphic component, 
 while in the basic granites the black bisilicates are first crys- 
 tallized. The average granite, therefore, shows generally 
 -well-crystallized feldspar, with mica following next, and 
 quartz last. With slow cooling the crystals touch one an- 
 other on all sides, and the quartz keys the others into a firm 
 ; mass, with " granitic habit," unlike the porous and open 
 " trachytic " texture of some of the rhyolites, where the 
 crystals touch one another only at one or two points. The 
 
PRIMARY ROCKS. 
 
 members of the granite group are named according to the 
 relative time when and the suddenness with which intratel- 
 luric crystallization was checked. We distinguish : 
 
 I. The entirely crystalline state without (or with few) 
 phenocrysts, and with no base of any sort. Under this is : 
 
 (a) Entirely crystalline and without phenocrysts, as typ- 
 ical granite. 
 
 (ft) The same with phenocrysts, as porphyritic granite. 
 
 II. The subcrystalline state, which is caused by cooling 
 rapid enough to produce a varying proportion of stony (fel- 
 sitic), but not glassy, base, as : 
 
 (a) A crystalline groundmass with more or less base, 
 and carrying phenocrysts, as granite-porphyry. 
 
 (b) A stone (felsophyre) groundmass carrying phenocrysts 
 of quartz and perhaps of other minerals. This can be defined 
 as a" quartzophyric felsophyre " (Dana), or quartz-porphyry. 
 When the phenocrysts of quartz become sporadic, or entirely 
 disappear, it becomes 
 
 (c) A felsophyre with phenocrysts of orthoclase (ortho- 
 phyre) or plagioclase (plagiophyre), and with little or no 
 visible quartz or felsite-porphyry. 
 
 (d) A felsophyre without phenocrysts, as felsite. 
 
 III. The vitrophyric state reached by a cooling rapid 
 enough to form glass, as : 
 
 (a) A vitrophyre with phenocrysts of some of the compo- 
 nent minerals and spherules of felsite, as pitchstone-por- 
 phyry. 
 
 (b) A clear vitrophyre without phenocrysts, as pitch- 
 stone. 
 
I2O MANUAL OF LITHOLOGY^ 
 
 la. GRANITE. 
 
 A coarse- to fine-grained completely crystalline com- 
 pound of quartz and an alkali feldspar (usually ortho- 
 clase, often microcline) and a mica. As essentials, 
 acid plagioclase (usually oligoclase, often albite, now 
 and then andesine), and sometimes hornblende ; rarely 
 a pyroxene. 
 
 Silica 60-82 ; Gr. 2.59-2.73. 
 
 This is an important economic rock in the United States, 
 but has been most highly developed in New England, 
 whence over one-half of the output for 1891 was taken. It 
 is found wherever the Archaean is exposed. The uniformity 
 of its grain increases with its fineness. In the so-called 
 " giant granite " the ingredients are in large masses. The 
 medium-coarse texture is so peculiar to this rock that it 
 supplies the adjective " granitoid " to similar textures in 
 other mineral combinations. A very fine texture forms a 
 " microgranite," as in the states found in dikes and apoph- 
 yses, which are both of fine grain, and, as in quickly cooled 
 states, of higher acidity than the average. The quartz in 
 granite is in angular grains with greasy-vitreous luster, con- 
 choidal fracture, and grayish-white to light-gray color. It 
 is sometimes light blue, dark blue, bluish gray, dark red, and 
 smoky. It fills the interstices between the other minerals, 
 as it was the last to crystallize completely, and locks them 
 together. It frequently occurs crystal in double pyramids, 
 and then, contrary to its habit, is idiomorphic with respect 
 to feldspar, the opposite usually being the case. As crystal 
 it is sometimes % of an inch in size in ordinary granite ; 
 in giant granite it occurs in large masses. In graphic 
 granite and pegmatite it forms thin plates along certain cleav- 
 age-planes of the feldspar (microcline). It is not affected by 
 weathering. The orthoclase is mostly in regular crystalline 
 
PRIMARY ROCKS. 121 
 
 grains. On fresh cleavages it shows a pearly luster. The 
 color is usually reddish white, flesh-red, or yellowish white, 
 infrequently grayish or greenish (amazonstone), rarely deep 
 red, reddish gray, grayish blue. When very fresh, it has a 
 luster like adularia, rarely like sanidine. Twinning occurs 
 generally in porphyritic phenocrysts, not in granitic grains. 
 It twins mostly according to the Carlsbad law (some are 
 five inches long) also that of Baveno. It weathers to mica, 
 kaolin, talc, pyrophyllite, and epidote. Microcline occurs 
 alone ; intergrown with orthoclase ; and replacing it as in 
 pegmatite. Microperthite is frequently found (m). Mica 
 is either in thin irregular folia or hexagonal tables, and 
 scattered sporadically through the mass, except along the 
 selvages of bosses and dikes, where it sometimes (from press- 
 ure, or the influence of the cooling surface) has its planes 
 arranged parallel to the walls of the country-rock to form a 
 schistoid structure. It also occurs in spherical and len- 
 ticular concretions. While muscovite and biotite are gen- 
 erally separate from one another, they are sometimes found 
 (Rosenbusch) in the same folia, one being the rim to the 
 other, or in the same tabular crystal, where they form alter- 
 nate folia, so that optical tests are necessary to distinguish 
 between them. In general, biotite predominates over musco- 
 vite in amount and in regularity of crystallization. Biotite 
 is the more basic, and in varieties of average composition is 
 the earliest crystallization of those already named, and this 
 accounts for its greater regularity of form. It is usually 
 dark brown to iron-black, and seldom greenish. Lepidome- 
 lane also occurs in black folia, often of large size. Zinnwald- 
 ite is found in tin-bearing granites (greisen) in black folia, 
 brown to brownish red by transmitted light. Muscovite is 
 more irregular in its habit than biotite and crystallizes after 
 it, but usually before the feldspars. It occurs in folia and 
 rhombic tables. Lepidolite rarely occurs in ordinary gran- 
 
122 MANUAL OF LITHOLOGY. 
 
 ite. Rosenbusch describes it as the mica in pegmatite. 
 Of the essentials, oligoclase occurs in tabular crystals which 
 are generally idiomorphic with respect to orthoclase and 
 quartz. It is less transparent than the former. To a small 
 extent it forms pegmatitic structures with quartz. Albite 
 and andesine occur now and then in the more basic granites, 
 and labradorite has been reported in one case. Plagioclase 
 is found more abundant in the granitites (biotite-, hornblende-, 
 and augite-granites). Hornblende usually crystallizes in 
 long regular prisms with irregular terminations. It some- 
 times has a uralitic habit. Augite is not common, and then 
 (m) in long thin prisms or crystalline grains. Light yellow- 
 ish brown bronzite occurs in rare cases. Calcite some- 
 times occurs in what seems to be a primary crystalli- 
 zation; but more generally it is a secondary product in 
 the so-called "kalkgranit." In rare cases altered olivine 
 occurs (m). 
 
 To ascertain which minerals are idiomorphic to others 
 it is only necessary to remember that crystallization proceeds 
 from basic to acid. In granite the principal necessary, es- 
 sential, and accessory minerals can be arranged as follows : 
 zircon, apatite, magnetite, specular hematite, iimenite, bio- 
 tite, pyroxene (usually an alkali variety), hornblende, lepido- 
 lite, muscovite, the lime-soda plagioclases, albite, orthoclase, 
 microcline, quartz. 
 
 In the Brocken granite shades into gabbro in a narrow 
 zone through augite-biotite-granite, augite-diorite, diorite, 
 and quartz-biotite-augite-gabbro. In Skye some frag- 
 ments of porphyritic hornblende-granitite, included in a 
 later gabbro, have been heated so that the granophyre be- 
 tween the phenocrysts has been changed to rhyolite glass 
 full of flow-lines, spherulites, lithophysae, etc. In Sweden 
 Nordenskiold reports that halleflinta is a devitrified rhyolite 
 that shades into aplite, and that into granite. 
 
PRIMARY ROCKS. 123 
 
 The (M) accessories in the United States include the fol- 
 lowing species anjd the following localities : Maine : Paris 
 tourmaline ; Readfield andalusite. Massachusetts : Chester 
 spodumene ; Chesterfield cassiterite ; Greenfield colum- 
 bite ; Gloucester danalite ; New Bedford molybdenite ; 
 Goshen cassiterite, tourmaline; Connecticut: Haddam 
 -anthophyllite, allanite, chrysoberyl, columbite, gahnite, 
 garnet, zircon ; Middletown columbite ; Trumbull topaz. 
 New York : Greenfield apatite; Warwick rutile. In ad- 
 dition to the above there are found in foreign localities cor- 
 dierite, fluorite, graphite, native gold, pyrite, specular iron, 
 allanite, chlorite, and hydromica. Granites also carry con- 
 cretions of varying size and composed of- various mixtures 
 of the components. The granite group embraces the fol- 
 lowing varieties : 
 
 (a) GRANITE (Muscovite-biotite-granite, " Eigent- 
 licher Granit " of Rosenbusch not of G. Rose ; 
 " Zweiglimmeriger Granit " of Zirkel). 
 A granite composed of quartz, orthoclase, more or less 
 plagioclase, and both muscovite and biotite in about 
 equal amounts. 
 
 With predominating muscovite or biotite it passes into 
 those varieties. Hornblende is rare and pyroxene absent, 
 garnet abounds, and cordierite occurs. It is coarse- to fine- 
 grained and porphyritic. This variety is the great moun- 
 tain-former, but also occurs in bosses and dikes. It is found 
 in Germany, the Vosges, France, extensively in Cornwall 
 and other parts of Great Britain, Spain, Mexico, and in New 
 England. Rosenbusch places here the occurrences with 
 tourmaline, while Zirkel puts them under biotite-granite 
 {granitite). The former states that tourmaline has been 
 formed at the expense of biotite. As muscovite-granites are 
 rich in tourmaline, garnet, topaz, cassiterite, etc., and as the 
 
124 MANUAL OF LITHOLOGY. 
 
 tourmaline rocks, etc., are drusy, they will be placed under 
 muscovite-granite. 
 
 (b) MUSCOVITE-granite (Rosenbusch). 
 A granite composed of quartz, orthoclase, some plagio- 
 clase, and muscovite. 
 Silica 75. 
 
 This is the most acid of the varieties ; the richest in quartz, 
 and the poorest in basic silicates, magnetite, etc. It occurs 
 less frequently in dikes than the other varieties. Biotite 
 may occur to a small extent. It runs to extremes in texture, 
 either fine-grained or very coarse. It is frequently drusy, 
 but porphyritic states are rare. It is rich in accessory min- 
 erals, especially tourmaline, garnet, topaz, cassiterite, etc., 
 and is found extensively in Europe, throughout New Eng- 
 land, and in the western States. Here may be placed : 
 
 I. Pegmatite (Hauy) Graphic Granite. A compound of 
 reddish feldspar, quartz of dark color, and silver-white mica, 
 so arranged that the rock consists almost entirely of the for- 
 mer, which is pierced along certain cleavage-planes by the 
 quartz so as to produce figures similar to Assyrian or 
 Hebrew letters. The mica is in aggregates, or arranged 
 parallel to the quartz tables, and frequently coating them. 
 A coarse texture forms pegmatite, a fine one graphic granite. 
 Both form dikes and subordinate masses in granite, and dikes 
 and interbedded intrusives in metamorphic schists. They 
 are of limited extent, are associated with an abundance of 
 accessory minerals given above, and contain 78 per cent of 
 silica. According to the best authorities, the feldspar is mi- 
 crocline and the mica lepidolite. V.Cotta calls the granites 
 rich in feldspar, which have their content of mica arranged in 
 stripes or branching as flower-stalks, blumengranit (Ger.). 
 It occurs in Germany, France, Sweden, and Normandy. 
 
PRIMARY ROCKS. 12$ 
 
 2. Aplite, Granitell, (Ger. "Halbgranit"). A dike-granite 
 of uniformly fine grain, composed of quartz, orthoclase, and 
 some plagioclase, generally without mica, or with a very 
 small amount of silver-white or greenish potash-mica. It 
 occurs mostly in dikes, but in one or two cases it is wide- 
 spread. The localities of the typical rock are few. It is 
 found in Hungary, the Vosges, Germany east of the Rhine, 
 in South Africa (with calcite). It is distinguished from 
 granulite by its want of schistose structure and the absence 
 of metamorphic minerals, especially garnet. According to 
 the later differentiation theories, this is the " complemen- 
 tary " rock to minette from a granitic magma. In the 
 Melibocus a dike runs from the gneiss on the east side to 
 the granite on the west side. The filling in the gneiss is 
 rnicaless aplite ; in the granite, aisbachite, a highly micaceous 
 .granite-porphyry. 
 
 3. Cordierite-granite. A rock of limited occurrence in 
 Norway, Greenland, Bavaria, Australia, in which cordierite 
 (iolite) is abundant and mica scarce. Gr. 2.6-2.7. 
 
 Here follow a series of rocks formed during granitic 
 eruptions through the influence of what the French authori- 
 ties call " mineralizing agencies." These are the gases 
 accompanying the ascent of the magma, and which some 
 authorities think were absorbed during the cooling of the 
 earth from a nebulous to a fluid state, and which are included 
 in all magmas. Acid magmas are supposed to possess them 
 to a high degree ; some authorities would substitute the 
 word " retain " for " possess," as acid magmas are less fluid 
 at the time of eruption and gases can less readily escape 
 from them than from those more basic and fluid. The " min- 
 eralizers " are aqueous vapor, fluorine, boric acid, and other 
 volatile acids the ones acting on the following rocks being 
 those named. These in their effort to escape leave the 
 
126 MANUAL OF LITHOLOG Y. 
 
 greater part of the magma, but are entangled in other por- 
 tions (according to one view) ; or they are forced into the 
 still molten mass along lines of greater fluidity (according 
 to another view), and form new compounds, some of which 
 are pseudomorphs after the original minerals, such as tour- 
 maline, topaz, cassiterite, lepidolite, zinnwaldite, fluorite, etc. 
 These rocks are : 
 
 4. Tourmaline-granite. A granitoid compound of ortho- 
 clase, quartz, and tourmaline, with little or no muscovite. 
 Gr. 2.6-2.9. Here tourmaline replaces biotite (Rosenbusch).. 
 It occurs in Saxony, at Predazzo, Italy (in typical form), 
 near Eisenach, Hungary, at the Eibenstock (where the 
 tourmaline is frequently in masses as large as the head), ira 
 Bohemia, near Heidelberg, in the Tyrol, Spain, etc. Tour- 
 maline-bearing muscovite-granites are found in the Vosges. 
 extensively, and elsewhere. In some instances they are 
 pegmatitic, and with tourmaline one foot long. The other 
 tourmaline compounds will be placed here to group them 
 in a compact body, though they may fall under other varie- 
 ties of granite. 
 
 (a) Luxullianite (Pisani). This is named from the parish 
 of Luxullyon, Cornwall, where the rock occurs in loose 
 blocks (not massive). It is a dark mass composed (m) of 
 a quartz ground filled with hairlike tourmalines, and carry- 
 ing large grains of the same, small orthoclases, and beautiful 
 large phenocrysts of the same, of yellowish-red color, twa 
 inches in size, and flecked with spots of tourmaline. The 
 tourmaline is said to be an altered zinnwaldite. 
 
 (b) Trowlesworthite (Bonney). Another Cornish granitic 
 compound of reddish orthoclase, acicular tourmaline, purple- 
 red fluorite, and scanty quartz. The fluorite has replaced 
 the quartz so as .to form one-fifth of the whole mass. 
 
 (c) Hyalotourmalithe (Daubre), Carvoeira (von Eschwege), 
 
PRIMARY ROCKS. 
 
 Tourmaline-quartzite, Tourmaline Rock. These are names of 
 two extremes in composition of a Cornish granitic segre- 
 gation which has been formed, through the entrance into 
 the body of the mass, and not along its selvages, of fluoric 
 or boric ingredients as exhalations. The tourmaline has 
 grown at the expense of the feldspar and mica. In some 
 cases there is a small amount of orthoclase in the mass or in 
 the many drusy cavities. The mixture of black tourmaline 
 (blue or brown by transmitted light) and quartz as a granu- 
 lar compound is the " tourmaline-quartzite," while the aggre- 
 gate of tourmaline with little or no quartz is the " tourmaline 
 rock." " Carvoeira " is the name given to a similar rock in 
 Brazil. 
 
 5. TOPAZ ROCK, Topazfels (Werner), Topazosfcme 
 
 (Brongniart). 
 
 A usually granitoid rock which is sometimes (owing to 
 the age of its formation) greatly decomposed by 
 weathering. It is composed of predominant topaz 
 (which sometimes forms 90 per cent of the mass), with 
 quartz, mica' (frequently zinnwaldite), cassiterite, tour- 
 maline, sphalerite, and fluorite. 
 
 The first noted occurrence of the rock was at the 
 Schneckenstein in the Voigtland, where a dike of tourmaline 
 rock has broken through phyllite and formed a breccia. 
 Both phyllites and breccia are impregnated with topaz. 
 In this case it is a secondary rock, but it occurs at the 
 Eibenstock, Markersbach, and elsewhere as a regular crys- 
 talline primary rock, and is, therefore, placed here rather 
 than among the secondary rocks. 
 
128 MANUAL OF LIT HO LOG Y. 
 
 6. GREISEN (Old German mining name), Hyalo- 
 micte (Brongniart). 
 
 A grayish granitoid compound of light-gray quartz and 
 a grayish, yellowish, or greenish mica (zinnwaldite). 
 Silica 80. 
 
 This is another granite without feldspar, as the exhala- 
 tions have replaced this and other minerals, so that quartz 
 is found pseudomorphed after feldspar (which is sometimes 
 twinned) and mica, while cassiterite forms pseudomorphs 
 after feldspar, similarly twinned in some cases. It is of 
 limited extent and is valuable as the gangue of cassiterite. 
 It resembles granite in its irregular jointing, and is associated 
 with it in strings and pockets. Scattered through it are 
 cassiterite, fluorite, tourmaline, and topaz. It is found in 
 Saxony, Cornwall, and the Black Hills, S. Dak. When 
 cassiterite is uniformly scattered through the rock, it forms 
 /z-granite. 
 
 7. ZWITTER ROCK. 
 
 A medium- to fine-granitoid, dark-green (or gray) com 
 pound of (M) quartz, with smaller topaz and cas- 
 siterite, with or without (m) potash-iron mica. 
 Quartz 50-70$. 
 
 This is the gangue of the tin ore of Altenberg, Saxony, 
 called" zwitter." The quartz is all that can be detected 
 by the naked eye, the other ingredients being visible only 
 through the lens. With this are associated mispickel, mica- 
 ceous hematite, and chlorite. 
 
 8. Epidote-granite, Unakite. A granite with epidote 
 abundant. It is an altered granite, the epidote coming from 
 the black bisilicates, mica, or hornblende (sometimes feld- 
 spar). It is found in the Fichtelgebirge, Schwarzwaid, 
 
PRIMARY ROCKS. 
 
 Pyrenees. In the United States a variety with flesh-red feld- 
 spar, quartz, and epidote, from the Unaka Mountains, N. Y., 
 and from Tennessee, is called unakite. 
 
 (c) GRANITITE (G. Rose), Biotite-granite. 
 A basic granite composed of quartz, red orthoclase, pla- 
 gioclase, and magnesia-mica (biotite). 
 Silica 67-70. 
 
 This is the most widely disseminated variety of granite. 
 It occurs in bosses and dikes, is denser than the muscovite 
 variety, and does not, like it, contain drusy cavities. It 
 abounds in porphyritic states and in plagioclase, and (as 
 shown in the silica content) is poorer in quartz than any of 
 the other varieties. As a basic variety it is richer in horn- 
 blende as essential, and, by its increase, shades into horn- 
 blende-granite. In this case there is a diminution in or- 
 thoclase, and a still further loss of quartz, so that the excess- 
 ive reduction of these two components causes it to shade 
 into quartz-diorite and diorite. As the muscovite-granites 
 are rich in essential tourmaline and quartz, these basic gran- 
 ites are free from the former, and almost free from garnet 
 -and iolite (cordierite) ; but magnetite and specular hematite 
 are higher than in other granites. It is found in Germany, 
 Bohemia, Tyrol, Alsace, Italy, Corsica, Great Britain, widely 
 spread in Sweden, in Greenland, China, Australia, the west- 
 ern continent, and especially western North America. A 
 small amount of hornblende and augite causes varieties that 
 take those minerals as adjectives, as hornblende-grzmtite, 
 
 I. Kalkgranit (Pichler), Lime-granite. From the Flag- 
 gerthal in the Tyrol. A granitoid compound of quartz, 
 biotite, dark-green chlorite, reddish orthoclase, white plagio- 
 clase, and transparent particles of calcite. Granites with 
 
130 MANUAL OF LITHOLOGY. 
 
 calcite occur in the Odenwald and in Sweden, and Hawes 
 found it at Columbia, N. H. While some authorities find 
 that calcite is an infiltration product, others see in it a 
 primary generation. 
 
 2. Hornblende-granitite (Rosenbusch). A granite with 
 an equal amount of hornblende and biotite. These granites 
 occur in the Scottish Highlands, Saxony, Alsace, the Oden- 
 wald, Fichtelgebirge, the Channel Islands, Scandinavia, the 
 Troad, and, in the United States, in the Wasatch, Shoshone, 
 and Havillah mountains, at the famous quarry at Quincy, 
 Mass., and in Minnesota. 
 
 (a) Kammgranite (Groth). A porphyritic variety much 
 developed in dikes in the Vosges, with silica 62. 
 
 (b) Rapakivi (Finnish local name). A " rotten stone "- 
 hence the name extensively distributed near Wiborg, Fin- 
 land. A coarse-grained aggregate of egg-shaped orthoclase 
 (never crystalline) up to two inches in length, of brownish- 
 red color, and covered with a scaly shell of oligoclase, lepi- 
 domelane, and hornblende, and generally of two or more 
 colors. The darker has irregular dark-gray quartz scattered 
 through it ; the lighter and weathered state has the quartz 
 more crystalline and the feldspar more weathered. Silica 
 70. The high silica content is due to the leaching of the 
 alkalies. 
 
 (c) Granio-diorite (Becker). A granite poor in potash, 
 with predominant plagioclase, orthoclase, quartz, horn- 
 blende, and brown mica. With orthoclase in excess it is a 
 hornblende-granitite ; with little orthoclase, it is a quartz- 
 mica-diorite. Silica 60. It is the rock of the Yosemite 
 Valley. 
 
 3. Augite-granitite (Rosenbusch), Pyroxene-biotite-gran- 
 ite. A granitite with usually monoclinic pyroxene (augite). 
 The localities are noted below under the varieties. 
 
 (a) Gabbro- granite (Tornebohm). From Haakanbols, 
 
PRIMARY ROCKS. 
 
 Sweden, where it is composed of gray plagioclase, ortho- 
 clase, brown mica, green diallage (or a diallage-like augite), 
 hornblende, and quartz. As accessories are titanite, mag- 
 netite, and apatite. 
 
 (b) Augite-gramte. A gabbro-like granite, with monoclinic 
 augite, rich in plagioclase and biotite. The pyroxene in all 
 these varieties is the idiomorphic mineral. It occurs in 
 England, Labrador, the Vosges, etc., and the augite is fre- 
 quently uralitized. 
 
 (c) Augite-soda-gramte. A red, drusy, fine-grained granite, 
 sprinkled with dark spots. It is composed of orthoclase, 
 anorthoclase, quartz, and augite, with accessory hornblende, 
 biotite, apatite, sphene, and secondary chlorite. Silica 66-72. 
 This is said to be one of those very infrequent occurrences 
 an alteration product of a sediment as it occurs between 
 eruptive gabbro and slate. It is reported from St. John, 
 N. B., and Minnesota. 
 
 (d) HORNBLENDE-GRANITE (Naumann), Sye- 
 nitic Granite (v. Cotta), Syenite (in part, of G. 
 Rose). 
 
 A granite usually poor in quartz, with little or no mus- 
 covite, but generally containing biotite, orthoclase 
 (and sometimes red microcline), plagioclase, and horn- 
 blende. 
 
 Silica 71.78. 
 
 It occurs in bosses, dikes, and widely distributed masses 
 in Saxony, Bohemia, Austria, Sweden, Finland, Pyrenees, 
 France, Great Britain, Greece, Mount Sinai, Egypt, Altai 
 Mountains, and in the United States in Minnesota, Nevada, 
 and Canada. The quartz is variable from abundant to 
 rare. In the former case biotite fails. Plagioclase is more 
 abundant than in biotite-granite (granitite). Orthoclase 
 varies in color from light to deep red ; plagioclase is usually 
 
132 MANUAL OF LITHOLOGY. 
 
 white. Hornblende is in green crystals (sometimes over an 
 inch long) and sometimes appears uralitized. Titanite and 
 apatite, malakolite (or a diallage-like augite) and rhombic 
 pyroxene, are accessories. It is frequently porphyritic from 
 large phenocrysts of orthoclase. Unfortunately for the 
 name " syenite," both the localities whence its name might 
 be derived (Mount Sinai, and Syene, Egypt) have this 
 variety of granite. 
 
 (e) PROTOGINE-GRANITE, Jurine (Haiiy), "Ai- 
 
 pen-granit " (Studer). 
 
 A granite breaking with a sandy, crumbly fracture, com- 
 posed of abundant quartz, scanty dark biotite, abun- 
 dant sericite, white orthoclase, microcline (and some- 
 times an^drthoclase), with accessory small (M) grains 
 of garnet, pyrite, titanite, hornblende, and sometimes 
 large beryls. 
 
 Silica 66-76. 
 
 This is extensively developed in the Alps and is the mass 
 of Mont Blanc. The sericite was formerly thought to be 
 talc or chlorite. The rock has undergone extensive altera- 
 tion, so that in addition to the change of biotite to sericite 
 the plagioclase has become saussurite, and the orthoclase 
 kaolin and sericite. On the peripheries of the granite 
 masses there is a widely developed change of structure from 
 massive to schistoid, as will be noted later. 
 
 Here follow a series of variations in texture and structure 
 that effect all or most ol the foregoing granites to a greater 
 -or less degree, and also some variations in the ingredients 
 that are insufficient to cause the rock to form a definite sub- 
 jspecies : 
 
 Miarolite (Fournet). This is a cavernous, drusy granite, 
 rich in soda or soda-potash feldspars. " Miarolo " is the 
 
PRIMARY ROCKS. 133 
 
 Italian folk-name for the rock. The specimen described 
 by Fournet came from Lyons. It is also found in the 
 Vosges ; the Mourne Mountains, Ireland; and in Italy. 
 From this structure Rosenbusch has drawn the name miaro- 
 litic for all drusy granites. The structure is peculiar to the 
 muscovite varieties. 
 
 Spherophyric Granite, Pudding-granite, Variolitic Granite 
 (v. Chrustschoff). A granite containing concretions of a 
 concentric-shaly (rarely of a radial) structure. This is not 
 common in granite ; but is more frequent with varieties rich 
 in biotite and hornblende than in muscovite. The con- 
 cretions are composed of predominant mica ; of scanty 
 quartz and mica (at Craftsbury, Vt.) ; of concentric layers of 
 a compound alternately rich and poor in mica ; of a horn- 
 blendic or feldspathic kernel with external growths, as 
 feldspathic aggregates of pegrnatitic structure, and (in 
 Siberia and Finland) as apparently uniform bodies. These 
 vary from minute grains to masses eighteen inches in di- 
 ameter. The rock is found in the Fichtelgebirge, France, 
 Sardinia, Sweden, and in the United States in Colorado, 
 Craftsbury, Vt., southern Rhode Island (where the concre- 
 tions have the rare radial structure), and in California. 
 
 Schistoid Granite. Here will be placed those states found 
 on the selvages of dikes and bosses where, through pressure 
 during or after cooling, the minerals, especially mica, as- 
 sumed a position parallel to the walls of the country-rock. 
 Many of these states have been classed with the gneisses, as 
 in protogine-gneiss, but, even when they are of large extent, 
 they can be traced to a central portion which shows no 
 signs of foliation. They are also found in shear-zones, so 
 that we may have schistoid structures imposed on rocks 
 without their undergoing sedimentation. When these 
 variations result in a perfect foliation, the rock must be 
 classed as secondary, but the transitional states that are 
 
134 MANUAL OF LITHOLOGY, 
 
 neither massive nor schistose will be styled " schistoid," as 
 above. Under this will come the alternations of granite 
 and tourmaline rock in Cornwall, the parallel arrangement 
 of minerals in dike-selvages, etc. Examples of this are 
 found at Port Deposit, Md. ; and abundantly along the shores 
 of Lake Superior, in Europe, etc. 
 
 PORPHYRIES OF THE GRANITE GROUP. 
 
 II*. GRANITE-PORPHYRY (Kittel). 
 
 A brownish, greenish, sometimes yellowish, but gener- 
 ally not very dark, completely crystalline (m) ground- 
 mass of predominant feldspar and quartz, carrying 
 phenocrysts of orthoclase (gray, flesh-red, brick-red), 
 mostly twinned, yellowish or greenish plagioclase, 
 gray to dark-colored grains of quartz, plates and 
 hexagonal tables of brown mica, or rounded aggre- 
 gates of chlorite ; with accessory magnetite, zircon, 
 apatite, pyrite, infrequent titanite, rarely red garnet, 
 iolite, or pinite the accessories generally (m). 
 Silica 61-75 J GT. 2.6-2.7. 
 
 It occurs almost entirely in large dikes which have 
 parallel structures along the selvages, as in other dike- 
 forms, especially when mica is present. In the Eureka dis- 
 trict, Nev., the selvages of a granite dike are granite-por- 
 phyry. It is unknown in surface forms, and is found abun- 
 dantly in the Thuringian Forest, the Drusenthal, Erzge- 
 birge, Bohemia, Vosges, France, Egypt, China, and in the 
 western United States at Goose Creek, Franklin Buttes, 
 Eureka district, Nev., and Parkview Peak, Col. It is 
 intermediate between granite and quartz-porphyry, which 
 it becomes by gaining a felsitic base. The groundmass is 
 (m) wholly crystalline with predominant feldspar, which is 
 idiomorphic with respect to quartz, and interlocked by it as 
 
PRIMARY ROCKS. 135 
 
 in granite. Black bisilicates are rare in typical forms with 
 a full quartz content ; but biotite and chlorite appear as 
 quartz disappears. Muscovite is of little importance ex- 
 cept in the porphyries of kammgranite (see p. 130). The 
 quartz is sometimes as large as a walnut. Feldspar varies 
 between tabular and prismatic shapes ; orthoclase is some- 
 times three inches long ; plagioclase is usually oligoclase or 
 oligoclase-andesine, but is seldom more basic. Biotite is in 
 sharply denned hexagonal tables, and alters to chlorite. 
 Hornblende is green (seldom brown), and chloritizes and 
 epidotizes readily. Pyroxene is usually monoclinic and green, 
 and usually serpentinized or chloritized it also alters to 
 carbonates. The three black bisilicates are in nearly equal 
 proportion, but the local increase of each enables us to dis- 
 tinguish varieties. The most common is with biotite, as 
 the micas have the greatest affinity for acid minerals. 
 
 (a) Granitic Granite-porphyry (v. Cotta), where the matrix 
 can be recognized as extremely fine-crystalline, but where 
 it carries phenocrysts of all the three granitic minerals, 
 quartz, orthoclase, and mica. Common in the Erzgebirge, 
 near Freiberg, in the Thuringian Forest, etc. 
 
 (b) Biotite-granite-porphyry. Under this variety comes 
 the original granite-porphyry noted by Kittel from Aschaf- 
 fenburg. 
 
 1. Aschaffite (Giimbel). A fine-grained to compact mass, 
 rich in mica, and with hornblende and augite, carrying 
 phenocrysts of quartz and sporadic large feldspars (single 
 and twinned) ; but all have their edges rounded by abrasion 
 received during eruption, so that sections are elliptical. The 
 large mica content makes this rock a transition to the ker- 
 santites, so that it may be complementary to an aplite 
 
 orm of granite by differentiation from a granitic magma. 
 
 2. Alsbachite (Chelius). From the west side of the Meli- 
 bocus. Silica 73-75. It occurs in a dike in granite ; brown 
 
136 MANUAL OF LITHOLOGY. 
 
 or red ; with (M) quartz, feldspar, large laminae of mica, and 
 rose-red garnets. The filling of the same dike changes to 
 aplite when it enters the gneiss of the east side of the moun- 
 tain. Here we have the differentiation of granite in the 
 same dike. 
 
 (c) Hornblende-granite-porphyry, where hornblende is 
 quite abundant among the other phenocrysts. It occurs in 
 the Vosges (where it resembles minette) and in Nevada. 
 
 (d) Pyroxene-granite-porphyry, with abundant pheno- 
 crysts of pyroxene. It occurs in Minnesota, Sweden, etc. 
 
 Grorudite (Brogger). From Grorud, near Christiania. 
 A fine-grained, greenish (m) groundmass of orthoclase, asgi- 
 rite, and quartz. A similar rock from Varingkollen afforded 
 silica 74,5. 
 
 (e) Chloritic Granite-porphyry (v. Cotta), Green Porphyry 
 (Naumann), so-called " Syenit-porphyr," where the black 
 bisilicates have chloritized, and the rock assumes a green- 
 ish color. The groundmass is fine- to micro-crystalline, and 
 brown to dark green, and composed of flakes of chlorite, 
 quartz, and feldspar, with phenocrysts of the same. It is 
 found in the Erzgebirge, and elsewhere in Germany. 
 
 II*. QUARTZ-PORPHYRY, Elvan (Cornish mining 
 
 term), Quartzophyric Felsophyre (Dana). 
 A compact groundmass not resolvable (M), carrying 
 phenocrysts of quartz, orthoclase, and generally plagi- 
 oclase, with one or more of the black bisilicates. 
 Silica 69-81 ; Gr. 2.5-2.7. 
 
 It occurs principally in dikes, which have intersected, 
 and been extruded upon strata of varying ages from early 
 geological time down to the Eocene. In one case the dike 
 was 30 feet wide and 16 miles long. These dikes, as usual, 
 send apophyses into the dike-walls, and contain more vitreous 
 
PRIMARY ROCKS. 137 
 
 states of the rock. It rarely occurs in intruded sheets or 
 isolated plugs. It is found in Germany, Belgium, Tyrol, 
 Transylvania, Bohemia, Great Britain, France, Sweden, 
 Italy, Spain, Sardinia, Corsica, Egypt, Japan, China, Brazil,, 
 and in the United States in New England, Pennsylvania, 
 Michigan, Colorado, Nevada, etc. It is the porphyry of 
 granitite (biotite-granite). The groundmass fuses in thin 
 splinters bp., and is Vogelsang's " granophyre " (see p. 56), 
 and may be microgranitic or micropegmatitic ; its reddish 
 color is due to ferrite (see p. 53). Of the phenocrysts, quartz 
 varies from minute grains to the size of peas, either rounded 
 or in double pyramids, with grayish or dark smoke-gray 
 color and vitreo-greasy luster. When (M) quartz disap- 
 pears, the rock becomes Tschermak's felsite-porphyry. (m) 
 both granitic and trachytic structures are seen in the 
 quartz, as would be the case when it formed under great or 
 small pressures. Orthoclase is usually colorless, yellow- 
 ish-white, or flesh red (and of lighter color than the ground- 
 mass), and its cleavage surfaces have a strong pearly 
 luster. It occurs in tabular or prismatic shapes, as in 
 granite-porphyry ; and the large phenocrysts commonly 
 twin in Carlsbad forms, less frequently in those of 
 Baveno, least in those of Manebach. Stout twins an 
 inch long are frequent, and with (M) inclusions of other 
 minerals. A sanidine-like habit in the feldspar causes a tra- 
 chytic facies in the rock. The Washoe quartz-porphyry 
 carries feldspar of so vitreous a habit that it was misnamed 
 dacite (when fresh) and quartz-propylite (when weathered). 
 Plagioclase is distinguished from fresh orthoclase by its 
 white color, its softness and incipient kaolinization, so that 
 striations are infrequent. It is usually oligoclase or one of 
 the albite-oligoclase series. Perthitic structures are com- 
 mon between orthoclase and plagioclase. These min- 
 erals (m) are usually like their forms in granite ; but 
 
138 MANUAL OF LITHOLOGY. 
 
 orthoclase in many cases has the habit of sanidine, as 
 just mentioned. Orthoclase weathers to kaolin, muscovite, 
 and sericite ; plagioclase epidotizes. Microcline is not 
 as abundant as in granite. Biotite shows hexagonal dark- 
 green or brown tables ; muscovite is seldom alone in 
 the groundmass, but sometimes is one-third of an inch in 
 size. Only few varieties carry hornblende in abundance ; it 
 is sometimes in prisms visible with a lens, as in the Truckee 
 rock. Pyroxene is as in granite. As accessory (M) minerals 
 are cordierite (iolite), garnet (Twin Mountains., N. H.), 
 tourmaline, topaz, fluorite, orthite (Colorado), and zeolites. 
 Some varieties have abundant concretions, as in granite. 
 The structure of quartz-porphyry varies from massive to 
 amygdaloidal, cavernous, fissured, and cracked. The first 
 two are filled with calcite, quartz, chalcedony, hornstone, 
 opal, jasper, and amethyst ; the others only with crystals. 
 Occasionally a vesicular structure with parallel arrange- 
 ment is met with (cavities sometimes two inches long). In 
 rare cases small slaggy particles appear in the dense ground- 
 mass, which may be pyroclasts of portions of the first erup- 
 tion that cooled against the dike-walls, and have been partly 
 re-fused in the mass. In addition to concretions there are 
 also compact, radial, or concentric-shelly spheroids, which 
 are sometimes like rhyolitic lithophysas (South Mountain, 
 Pa. and Md.). (M) fluidal structures are common, especially 
 along selvages. Quartz-porphyry weathers to clay-porphyry, 
 clay stone, and kaolin. It occurs with irregular fissures; some- 
 times with columnar and tabular jointing, as in basic dike- 
 rocks. The great proportion of accessory minerals is due 
 to infiltration into the cracks, nests, etc. Dendritic mark- 
 ings are common, as well as stainings from ferruginous 
 solutions, as the mass weathers. Spheroidal weathering is 
 rare. 
 
 a. Typical Quartz-porphyry. A compact matrix with 
 phenocrysts of quartz, feldspar, and sometimes mica and 
 
PRIMARY ROCKS. 139 
 
 hornblende, rarely pyroxene. According to the texture of 
 the matrix it can be divided into : 
 
 1. Hormtone- porphyry, Elvan, with a cryptocrystalline 
 groundmass that breaks with a splintery fracture like chert, 
 and has a faint glimmer or waxy luster on a freshly broken 
 surface. It will strike fire with steel, but can be told from 
 .hornstone by its fusibility. 
 
 2. Felstone-porphyry, when the compact mass is not so 
 hard, and has a smoother fracture. 
 
 j. Clay stone-porphyry, Argillophyre, when there is a 
 rough, almost earthy groundmass, soft enough to be cut 
 with a knife. This is the state of (i) and (2) after weather- 
 ing. This last occurs extensively at Leadville, Col., under 
 the name of white-porphyry. It joints readily into blocks, 
 whose faces are covered with dendritic markings. 
 
 4. Pyritiferous Porphyry. A decomposed hornblende- 
 biotite variety, with those minerals replaced by pseudo- 
 morphs of pyrite. From Leadville, Col., where it has been 
 formed from quartz-porphyry by the action of thermal 
 waters charged with H a S. The hornblende-biotite variety 
 is found in a fresh state at depths in the mines, but near the 
 outcrops the hornblende has disappeared, and is represented 
 by pyrite, as above stated, while the biotite has been 
 -altered to chlorite and pyrite. The quartz-porphyry of 
 Freiberg has a small quartz content and carries pyrite. 
 
 (a) Beresite (G. Rose). A dike-rock from Beresowsk 
 in the Urals, and elsewhere which is much decomposed. 
 It shows kaolinized orthoclase and plagioclase, pyrite, 
 and not much quartz nor mica, and occurs with auriferous 
 veins. It was once thought to be a dike-form of musco- 
 vite-granite, but Helmhacker places it under quartz-por- 
 phyry. 
 
 j". Slaty Porphyry, Band Porphyry, Striped Porphyry. 
 The result of flow, and composed of layers of different color, 
 composition, or texture. These are usually parallel to 
 
I4O MANUAL OF LITHOLOGY. 
 
 the selvages of the dike ; are often bent and twisted, and 
 (m) are found to be of alternately coarse- and fine-crystalline 
 texture. In many cases the parallel arrangement of color is 
 accompanied by a decided schistose structure, so that the 
 rock splits more readily with than against the layers. An- 
 other variety of slaty porphyry is due to orogenic forces. 
 Examples of the first are found near Freiberg, in the 
 Thuringian Forest, etc.; of the second, in Switzerland, 
 France, Nassau, etc. 
 
 6. Millstone-porphyry, Drusy Porphyry, Porous Por- 
 phyry. A quartz-porphyry filled with irregular druses and 
 geodes, which are usually the result of weathering, are not 
 vesicular, and are lined with thin layers of hornstone,, 
 chalcedony, amethyst, calcite, fluorite, specular iron, etc. It 
 is quarried for millstones (whence the name), and is found 
 in the Erzgebirge, Thuringian Forest, Fichtelgebirge, 
 Odenwald, Schwarzwald, etc. 
 
 7. Vesicular Porphyry. A rare variety, with numbers of 
 steam blow-holes (sometimes two inches long), drawn out 
 by flow and arranged in parallel structure, or with small 
 vesicular pyroclasts enclosed in a dense groundmass. The 
 former is found at Rochlitz, Saxony, and Friedrichroda, 
 the latter in the Falkenstein. In some cases these are filled 
 with quartz and specular iron to form amygdaloidal porphyry ~ 
 
 8. Pyromeride (Haiiy), Ball Porphyry. A variety abound- 
 ing in spheroids in addition to the usual crystals. It is 
 found in the Thuringian Forest, Harz, Corsica, Eiba, Sar- 
 dinia, Jersey, and in the western United States and in 
 Pennsylvania. The balls are compact, radial-fibrous, and 
 shelly. Some are like lithophysae in rhyolite, and the rock 
 may have been derived from that extrusive by devitrifica- 
 tion. The cavities in the balls are filled with hornstone, 
 agate, etc. It is found with both microgranitic and micro- 
 pegmatitic groundmasses. 
 
PRIMARY ROCKS. 141 
 
 (b) Samdme-quartz-porpriyry. A variety containing 
 sanidine from Baden-Baden, southern Tyrol, and Zwick- 
 au, Saxony. These are geologically late varieties, and, 
 probably on that account, near the tops of the dikes. 
 The feldspar is fresh sanidine, with high luster, well 
 fissured, and easily fractured. 
 
 (c) Hornblende-quartz-porphyry. A variety with large 
 (^ inch) hornblende columnar phenocrysts, in a greenish- 
 gray to grayish groundmass. It is found at Mount 
 Sinai, the Pyrenees, Sardinia, France, Germany, Corea, 
 Scotland, and Nevada. 
 
 (d) Pyroxene-quartz-porphyry. A variety with pyrox- 
 ene phenocrysts that can be distinguished with a lens 
 (sometimes -fa inch long). It is usually monoclinic and 
 serpentinized. The rock is found in Siberia, Alsace, Eng- 
 land, Egypt, and in New Hampshire at Waterville. 
 
 lie. FELSITE-PORPHYRY (Tschermak). 
 A quartz-porphyry where the quartz is in (m) pheno- 
 crysts, and the only (M) phenocrysts of feldspar 
 appear. 
 
 As quartz is in phenocrysts, though (m), the rock is a 
 true quartz-porphyry. The groundmass is colored red 
 or brown by ferrite, and shows phenocrysts of feldspars, 
 .hornblende, and specular iron. It is found in Sweden, 
 Nassau, China, etc. 
 
 Here belong the states of Giimbel's keratophyre, which 
 are quartzose and have a compact groundmass (see " Kerato- 
 phyre," p. 155). Such a soda-orthoclase-quartz-porphyry is 
 found at Pigeon Point, Minn., as a (m) fine-grained ground- 
 mass, of dark-red or purple color, carrying phenocrysts of 
 greenish-white and brick-red feldspars. It is said to form 
 the contact product of gabbro on slate. If so, it is an in- 
 stance of a transition between a sediment and an eruptive. 
 
142 MANUAL OF LITHOLOG Y. 
 
 GRANITIC FELSOPHYRES. 
 
 lid. FELSITE (Gerhard), Eurite (Daubuisson), Pe- 
 
 trosilex (Brongniart). 
 
 A compact rock as hard as feldspar ; yellowish, reddish, 
 gray, greenish, bluish ; weathering white, with dull, 
 smooth, conchoidal, or fissile fracture. It has the same 
 (m) composition as the groundmass of quartz-por- 
 phyry, and like it fuses in thin splinters. 
 Silica 71-81 ; Gr. 2.5-2.7. 
 
 It occurs in masses 1500 feet thick, and in dikes, abun- 
 dantly in Great Britain and in Saxony, elsewhere less abun- 
 dantly as a state of quartz-porphyry. It has a massive- 
 jointed structure, but is not so much fissured as quartz- 
 porphyry. Devitrification has been claimed as the agent 
 which has altered this from an extruded glass. In many cases 
 it holds spherules, which Rutley claims to indicate that the 
 rock in question is a devitrified perlite. It shows fluxion 
 and parallel structures, and in this respect resembles halle- 
 flinta, which v. Cotta classed here, and which has just been 
 shown to be a devitrified rhyolite. Parallel structures are 
 shown on a grand scale in Great Britain, where high moun- 
 tains are formed of this rock. 
 
 GRANITE GLASS. 
 
 Ilia. PITCHSTONE- PORPHYRY, Vitrophyre 
 
 (Vogelsang). 
 
 A compact glass, with considerable water, of greasy, 
 resinous luster, conchoidal fracture, translucent on 
 thin edges, with the hardness of feldspar ; colored 
 olive-green, blackish green, yellowish brown, brown- 
 ish red, and black; exhibiting (M) phenocrysts of 
 vitreous feldspar, laminae of mica (biotite), grains of 
 quartz, and reddish spheroids. 
 
PRIMARY ROCKS. 143 
 
 PITCHSTONE, Retinite. 
 A similar glass entirely free from phenocrysts and 
 spherules. 
 
 Silica 63-76; Gr. 2.25-2.4; water 5-8$. 
 
 This occurs in beds or sheets 2000 feet thick, also in 
 bosses and dikes, and usually associated with quartz-por- 
 phyry. It is especially found in the vicinity of Meissen, the 
 Fichtelgebirge, Tyrol, Italy, Arran, Scotland; and in the 
 United States at Isle Royal, Lake Superior, and in Colorado. 
 .The groundmass (m) is seldom free from phenocrysts, which 
 are of the minerals noted under quartz-porphyry. There 
 are two types of the rock trachytic and felsitic associated 
 with the rocks of the name. They are alike at sight and 
 under chemical analysis, and only the microscope can distin- 
 guish between them. Orthoclase is fresh and like sariidine ; 
 plagioclaseisoligoclase-labradorite: quartz occurs in double 
 pyramids. In the groundmass are (m) augite, hornblende, 
 apatite, zircon, magnetite, tridymite, and hyalite, but rarely 
 and scantily. The regular spheroids vary from (m) propor- 
 tions to six inches, and the irregular ones may be two feet. 
 The smaller ones are felsitic (sometimes like sanidine), with 
 starry internal cracks lined with (m) quartz, chalcedony, 
 agate, etc. The larger ones are irregular, sometimes angular 
 and with re-entering angles, sometimes roughly rounded as 
 by abrasion. These latter are pyroclasts of quartz-porphyry, 
 and even spherulitic pitchstone rent from older masses, and 
 somewhat metamorphosed, as their peripheries are more 
 dense than their interiors. They contain spherules of differ, 
 ent character from those of the enclosing mass (near Meissen), 
 and are older than it, as their nodules are rusty and weath- 
 ered. The Planitz (Saxony) pitchstones contain mineral 
 charcoal pyroclasts from coal deposits through which they 
 have broken. Those near Zwickau and Wechselburg show 
 devitrification, as the selvages are quartz-porphyry (with a 
 crystalline groundmass in the latter instance). 
 
144 MANUAL OF LITHOLOGY. 
 
 Argillaceous Pitchstone, Pitchstone-felsite (Naumann), " Ar- 
 gilorelinite." From near Meissen, somewhat weathered, 
 wax-yellow or olive-green, conchoidal fracture, and greasy 
 luster. Silica 79.85. 
 
 INTERMEDIATE DIVISION AMPHIBOLE ROCKS. 
 
 These are intermediate in two ways through the alkali 
 minerals (orthoclases and feldspathoids), and through the 
 lime-soda minerals (plagioclases), as follows : 
 
 I. ALKALI SECTION: 
 
 (a) Groups 3 and 4. Alkali feldspar, plagioclase, feldspathoids, 
 quartz, mica, pyroxene, magnetite, olivine. 
 Extrusive, Trachyte ; Intrusive, Syenite. 
 
 (&) Groups 5 and 6. Alkali feldspar, feldspathoids, plagioclase, 
 quartz, mica, pyroxene, magnetite, olivine. 
 
 Extrusive, Phonolite; Intrusive, Elaeolite-syenite. 
 
 II. ALKALI-LIME-SODA SECTION: 
 
 (a) Group 7. Alkali feldspar, mica, quartz, plagioclase, pyroxene, 
 magnetite, feldspathoids, olivine. 
 
 Extrusive, none ; Intrusives, Syenitic Mica-traps. 
 
 (b) Groups 8 and 9. Plagioclase, mica, quartz, pyroxene, alkali 
 feldspar, magnetite, olivine, feldspathoids. 
 
 Extrusive, none; Intrusives: Group 8, Dioritic Mica-traps ; 
 Group 9, Porphyrite and Mica-porphyrite. 
 
 III. LIME-SODA SECTION: 
 
 (a) Groups 10 and n. Plagioclase, mica, quartz, pyroxene, mag- 
 netite, alkali feldspar, olivine, feldspathoids. 
 
 Extrusive, Dacite ; Intrusive, Quartz-diorite. 
 (K) Groups 12 and 13. Plagioclase, pyroxene, mica, alkali feldspar, 
 magnetite, olivine, feldspathoids, quartz. 
 
 Extrusive, Andesite ; Intrusive, Diorite. 
 
 (c} Groups 14 and 15. Plagioclase, pyroxene, magnetite, olivine, 
 mica, feldspathoids, alkali feldspar, quartz. 
 Extrusive, Pyroxene-andesite ; Intrusive, Pyroxene-diorite. 
 
PRIMARY ROCKS. 145 
 
 GROUP 3. TRACHYTE. 
 la. TRACHYTE-SYENITE EXTRUSIVES. 
 (Necessary minerals : Amphibole and an alkali feldspar.) 
 
 TRACHYTE (Haiiy). 
 
 A rough, porous, (M) microcrystalline or aphanitic 
 groundmass carrying (m) a small proportion of glass 
 base with a felt of minute crystals of sanidine (and gen- 
 erally plagioclase), with small amounts of the black 
 bisilicates, magnetite, and titanite, and showing large 
 (M) phenocrysts of sanidine, plagioclase, and (in small 
 proportions) hornblende, augite, and magnesia mica. 
 Quartz, nepheline, and leucite are absent, and olivine 
 generally so. 
 
 Silica 58-67; Gr. 2.6; H. 5-6. 
 
 Trachyte occurs in dome-shaped masses, generally in 
 lava-streams, infrequently in dikes, also in tuffs. It is ex- 
 tensively developed in western Germany, Hungary, France, 
 Spain, Italy, Asia Minor, East Indies, Azores, South Africa, 
 New Zealand. It forms the greatly extended and most 
 acid of recent lavas. The groundmass differs from that of 
 rhyolite in the almost entire absence of a vitreous portion, and 
 fewer developments of fluxion structure. Zirkel states that 
 the roughness of the groundmass is due to (a) the fact that 
 the crystals of the mass are not intergrown, as in granite, but 
 touch at but few points, so as to leave interstices, and 
 (b) that there are many round or egg-shaped gas-pores 
 which form trachyte-pumice when they comprise the greater 
 part of the mass. Trachyte is generally considered a por- 
 phyritic rock. The usual, colors are brownish, yellowish 
 white, reddish, gray, and (rarely) bluish. The name refers 
 
146 MANUAL OF LITHOLOGY. 
 
 to the rough feeling of the groundmass (from the Greek for 
 rough) when the fingers are rubbed over the fractured 
 surface of a fresh specimen. The pores above mentioned 
 cause the rock to fracture irregularly and unevenly. The 
 luster differs from that of rhyolite in being dull, and, at best, 
 clayey and semivitreous. The feldspar seems to be the 
 prevailing mineral. Of the phenocrysts, sanidine appears 
 in tabular crystals, crystalline grains, and fragments. Twin- 
 ning occurs in Carlsbad and Baveno types. Anorthoclase 
 is reported in an acmite-trachyte from South Africa, and 
 microcline in an andesitic variety from the Azores. Plagio- 
 clase occurs, striated and white, with high luster, but in 
 much smaller individuals than does sanidine/ The old divi- 
 sions into sanidine and oligoclase trachytes were based on 
 the (M) examination of the phenocrysts, but they cannot 
 hold, as plagioclase is generally present in all trachytes, 
 and especially in the groundmass, and the divisions are 
 now made by many authorities on other grounds. The 
 plagioclase is usually oligoclase ; but albite, andesite, and 
 labradorite occur in a few specimens. Of the black bi- 
 silicates (hornblende, augite, and biotite), the greater pro- 
 portion occurs as phenocrysts, and not in the groundmass. 
 They form large individuals sparsely scattered through the 
 mass. Augite seems to be the only one that appears alone, 
 or in company with either of the others. Hornblende occurs 
 in large, lustrous, black, stout prisms, long needles, or irregu- 
 lar grains. The prisms have the habit of basaltic hornblende. 
 In the groundmass arfvedsonite and aegirite appear (;) 
 Hornblende is altered to chlorite and epidote in some tra- 
 chytes. Monoclinic augite is seldom (M) (as in the Drachen- 
 fels variety). Acmite is occasionally found. Rhombic 
 pyroxene (hypersthene) is rarely (M). Magnesia-mica in 
 black folia is common in many trachytes (M). It is gener- 
 ally biotite and in hexagonal leaves. It is usually absent 
 
PRIMARY ROCKS. - 1 47 
 
 from the groundmass, which can thus be distinguished from 
 that of minette, when the trachyte carries a large proportion 
 of the mineral. Magnetite (m) is more abundant than in 
 rhyolite, and can be gathered from the powdered rock with 
 the magnet. Epidote and titanite occur as (M) accessories. 
 Olivine is generally absent; quartz, nepheline, and leucite 
 always so ; hauyne is present in rare cases ; apatite and zir- 
 con usually present, as in all rocks, in small amounts, but (m). 
 
 I. Typical Trachyte (of Rosenbusch). A compound of 
 feldspar with phenocrysts of either or both of the minerals 
 hornblende and biotite, while augite is confined to the 
 groundmass. Under this are distinguished : 
 
 1. Biotite-trachyte. 
 
 2. Biotite-hornblende-trachyte. 
 
 3. Hornblende-trachyte. 
 
 Under the second comes the so-called " oligoclase- 
 trachyte," or domite, from the Siebengebirge and the Puy 
 de Dome (whence the name). It is a dark-colored com- 
 pound of oligoclase, hornblende, and biotite, with (m) augite. 
 Silica 62-68 ; Gr. 2.6-2.8. It is reddish, soft, and sandy. 
 
 Typical trachytes occur in Germany, Hungary, France, 
 Bohemia, Italy. 
 
 II. Augite-trachyte (of Rosenbusch). A compound of 
 feldspar with phenocrysts of monoclinic pyroxene, while 
 mica and hornblende are absent, or play a very unimportant 
 part. This variety is important in Italy. 
 
 i. Acmite-trachyte (Miigge). First noted from the Trans- 
 vaal, also from Crazy Mountains, Mont. In the latter 
 regions it is in sheets, dikes, and laccoliths. The rock is 
 composed of a groundmass of lath-shaped feldspars and 
 acicular segirites and acmites, with colorless interstitial 
 matter, and carrying phenocrysts of anorthoclase, sodalite, 
 and augite. The interstitial matter is composed (?) of 
 nepheline and analcite. Silica 62.17. 
 
I4 8 MANUAL OF LITHOLOGY. 
 
 III. Phonolitic Trachyte (of Zirkel). A compound of 
 feldspar (sanidine, anorthoclase, oligoclase), augite, sparse 
 biotite and hornblende, (in) segirite and acmite, and (in 
 druses) sodalite and sometimes nepheline. Nepheline does 
 not occur as a typical ingredient of the mixture. These 
 trachytes are found at Monte di Cuma, Ischia, San Miguel 
 and Terceira of the Azores, and Massai Land, South Africa. 
 Its greenish groundmass is sometimes schistose. 
 
 IV. Andesitic Trachyte (of Miigge). A dark to blackish 
 gray compound of feldspar (mostly triclinic), with a great 
 proportion of (m) black bisilicates and ores in the ground- 
 mass, which carries a distinct amount of dark-colored glass. 
 Among the phenocrysts appear feldspars of good size, 
 augite, biotite, and sometimes olivine. Hornblende is rarely 
 present. The microstructure is trachytic, and thus separates 
 the rock from the andesites. The rock epidotizes and 
 uralitizes. It occurs at Schemnitz, the Arso lava of Ischia, 
 the Azores, and Mont Dore in Auvergne. 
 
 V. Hypersthene-trachyte (J. F. Williams). This is a 
 rock first studied at Monte Amiata, with 63-67 per cent of 
 silica. It is andesitic, but of grayish or reddish color, 
 with sanidine, hypersthene, and a high acidity. Bronzite- 
 trachyte is reported from Japan. 
 
 To the trachytes are annexed certain rocks that are 
 found geologically connected with them, as : 
 
 VI. Laacher Trachyte (v. Dechen). In the tuffs about 
 the lake of Laach are round masses of a sanidine-trachyte not 
 found in place in the neighborhood. It is partly compact, 
 partly porous, light- to dark-gray groundmass, with pheno- 
 crysts of white sanidine, and partly intergrown with them 
 and partly in druses are hauyne (or nosean), hornblende, 
 augite, mica, olivine, plagioclase, and titanite. The ground- 
 mass often carries an abundant porous glass. In the Azores 
 
PRIMARY ROCKS. 149 
 
 is a somewhat similar rock. This is also called haiiyne- 
 trachyte. 
 
 VII. Sanidinite (Zirkel), Sanidine Bombs. These occur at 
 the same place, and are composed of a soda-sanidine, haQyne 
 (or nosean), augite, hornblende, biotite, plagioclase, scapolite, 
 garnet, nepheline, olivine, hypersthene, calcite, apatite, and 
 magnetite. There is neither quartz nor leucite. It occurs 
 also in the Azores. 
 
 The trachytes occur generally compact, porous, and por- 
 phyritic ; sometimes the pores become so numerous as to 
 form scoriaceous states on the surface of lava-flows, but the 
 vesicles are never filled, and the rock is never amygdaloidal. 
 With the entrance of nepheline the rock passes into the 
 phonolites ; with the addition of a glassy groundmass and 
 the absence of alkali feldspars, to the andesites ; and with the 
 entrance of free quartz, to the rhyolites. The products of 
 contact metamorphism are similar to basalt. 
 
 (For " Trachyte Glass " see p. in, where it is described 
 with rhyolite glass, owing to the similarity between them.) 
 
 GROUP 4. SYENITE. 
 
 Ib. TRACHYTE-SYENITE INTRUSIVES. 
 (Necessary minerals: An alkali feldspar and amphibole.) 
 
 SYENITE (G. Rose). 
 
 A granitoid compound of an alkali feldspar and horn- 
 blende (with mica, pyroxene, and without quartz). 
 Silica 55-63 ; Gr. 2.7-2.9. 
 
 All of the varieties of this group contain hornblende, but 
 some have the other black bisilicates predominant, or as 
 prominent as hornblende, so that varieties are formed by 
 the variation of minerals. There is also the same variation 
 in texture due to rates of cooling as in granite, so that the 
 following divisions are generally recognized : 
 
ISO MANUAL OF LITHOLOGY. 
 
 I. Hornblende-syenite, or typical syenite. 
 
 II. Mica-syenite. 
 
 III. Pyroxene-syenite. 
 
 IV. Syenite-porphyry. . 
 V. Syenite-aphanite. 
 
 These are quartzless granites. This statement must not 
 be taken as preventing the admission of a small amount of 
 that mineral to form quartzose varieties, but a large amount 
 would form quartz-poor granites. V. Cotta states that near 
 Dresden a transition from syenite to granite can be traced 
 in the same mass. As augite is a usual component of 
 nepheline mixtures, the augite-syenites are more nearly 
 connected with the elseolite-syenites than the other mem- 
 bers of the group. The more basic the rock the more 
 plagioclase is found accompanying, and replacing, ortho- 
 clase. Syenites occur in the same forms as does granite, 
 but in smaller bosses and fewer dikes. They joint less 
 readily than granite, and do not weather spheroidally as 
 readily. They differ from the diorites in their feldspar. A 
 iine-grained syenite is sometimes confused (M) with diorite, 
 but it can be distinguished by its being red or gray, while 
 diorite is dark or green. Diorite is usually more fine- 
 grained than syenite ; oligoclase weathers faster than the 
 hornblende, so that the latter is prominent on a weathered 
 surface, but the rock remains solid; orthoclase and horn- 
 blende weather more nearly together in syenite, so that the 
 rock falls into a rusty sand. Diorite carries more pyrite, 
 syenite more titanite. When other signs fail, the fusibility 
 of the feldspars usually settles the question. 
 
 " Syenite" is a misnomer, as the original syenites did 
 mot come from Syene, Egypt, and Rozifcre's Sinaite would 
 be no nearer correct, as the rocks in both localities are 
 hornblende-granite. 
 
PRIMARY ROCKS. !$! 
 
 I. HORNBLENDE-syenite. 
 
 A granitoid compound of an alkali feldspar and primary 
 hornblende, with plagioclase, occasionally biotite and 
 quartz, and usually magnetite, titanite, and apatite. 
 
 It is found in Saxony, the Thuringian Forest, Great 
 Britain, Norway, Sweden, Bulgaria, Russia, Greenland, New 
 .Zealand, Nevada, Arkansas, Massachusetts, etc. Orthoclase 
 is usually flesh-red, yellowish red with bluish schiller, some- 
 times white; common in Carlsbad twins, rare in Baveno. 
 Microcline is now and then present. Both alter as in granite. 
 The plagioclase belongs to the soda end of the series. Horn- 
 blende occurs in stout prisms, dark-green, grayish black to 
 black (greenish by transmitted light). Biotite occurs in 
 brown (sometimes green) irregular folia, and replaces the 
 hornblende, not the feldspar. It is the oldest generation 
 of the necessary minerals. Quartz occurs sparingly, and 
 occasionally forms a micropegmatitic texture. It is usually 
 (in). Apatite occurs more abundantly as the mixture gro\vs 
 basic. Concretions of the black bisilicates with scanty 
 plagioclase are common. The texture is medium to coarse 
 granitoid, and frequently porphyritic from large feldspar 
 phenocrysts in some dike-forms, which are usually of ortho- 
 clase (sometimes three inches long), while plagioclase is absent 
 as phenocrysts. In some localities there is a parallel arrange- 
 ment of alternate feldspathic and hornblendic mixtures. As 
 accessories occur titanite, zircon, garnet, orthite never 
 tourmaline ; as secondary products hornblende epidotizes, 
 while feldspar remains fresh to form epidote-syemte. 
 
 (a) Nordmarkite (Brogger). A quartzose syenite of flesh- 
 red color, medium grain, minute drusy structure, composed 
 of feldspar (orthoclase, microperthite, and acid oligoclase) 
 and quartz, with biotite, hornblende (arfvedsonite or 
 glaucophane), light-green pyroxene, sparse asgirite, titanite, 
 zircon, apatite, and iron ores. Silica 60-64. 
 
I5 2 MANUAL OF LITHOLOGY. 
 
 II. MICA-syenite, Biotite-syenite. 
 
 A rare variety with predominant mica. It is found in 
 Austria, Norway, Italy, Greenland, Black Forest, etc. 
 Silica 51. 
 
 (a) Durbachite (Sauer). A biotite-syenite with large 
 phenocrysts of orthoclase over inch long. 
 
 (b) Augite-bearing Mica-syenite. In Norway, as a transi- 
 tion between the mica- and augite-syenites, carrying anortho- 
 clase, cryptoperthite, oligoclase, hornblende, lepidomelane 
 in tables nearly half an inch square, and augite. Silica 
 55.18. 
 
 III. PYROXENE-syenite. 
 
 A syenite with predominant pyroxene. The feldspar is 
 orthoclase (also anorthoclase and microperthite) and 
 a soda-rich plagioclase. The pyroxene may be a 
 titaniferous diallage or diopside, augite, hypersthene, 
 or uralite. Mica is usually biotite, sometimes lepi- 
 domelane ; elaeolite is seldom absent in some varieties. 
 Hornblende is brown. Olivine is usually present, 
 and quartz and plagioclase absent. In color it is 
 grayish, greenish, brick-red, blackish green, and violet- 
 red when weathered. It resembles gabbro in some 
 varieties. 
 
 Silica 55-59. 
 
 This combination is not a common one, though it is of 
 importance in Norway, Italy, and less prominent elsewhere. 
 
 (a) Orthoclase -monzonite. A compound of orthoclase, 
 plagioclase, hornblende, and augite, with an abundance of 
 the ores. At Monzoni, Italy, and in Silesia. 
 
 (b) Laurvikite (Brogger). From southern Norway, with 
 56.8-58.8 silica. A grayish gabbro-like rock composed of 
 brown hornblende, the soda-orthoclases, titaniferous pyrox- 
 ene, biotite, and some nepheline and olivine. 
 
PRIMARY ROCKS. 1 53 
 
 (c) Akerite (Brogger). A quartzose variety of the above 
 and at the same place, carrying orthoclase, plagioclase, 
 quartz, hornblende, pyroxene, brown biotite ; no nepheline, 
 sodalite, nor olivine. It is in a laccolith ; medium- to coarse- 
 grained and granitic ; gray to red. The variety from New 
 Hampshire described by Hawes is like this. 
 
 (d) Hypersthene-syemte. Zirkel places here the " norite" 
 of G. H. Williams, from Cortlandt, N. Y., as it contains 
 orthoclase. 
 
 (e) Uratite-syemte (v. Jeremejew). A uralitized augite- 
 syenite from the Urals. 
 
 PORPHYRIES OF THE SYENITE GROUP. 
 
 IV. SYENITE-PORPHYRY (v. Richthofen). 
 This subgroup includes the quartzless orthophyric felso- 
 phyres that exhibit phenocrysts of one or more of the black 
 bisilicates to form a series which has the same relation to 
 syenite that quartz-porphyry has to granite. According to 
 the mineral of the phenocrysts which shows predominantly, 
 they are divided : 
 
 (a) Felsophyre with orthoclase phenocrysts is quartzless 
 orthoclase-^or^>\\yry, or quartzless orthophyre. 
 
 (b) Felsophyre with phenocrysts of orthoclase, horn- 
 blende, biotite, and augite, syenite-porphyry. 
 
 (c) The same with orthoclase and hornblende is horn- 
 ^^^-syenite-porphyry. 
 
 (d) The same with orthoclase and biotite is ^'^^-syenite- 
 porphyry. 
 
 (e) The same with orthoclase and augite is ^^'/^-syenite- 
 porphyry. 
 
154 MANUAL OF LITHOLOGY. 
 
 IV0. QUARTZLESS ORTHOCLASE-POR- 
 PHYRY, Quartzless Orthophyre (according to 
 J. D. Dana). 
 
 A feldspathic groundmass in which only potash-feldspar 
 occurs in phenocrysts, with no appearance of black 
 bisilicates except as (m) in the groundmass, where 
 they are usually altered to secondary products, such 
 as calcite, chlorite, and hydrated ferric oxide. 
 Contains silica 56-62 ; Gr. 2.55-2.60. 
 
 It occurs in dikes and sheets in the Thuringian Forest, 
 Tyrol, the Balkans, Scotland, Greenland. These rocks are 
 separated from the quartzless felsite-porphyries by their 
 lower acidity. The groundmass is light to dark through 
 shades of red, yellow, gray, and green, and consists almost 
 entirely of (m) feldspar crystals usually orthoclase with 
 th alteration products of the black bisilicates. It seems to 
 be entirely without base, and holocrystalline. The glassy 
 habit of the feldspar gives it frequently a trachytic appear- 
 ance. Orthoclase is milk-white, yellowish, or reddish; 
 plagioclase is almost absent. 
 
 i. Rhomb Porphyry (L v. Buch). From Norway. The 
 light-violet groundmass carries deep-gray crystals of ortho- 
 clase, which give rhombic sections. When weathered the 
 mass is reddish. It is compact and shows (m) orthoclase, 
 augite, magnesia-mica, olivine, and magnetite. Weathering 
 affords a good number of secondary minerals, as carbonates 
 quartz, iron ores, from the chloritized augite and biotite, ser- 
 pentine from the olivine, and sometimes epidote and sericite. 
 The orthoclase feldspar is sometimes microcline, and some- 
 times anorthoclase. It occurs in surface sheets and dikes. It 
 contains 55-61 silica, with Gr. 2.61. The orthoclase crystals 
 are sometimes two inches long. The carrying only these 
 phenocrysts places this rock under the orthophyres ; but 
 
PRIMARY ROCKS. 155 
 
 the chemical composition places only the more acid here, the 
 main body belonging with the augite-syenite porphyries. 
 
 2. KERATOPHYRE (Giimbel). 
 
 A ( M) compact groundmass resembling hornstone 
 (whence the name), carrying very small phenocrysts 
 of feldspar, (m) the groundmass is fine crystalline 
 granular and composed mainly of feldspar, which 
 somewhat resembles trachyte, and sometimes ortho- 
 phyre. It has a variable quartz content which is (M) 
 in the quartz variety. 
 
 Silica 6 1-66 ; Gr. 2.61. 
 
 QUARTZ-KERATOPHYRE (Lossen). 
 A similar rock containing a large amount of quartz in 
 the groundmass and as phenocrysts in small number. 
 The groundmass is coarser grained than in the basic 
 variety. It occurs at Baraboo, Wis., like a lava, and 
 associated with tuffs. 
 
 Silica 70-80 ; Gr. 2.64. 
 
 The basic variety occurs in the Fichtelgebirge, Harz, 
 Nassau, and in New England (see below) ; the quartz variety 
 in Saxony, Great Britain. Both are soda-orthoclase rocks, 
 where the feldspar is sometimes a mixture of both orthoclase 
 -and albite, and sometimes microperthite. The phenocrysts 
 .are variable from few to abundant. In the groundmass 
 appear also (m) grains of magnetite, folia of brown mica, 
 .and specks of hornblende. (See under " Quartz-porphyries " 
 p. 141). 
 
 (a) Bostonite (Hunter and Rosenbusch). From Marblehead 
 Neck, Mass., Chateaugay Lake, N. Y., the Champlain val- 
 ley ; Montreal, Canada, Norway, Brazil, as basic keratophyre 
 in dikes. It is a light-colored rock, with rough trachytic 
 feel on a fracture, carrying phenocrysts of orthoclase, while 
 the groundmass carries the same with anorthoclase. It is 
 
1 56 MANUAL OF LITHOLOGY. 
 
 essentially a feldspathic rock, without black bisilicates, and 
 carrying (Norway) 61 silica. Brogger's exhaustive study of 
 the associated bostonites and comptonites of Gran, Norway, 
 conclusively shows that they are differentiations from a 
 gabbroitic magma, and extrude sometimes at the same time 
 and in the same dike, where each is at times the envelope 
 of the other, and he suggests for these and similarly differ- 
 entiated rocks the term " complementary," and states that 
 they should be classed with the rock-form of the undiffer- 
 entiated magma. 
 
 IV. SYENITE-PORPHYRY. 
 
 A (M) fine-grained to compact groundmass without 
 base, and carrying phenocrysts of orthoclase, horn- 
 blende, mica, and augite at the same time, the first 
 predominating. 
 
 The groundmass is always crystalline-granular and com- 
 posed of the minerals noted above, and with feldspar greatly 
 predominant. They weather to chlorite and carbonates. As 
 accessories are titaniferous magnetite, titanite, apatite, and 
 zircon. In the augitic variety olivine is also accessory. 
 They occur in dikes, and are distinguished from similar 
 dioritic porphyries by their color, their freedom from 
 amygdaloidal states, and their having orthoclase, which gives 
 a potash rather than a lime-soda result to the chemical 
 analysis. Quartz may be sparingly present without placing 
 the rock among the quartz-porphyries. As varieties : 
 
 I. Hornblende-syenite-porphyry. A rock found in dikes 
 and sheets, of compact groundmass, and carrying pheno- 
 crysts of orthoclase and hornblende. The groundmass 
 shows usually all the syenitic minerals, and the black bisili- 
 cates weather to chlorite, epidote, and calcite. This 
 changes the fresh brown or reddish-brown rock to green 
 or grayish green. It contains 61 silica, and occurs in the 
 Vosges, Tyrol, and Black Forest. 
 
PRIMARY ROCKS. 1 57 
 
 2. Biotite- syenite -porphyry. A dike-rock of limited 
 extent in the southern Vosges, Sweden, Portugal. It is 
 deep reddish brown when fresh, and chloritizes to greenish 
 -shades. Augite generally accompanies the biotite, and more 
 or less plagioclase the orthoclase. 
 
 3. Augite-syenite-porphyry. A similar occurring rock 
 from Brazil, the Caucasus, Montenegro, Spain, Albany, N. 
 Y. The groundmass is greenish gray, and composed of 
 large proportions of plagioclase with the orthoclase, augite, 
 magnetite, pyrite, and altered olivine. The phenocrysts 
 are usually large orthoclases and augites. The latter is 
 usually dark green, but at Albany, N. Y., it is violet- 
 brown and accompanied by a bluish amphibole. Olivine 
 .appears sparingly. 
 
 V. COMPACT SYENITE (Kalkowsky), Microsy- 
 enite (Wadsworth), Syenite-aphanite (Zirkel). 
 
 A compact mixture of syenite minerals (sometimes fine- 
 granular), of dark greenish gray color, in narrow dikes, and 
 bearing to syenite the same relation that felsite does to 
 granite. It is usually weathered and the black bisilicates 
 cloritized (which accounts for the color), and calcite is 
 sometimes primary and sometimes secondary. This is 
 distinguished from syenite by the failure to detect by the 
 naked eye the syenitic minerals ; but the lens and micro- 
 scope show them. The fineness of the grain is peculiar to 
 dike-rocks and the peripheries of larger masses where the 
 walls are somewhat heated, so that cooling is not instantane- 
 ous, but more rapid than in the center of large masses. 
 Wadsworth's microsyenite is the parallel of Rosenbusch's 
 microgranite of similar rate of cooling. Aplite is of like 
 origin. This may be taken as the groundmass of the above 
 syenite-porphyries, and is associated with syenites and sye- 
 nitic mica-traps. 
 
 There is no syenite glass. 
 
MANUAL OF LITHOLOGY. 
 GROUP 5. PHONOLITE. 
 
 PHONOLITE-EL&OLITE-SYENITE EXTRUSIVES. 
 (Necessary minerals: An alkali feldspar, elaeolite, or nepheline, and 
 
 hornblende.) 
 
 PHONOLITE (Klaproth), Clinkstone. 
 A (M) compact groundmass which, in its fresh state, is 
 dark greenish or yellowish gray, showing sporadic 
 individual cleavage surfaces of sanidine. The mass 
 shows a great tendency to fracture like slates and 
 schists, or is thin tabular-jointed. Under these con- 
 ditions it gives a clear sound when struck with a 
 hammer (whence the name). On weathering a sharply 
 defined yellowish-white or white crust is formed, 
 (m) it is a compound of sanidine and nepheline (or 
 leucite), with essential nosean (or hauyne), monoclinic 
 pyroxene, hornblende, magnesia-mica rarely, and still 
 more rarely plagioclase. The last seems to be re- 
 stricted to trachytic phonolites poor in nepheline. 
 This is divided into : 
 
 (A) TYPICAL PHONOLITE, or Nepheline-tra- 
 
 chyte (Zirkel). 
 
 A compound, as above described, of sanidine and nephe- 
 line, with the other minerals as accessories only. 
 Silica 50-62 ; Gr. 2.4-2.65. 
 
 Phonolite occurs generally in isolated and precipitous 
 dome-shaped masses ot large size (Fernando do Noronha), 
 as surface sheets of great extent, as lava-flows, and in 
 dikes. It is found in Great Britain, Germany, Bohemia, 
 central France, northern and eastern Africa, Cape Verdes, 
 Canaries, Asia, Paraguay, Brazil, the Black Hills, and (in 
 loose blocks) in Pasolty County, Col. The sanidine is 
 (m) in the groundmass and (M) as large tabular phenocrysts,. 
 
PRIMARY ROCKS. 1 59 
 
 with the clinopinacoid parallel to the cleavage plane, and 
 with twinning after the Carlsbad type. Anorthoclase 
 occurs (m). Nepheline is generally (m) ; but it is (M) in 
 some Bohemian types, and in New Zealand it occurs in 
 reddish phenocrysts one-half by one-fourth of an inch in size. 
 Nosean is (M) occasionally, and hatiyne rarely ; the latter has 
 been noted 3-4 mm. long. Sodalite (which has been mis- 
 taken for the latter) is sometimes 2-3 mm. long. Plagioclase 
 is very irregular in this variety. Hornblende is common in 
 (M) black needles that do not change to chlorite or epidote. 
 Large augite phenocrysts are infrequent, but sometimes 7 
 mm. long. Part of these approach aegirite, which occurs 
 (m). Great brown folia of magnesia-mica occur sparingly 
 in a few localities. Magnetite is constant, but (m). Honey- 
 yellow titanite (also yellowish red) is abundant (M); also 
 zircon 1-2 mm. long. Olivine is wanting as a characteristic 
 mineral; but occasionally it is found, and sometimes 2-15 
 mm. long. Quartz and tridymite are scarce and (m). Zirkel 
 states that the groundmass is of two kinds, a typical phono- 
 litic and a trachytic state. The former is dark-colored, with 
 greasy luster, compact and non-porous, except as small 
 haiiyne or nepheline crystals have been removed by 
 weathering ; with ready cleavage, and small phenocrysts,, 
 which are generally sanidine. The cleavage is less marked 
 in the highly porphyritic states. The groundmass fuses 
 bp. more or less readily to a yellowish or greenish glass, 
 and gives water in the closed tube. This type is found in 
 Bohemia, the Mittelgebirge, the Lausitz, Cornwall (Wolf 
 Rock), central France, Teneriffe, and the Canaries. The 
 groundmass, of trachytic habit, is cleavable with difficulty or 
 not at all ; luster sub-greasy ; color generally light-gray or 
 yellowish gray ; of rough porous feel. In rare cases small 
 phenocrysts of nepheline appear with plagioclase. This 
 is found in the Rhone district and Bohemia, and must 
 
MANUAL OF LIT HO LOG Y. 
 
 be distinguished from the old so-called " trachytic phono- 
 lite," which had lost its cleavage from weathering. The 
 groundmass is partly soluble in HC1, the soluble part 
 being nepheline and zeolites, while the feldspathic part is 
 insoluble. The specific gravity, and the percentages of 
 soluble matter and of water, are inversely proportionate to 
 the percentage of silica. The cleavable states generally 
 split readily and in thin sheets, so that the rock can be used 
 for slating (Cantal in central France). Whole mountains 
 of phonolite are divided by joints one foot apart. It also 
 separates into long prisms, but not with such regularity 
 as in basalt. The cleavages seem to be parallel to the cool- 
 ing surface, and the prisms perpendicular to the same. 
 Phonolite weathers with a sharply defined grayish-white to 
 yellowish-white crust, which at first adheres to the tongue. 
 Zirkel states that the minerals are removed in the following 
 order: magnetite, hauyne, sodalite, the glass base (if pres- 
 ent), and nepheline. All form zeolites, which next go, and 
 leave hornblende, augite, and sanidine. After the alteration 
 of the bisilicates the feldspar kaolinizes after prolonged 
 weathering, to form a gray or mottled clay. Other states 
 are as follows : 
 
 (a) Porphyritic Phonolite. Though the rock is generally 
 porphyritic, there is now and then a specially porphyritic 
 state, as in Bohemia, the Rhone district, etc. It is a (m) 
 fine-grained aggregate of phonolitic minerals, rich in horn- 
 blende, with either an abundance of large hornblende 
 prisms (sometimes 5 cm. long), an aggregate of hornblende 
 and titanite, or a mixture of light-yellow transparent titan- 
 ite, black hornblende, mica, nepheline, and zircon, which is 
 like the allied rock at Ditro. 
 
 (ft) Vesicular Phonolite is reported from Blattendorf, near 
 Haida, Bohemia. 
 
 (c) Spotted Phonolite is only a colored state due to local 
 
PRIMARY RGCKS. l6l 
 
 decomposition, at Luschwitz, near Aussig, Bohemia ; or to 
 a more coarse agglomeration of the mineral ingredients in 
 patches, as on one of the Cape Verdes. 
 
 PHONOLITE GROUP B. (Zirkel.) 
 
 Nosean - trachyte (Lenk), Haiiyne - trachyte, Nosean- 
 phonolite (Zirkel). 
 
 A variety of phonolite in which nepheline is replaced by 
 nosean (haiiyne), of a deep-black color, splintery fracture, 
 thin jointed structure, and gray weathered state. The 
 groundmass is compact, and shows (M) only sporadic long 
 prisms of hornblende ; but (m) exhibits sanidine, augite, 
 magnetite, and abundance of minute nosean. Plagioclase 
 and nepheline seem to be absent. It occurs in loose blocks 
 at the Kreuzberg, Mont Dore, in northern Bohemia, in a 
 dike at La Rochette, etc. 
 
 Taimyrite (v. Chrustschoff). From Taimyr Land, Siberia. 
 An ophitic aggregate of nosean and anorthoclase, with ac- 
 cessory plagioclase, amphibole, biotite, melanite, magnetite, 
 sphene, zircon, and glass. Anorthoclase is in long slender 
 crystals and nosean abundant. Zircon is the only accessory 
 of importance and is of trachytic type. Associated with 
 this is a similar compound, except that sodalite replaces 
 nosean, and that zircon is granitic. Gr. 2.57-2.62. The rock 
 is nearly ophitic. 
 
l62 MANUAL OF LITHOLOG Y. 
 
 PHONOLITE GROUP C. (Zirkel.) 
 
 LEUCITE - PHONOLITE, Leucite-nepheline-tra, 
 
 chyte (Zirkel), Leucitophyre (Rosenbusch). 
 A microcrystalline groundmass, with a small amount of 
 glass, carrying phenocrysts of sanidine, leucite, nephe- 
 line, and haiiyne (colorless, bluish gray to black, or, 
 when weathered, white or reddish), hornblende, and 
 no plagioclase nor olivine. 
 Silica 45-54 ; Gr. 2.5-2.9. 
 
 It is found in loose blocks, in plugs, in tuff, also in dikes 
 near the lake of Laach, Rieden, Selberg, etc.. in Bohemia,, 
 Italy, Persia, etc. The groundmass consists (m) of a small 
 amount of glass base with an abundance of crystallized 
 sanidine, leucite, nepheline, hauyne, augite, biotite, horn- 
 blende, titanite, apatite, magnetite, and melanite. Some 
 occurrences are porous. By weathering calcite and zeolites 
 appear, and analcite forms pseudomorphs after the leucite. 
 
 (a) Nosite-melanite Rock (vom Rath). A fine-grained to 
 compact compound of leucite, nepheline, nosite, sanidine, 
 black garnet (melanite), with some hornblende, pyroxene, 
 and titanite. Contains silica 48-5 5; Gr. 2.7-2.9. This is a 
 grayish dark-colored rock that frequently shows hyalite 
 crusts, from the decomposition of the silicates it contains. 
 
 PHONOLITE GROUP D. (Zirkel.) 
 
 LEUCITE-TRACHYTE (vom Rath). 
 In a compact light-gray, bluish-gray, or dark-gray ground- 
 mass, with splintery fracture, occur fresh sanidine, 
 white and somewhat decomposed leucite, blue hauyne, 
 augite, mica, magnetite, and seldom titanite. The 
 vesicular cavities are filled with (m) small nephelines. 
 Silica 60. 
 
 This occurs in a few places in Italy and Brazil in lava- 
 
PRIMARY ROCKS. 163 
 
 streams. The leucite appears to be as phenocrysts, and 
 does not show in the groundmass to any extent. This latter 
 is macrocrystalline. The leucites are sometimes 10 cm. 
 
 (a) Olivine-leucite-phonolite (A. Hague). As detritus in 
 the Ishawooa River, Wyoming, consisting of numerous 
 phenocrysts of olivine and augite in a groundmass com- 
 posed (m) only of leucite and an alkali feldspar, with a small 
 showing of plagioclase and folia of biotite. 
 
 PHONOLITE GLASS. 
 
 As stated at the beginning of the rocks, the tendency to 
 form hyaline states decreases with the lowering of the con- 
 tent of silica in a rock, and, at the same time, the tendency 
 to crystallize increases. There may be numerous instances 
 of glassy states of this rock, but, as yet, few have been 
 noted. They have, probably, long since been removed by 
 erosion, as phonolite is not found in very recent effusions. 
 
 Phonolite-pitchstone (Laube). Near Weipert is a brownish 
 black rock, of pitchy luster and fluidal structure, in which 
 are (m) numerous phenocrysts of sanidine, magnetite, and 
 nepheline. 
 
 Phonolite-obsidian. As selvages to phonolite dikes and 
 lava-streams in Teneriffe ; in phonolite tuffs, and as volcanic 
 bombs, with silica 73. It is black, gelatinizes with HC1, 
 and gives crystals of NaCl. (m) it shows sanidine, aegirite, 
 and Tiaiiyne, with chalcedonic nepheline. 
 
 Leucite-phonolite-pumice. In minute fragments in a tuff 
 of this rock at the foot of the Olbruck. They show an 
 almost colorless foamy glass with sharply defined (m) 
 phenocrysts of leucite, augite, nepheline, rarely hauyne, 
 magnetite, or titanite, and as the arrangement is the same 
 as in the rock of the Olbruck, it is accepted as a true phono- 
 lite-pumice. 
 
164 MANUAL OF LITHOLOGY. 
 
 GROUP 6. EL^OLITE-SYENITE. 
 PHONOLITE-EL&OLITE-SYENITE INTRUSIVES. 
 (Necessary minerals : Alkali feldspar, elaeolite, and hornblende.) 
 
 EL^OLITE-SYENITE. 
 
 A compound of an alkali feldspar, elaeolite (leucite, etc.), 
 one of the black bisilicates, and no quartz. 
 Silica 43-68 ; Gr. 2.46-2.63. 
 
 This rock occurs in extended masses, bosses, laccoliths, 
 and dikes, like syenite, and is also found in erratic blocks 
 (probably distributed through glacial agencies). It is found 
 in the Tyrol, Portugal, Pyrenees, Transylvania, southern Nor- 
 way, Sweden, Lapland, Ilmen Mountains, Greenland, Brazil, 
 Africa, the Cape Verdes, Great Britain, and 'in North 
 America in eastern Ontario, and near Montreal, Canada ; at 
 Salem and Marblehead, Mass. ; Red Hill, N. H. ; Litchfield, 
 Me. ; Magnet Cove and elsewhere in Arkansas ; Beemers- 
 ville, N. J. ; through the Champlain valley of Vermont ; in 
 New York ; Trans-Pecos region, Tex. ; Crazy Mountains, 
 Mont., and Rocky Mountains of Canada. It occurs massive, 
 schistose, and porphyritic, as follows : 
 I. Elaelite-syenite. 
 
 (a) Z^^-elaeolite-syenite. 
 
 (b) J/^/tfwzV^-elseolite-syenite. 
 II. Monchiquite. 
 
 III. Elasolite-syenite-/0r/^/rj/. 
 
 (a) Z^a/^-elasolite-syenite-porphyry. 
 
 I. EL^EOLITE-SYENITE, Laurdalite (Brogger). 
 
 A generally light-colored granitoid compound, varying 
 from medium fine-grained to irregular coarse-grained, 
 of an orthoclase, amphibole, mica (mostly biotite), and 
 pyroxene, with quartz almost always absent. 
 Average silica 53 ; Gr. 2.55. 
 
 This is a smutty red (M) compound of variable mixture ; 
 
PRIMARY ROCKS. 1 $ 
 
 at times regularly or irregularly coarse granitoid ; at times 
 trachytic from tabular minerals ; at times with parallel 
 arrangement of the minerals as in phonolite. Fluidal struc- 
 tures show (m). Orthoclase forms stout crystalline grains 
 with Carlsbad twins (rarely of Baveno) ; often microper- 
 thitic. Sometimes microcline, anorthoclase, and crypto- 
 perthite are present ; also plagioclase in varying amount. 
 Elasolite is generally idiomorphic with respect to feldspar, 
 and occurs crystal, and in irregular grains of whitish, 
 grayish, reddish color, and sometimes 2J- feet long. It alters 
 to Ca-Na-zeolites and calcite. Melanite is sometimes found 
 (m). Well-crystallized blue sodalite is common. Cancrinite 
 is present as a primary and as an alteration product. Leu- 
 cite is not present, but represented by analcite. Pyroxene 
 is usually green and well-crystallized augite, which is some- 
 times epidotized ; sometimes colorless malakolite is found in 
 fine-grained rocks, sometimes aegirite in radial aggregates, 
 sometimes both augite and segirite together ; brown acmite 
 (at Beemersville, N. J.) occurs, to the exclusion of the others. 
 Rosenbusch says that pyroxene sometimes fails entirely. 
 Hornblende, as should be the case, is the most constant of the 
 black bisilicates, and when two are together one is generally 
 this mineral. It occurs green, brownish green (by trans- 
 mitted light), and generally idiomorphic. It is usually a 
 soda-hornblende, as shown by the flame, ^nigmatite some- 
 times occurs in long individuals. Mica is generally biotite 
 (dark-brown magnesia-mica) in hexagonal tables and irregu- 
 lar folia ; sometimes it is dark green. Lepidomelane occurs 
 in black lustrous tables at Litchfield, Me. Nosean is found 
 now and then. The common accessories, magnetite (ordi- 
 nary and titaniferous) and apatite, are (m) ; calcite is com- 
 mon as secondary, zeolites less so ; eudyalite (M) is rare ; 
 melanite, nosean, and wollastonite are (m) at Montreal; 
 scapolite (M) in eastern Ontario; zircon is sporadic* (the 
 
1 66 MANUAL OF LITHOLOGY. 
 
 so-called "zircon-syenite" of Norway is an elasolite-syenite 
 rich in the mineral) ; olivine and pyrite sometimes occur. 
 This rock seems to be a middle ground on which all the 
 other varieties meet. The sporadic and scanty quartz, with 
 orthoclase, sometimes causes a resemblance to granite: 
 nepheline and leucite (also melanite), with an increase of 
 plagioclase and the black bisilicates, ally it to the basic 
 rocks; while a predominance of the latter minerals places 
 it at their most basic end, as is shown by the great range of 
 its silica content. We can distinguish 
 
 I. Hornblende -pyroxene-elasolite-syenite, where the two 
 black bisilicates are equally predominant. The varieties 
 are: 
 
 (a) Foyaite (Blum). From the mountains Foya and 
 Picota in the province of Algarve, Portugal. A granitoid 
 compound of orthoclase, elasolite, hornblende, pyroxene, 
 and biotite. Orthoclase is prominent in white or grayish 
 white elongated tables with imperfect twinning ; plagioclase 
 is accessory ; reddish and weathered elasolite in hexagonal 
 crystals ; pyroxene (augite and aegirite) in green crystals ; 
 green hornblende , biotite in hexagonal folia. As accesso- 
 ries apatite and magnetite are constant and abundant ; soda- 
 lite and titanite sporadic ; melanite, tourmaline, and pyrite 
 occasional ; rarely cancrinite, epidote, or zeolites. The 
 texture varies rapidly from fine to coarse, but the crystals 
 are usually equidimensional. It is sometimes compact and 
 porphyritic, but without base, and of ash-gray color. The 
 content of black bisilicates varies greatly ; generally pyrox- 
 ene is predominant, sometimes it is alone ; sometimes horn- 
 blende is alone, and sometimes accompanied by mica all in 
 the same mass. The Libertyville (N. J.) rock carries yel- 
 lowish orthoclase two inches long, abundant elasolite, aegir- 
 ite, and sodalite, while biotite is rare. Brogger gives this 
 name to a trachytoid rock in Norway with a different com- 
 
PRIMARY ROCKS. 1 67 
 
 position. (Here would come the coarse-grained and trachy- 
 toid states of the Brazilian rock whose dike-forms are 
 called tinguaite (Rosenbusch), as Hussak states that this 
 rock is only a porphyritic state of foyaite. In the United 
 States there is the same variation in the values of the horn- 
 blende and pyroxene content, as well as the same changes 
 in structure of the principal mass.) 
 
 (b) Cancrinite-agirite-syzmtQ (Tornebohm). From the 
 Siksjoberge, Sweden, in dikes and masses the former are 
 porphyritic. It consists of tabular feldspar (orthoclase, 
 anorthoclase, microcline, and plagioclase), cancrinite in 
 crystals f inch and in irregular grains, in a (ni) mixture of 
 the same with elseolite, aegirite, titanite, and apatite. (See 
 later under " Elseolite-syenite-porphyry.") 
 
 (c) Sodalite-syzmtt (Steenstrup). From Julianshaab dis- 
 trict, Greenland. A light yellowish-gray, coarse-grained, 
 miarolitic granitoid principal mass of greenish-white lath- 
 shaped feldspar (microcline, -J inch long), black arfvedson- 
 ite (9 inches long by 3^ inches thick), asnigmatite, aegirite 
 (with submetallic luster), and sodalite (i inch thick). Gar- 
 net, red eudialyte, and infrequent elseolite are accessory, 
 and sometimes inch thick. Silica 56.45. 
 
 2. Mica-elaeolite-syenite, Miascite (G. Rose). From 
 Miask in the Urals. Composed of orthoclase (Breithaupt's 
 microcline), white or gray ; yellowish-white elaeolite with 
 subresinous luster ; gray to blue sodalite ; nearly equiaxial 
 leek-green mica. As accessories, wohlerite, zircon, ilmenite 
 3i by 2\ inches, cancrinite, pyrite, monazite, quartz, horn- 
 blende, and pyrochlore. It is also found near Lake Superior. 
 Silica 68.16. 
 
 (a) Litchfieldite (Bayley). From Litchfield, Me. It shows 
 snow-white feldspar (orthoclase, albite, microcline), large 
 yellowish cancrinite, dark-blue allotriomorphic sodalite, 
 gray greasy elasolite (2 inches), black loha of lepidomelane, 
 
1 68 MANUAL OF LITHOLOGY. 
 
 and sometimes brown zircon. Hornblende, pyroxene, and 
 titanite are absent. Silica 60.39. 
 
 (b) Pulaskite (J. F. Williams). From Pulaski and neigh- 
 boring counties, Ark. A porphyritic compound of biotite r 
 orthoclase, cryptoperthite, scanty elaeolite, arfvedsonite, and 
 diopside. The phendcrysts are orthoclase. Silica 60.03. 
 
 3. Hornblende-mica-elaeolite - syenite, Ditroite. From 
 Ditro in the Siebenburgen in Transylvania. A coarse- to 
 fine-grained rock somewhat finer grained than miascite 
 with occasional compact and schistoid states. The parallel 
 arrangement of sodalite adds to this last effect. It contains 
 white orthoclase (weathering red), microcline, plagioclase, 
 gray elaeolite, large (i inch) prisms of hornblende, usually 
 altered to chlorite or biotite, blue sodalite, and usually can- 
 crinite. Titanite and zircon are abundant accessories. 
 Secondary products are muscovite, calcite, chlorite, epidote, 
 and ferrite. 
 
 (a) Zircon- syenite. A variation of the last with abundant 
 zircon. Where it has been described as a separate rock, it 
 is a granitoid compound of orthoclase, microcline, elasolite, 
 occasional sodalite, abundant zircon (red, brown, yellow), 
 and scanty hornblende. It occurs in Norway, at Marble- 
 head, Mass., etc. Silica 50-55 ; Gr. 2.7-2.9. 
 
 (b) Endyalite-syemte (Vrba). From south Greenland, 
 composed of soda-orthoclase, much plagioclase, yellowish 
 white elaeolite, black hornblende, eudyalite (in blood-red 
 grains i mm.), magnetite, apatite and small nests of mica. 
 
 la. LEUCITE-elaeolite-syenite (Hussak). 
 A coarse-grained variety from Serra de Caldas, Brazil, 
 carrying analcite, which is pseudomorphed after leu- 
 cite. A similar rock is found at Magnet Cove, Ark. 
 There is no rock yet known where leucite entirely 
 replaces elaeolite, and where it remains unaltered. 
 
PRIMARY ROCKS. 169 
 
 \b. MELANITE-elseolite-syenite, Borolanite (Home 
 
 and Teall). 
 
 A similar rock in intrusive sheets and dikes near Lake 
 Borolan, Assynt, Scotland (whence the name). A 
 medium-grained mixture of soda-orthoclase and mel- 
 anite (with pitchy luster) mixed with what is probably 
 amorphous elseolite, green pyroxene, dark biotite, and 
 a sodalite mineral. Some varieties of the mass have 
 little or no melanite, but consist of feldspar and 
 pyroxene. 
 
 (Schistoid Elaeolite-syenite. This is not a variety, but a 
 state, of this rock which is found in many localities notably 
 at Ditro, near Christiania, and in Greenland, and is due to 
 the parallel arrangement of the minerals, especially the 
 black bisilicates. There are also lenticular concretions, 
 which make "pudding" varieties of the various rocks. 
 These latter are caused (as in granite) by aggregates of feld- 
 spar and elaeolite with some of the black bisilicates.) 
 
 II. MONCHIQUITE (Hunter and Rosenbusch). 
 A dike-rock associated geologically and mineralogically 
 with the elasolite-syenites, and having a distinct 
 facies. It is a porphyritic combination of augite and 
 olivine, with a glassy base, with which may be asso- 
 ciated either hornblende or mica (or both together). 
 The base includes (m) phenocrysts of plagioclase and 
 occasionally of nepheline. The rock is black or gray- 
 ish black when fresh, and, weathers sharply to brown. 
 It gelatinizes slightly in cold, readily in hot, HCL 
 This and its greasy luster are indications of nephe- 
 line. 
 
 Silica 43-47 ; Gr. 2.8-3. Rosenbusch divides the 
 species thus : 
 
MANUAL OF LITHOLOGY. 
 
 1. With olivine ; 
 
 (a) and augite, monchiquite ; 
 
 (b) and augite and amphibole, amflfa&ote-monchiquite ; 
 
 (c) and augite and biotite, *i/*/*-monchiquite ; 
 
 (d) and augite, amphibole, and biotite, amphibole-b\ot\te- 
 
 monchiquite. 
 
 2. Without olivine. 
 
 The combinations (a), (b}, etc., are as just stated. 
 
 (a) Fourchite (J. F. Williams). 
 
 (b) Amphibole-iourchite (Rosenbusch). 
 
 (c) Ouacliitite (Kemp). 
 
 (d) Amphibole-ou2iC\i\\.\tQ (Rosenbusch). 
 
 The name comes from the Serra de Monchique, Portugal, 
 where the first of the type was found. These rocks are an 
 entirely (m) series, and cannot be told in many cases from 
 basalt, except by their brown weathering. This and the 
 gelatinization with HC1 afford some chances of detection 
 (M). In the United States are found 
 
 Fourchite (Fourche Mountains, Ark.; Beemersville, 
 N. J.; Essex County, N. Y.; Lake Merpphremagog, Vt.; 
 Angel's Island, San Francisco Bay, Cal.). Silica 47. 
 
 Ouachitite (throughout Arkansas, Beemersville, N. J.). 
 Silica 36.40. 
 
 Monchiquite (in the Lake Champlain region of Vermont). 
 
 PORPHYRIES OF THE EL^EOLITE-SYENITE GROUP. 
 
 III. EL^EOLITE-SYENITE-PORPHYRY. 
 
 A more or less compact groundmass, like hornstone, 
 with subconchoidal "or splintery fracture; greasy 
 luster ; color light or dark green ; carrying pheno- 
 crysts of feldspars, elseolite, and sodalite. 
 Silica 44-56; Gr. 2.55. 
 
 It occurs mainly massive and in dikes, associated with 
 
PRIMARY ROCKS. I /I 
 
 the crystalline states. It is found in the Tyrol, Greenland, 
 Norway, Brazil, Portugal, Scotland, Montana, Beemers- 
 ville, N. J. It bears to elasolite-syenite the same relation 
 that quartz-porphyry does to granite. 
 
 1. Liebnerite-porphyry. From the southern Tyrol. 
 Gieseckite-porphyry. From Greenland. 
 
 In weathered dikes. A flesh-red to brown groundmass 
 (from ferrite) carrying (m) tabular brick-red, Carlsbad- 
 twinned orthoclase phenocrysts, and J-inch prisms of greasy 
 oil-green to bluish green liebnerite (geiseckite). This latter is 
 .a micaceous secondary product from elaeolite. Silica, 44.66. 
 
 2. Hornblende-pyroxene-elseolite-syenite-porphyry. 
 
 (a) Tinguaite (Rosenbusch). Dike-rocks from the Serra 
 de Tingua, Brazil, similar to foyaite. Hussak states that 
 these have a gneissoid habit. 
 
 3. Nepheline-rhomb-porphyry (Brogger). In a dike from 
 elaeolite-syenite in southern Norway, with 56-57 silica. A 
 somewhat dark-grayish to violet rock with (m) fine-grained 
 groundmass carrying large phenocrysts of soda-orthoclase 
 ;and microperthite. The groundmass (m) shows nepheline. 
 It cannot be distinguished from rhomb porphyry by the 
 naked eye, but HC1 reactions will show difference. 
 
 Ilia. LEUCITE-elseolite-syenite-porphyry. From 
 Serra de Tingua, Brazil, and with pseudomorphs 
 of analcime after leucite like the granular rock. 
 
 (Some authorities note a leucite-syenite-^Qrphjrj contain- 
 ing sanidine and what appear to be minute (m) orthoclases 
 in the groundmass, on the ground of its being a Silurian 
 extrusion, and state that it would be a phonolite if it had been 
 extruded as late as Tertiary times. As there is no good 
 reason for dividing rocks according to geological age, this 
 rock is a phonolite, no matter whether it belong to pre-Cam- 
 brian or recent times.) 
 
INTERMEDIATE DIVISION. 
 II. ALKALI-LIME-SODA SECTION. 
 
 MICA-TRAP INTRUSIVES. 
 (Necessary minerals: Feldspar, black bisilicates.) 
 
 MICA-TRAP ROCKS (v. Cotta), LAMPROPHY- 
 RES (Rosenbusch). 
 
 Naumann first used the name "mica-trap" for a rock in 
 the Erzgebirge, which he afterwards identified with the 
 " minette " of the miners of the Vosges, and in 1838 aban- 
 doned the old name. The name signified a rock with pre- 
 dominant mica that resembled " trap " in its jointing and 
 weathering. In his treatise on lithology v. Cotta refers to 
 the above and says : " Under the circumstances it may be 
 admissible to transfer the name of mica-trap to an entire 
 group of similar rocks, whose common attributes are that 
 they consist principally of compounds of mica and feldspar, 
 without marked porphyritic texture, and that they contain 
 no quartz, unless quite exceptionally. We count in this 
 group the following rocks (although it is uncertain if they 
 all are of igneous origin), viz., minette, fraidronite, kersan- 
 ton, and kersantite. Until that question is determined in 
 the negative they may be so classed on account of their 
 petrographic affinity ; and for the same reason they will be 
 most conveniently treated as varieties of the same rock." 
 
 Eight years after this was issued Gumbel described his 
 lamprophyre, and twenty-one years after the same date 
 Rosenbusch gathered the above rocks into the class of 
 
 172 
 
PRIMARY ROCKS. 173 
 
 ** lamprophyres," which differed from the original "diabase 
 like " rock of Giimbel in having orthoclase as one of the 
 constituents. It was at once seen that these rocks could not 
 be united under the present system of mineral compounds, 
 and the " syenitic' ' and " dioritic " divisions of the lampro- 
 phyres followed. Zirkel discards the later name entirely, 
 and places minette with the syenitic porphyries, and the 
 other three under the diorites. All of them show to a con- 
 siderable degree the columnar and tabular jointing and 
 spheroidal weathering of basalt, the original " trap "; and as 
 both v. Cotta and Rosenbusch think them worthy of a 
 separate classification, they should be called by the older 
 name. The variation in their feldspars, however, requires 
 that they be placed under the syenitic and dioritic groups, 
 as there is no good reason for separating dike-rocks from 
 other eruptives. The original lamprophyre of Gumbel was 
 placed by him with the mica-traps (minette, kersantite, ker- 
 santon, and mica-diabase), and the name " shining " refers to 
 the mica content. If it be proper to annex to this group a 
 rock like vosgesite, which is conspicuous for having little 
 mica, it is a matter of little consequence whether the name 
 of the group be " lamprophyre " or " mica-trap," as long as 
 both refer to the same mineral. The lamprophyres of the 
 Shap granite mass in England are shown by their containing 
 the same quartz, orthoclase, and sphene to have originated 
 in the same magma as the granite by differentiation. 
 
 These rocks may be imagined to be granite-porphyries 
 Door in quartz and rich in black bisilicates. They can be 
 divided according to their feldspar : 
 
 I. With an alkali feldspar, syenitic mica-trap. 
 
 II. With plagioclase, dioritic mica-trap. 
 
MANUAL OF LITHOLOGY. 
 
 GROUP 7. SYENTIC MICA-TRAP. 
 
 I. SYENITIC MICA-TRAP, Syenitic Lampro- 
 
 phyre (Rosenbusch). 
 
 A series of porphyritic rocks (and also porphyries) 
 having a (M) fine-grained to compact groundmass of 
 orthoclase and plagioclase in needles, with the other 
 syenitic minerals highly predominant, and carrying 
 some or all of them as phenocrysts. Biotite is always 
 present in the groundmass and usually as phenocryst. 
 They can be taken as intermediate between the syen- 
 ites and their porphyries. 
 
 Silica 48-65 ; Gr. 2.5-2.9. 
 
 These are a series of dike varieties of mica-syenite, or 
 states that have cooled under similar circumstances, and 
 they differ from the mica-porphyrites in the state of the 
 matrix and the fact that the mica is in folia rather than in 
 tabular crystals. They are characterized by columnar and 
 tabular jointing, by spheroidal weathering, and by resistance 
 to disintegration. They carry as accessories magnetite, 
 pyrite, abundant apatite, and the derivatives of their com- 
 ponents. Under this head will be grouped : 
 
 I. Minette (orthoclase and predominant biotite). 
 
 II. Vosgesite (Rosenbusch), (orthoclase, hornblende, and 
 augite). 
 
 I. MINETTE (old mining name; first noted by filie 
 
 de Beaumont). 
 
 In a matrix usually coarse enough to be resolved by the 
 lens (generally fine crystalline and porous, with dark- 
 gray color (also reddish to blackish-brown]); com- 
 posed of orthoclase and much mica with some horn- 
 blende, are abundant folia of biotite, with occasional 
 phenocrysts of qrthoclase, olivine, and hornblende. 
 Silica and gr. as above. 
 
 It was named first in the Vosges. It also occurs in 
 
PRIMARY ROCKS. 1/5 
 
 Saxony, Bohemia, France, Jersey, Great Britain, and Scan- 
 dinavia. The orthoclase is flesh-red ; mica brown to black 
 seldom green ; hornblende grayish to dark green. On 
 the selvages of the dikes and wherever quickly cooled it 
 becomes compact. The folia of mica are sometimes nearly 
 half an inch across; the feldspar weathers to pinite and 
 kaolin in the groundmass, and is seldom fresh. Calcite 
 and siderite are also secondary products. Chlorite some- 
 times occurs ; quartz never. 
 
 (a) Hornblende-miuette, with predominant hornblende, 
 occurs in Alsace, Erzgebirge, the Auvergne, etc. 
 
 (b) Axgtte-minette, with predominant augite, occurs in 
 the Vosges, Fichtelgebirge, Sweden, England. 
 
 (c) Fraidronite (E. Dumas) is a similar rock, much weath- 
 ered, from France in a limited number of localities (depart- 
 ments of the Lozere, Cevennes, etc.). It is of dirty green 
 color, with weathered felsitic mass carrying much mica, 
 with pyrite and quartz as secondary products ; also calcite 
 and siderite in veins and included balls. The rock is highly 
 fissile when weathered. The above rocks are variations 
 between mica-syenite and mica-syenite-porphyry. 
 
 II. VOSGESITE (Rosenbusch). 
 
 In a grayish-brown, greenish-gray to black groundmass 
 of similar structure to minette, composed of abundant 
 and generally (ni) orthoclase and other syenitic ingre- 
 dients ; but showing phenocrysts of only hornblende 
 and augite. A quartz-free syenite-porphyry with 
 predominant hornblende and augite. 
 Silica 48 ; Gr. 2.93. 
 
 It occurs in narrow dikes in the Vosges, Erzgebirge, in 
 Brazil, and (augite-vosgesite) at Livermore Falls, N. H. The 
 rock weathers like the syenites to a reddish or rusty brown 
 color, and is the parallel of minette, with biotite replaced by 
 the other two black bisilicates. These are so predominant 
 
MANUAL OF LITHOLOGY. 
 
 in certain localities that Rosenbusch has divided the rock 
 into amphibole- and augite-vosgesite. The former bears to 
 the hornblende-syenite-porphyry and hornblende-syenite the 
 same relation that the latter does to the augite varieties of 
 the rock. In both plagioclase appears with orthoclase ; 
 hornblende is in thin and augite in stout prisms. Uralite 
 sometimes appears. Orthoclase and biotite seldom appear 
 as phenocrysts. The orthoclase is rich in soda. This rock 
 is decidedly more like " trap " than minette, from its color 
 and higher gr. Holocrystalline and porphyritic textures 
 occur in the same dike. 
 
 GROUP 8. DIORITIC MICA-TRAP. 
 
 II. DIORITIC MICA-TRAP, Dioritic Lamprophyre 
 
 (Rosenbusch). 
 
 A series of dioritic compounds too decidedly porphyritic 
 to be classed as typical diorites, and too granular to be 
 placed with the diorite-porphyrites. Their peculiar texture 
 is observed in dike-rocks and masses that have cooled 
 against moderately hot walls. Their hornblende is usually 
 basaltic and rod-shaped, their magnetite content is good, 
 and they may have abundant augite. Rosenbusch has 
 distinguished : 
 
 1. Kersantite, which is intermediate in texture between 
 mica-diorite and mica-porphyrite. 
 
 2. Camptonite, which is intermediate between the horn- 
 blende varieties of the same, but both Zirkel and M.-Levy 
 have relegated the latter back to diorite, as there is no good 
 reason for its separation. This leaves kersantite and its 
 varieties where v. Cotta placed them. 
 
PRIMARY ROCKS. 
 
 I. KERSANTITE (Delesse). 
 
 A porphyritic rock, rarely so fine-grained as not to be 
 resolved by the lens, with a principal mass composed 
 of oligoclase (or oligoclase and biotite) and ortho- 
 clase (and sometimes sanidine), and carrying pheno- 
 crysts of oligoclase, laminae of biotite, fibers of horn- 
 biende, green augite, and some quartz, olivine, and 
 magnetite. 
 
 Silica 49-57 ; Gr. 2.62-2.86. 
 
 It occurs in narrow dikes, which sometimes are like sur- 
 face sheets, in Silesia, Thuringian Forest, Alsace, Austria, 
 Bretagne, and Great Britain. The rock is holocrystalline 
 without base. The oligoclase phenocrysts are striped 
 brown, green, red, etc., from decomposition products. They 
 vary from rod shapes in the fine-grained states to stout ones 
 in those of coarser grain (in some cases over an inch long). 
 Biotite (or anomite) laminae are sometimes nearly half an 
 inch across, and the mineral is abundant in the principal 
 mass as in minette, and on the selvages it is parallel to the 
 dike-walls. Pyroxene is usually green augite, also enstatite 
 and bronzite, which latter alter to bastite. Hornblende is 
 the brown basaltic kind, rod-shaped and sometimes inch 
 long; uralite is rare. Quartz occurs as in granite, and 
 sometimes forms micropegmatite with orthoclase. Now 
 and then it is an inch across. Quartz, orthoclase, and oligo- 
 clase also occur as secondary minerals, with calcite and 
 (rarely) epidote as alteration products. Pyrite, pyrrhotite 
 and garnet also occur. In some localities are lenticular 
 concretions of mica, also of chlorite, quartz, and reddish 
 calcite. 
 
 (a) Kersanton (Riviere). A rock which the microscope 
 has shown to be kersantite, so that the name is now aban- 
 doned. 
 
178 MANUAL OF LITHOLOGY. 
 
 (b) Aschaffite. Some authorities place this rock here. 
 (See under " Granite-porphyry.") 
 
 (c) 6>/zW;^-kersantite (Rosenbusch). Here olivine is 
 abundant enough to attract attention. From lower 
 Austria. 
 
 (d) gtftfrte-kersantite (Barrois). In small massives and 
 a dike in Spain. A bluish green dense groundmass (also 
 fine-grained) carrying large phenocrysts of plagioclase, 
 biotite, and quartz. Seldom granitoid or wholly dense. 
 Secondary calcite, chlorite, epidote, and muscovite occur. 
 
 (e) /V/zte-kersantite (Becke). Poor in mica and rich in 
 augite, the former having chloritized. Of rare occurrence. 
 
 GROUP 9. PORPHYRITE AND MICA-PORPHYRITE, 
 
 lib. ALKALI-LIME-SODA SECTION. 
 
 (Necessary minerals, plagioclase, mica.) 
 
 I. PORPHYRITE, Plagioclase-porphyrite. 
 
 A rock with a compact matrix of plagioclase and carry- 
 ing phenocrysts of feldspars, with few or no pheno- 
 crysts of the black bisilicates ; occasionally of quartz. 
 Silica 59-68 , Gr. 2.6-2.7. 
 
 II. MICA-PORPHYRITE. 
 
 A similar rock carrying abundant phenocrysts of mica, 
 and also of feldspar, hornblende, and infrequently of 
 pyroxene. 
 
 Silica 60-67; Gr. 2.6-27. 
 
 Kporphyrite, in distinction from a porphyry, is a rock with 
 a matrix of plagioclase rather than of orthoclase. Both 
 rocks contain both feldspars ; but in the porphyry the alkali 
 form predominates and the quartz content is high : in the 
 porphyrite the Ca-Na-form predominates and quartz is 
 
PRIMARY ROCKS. 1 79 
 
 rare (either in the groundmass or as phenocryst). The old 
 distinction between the two rocks on the score of the pres- 
 ence or absence of quartz as phenocryst or in the mass is 
 no longer held. As the phenocrysts are predominant 
 plagioclase, mica, hornblende, or pyroxene, the porphyrite 
 is called plagioclase-, mica-, hornblende-, or pyroxene-por- 
 phyrite. Zirkel classes all except the pyroxene varieties 
 under " diorite-porphyrite." The first two types (plagio- 
 clase and mica) will be treated here. The groundmass 
 varies alike in both, and the phenocrysts are similar. After 
 a general description they will be further noted apart. 
 They occur mostly in thin dikes ; intrusive sheets ; as bosses 
 and in tuffs. They are also frequently found as old extru- 
 sive sheets of great thickness, so that they partake of both 
 extrusive and intrusive characters. They therefore show 
 stretched vesicular structures, both empty and filled with 
 green earth and calcite, which frequently form the greater 
 part of the mass. The masses are irregularly jointed and 
 fissured ; rarely columnar and tabular. They are less wide- 
 spread than the quartz-porphyries, and do not form such 
 large masses. They are found in Saxony, the Harz, Black 
 Forest, Vosges ; in Belgium, Bohemia, Tyrol, Italy, Monte- 
 negro, Spain, Asia, Africa ; in the Augusta Mountains, 
 Nev. ; New Hampshire, Vermont, New York, and Canada. 
 The porphyrites will be separated from melaphyre by the 
 olivine content of the latter; so that both are plagioclase- 
 porphyries (using the term in its general meaning) ; porphy- 
 rite being without, and melaphyre with, olivine. As in all 
 mixtures there are points where several minerals seem to 
 be equally predominant, and where the rock is a transition 
 between two types. There is also the point where the black 
 bisilicates retreat into the groundmass and only plagio- 
 clase shows. Here the microscope must decide as to the 
 variety, unless either quartz or orthoclase appear, and then 
 
180 MANUAL OF LITHOLOGY. 
 
 it will belong to the micaless porphyrites. All types of 
 porphyrite with no (or few) phenocrysts of black bisilicates 
 will be grouped under porphyrite. Three types of ground- 
 mass are given for the purpose of making clear some of the 
 following divisions, though the types can only be dis- 
 tinguished (m). 
 
 (a) Greenstone-like porphyrite. With a (m) crystalline 
 groundmass like diorite, green through chloritization or 
 formation of epidote from hornblende ; greenish hornblende, 
 also green by transmitted light ; dirty greenish white feld- 
 spar; biotite not very dark; little or no base. It forms as 
 a rule bosses from which dikes run into the older schists, 
 and makes what may be extrusive as well as intrusive sheets. 
 Most of the hornblende- and mica-porphyrite dikes in cen- 
 tral Tyrol, beds in the Alps, dikes in the Falkenstein, in 
 Sweden, Belgium, etc., are examples of this type. 
 
 (b) Andesitic-porphyrite. (m) like andesite, with gray, 
 grayish black, brownish black color ; fresh and almost glassy 
 plagioclase ; hornblende brownish black and brown in sec- 
 tion ; biotite very dark; not much quartz; groundmass rich 
 in ferrite and with andesitic structure, sparingly microdio- 
 ritic; with small amount of glass base (colorless, yellowish, 
 grayish). Found in the Thuringian Forest, Saar-Nahe dis- 
 trict, etc., as dikes. 
 
 (c) Porphyry-like Porphyrite. (m) like the porphyries 
 and sometimes micropegmatitic and microfelsitic ; color 
 reddish, brownish red ; or chestnut-brown (from ferrite) ; 
 poor in black bisilicates ; richer in silica than (b] ; quartz 
 quite abundant as (M) phenocrysts and in the groundmass ; 
 in many cases the groundmass is (m) compact. In Alsace, 
 Silesia, Altai Mountains, Saar-Nahe district, as dikes. 
 
 Plagioclase phenocrysts are white, yellowish white, or 
 reddish white, and usually somewhat altered and dull. 
 They are oligoclase, sometimes andesine, less frequently 
 
PRIMARY ROCKS. l8l 
 
 labradorite. When hornblende is present it is as stout 
 prisms or acicular shapes of brownish black color. Biotite 
 occurs in regular hexagonal tables, sometimes in prisms, 
 rarely in folia. Quartz occasionally appears in large phen- 
 ocrysts, as do orthoclase and garnet. Augite is now and 
 then (M). 
 
 I. PLAGIOCLASE-PORPHYRITE, Porphyrite. 
 In a groundmass with a habit like that described in (c) 
 
 are phenocrysts of plagioclase (usually oligoclase, fre- 
 quently andesine, less so labradorite), and sometimes 
 orthoclase and quartz. 
 
 Silica 60-68 ; Gr. 2.6-2.7. 
 
 It occurs in the Black Forest, Bohemia, Scotland, Altai 
 Mountains, Ecuador. The groundmass is gray, red, violet, 
 or blue, in which the phenocrysts are well contrasted. In 
 the Rothliegenden formation of Germany it is found in a 
 thick extrusive sheet. 
 
 II. MICA-PORPHYRITE. 
 
 A groundmass as above, with predominant phenocrysts 
 of biotite and plagioclase, also orthoclase and quartz. 
 Silica 60-67 ; Gr. 2.5-2.8. 
 
 This is found in Saxony, the Thuringian Forest, Saar- 
 Nahe district, central Alps, etc. Kemp reports an augite- 
 mica-porphyrite in bosses west of Deckertown, N. J. 
 
 I. Quartz-mica-porphyrite. 
 
 A porphyrite with light green tabular plagioclase pheno- 
 crysts ; dark biotite tables (more frequently in folia than in 
 the quartzless varieties) ; rounded grains of quartz and 
 sometimes double pyramids ; frequently orthoclase f inch 
 long. The groundmass is a (m) aggregate of angular quartz 
 and feldspar prisms. Silica 62-78 ; Gr. 2.74. 
 
S 82 MANUAL OF LITHOLOGY. 
 
 It occurs in dikes and is found in Alsace, Austria, the 
 Alps, etc., and from'Gippsland, Australia, a variety with 
 the high silica content of 72-77.66 is reported. 
 
 (a) Malchite (Osann), from the Melibocus, as a dike- 
 rock of the diorite group, with silica, 63.18. The dense 
 groundmass carries rare phenocrysts of dark biotite, pale 
 green labradorite, and quartz ; with (m) green hornblende, 
 .sphene, and allanite. 
 
 INTERMEDIATE DIVISION LIME-SODA SECTION. 
 GROUP 10. DACITE. 
 
 Ilia. DACITE QUARTZ-DIORITE EXTRUSIVES. 
 (Necessary minerals: Plagioclase, hornblende, and quartz.) 
 
 DACITE (Stache), Quartz-hornblende-andesite. 
 Named from the old Roman province of Dacia, where it 
 was first found. The rock will be considered as always 
 showing free quartz either (M) or (m), though Zirkel classes 
 all rocks of similar mineral content with the average of silica 
 of the quartzose varieties as dacite, whether they show free 
 quartz or not. On the other hand, Rosenbusch includes 
 quartzose augite-andesites. As Lang has shown that bulk 
 analyses are of no value, and as the original rock was required 
 to show free quartz, it will be so considered. 
 This group comprises : 
 
 I. Dacite. 
 II. Mica-dacite. 
 
 III. Pantellerite. 
 
 IV. Dacite glass. 
 
 V. Pantellerite glass. 
 
PRIMARY ROCKS. 183 
 
 I. DACITE (Stache). 
 
 A somewhat lighter-colored groundmass than that of 
 hornblende-andesite, which shows large phenocrysts 
 of glassy (sanidine-like) plagioclase, much hornblende, 
 biotite, quartz, and sometimes sanidine. 
 Silica 62-72 ; Gr. 2.5-2.6. 
 
 It occurs as surface sheets and lava-streams, as dome- 
 shaped hills, and as dikes, associated with hornblende-ande- 
 site. It is found in Germany, Hungary, Iceland, Armenia, 
 Japan, Mexico, South America, New Zealand, and abun- 
 dantly in the western United States in the Great Basin. 
 The rhyolitic variety of groundmass is distinguished from 
 that of rhyolite with great difficulty, as the plagioclases 
 have (even (m) ) the habit of sanidine, and only the greater 
 silica content can settle the question. This is the case with 
 the American dacites (Zirkel). The plagioclase is usually 
 andesine ; oligoclase, labradorite, and anorthite follow in 
 decreasing importance. Quartz is (M) in round grains and 
 in sharp-angled double pyramids (f inch long in Java), be- 
 tween dark and bluish gray, in some cases yellow or rose- 
 red. In many varieties the quartz is only as phenocrysts. 
 Hornblende and biotite often replace one another. The 
 former is usually brown and alters to viridite and calcite. 
 In some intances biotite alone appears. Augite is not abun- 
 dant either (M) or (m). The (M) accessories are zircon, 
 orthite, cordierite, and red garnet. Olivine is usually ab- 
 sent. An increase in sanidine makes this a trachyte, and a 
 failing in quartz (or in the silica content) a hornblende-ande- 
 site. 
 
 (a) Timazite (in part). The more acid varieties of tima- 
 zite (plagioclase, gamsigradite, mica, magnetite, and quartz) 
 with silica 67.4 belong here. It is also found in the Vosges. 
 
184 MANUAL OF LITHOLOGY. 
 
 II. QUARTZ MICA-ANDESITE, Mica-Dacite. 
 This bears to dacite the same relation that mica-andesite 
 
 does to hornblende-andesite. 
 
 III. PANTELLERITE (Foerster). 
 Rosenbusch calls this a transition between the " dacites " 
 
 (using the term for all quartz-andesites) and the rhyolites, 
 from its high silica content. It forms extensive lava-streams 
 in the island of Pantelleria, which have at times a trachytic 
 and a rhyolitic facies, with a third which is a mean between 
 them. The groundmass is rich in iron and carries pheno- 
 crysts of plagioclase, anorthoclase, triclinic amphibole 
 (cossyrite), aegirite-like augite, and no quartz, tridymite, or 
 biotite. The " trachytic " groundmass has a web of feld- 
 spars and augite needles. The "rhyolitic" groundmass 
 has considerable glass base and carries the same minerals. 
 It contains silica 66.8-72.5 ; Gr. 2.6. Some authorities style 
 it a pitchstone-porphyry with a granular groundmass. 
 
 (a) Volcanite (Hobbs). From Volcano, Italy, in bombs. 
 A rock with glass base and groundmass of anorthoclase, 
 andesine, acmite, and olivine, carrying phenocrysts of the 
 minerals, and with silica 66.99. I n structure and composi- 
 tion this is an augite-pantellerite. 
 
 IV. DACITE GLASS. 
 
 This weathers by changes occurring along the perlitic 
 cracks, and working inward till the whole mass is white and 
 opaque, and soft enough to be scratched by the finger-nail. 
 When put into cold water it breaks into small fragments 
 which fall to powder. By levigating this the unweathered 
 feldspar phenocrysts can be secured intact. 
 
 (a) Dacite-felsite. Although this is not a glass, it is prob- 
 ably a devitrified one, and runs readily into perlite. It 
 occurs at Arran, Scotland. 
 
PRIMARY ROCKS. 1 8$ 
 
 i. Blue Porphyry. At Mt. Esterel, department of Var, 
 France. Silica 69. A (m) microfelsitic mass carrying pheno- 
 crysts of andesine (3 mm.), abundant sanidine, and acicular 
 hornblende. Zirkel puts this as rhyolite from its high acid- 
 ity, but chemical analyses are uncertain guides, and some 
 dacites have been reported with still higher silica content. 
 
 (b) Dacite-pitchstone-porphyry. From Arran. .A black 
 rock readily breaking into spheroids when struck with a 
 hammer. These are momentarily bright, but immediately 
 cloud with a whitish film, which is considered to be caused 
 by relief from strain and corresponding molecular change. 
 
 (c) Perlitic Dacite. From Mitake, Japan ; Colombia, 
 Ecuador. A dacite glass carrying (m) phenocrysts and per- 
 litic globules some 3 mm. In one case the dacite lava- 
 stream had a layer of perlite crusted with pumice. 
 
 (d) Dacite-obsidian. Is reported in Hungary, Cabo de 
 Gata, Ecuador, Italy. 
 
 (e) Perlitic Dacite-pumice. Containing spherules and 
 phenocrysts, from northwestern South America. 
 
 (f) Dacite-pumice. From the west coast of South Amer- 
 ica. In some cases the phenocrysts are quite large. Quartz 
 is 1-3 mm. 
 
 V. PANTELLERITE GLASS. 
 
 A third variety of pantellerite (see p. 184) is a highly 
 glassy base with a few microliths of augite and cossyrite, and 
 carrying phenocrysts of plagioclase, augite, and cossyrite. 
 
 A fourth variety comprises the following states: obsid- 
 ian, obsidian-porphyry, porphyritic pumice, pumice. 
 
1 86 MANUAL OF LITHOLOGY. 
 
 GROUP n. QUARTZ-DIORITE. 
 
 Ilia. DACITE-QUARTZ-DIORITE INTRUSIVES. 
 (Necessary minerals : Plagioclase, hornblende, and quartz.) 
 
 QUARTZ-DIORITE. 
 
 A diorite carrying either (m) or (M) free quartz. This 
 can be divided into : 
 
 I. Quart z-hornblende-<Mor\te. 
 II. Quart z-mica-di\or\te. 
 
 III. Quart 'z-frornlt/ende-porphyrite. 
 
 IV. Q2iartZ'mica-hornblende-pQYp\iyrite. 
 V. Diorite-glass, 
 
 I. QUARTZ-HORNBLENDE-diorite. 
 A coarse- to fine-grained crystalline-granular compound 
 of Ca-Na-feldspar (frequently (m) orthoclase), horn- 
 blende, grayish-white quartz, and the other minerals 
 . more fully given under diorite ; of dark-blue, blackish 
 green, sometimes light-brown color. The minerals 
 are as given under diorite (q. v.\ except that quartz is 
 always present. It occurs in rounded and angular 
 grains, generally (M), rarely in double pyramids in 
 the granular states. 
 
 Silica 55-67; Gr. 2.6-2.9. 
 
 It occurs like diorite, and is found with it, and especially 
 in the Black Forest, the Vosges, the Odenwald, Servia, 
 Bohemia, France, Belgium, Scotland, Hungary, Spain, 
 Portugal, and at Cortlandt, N. Y. In the Andes quartz 6-8 
 mm. occurs. V. Cotta's banatite is a quartz-diorite in part, 
 and part diorite, with andesine. The anorthite-diorite of 
 Corsica has quartzose varieties. Orthoclase and quartz 
 form micropegmatitic textures. 
 
PRIMARY ROCKS. l8/ 
 
 II. QUARTZ-MICA-diorite, Tonalite (vom Rath). 
 A fine-crystalline-granular compound of oligoclase, 
 
 orthoclase, quartz, blackish-green hornblende, and 
 brown mica. 
 
 Silica 66-70 ; Gr. 2.7-2.9. 
 
 It forms the principal mass of the Adamello Mountains 
 In southern Tyrol and is named from the Tonale Pass. It 
 also occurs in France, Saxony, Mexico, Australia, Japan, 
 St. John, N. B., and in the Highlands of Scotland it 
 grades on the one hand into quartz-diorite, and on the other 
 into hornblende granitite. Oligoclase is snow-white and 
 -contains but 57 per cent of silica ; quartz is one-third of 
 the mass in grayish grains ; hornblende and mica are in 
 small amounts the hornblende in stout prisms (sometimes 
 one foot long), and the mica in irregular folia. As acces- 
 sories are orthoclase (which forms pegmatite (m) with 
 quartz), zircon, garnet (an inch in diameter), sphene, titanite, 
 magnetite, pyrite, and corundum. It was once called a 
 .granite. In some specimens primary concretions occur of 
 dark mica and hornblende, with but little feldspar and no 
 -quartz, and the Japanese rock abounds in acicular tourma- 
 line. Garnet is common. 
 
 III. QUARTZ-HORNBLENDE-porphyrite. 
 
 For the varieties of groundmass in diorite-porphyrite see 
 p. 179, as well as for the predominant minerals. The 
 presence of quartz phenocrysts is necessary to form 
 this variety. 
 
 Silica 50-65; Gr. 2.6-2.7. 
 
 (a) Black Porphyry. From near Lugano, Italy. A light- 
 gray to dark-green or dark-red groundmass with predomi- 
 nant feldspars, chloritized hornblende prisms, sporadic mica 
 folia, and quartz. 
 
1 88 MANUAL OF LITHOLOGY. 
 
 (b) Amygdalophyre (Jenzsch). From near Dresden as sheets 
 and tuffs. The groundmass is greenish brown and some- 
 what transparent on thin margins. As phenocrysts are 
 feldspar and hornblende. The former is altered, the 
 groundmass chloritized, but shows brownish glass in fresh 
 specimens. On the hanging-wall side are amygdules filled 
 with hornstone, chalcedony, quartz, chlorophasite, pyrite, 
 and galenite. 
 
 (c) Bergamaskite. From Bergamo. Carries arfvedsonite. 
 
 (d) Diorite-quartzifera-porfiroide (Alfonso Cossa). From 
 Cossato. Shows a grayish (m) crystalline groundmass with 
 green and brown hornblende and quartz. 
 
 IV. QUARTZ-MICA-hornblende-porphyrite. 
 (a) Paleophyre (Giimbel). A dike in the Silurian of the 
 Fichtelgebirge. A fine-grained reddish groundmass with 
 well-crystallized phenocrysts of oligoclase, brown horn- 
 blende, brown biotite, and corroded quartz. Hornblende 
 and biotite are strongly chloritized, and the groundmass is 
 full of ferrite and calcite. It is an aggregate of (m) feldspar 
 without any of the black bisilicates. 
 
 V. DIORITE GLASS 
 
 As the vitreous states of a rock are found to be more 
 siliceous than the crystalline ones, the diorite glasses will be 
 placed here. They are rare, but are found with all sorts of 
 diorite eruptions, and are due to the rate of cooling rather 
 than to the chemical composition. Following the analogy 
 of other rocks, it may be permitted to say that the more 
 acid diorites would be more ready to show glassy states on 
 sudden cooling than the more basic, and to a greater extent. 
 
 1. Diorite - mica -pitchstone- porphyry. With conchoidal 
 fracture ; black ; carrying phenocrysts of small rust-colored 
 feldspars (mostly plagioclase), much mica in folia, few 
 
PRIMARY ROCKS. 189 
 
 grayish quartz grains. The base is light brown, dark-gray 
 to black, and shows flow structure. Hornblende is scanty. 
 Silica 62.02 ; Gr. 2.466. It is found in Italy and Scotland. 
 
 2. TdioicitQ-inica-hornblende-pitchstone-porphyry. From the 
 southern Tyrol, with mica and hornblende abundant (also 
 enstatite), and with microfelsitic (m) base. 
 
 3. Pitchstone-peperite (v. Lasaulx). From Monte Trisa. A 
 vesicular glass that changes to compact and granular 
 states, with abundant (and often chloritized) hornblende, 
 small feldspars (usually plagioclase), folia of mica, and 
 pyroclasts of country-rock. It is amygdaloidal from a 
 chalcedonic filling of vesicles. 
 
 (A full discussion of the various lorms of occurrence, 
 the states, textures, structures, minerals, as well as a 
 definition of the porphyrites, will be found in its proper 
 place under " Diorite," as these quartzose forms are infre- 
 quent, of small extent, and are but appendages to the large 
 group of the diorites.) 
 
 GROUP 12. ANDESITE. 
 
 I lib. HORNBLENDE-ANDESITE-DIORITE EXTRUSIVES. 
 (Necessary minerals: Ca-Na-feldspar and hornblende.) 
 
 ANDESITE (L. v. Buch). 
 
 A group of extrusives, generally dark-colored, with a 
 restricted amount of glass base, but larger than in 
 trachyte, and carrying a similar (m) web of minute 
 crystals, plagioclase, hornblende, biotite, and pyrox- 
 ene, either monoclinic (augite or diallage) or rhombic 
 (enstatite or hypersthene), and with or without 
 quartz. In this groundmass plagioclase and some, or 
 all, of the above appear as phenocrysts. 
 
 These rocks were first studied in the Andes, whence the 
 name, and in them was found a feldspar that was first called 
 
MANUAL OF LITHOLOGY. 
 
 albite, then oligoclase, and afterwards (from the locality) 
 andesine. It is now known that all of the albite-anorthite 
 series are present (except albite). In some varieties the 
 prevalent minerals are andesine and labradorite, with oligo- 
 clase frequently, and rarely bytownite or anorthite. These 
 carry, as a r^le, hornblende and more or less black mica. 
 In other varieties the feldspars belong to the andesine- 
 anorthite end o\ the series, and carry the pyroxenes as 
 necessary minerals. There is thus a more acid and a more 
 basic division, which were called by J. Roth hornblende- 
 andesite and augite-andesite. The latter is distinguished from 
 basalt by its texture, and the much smaller amount of 
 olivine. These were first classed with the trachytes, but 
 were distinguished by the absence of alkali feldspars. There 
 are certain rocks, however (to be described), which are 
 transitions between these effusive groups, as they carry both 
 feldspars. The group will be divided as follows : 
 
 I. Hornblende-andesite. Plagioclase and hornblende. 
 
 la. Mica-andesite. Plagioclase and biotite (always some 
 hornblende). 
 
 The andesites are effusive equivalents of abyssal diorite,, 
 and Judd reports that in the island of Mull there exist 
 laccoliths that can be traced from diorite to andesite. 
 
PRIMARY ROCKS. IQI 
 
 I. HORNBLENDE -ANDESITE (Roth), Gray 
 
 Trachyte (v. Richthofen). 
 
 A (m) fine-grained to compact (sometimes coarse gran- 
 ular) groundmass of light or dark color (usually gray- 
 ish or brownish black) and waxy, greasy luster, which 
 '(m) shows a moderate amount of glass base filled with 
 a matt of minute feldspars, magnetite grains, horn- 
 blende, augite, and (sparingly) biotite, and carrying 
 (M) phenocrysts of vitreous plagioclase, hornblende 
 in large black prisms and needles, and some augite. 
 As accessories appear (M) magnetite, apatite, quartz, 
 tridymite, haiiyne, garnet, and sometimes olivine,, 
 and (m) an abundance of cordierite, zircon, and 
 (rarely) titanite. 
 
 Silica 55-62 ; Gr. 2.6-2.8. 
 
 It ocgurs in isolated peaks and dome-shaped masses (as 
 in Germany, Scotland, etc.), in laccoliths ; is common in 
 lava-streams (as in the Andes), sometimes as surface sheets,, 
 rarely in dikes. It is found in the Siebengebirge, Eifel, 
 Westerwald, Hebrides, central France, Hungary, Bosnia,, 
 the Canaries and Azores, East Indies, Japan, Australia, 
 South and Central America, Nevada, California, Oregon. 
 The (M) structure of quartzless hornblende- and mica-ande- 
 sites varies greatly. The shades may be light or dark; as a 
 rule, they are gray or brown, also bluish, reddish, red, bluish 
 red, and reddish purple, and the reddening is due to the 
 oxidation of the iron in the black bisilicates (usuaHy augite). 
 The groundmass is sometimes compact, as in augite-andesite, 
 but usually rough and porous, as in trachyte; (M) fluidal 
 structures are uncommon. In some localities the laminae of 
 mica are parallel. The phenocrysts are usually plagioclase, 
 with either hornblende or mica, or both, and sometimes 
 sanidine. When both feldspars are present, the variety is 
 intermediate with trachyte. The plagioclase is generally in 
 
I9 2 MANUAL OF LITHOLOGY. 
 
 regular crystals, sometimes tabular, and rarely irregular. It 
 is usually andesine or labradorite, sometimes an oligoclase 
 near andesine in composition (crystals sometimes over two 
 inches in length), and sometimes one of the basic plagio- 
 clases, but rarely as basic as anorthite. Hornblende is 
 in large black prisms and needles which are frequently 
 several inches long ; brown by transmitted light, but green 
 when altered (to epidote, ferrite, or opal). In some cases the 
 (M) phenocrysts disappear and hornblende is found only in 
 the groundmass and (M). Biotite is in large hexagonal 
 folia, brownish to blood-red by transmitted light. It rarely 
 occurs in the groundmass, but exists as phenocrysts (M) 
 and (m), and seldom without hornblende. Augite is abundant 
 in the groundmass and as (M) phenocrysts (which are some- 
 times f. inch long) in both hornblende- and mica-andesites, 
 and is rarely absent. Delessite is also reported from Italy. 
 Rhombic pyroxene is found in such amounts as* to form 
 hypersthenic varieties. In such cases it is also found in the 
 groundmass. Of the accessories, quartz appears in reddish 
 grains, and an abundance of it changes the rock to dacite. 
 Tridymite is sometimes 1.5 mm. long, but it generally is an 
 uncertain component. Hauyne is in blue or white (from 
 weathering) grains, and is essential in some varieties. Gar- 
 net is sometimes half an inch in diameter. Olivine is rare 
 and sporadic; sometimes 4 mm., but usually (m). The 
 secondary minerals are carbonates of lime and iron, bastite, 
 quartz, opal, chalcedony, zeolites, and specular iron. Black- 
 ish-blue concretions are sometimes nearly an inch in diam- 
 eter, and are composed (m) of plagioclase and some of the 
 black bisilicates. We can distinguish : 
 
 i. Granitoid Hornblende - ande site (Miigge). A coarse- 
 grained rock from S. Miguel, Azores, with neither ground- 
 mass nor glass base, but consisting of equally large grains 
 (M) of plagioclase, hornblende, biotite, augite, and apatite. 
 
PRIMARY ROCKS. 193 
 
 A similar compound of plagioclase and hornblende with a 
 small amount of glass and apatite, but no groundmass, is also 
 reported. 
 
 2. Augite-free Hornblende-andesite (Hague). From the 
 Eureka district, Nev., with (m) abundant glass inclusions, 
 and needles of apatite. 
 
 3. Hyper sthene-hornblende-andesite. At Lassen's Peak and 
 Mount Shasta, CaL, San Salvador, the Siebengebirge, South 
 America, and elsewhere. This is mostly hypersthene, with 
 a little augite (m) in the groundmass, with phenocrysts of 
 the same, plagioclase, hornblende, and mica. 
 
 la. MICA-ANDESITE, Biotite-andesite. 
 
 A variety of the above where biotite is predominant over 
 hornblende. In some cases the latter is almost absent from 
 the groundmass. The rock resembles hornblende-andesite, 
 and has similar essentials and accessories. The groundmass 
 weathers to opal. Its usual colors are dark gray, red, red- 
 dish brown. It occurs in Greece, Asia Minor, South 
 America, California. 
 
 Under this general subdivision come : 
 
 1. Isenite (Bertels). From the Sengelberg in the Wester- 
 watd, which was wrongly defined till Rosenbusch found a 
 labradorite-bytownite-plagioclase, hornblende, much light- 
 green augite (in the groundmass), irregular light-green 
 grains of olivine, and sporadic biotite and apatite. It is 
 named from a small stream (Eis, Latin Isena) in the neighbor- 
 hood. 
 
 2. Timazite (Breithaupt), (in part) Trachytic Green- 
 stone. From Timok valley in eastern Servia. A gray or 
 greenish-gray felsitic groundmass carrying phenocrysts of 
 white plagioclase, velvet-black hornblende (gamsigradite), 
 mica, magnetite, and pyrite. Silica 51. A more acid 
 variety belongs to dacite (q. v.). 
 
194 MANUAL OF LITHOLOG Y. 
 
 3. Trachydolerite (Abich). A fine-grained compound of 
 oligoclase or labradorite, hornblende, magnetite, augite, and 
 sometimes mica, forming a gray or brown groundmass, and 
 carrying the same as phenocrysts. Silica 54-61$ ; Gr. 
 2.7-2.8. This is an intermediate, as its name implies. It 
 occurs compact, vesicular, etc., at the Peak of Teneriffe, in 
 Kamtschatka, Italy, etc. This is an augitic hornblende- 
 andesite, which frequently becomes augite-andesite by in- 
 crease in augite and by entrance of olivine, as at Lowen- 
 berg, Siebengebirge shades into dolerite. It is no longer 
 known as a separate rock. 
 
 HORNBLENDE-ANDESITE GLASS. 
 
 This is reported as yet only in a few cases. Zirkel 
 states that it is not found in Hungary nor the Sieben- 
 gebirge, where there occurs the greatest development of the 
 rock. 
 
 (a) Perlitic Hornblende-andesite. In a (m) crystalline 
 groundmass occur perlitic spheres of glass. From Akerotivi, 
 island of Thera. At Balos the spheres can be separated 
 from the matrix when it is fractured. 
 
 (b) Perlitic Hornblende-andesite-pitchstone. A black 
 pitchstone with great spherules, from Muzukishima, Japan, 
 with almost (m) biotite and garnet, and great (M) plagio- 
 clases as phenocrysts. 
 
 (c) Perlitic Hornblende-andesite-/&w^. At the last local- 
 ity, and the Isle of Luzon. The pumice is a white glass 
 with dark-green hornblende, glassy andesine, and biotite, 
 among which are distributed the glassy spherules. 
 
 (d) Hornblende-andesite-/?/ mice. At Montserrat, San 
 Salvador, and Peru. The pumice is rose-red, and frequently 
 has the vesicles so much stretched as to resemble fine 
 fibers in a glassy mass that carries phenocrysts of the com- 
 ponent minerals. 
 
PRIMARY ROCKS. 
 
 GROUP 13. DIORITE. 
 
 f IHb. HORNBLENDE-DIORITE-ANDESITE INTRUSIVES. 
 (Necessary minerals : Ca-Na-feldspar and hornblende.) 
 
 DIORITE (Hatty). 
 
 A holocrystalline, usually coarse- to fine-grained com- 
 pound of a Ca-Na-feldspar and hornblende, with mica 
 and pyroxene. This also shbws compact and vit- 
 reous states and exhibits phenocrysts. 
 Silica 45-67 ; Gr. 2.6-2.9. 
 
 It occurs rarely in small bosses, but mostly as dikes 
 and intrusive sheets ; the former are usually fine-grained 
 at their margins and coarsely crystalline-granular towards 
 their middle. The intrusive sheets are sometimes of 
 considerable extent, and follow more or less closely the 
 planes of stratification of the rocks, usually crystalline 
 schists, gneiss, etc., into which they have been intruded. 
 Dikes of diorite are occasionally to be seen breaking 
 through granite. Diorites are generally more or less irregu- 
 larly jointed, but in some instances a rude columnar struc- 
 ture is developed. Sometimes the diorites show a concen- 
 tric spheroidal structure when weathered. The selvages 
 of dikes abound in schistoid structures parallel to the dike- 
 walls, and there is sometimes a quite sharp line of demarka- 
 tion between the massive-granular and the schistoid parts. 
 Passages between quartz-diorites, mica-diorites, etc., may 
 occasionally be seen, and the different varieties appear to 
 be mere local differentiations of the same rock. Diorite is 
 also reported as passing (in the same mass) into picrite, and 
 at Cortlandt, N. Y., it passes, in a dike, into hornblendite. 
 It is found in Sweden, Finland, the Urals, Austria, 
 Saxony, Bohemia, the Thuringian Forest, Odenwald, 
 Schwarzwald, Vosges, Hungary, Switzerland, Italy, Corsica, 
 
ig MANUAL OF LITHOLOGY. 
 
 France, Spain, Great Britain, Greenland, Asia, South Africa, 
 Canada, and in the United States at Cortlandt, Ft. Mont- 
 gomery, and in Orange County, N, Y. ; Deckertown, N. J. ; 
 Kennebunkport, Me. ; Livermore Falls and Dixville Notch, 
 N. H. ; the valley of Lake Champlain, Nevada, California, 
 Yosemite Park, Michigan, Minnesota, and Alaska. The 
 principal mass is coarse- to medium- and uniform fine-grained; 
 microcrystalline with faint glimmer, and colored dark green 
 to black, and compact, black, and basaltic. The medium 
 fine-grained state has been called " microdiorite " in some 
 cases, as analogous to " microgranite," " microsyenite." 
 These are not separate rocks, but states peculiar to the 
 manner of cooling. In the following varieties hornblende 
 is never absent, and the other black bisilicates never pre- 
 dominate: 
 
 I. Hornblendt-diorite, or typical diorite. 
 II. Mica-diorite. 
 
 III. Diorite-porphyrites. 
 
 IV. Diorite-aphanite. 
 
 I. DIORITE (Haiiy). 
 
 A usually granitoid compound of oligoclase (sometimes 
 andesine, labradorite, or anorthite) and hornblende, 
 with mica, pyroxene, and quartz, occasionally ortho- 
 clase, usually apatite, and ordinary and titaniferous 
 magnetite. 
 
 Silica 45-63 ; Gr. 2.6-2.95. 
 
 This varies in texture according as the rock is in large 
 <or small masses. In bosses it is coarse-grained in the center, 
 in dikes usually uniformly fine-grained (like aplite), and in 
 ismall dikes or on the selvages of some large ones and of 
 .bosses it is compact. The color is usually greenish, and 
 on this account the rock was formerly classed (with dia- 
 base and gabbro) as a "greenstone." The absolutely 
 
PRIMARY ROCKS. 197 
 
 compact states in small dikes are black and basaltic. It 
 is frequently porphyritic, globuliferous, and sometimes 
 drusy, rarely amygdaloidal, and by squeezing- is altered 
 frequently to hornblende-schist. Plagioclase is usually 
 oligoclase, anorthite causes a distinct variety, and ande- 
 sine and labradorite are sometimes predominant. The 
 color is usually white with yellowish or greenish shades 
 occasionally reddish. The luster is as frequently dull as 
 strong, and when fresh they lack the glassy habit of ande- 
 sine in the andesites, though they may be transparent. 
 They are not so perfectly crystallized as are the orthoclases, 
 and usually occur in regular and tabular forms with abun- 
 dant twinnings ; but the angles are more rounded and the 
 granular habit more prominent. Hornblende is the ordi- 
 nary black mineral with shades of green ; in stout prisms 
 or grains, sometimes in lath shapes, acicular, and in irregu- 
 lar patches ; strong luster on cleavages. By transmitted 
 light it shows greenish shades, and thus differs from the 
 brown basaltic form, which occasionally occurs especially 
 in the porphyritic and basic varieties. The brown color is 
 generally associated with the stout crystals, and the green 
 with the lath and acicular shapes. It alters to viridite, ser- 
 pentine, chlorite, and epidote, which accounts *or the 
 greenish color of the rock, and allows us to suppose that 
 the original color was black or gray. The only essential in 
 this variety is mica, but it occurs more prominently in the 
 quartz-diorites (as would be supposed). It is biotite. The 
 other minerals are only accessory. Quartz, when promi- 
 nent, forms quartz-diorite. It is then, as already stated, in 
 (M) rounded or angular crystalline grains, but in the por- 
 phyritic states shows sometimes double pyramids, and is 
 generally more idiomorphic. Pyroxene cannot be depended 
 upon. In many localities it is wanting, and when abundant 
 forms pyroxene-diorite ; when highly predominant, diabase. 
 
198 MANUAL OF LITHOLOG Y. 
 
 As the basic component it is usually idiomorphic. It is 
 found (m) in the groundmass of some diorite-porphyrites. 
 Orthoclase frequently occurs (;), but more especially in the 
 quartzose varieties, and forms micropegmatite with quartz. 
 Apatite, magnetite, olivine, and orthite are usually present 
 and (m) ; titanite, garnet, and tourmaline are (M), and the 
 last two especially in the quartzose mica varieties. Diorite 
 differs from syenite in having plagioclase for orthoclase ; in 
 its greenish (rather than red) color; its prominent horn- 
 blende on a weathered surface (by loss of feldspar) ; by the 
 fusibility of the feldspar, and the greater specific gravity. 
 It differs from the granulitic gabbros by having hornblende 
 instead of pyroxene ; by its lower density ; and by its less 
 strong effervescence with acids when fine-grained or com- 
 pact, owing to the greater proportion of secondary calcite 
 in the gabbros. Some authorities place the coarse-grained, 
 fine-grained, porphyritic, and similar states of diorite in 
 separate divisions ; but these are found more or less with 
 all occurrences, and can be readily noted in the field, as 
 they have the same mineral composition. The following 
 varieties have been noted : 
 
 1. Leuciite is only a fine-grained dike-form from the 
 Melibocus. 
 
 2. Scapolite-diorite. An altered gabbro from southern 
 Norway, where plagioclase is almost entirely altered to 
 scapolite, and pyroxene uralitized. It is also found along 
 the Ottawa River in Canada. 
 
 3. Anorthite-diorite, Corsite (Zirkel). A diorite com- 
 posed of anorthite and some oligoclase, blackish-green horn- 
 blende and some quartz. Silica 48 ; Gr. 2.76. Named by 
 Zirkel from its abundance in Corsica. 
 
 (a) Orbicular Diorite, Napoleonite. A variety of the 
 above where the components form alternating concentric 
 layers about kernels. The kernels consist either of anorthite 
 
PRIMARY ROCKS. 1 99 
 
 or hornblende, or both, and they likewise show a radial 
 structure. The balls are from one to three inches in size, 
 and a section shows alternating rings of light and dark 
 color. It is found near Ajaccio, Corsica. This is accepted 
 as a peculiar arrangement, but not as a new compound, and 
 thus has no claims to be a separate species. 
 
 4. Labradiorite. A diorite where labradorite replaces 
 oligoclase. Silica 47-50; Gr. 2.7-2.9. This has no claims 
 to be classed as a separate rock, as Tschermak's theory of 
 plagioclase allows all variations between oligoclase and 
 labradorite to occur in diorite. 
 
 5. Hemithrtne (Brongniart). Kalkdiorit (Senft). A name 
 given by Brongniart to rocks composed of hornblende and 
 calcite, part of which are now found to be diorites. In any 
 case the calcite is an alteration product. Senft's rock is a 
 dark-green compound of oligoclase, hornblende, and mica 
 with calc-spar. The French rock is from the Auvergne ; 
 the German variety from the Thuringian Forest. 
 
 II. MICA-DIORITE (Delesse), Biotite-diorite. 
 A uniformly granular compound of oligoclase or andesine, 
 orthoclase, biotite in irregular folia, brown and green 
 hornblende, pyroxene (augite or hypersthene), and 
 quartz in rounded or angular grains. Generally of a 
 dark color and almost black. 
 Silica 47-59 ; Gr. 2.65-2.89. 
 
 It occurs in bosses and dikes in crystalline schists and 
 older sediments; rarely in surface extrusives. It is found in 
 the Tyrol, Frankenwald, France, Norway, Mexico, Califor- 
 nia, the Pah-Ute range, Cortlandt, N. Y., etc. V. Cotta 
 objects to calling this a diorite on account of its orthoclase. 
 It is a transition to quartz-mica-diorite, and that to granite, 
 as already stated (p. 187). The plagioclase is sometimes 
 altered ; the hornblende more often brown than green, and 
 
2OO MANUAL OF LITHOLOGY. 
 
 altered to chlorite and epidote. Augite, when present, is 
 altered to chlorite, calcite, and ores, rarely uralitized. 
 Hypersthene is sometimes altered to bastite. Garnet is 
 accessory. Its fine-grained form is like kersantite without 
 calcite. 
 
 III. DIORITE-PORPHYRITES. 
 
 As stated on p. 178, a porphyrite is a rock with a compact 
 matrix of plagioclase and exhibiting phenocrysts. It differs 
 from a porphyry, which is a compact rock of orthoclase or 
 orthoclase-quartz mixture. The porphyrites can be divided 
 according to their content of the black bisilicates. The 
 mica-porphyrites have already been described, and the mix- 
 ture with pyroxene forms the gabbro-porphyrites. Those 
 with hornblende will follow here as diorite-porphyrites. 
 These can be divided into : 
 
 1. T)\or\te-porphyrite. 
 
 2. J/zVtf-diorite-porphyrite. 
 3. 
 
 I. DIORITE-PORPHYRITE, Hornblende-porphy- 
 
 rite. 
 
 In a groundmass (described on pp. 180, 202,) are pheno- 
 crysts of hornblende, also plagioclase and mica. The 
 groundmass weathers lighter. 
 Silica 39-65 ; Gr. 2.6-2.7. 
 
 It occurs in sheets and dikes in Asia, Africa, central 
 and eastern Europe, Scotland, the New England States, and 
 Nevada. Its states resemble those of the porphyrites and 
 mica-porphyrites, and with the above occurrences are vesic- 
 ular states, tuffs, etc. The vesicles are sometimes empty 
 and sometimes filled with green earth, calcite ; and in some 
 localities the amygdules form the greater part of the mass. 
 The rock is usually irregularly jointed and fissured ; rarely 
 columnar or tabular. It is not so abundant as the more acid 
 
PRIMARY ROCKS. 2OI 
 
 porphyrites. Plagioclase phenocrysts are white, yellowish, 
 or reddish, and usually dull. Hornblende is in irregular 
 stout prisms or acicular shapes, and brownish black. Biotite 
 is in hexagonal tables, seldom in folia. Quartz is rare. 
 
 .(The first three types following are entirely dependent 
 on (m) characteristics.) 
 
 (a) Suldenite, Andesitic Porphyrite (Stache and v. John). 
 From the Suldenfern in the Ortler Alps, with 54-62 silica. 
 The groundmass is light to dark gray, with (m) phenocrysts 
 of black hornblende (prisms) ; (m) plagioclase and orthoclase 
 in small amount, with accessory augite, biotite, and quartz. 
 
 (b) Ortlerite, Greenstone-porphyrite (Stache and v. John). 
 From the Ortler Alps, with silica 48-54. Blackish-green to 
 grayish-green groundmass, fresh glassy black prisms of horn- 
 blende (4-6 mm.), and sometimes in bundles. Part of 
 Gumbel's nadeldiorit, from eastern Bavaria, is placed here 
 by Zirkel. 
 
 (c) Propylitic Porphyrite (Stache and v. John). From the 
 Ortler Alps, with silica 52-57. Blackish-green to grayish- 
 black groundmass of monotonous appearance, carrying 
 phenocrysts of plagioclase (with orthoclase) in abundance,, 
 always hornblende (mostly mixed with chlorite, epidote, and 
 calcite) ; biotite is only accessory. 
 
 (a) Porfido-rosso-antico. From the west coast of the Red 
 Sea, in a dike in granite. This is the famous red porphyry 
 of history. In a blood-red (M) compact groundmass are 
 abundant small snow-white or rose-red striated plagioclase 
 phenocrysts and lustrous black acicular hornblendes, with 
 usually small scales of specular hematite. Quartz occurs in 
 irregular veins, never in regular primary grains. Silica 64. 
 
2O2 MANUAL OF LITHOLOGY. 
 
 2. MICA-diorite-porphyrite. 
 
 In a typical porphyrite groundmass are phenocrysts of 
 oligoclase and orthoclase, with hornblende and mica 
 in equal proportions. 
 
 Silica 61 ; Gr. 2.6-2.7 
 
 This occurs as a transition between the hornblende- and 
 mica-porphyrites, and is found with porphyrites of both 
 species. It is especially found in the Saar-Nahe district, the 
 central Alps, in China, and elsewhere. 
 
 3. DIORITE-APHANITE. 
 
 A greenish-gray to black (m), holocrystalline to compact 
 groundmass similar to those noted on pp. 180, 200, 
 and carrying few or no phenocrysts. 
 
 The term aphanite was applied to a mass so compact 
 that its constituents could not be resolved with a lens, and 
 whose color was green to black. It was the compact state 
 of the " greenstones," diorite, diabase, and gabbro. The 
 same term is still employed to denote the compact state, 
 which bears to the granular states the relation that basalt 
 does to dolerite. 
 
 The silica and specific gravity are as in the diorite-por- 
 phyrites, and this may be said to be their clear groundmass. 
 Jt is recognized mainly by its actual association with diorite. 
 Its bulk analysis will vary so that it may approach and equal 
 that of many diabase-aphanites, but its specific gravity is 
 generally lower. It carries a much lower amount of calcite 
 than does diabase-aphanite, and will not effervesce so 
 strongly. It occurs at Bischofswerda, Saxony, and else- 
 where, in narrow dikes and apophyses from dioritic dikes 
 and bosses. 
 
PRIMARY ROCKS, 2O$ 
 
 GROUP 14. PYROXENE-ANDESITE. 
 
 IIIc. PYROXENE-ANDESITE-DIORITE EXTRUSIVES. 
 (Necessary minerals! Plagioclase, hornblende, and a pyroxene.) 
 
 PYROXENE-ANDESITE. 
 
 An andesite containing abundant pyroxene. 
 Silica 50-68 ; Gr. 2.72-2.8. 
 
 Pyroxene-andesite is the mineralogical equivalent of 
 basalt. It is more than that, as it is seen passing into basalt 
 at Lowenberg in the Siebengebirge, where the so-called 
 " trachydolerite " shades into augite-andesite, and this by 
 the acquisition of a somewhat higher olivine content be- 
 comes basalt. At Arran, Scotland, augite-andesite passes 
 into tholeite (with intersertal texture), and that by still 
 further crystallization of the groundmass into diabase. 
 Augite-andesite is therefore a transition between horn- 
 blende-andesite and the gabbros. As an appendix to this 
 group will be placed the so-called " propylite " and " quartz- 
 propylite." The majority of authorities recognize these 
 only as peculiarly metachemized states of a number of dif- 
 ferent rocks ; but the name, as Rosenbusch suggests, is 
 "valuable as distinguishing those alterations. Pyroxene- 
 andesite can be divided into : 
 
 I. PYROXENE-<m&zs\te (Zirkel). Plagioclase and one of 
 the pyroxenes. 
 
 (a) ^ogV/^-andesite (Roth). Plagioclase and augite. 
 
 (b) Diatlage-andesite (v. Drasche). Plagioclase and dial- 
 lage. 
 
 (c) ffyfierstkene-andesite. Plagioclase and hypersthene. , 
 (</) Enstatite-andesite (Koto). Plagioclase and enstatite. 
 (e) Olivine-pyroxene-zridesite. 
 
 II. PYROXENE-andesite glass. 
 
204 MANUAL OF LITHOLOGY. 
 
 \\\a. PROPYLITE, a metachemized state of diabase, 
 diorite, or any of the andesites, due to solfataric action. 
 
 b. Quartz-propylite, a similar state of any of the quartz- 
 ose varieties of the above, and of quartz-porphyry of the 
 Washoe type. 
 
 I. AUGITE-ANDESITE (Roth). 
 
 A dark-colored groundmass varying from glassy to tra- 
 chytic, composed of (m) plagioclase, augite (mono- 
 clinic, rhombic, or, infrequently, triclinic), carrying 
 (M) phenocrysts of plagioclase, hypersthene (and 
 rarely augite), scanty hornblende, tridymite, quartz 
 seldom, biotite, and olivine. 
 
 Silica 56-68 (average 60) ; Gr. 2.72-2.74. 
 
 It occurs in lava sheets and streams, and in dikes, widely 
 spread among the active volcanoes of Europe and Asia, 
 Azores, South and Central America, and in the Great Basin 
 of the United States. The famous eruption of Krakatoa. 
 extruded great amounts of this rock, so that the floating 
 pumice hindered navigation in the Sunda Straits for several 
 days, and the ashes were scattered so widely and profusely 
 that thirty tons were shoveled from the deck of an Ameri- 
 can ship sixty miles distant. Zirkel notes four types of the 
 rock: 
 
 (1) Semivitreous ; luster waxy, pitchy ; color more nearly 
 deep brown than greenish black ; sometimes compact, some- 
 times fine-porous ; groundmass carrying a few phenocrysts 
 of whitish or yellowish feldspar. This is the type in North 
 and South America, Hungary, Java. 
 
 (2) Less characteristic and widely distributed ; is like 
 hornblende-andesite, or the light basalts, as in Japan. A 
 gray or dark-brown groundmass, somewhat porous and 
 " coarse porphyritic," with (M) phenocrysts. 
 
 (3) A more extended type (trachytic) ; light grayish red ; 
 
PRIMARY ROCKS. 2O$ 
 
 rough ; somewhat porous ; carrying the ingredients in the 
 pores as crystals. In Hungary, Mexico, Italy. 
 
 (4) A light-weight, gray, and porous groundmass, carry- 
 ing specular iron, and biotite in the pores, as in the lava of 
 Auvergne (Little Puy de Dome). 
 
 The plagioclases are stout tabular, and twin in the Carls- 
 bad and Baveno types. They are andesine to anorthite, 
 mostly fresh, but weather to opaline masses and epidote. 
 Sanidine also appears in small amounts. Augite is abun- 
 dant (m), but infrequent (M\ and yellowish to greenish 
 brown by transmitted light ; usually fresh in the rocks with 
 glass base. Rhombic pyroxene is usually hypersthene in 
 slender needles, sometimes enstatite and bronzite, sometimes 
 the triclinic variety, sometimes diallage. Hornblende is 
 not so frequent or abundant as in the other variety of ande- 
 site, and generally occurs only in a few large prisms. Bio- 
 tite is infrequent; quartz in a few cases (M) and 2 mm., 
 generally (m) ; tridymite more frequent than quartz in both 
 pores and groundmass ; olivine infrequent (mainly occurring 
 when augite increases and rhombic pyroxene diminishes). 
 
 Judd describes the weathering of augite-andesite as 
 having four phases: (i) the conversion of augite to viridite ; 
 {2) the formation of opacite ; (3) the hydroxidation of opacite 
 to red or brown ferrite, to form the tints that color all por- 
 phy rites ; (4) the kaolinization of feldspar, and formation of 
 calcite and chalcedony. The result is a tuff. Emmons 
 states that tridymite is found in the cavities and clefts of 
 the partly weathered rock, and more rarely opal. When 
 weathering advances, the reddening of the groundmass takes 
 place, and the fluxion structure not seen in the fresh rock 
 appears. The feldspar remains fresh while the red color 
 iades to pink, and this to yellowish gray, and then kao- 
 linizes, while the black bisilicates bleach and disintegrate. 
 
2O6 MANUAL OF LITHOLOGYS, 
 
 The rock in some localities shows a white crust on weather- 
 ing, while the interior is dark. 
 
 1. Oar^-augite-andesite (Tschermak), when the 
 quartz is in phenocrysts and also in the groundmass. Silica 
 63-65 ; Gr. 2.61. Found in South America, New Zealand, 
 Japan. 
 
 2. Mijakite (Petersen). From the island of Mijakeshima, 
 Japan. An andesite where the pyroxenic mineral is (m) in 
 short pellucid columns, and is triclinic, like babingtonite. 
 An American triclinic pyroxene-andesite is also reported. 
 
 lb. Diallage-andesite. From the Smrkouz Mountains, 
 Steiermark. A dark-brown, fine-grained rock with numer- 
 ous phenocrysts of plagioclase and darker foliated crystals 
 of diallage. A similar rock occurs in Bohemia. Some 
 authorities place ophite here. 
 
 lc. Enstatite-andesite. With enstatite more or less 
 abundant and monoclinic pyroxene ; generally weathered. 
 Bronzite is reported in one variety from Japan. Occurs 
 there and in South America and New Zealand. 
 
 Id. Hypersthene-andesite. This mineral is found in 
 many andesites in slender (m) prisms, frequently altered 
 sometimes to bastite, and sometimes to fibrous hornblende. 
 It is frequently (M) in great individuals. The rock occurs 
 in Japan, the Caucasus, Mexico, Colombia, and the Great 
 Basin of the western United States. 
 
 \e. Olivine-pyroxene-andesite. It is a dark-colored (M) 
 fine-grained rock, with holocrystalline groundmass of pla- 
 gioclase, pyroxene, and magnetite, with phenocrysts of pla- 
 gioclase and olivine. Here part of the so-called " trachy- 
 dolerite " with olivine would be placed. This rock is 
 transitional to basalt. Found in South America, etc 
 
 (NOTE. Some authorities place tholeite here.) 
 
PRIMARY ROCKS. 2O/ 
 
 II. PYROXENE- ANDESITE GLASS. 
 
 There are abundant cases of vitreous states to this group 
 in connection with the widespread lavas of the same. 
 
 AUGITE-ANDESITE. 
 
 1. Pitchstone. From the Caucasus, Scotland. 
 
 (a) Felsite. From Eskdale, Scotland. A devitrified 
 pitchstone. 
 
 2. Perlite. From Japan. 
 
 3. Obsidian. From Armenia, island of Melos, Ardna- 
 murchan, Scotland, island of Hokkaido, Japan. Silica 53- 
 59. Color brownish to greenish black. 
 
 4. Obsidian-/<9r///jj/rj/. From Mount Ararat, with silica 
 77 ; carrying numerous phenocrysts of plagioclase and dirty 
 green biotite ; found in connection with a rock of this 
 class. From Hokkaido, Japan, is a black glass, transparent 
 on thin edges, with silica 74, and many phenocrysts. 
 
 5. Pumice. In many flows as a more or less thick crust, 
 and in large masses (as from Krakatoa). It has the vesicles 
 filiform and carries a small number of phenocrysts. Im- 
 mense masses of this state of the rock blocked the Straits of 
 Sunda after the eruption of Krakatoa. Color straw-yellow 
 light yellowish gray. Silica 61-71. 
 
 BRONZITE-ANDESITE. 
 
 Here come two varieties of this rock with and without 
 olivine : 
 
 1. Boninite, Bronzite-limburgite (Petersen and Kikuchi). 
 A glassy state with no feldspar from the Peel Island group, 
 near Japan ; carrying olivine and diallage-like augite. 
 
 2. Sanukite (Weinschenk). A dense gray or black rock, 
 with conchoidal fracture and (m) abundance of magnetite^ 
 acicular crystals of bronzite, and monoclinic augite, forming 
 a colorless glass with infrequent large phenocrysts of pla- 
 
208 MANUAL OF LITHOLOGY. 
 
 gioclase and garnet. From Sanuki, Japan, and elsewhere in 
 that country. This bears to andesite the relation that augit- 
 ite does tq basalt. 
 
 PROPYLITE (v. Richthofen), Greenstone 
 Trachyte (in part). 
 
 1116. QUARTZ-propylite (same authority). 
 
 A fine-crystalline rock with devitrified base, consisting 
 of a feldspar from whicn calcite has been removed, 
 and a light-green mineral, mostly epidote, which is 
 the secondary (or even later) derivative from one of 
 the black bisilicates. Always soft from weathering. 
 
 Silica 57-72 ; Gr. 2.7-2.9. 
 
 These are no longer classed as separate rocks by all 
 authorities. Zirkel still holds to their being distinct varieties. 
 Propylite is the country-rock of the Comstock lode, and is 
 derived, as first claimed by Wadsworth and later shown by 
 Becker, from the weathering of a number of rocks into 
 which it can be traced. The black bisilicates of these rocks 
 (hornblende, augite, and mica) uniformly pass into a 
 chloritic mineral which, in its turn, becomes epidote of a 
 vivid yellow tinged with green. The weathering of an- 
 desite, augite-andesite, diorite, and diabase produce what 
 is known as propylite ; while the same process in their 
 quartzose varieties, and in some quartz-porphyries, forms 
 what has been called quartz-propylite. It also occurs in 
 the Western Isles of Scotland, the Siebengebirge, and Hun- 
 gary. Szabo was the first to object to the rock on the 
 ground that it was a solfataric product. In 1882 Becker 
 reported that the Washoe rock was altered as above stated. 
 The arguments of Zirkel against the rejection of the name 
 for a distinct rock seem to fail, as the want of an andesitic 
 
PRIMARY ROCKS. 
 
 glass base in propylite may be due to the fact that the 
 original rocks had none, as in other cases ; or to its loss by 
 devitrification ; or, again, in the general wreck of the rock, 
 as Emmons reports the complete kaolinization of an augite- 
 andesite in the island of Capraja. The other argument, that 
 propylite is not found as a decomposition product in many 
 andesite regions, may be answered by the fact that solfa- 
 taric action, which produces propylite, is not common ; but 
 in this case propylite is directly traced into rocks of vary- 
 ing name. Rosenbusch remarks that the name may be 
 useful to denote a peculiar kind of alteration of the above 
 rocks. As such it is used here. 
 
 GROUP 15. PYROXENE-DIOR1TE. 
 IHc. PYROXENE-ANDESITE-DIORITE INTRUSIVES. 
 (Necessary minerals : Plagioclase, hornblende, and a pyroxene.) 
 
 PYROXENE-diorite. 
 
 A transition between diorite and the granulitic gabbros, 
 as pyroxene-andesite is between andesite and basalt. The 
 rock is more basic than diorite ; hornblende is very subor- 
 dinate, and the plagioclases more basic than oligoclase. 
 Olivine becomes more prominent, and mica, quartz, and 
 orthoclase are rare. The monoclinic pyroxene is usually 
 augite, and this mineral is more frequent than any pyroxene. 
 Diallage is rare. The augite is green (sometimes brown) 
 and idiomorphic (also in grains). Rhombic pyroxene is 
 hypersthene or bronzite, which now and then occur, and are 
 more or less altered to bastite. Occasionally quartz is 
 found quite abundant. The texture varies between the 
 holocrystalline one of diorite and the ophitic one of diabase! 
 Its lower specific gravity tells it from diabase, as well as its 
 association with dioritic rocks. 
 
2IO MANUAL OF LITHOLOGY. 
 
 I. AUGITE-diorite (Zirkel). 
 
 A diorite with predominant augite (diallage or malaco- 
 lite), green (and generally brown) hornblende, labra- 
 dorite, some olivine and titanite. 
 Silica 47-5 7; 0^2.7-2.98. 
 
 It is found in Great Britain and the Channel Islands, 
 Argentine Confederation, Bohemia, Norway, Odenwald, 
 Hungary, the Alps, Sumatra, the Andes, Minnesota, and 
 elsewhere. Of the accessories, titanite is (M), olivine rarely 
 (M), magnetite and apatite (m). 
 
 i. Brown Diorite, when hornblende is brown and basaltic. 
 This variety is usually associated with pyroxene rocks, and 
 tends to pass into gabbro by increase in pyroxene, and 
 into pyroxenite by failure of feldspar and hornblende. It 
 is associated with norite and passes into it, and also into 
 massive brown hornblendtite at Cortlandt, N. Y. It also 
 occurs in a few localities in Europe, and at Montreal, 
 Canada. This color is common in porphyritic diorites, 
 camptonites, etc. As accessories are apatite, magnetite, and 
 hypersthene. 
 
 II. QUARTZ-augite-diorite. 
 
 A variety of the above carrying more biotite and quartz, 
 and less olivine. The silica content is higher also. 
 Sometimes scapolite occurs. It occurs in Brazil, the 
 West Indies, the Andes, etc. 
 
 III. HYPERSTHENE-diorite. 
 
 A coarse- to medium-grained compound of plagioclase 
 (sometimes epidotized), brown hornblende, and hyper- 
 sthene. The latter also forms concretions. In Portu- 
 gal, West Indies. 
 
PRIMARY ROCKS. 211 
 
 IV. GABBRO-diorite (Tornebohm). 
 
 An alteration product of gabbro and norite where the 
 pyroxene has uralitized. In Scandinavia. 
 
 V. CAMPTONITE (Rosenbusch). 
 
 (M) a rock rarely coarse-grained, but usually dense 
 hypidiomorphic granular compound of plagioclase, 
 hornblende, pyroxene, mica, with occasional olivine, 
 and carrying phenocrysts of lustrous (M) rod-shaped 
 basaltic hornblende, andesine, magnetite, and weather- 
 ing to a rusty brown. 
 
 Silica 39-54 ; Gr. 2.7-2.9. 
 
 This rock is found in dike and surface effusions, and is 
 intermediate between the diorites and diorite-porphyrites, 
 and between the diorite-porphyrites and the melaphyres. It 
 was placed by Rosenbusch with his lamprophyres ; but 
 M.-Levy and Zirkel have relegated it back to diorite on 
 the ground of the impropriety of separating dike- forms. It 
 generally has a low augite content, but sometimes has a 
 very high one. Rarely it is amygdaloidal. It is placed 
 with the augite-diorites on account of its having basaltic 
 hornblende entirely, and thus coming under the same head 
 as " brown diorite " above. It was first noted by Hawes at 
 Campton, N. H., and has been since noted in the Champlain 
 valley of Vermont, in New York, Maine, Montreal, Canada, 
 Sierra Nevada range of California, U. S. Colombia, Tyrol, 
 south Norway, etc. 
 
 i. ^K^t'/^-camptonite. From near Christiania, Norway, 
 and near Lewiston, Me. With abundant augite and much 
 olivine, so that, as Kemp reports, it forms a transition to 
 the melaphyres. 
 
212 MANUAL OF LITHOLOG Y. 
 
 VI. HORNBLENDITE (Dana). 
 
 A coarse to fine granitoid (sometimes compact) blackish 
 aggregate of compact brown hornblende, which is 
 usually a paramorph of one of the pyroxenes. 
 Silica 46-49 ; Gr. 3-3.1. 
 
 A dike-rock of rare occurrence, and not to be confounded 
 with the metamorphic massive rock called amphibolite. It 
 is sometimes a segregation in part of the dike, and generally 
 the altered form of a pyroxenite, as above stated. It occurs 
 in the Cortlandt (N. Y.) diorite series, Amador and Calaveras 
 counties, Cal., the Argentine Confederation. Mica-horn- 
 blendite is found in Nova Scotia. 
 
PRIMARY RQCKS. 2I 3 
 
 BASIC DIVISION PYROXENE ROCKS. 
 
 These are divided, according to their alkali and Ca-Na 
 content, as follows : 
 
 I. ALKALI SECTION: 
 
 (a) Groups 16 and 17. Feldspathoids, alkali feldspar, magnetite, 
 olivine, plagioclase, amphibole, mica, quartz. 
 
 Extrusives, Nephelinite, Leucitite ; Intrusive, liolite. 
 
 (b) Group 1 8. Feldspathoids, olivine, magnetite, alkali feldspar, 
 plagioclase, amphibole, mica, quartz. 
 
 Extrusives, Nepheline, Leucite, and Melilite Basalts; In- 
 trusive, none. 
 
 II. ALKALI-LIME-SODA SECTION : 
 
 (a) Groups 19 and 20. Feldspathoids, plagioclase, magnetite, oli- 
 vine, amphibole, mica, alkali feldspar, quartz. 
 
 Extrusives, the Tephrites ; Intrusive, Theralite. 
 (b} Group 19 (con?). Feldspathoids, plagioclase, olivine, magnetite, 
 amphibole, mica, alkali feldspar, quartz. 
 Extrusives, the Basanites. 
 
 III. LIME-SODA SECTION: 
 
 Groups 21 and 22. Plagioclase, magnetite, olivine, amphibole, 
 mica, feldspathoids, alkali feldspar, quartz. 
 Extrusive, Basalt ; Intrusive, Gabbro. 
 
214 MANUAL OF LITHOLOGY. 
 
 GROUP 16. NEPHELINITE-LEUCITITE. 
 
 la. NEPHELINITE (LEUCITITE)-IIOLITE EXTRUSIVES. 
 
 (Necessary minerals : Feldspathoids and pyroxene.) 
 
 In this group there is no plagioclase nor olivine. We 
 distinguish : 
 
 1. Nephelinite, where the feldspathoid is nepheline. 
 
 2. Leucitite, where it is leucite. 
 
 I. NEPHELINITE (Rosenbusch). 
 A coarse-granular to compact (usually porous) principal 
 mass, usually bluish to dark green, or greenish, gray- 
 ish, or pitch black, less frequently grayish white, 
 rarely light wine-yellow ; subgreasy or pitchy luster ; 
 composed of nepheline and augite, with magnetite, 
 apatite, leucite, haQyne, and melilite. 
 Silica 41-47 ; Gr. 2.9. 
 
 This occurs as slaggy lava-streams and in dikes and 
 plugs, in the Erzgebirge, near the lake of Laach, in Bohe- 
 mia, Sweden, Cape Verdes, South Africa. The states are : 
 
 (a] Doleritic Nephelinite. A coarse-grained compound of 
 nepheline, reddish-brown augite and magnetite, with some- 
 times sanidine, with the interstices filled with a mixture of 
 them, and no glass base. This state is difficult to distinguish 
 from nepheline-dolerite, as the olivine in the latter is seldom 
 readily recognized (M), and it is only by tracing it into the 
 basaltic state that a distinction can be made. A small pro- 
 portion oi olivine would make this a nepheline-dolerite. 
 
 (b) Fine-grained to Compact (Basaltic) Nephelinite. In a 
 groundmass colored as above, and rarely without pheno- 
 crysts, are (M) haiiyne, green and brown augite, black mica, 
 .apatite, magnetite, and, rarely, melanite ; and (m), in addi- 
 tion, nepheline, melilite, leucite, and more or less glass base. 
 
PRIMARY ROCKS. 2I 5 
 
 As accessories, hornblende is rare, sanidine and olivine spo- 
 radic. The haiiyne is often half an inch in size and is the 
 predominant accessory, the others being quite subordinate. 
 In the Erzgebirge and Bohemia. 
 
 (c) Camptonitic Nephelinite (Rosenbusch). A (m) ground- 
 mass rich in hauyne and poor in nepheline, with augite, 
 hornblende, and meliiite, carrying large phenocrysts of 
 biotite and melanite. It also carries a little sanidine, and is 
 found in the region about the Kaiserstuhl. 
 
 2. LEUCITITE, Sperone (Italian local name). 
 In a usually microcrystalline to compact groundmass of 
 shades of gray (from very light to black), and usually 
 porous, are phenocrysts of (M) leucite, augite, tita- 
 nite, and magnetite that are rarely so abundant or 
 so large as to make the rock appear doleritic. As 
 accessories are nepheline, hauyne, biotite ; sometimes 
 meliiite and garnet. 
 
 Silica 40-50 ; Gr. 2.5-2.81. 
 
 This occurs in lava-streams in the Eifel, Erzgebirge, 
 Bohemia, abundantly in Italy, Cape Verdes, Algiers, and in 
 the Leucite Hills of Wyoming. The amount of leucite and 
 its habit vary in these rocks. When it is prominent, augite, 
 magnetite, and titanite are less so ; in other rocks all are 
 equally prominent. Leucite varies from a well-crystalline 
 to a rounded form, and when the latter it is accompanied 
 by brown augite and forms basaltoid leucitite ; when well 
 crystallized, the augite is green and they form tephritoid 
 leucitite (both states are (m) ). 
 
 (a) Lava Sperone (local name). From the Alban Hills and 
 elsewhere in Italy. A light, porous, brownish or yellowish 
 gray rock composed of small grains of leucite and much 
 smaller crystals of yellowish brown garnet, with augite, 
 hauyne, biotite, and sometimes magnetite and specular 
 
2l6 MANUAL OF LITHOLOGY. 
 
 hematite ; in a groundmass of leucite and augite, with some 
 glass base, magnetite and sporadic plagioclase. 
 
 (b) Haiiynophyre (Rammelsberg). From the volcano 
 Vultur, near Melfi, in S. Italy. A rough, porous, dark-gray 
 to black, generally fine-grained groundmass, composed of 
 abundant (m) leucite, much nepheline, augite, melilite, 
 magnetite, apatite, scanty sanidine, some olivine, and 
 black magnesia-mica ; carrying phenocrysts of hauyne, 
 augite in abundance, and some olivine, mica, and leucite. 
 Silica 40-50; Gr. 2.5-2.8. The hauyne is abundant, and 
 2-10 mm.; blackish-gray conchoidal fracture and scaly struc- 
 ture ; cleavable when sky-blue ; sometimes red from sec- 
 ondary growths of sesquioxide of iron ; sometimes colorless 
 and cleavable. This is a transition between nephelinite, 
 leucitite, and a similar hauyne rock, as it contains an abun- 
 dance of each. Zirkel puts it here, Rosenbusch under 
 nephelinite, and Deecke under Rosenbusch's " nepheline- 
 leucite-tephrite," as a haiiyne-melilite variety. If the feld- 
 spar be sanidine, as reported by Mann, it would fall, not 
 under tephrite, but under phonolite. This is a good exam- 
 ple of the small variation in mineral content that is neces- 
 sary to move a rock from one species to another, and this is 
 a good example of the meeting of the black bisilicates, felds- 
 spars and feldspathoids in one rock. It is a transition be- 
 tween phonolite, trachyte, rhyolite on the one hand, and 
 basalt, pyroxenite, and the peridotites, on the other. 
 
 (c) J/zVtf-leucitite. From Leucite Hills, Wyo. A light 
 yellowish gray, very fine-porous, felsitic rock, showing 
 only stripings of bronzy, brownish ye/low, and brownish red 
 mica, (m) it appears as a crystalline-granular compound 
 of predominant leucite and some augite, with a small 
 amount of magnetite, apatite, and nepheline. Silica 56.30. 
 
PRIMARY ROCKS. 
 
 GROUP 17. IOLITE. 
 la. NEPHELINITE-IIOLITE INTRUSIVES. 
 
 (Necessary minerals : Pyroxene and feldspathoids.) 
 
 IIOLITE (Ramsay and Berghell). 
 
 A coarse- to micro-crystalline compound of elseolite and 
 augite with garnet (iiwarrite). 
 Silica 42.79 ; Gr. 2.9. 
 
 An elaeolite-augite rock free from feldspar and olivine, and 
 considered as the intrusive equivalent of nephelinite. It oc- 
 curs in dikes and narrow apophyses in the liwarre Mountains 
 in northern Finland, where it was thought to be an elaeolite- 
 syenite, but was found to be without feldspar. The elaso- 
 lite is fresh, grayish white to light gray, and in small allotri- 
 omorphic grains with greasy-vitreous luster. Augite is 
 idiomorphic (prisms and tables) ; apatite is abundant. The 
 garnet is a titaniferous lime-iron variety, and titaniferous 
 melanite is common, and also light-red titanite. Elaeolite 
 alters to cancrinite and calcite. In the mass apatite and 
 elaeolite are equally predominant. Thirty-seven per cent of 
 the rock powder is soluble in acids. 
 
 GROUP 18. NEPHELINE-, ETC., BASALTS. 
 Ib. FELDSPATHOID BASALTS. 
 
 (Necessary minerals : Pyroxene, feldspathoids, and olivine.) 
 
 These are divided, according to the feldspathoid, into : 
 
 1. Pyroxene, olivine, and nepheline, Nfpkeline-\>2S>oM. 
 
 2. Pyroxene, olivine, and leucite, Ziaiz/i-basalt. 
 
 3. Pyroxene, olivine, and melilite, 
 
2l8 MANUAL OF LITHOLOGY. 
 
 I. NEPHELINE-basalt, Anamesite, and Dolerite. 
 A coarse- to micro-crystalline (and compact) compound 
 of nepheline, augite, and olivine (usually of dark color) 
 which in the dolerites shows the ingredients plainly, 
 but in the basalts usually shows (M) olivine alone, 
 sometimes augite. As (M) accessories are sporadic 
 hornblende and mica. Plagioclase is generally absent. 
 Silica 38-45 ; Gr. 2.89-3.22. 
 
 This occurs as widely spread in the old world (espe- 
 cially in Germany) as the feldspar-basalts, and is found as 
 surface and intrusive sheets, lava-streams, plugs and dikes. 
 In the United States it is rare, and the basalt state is reported 
 from Austin, Tex., Kawsoh Mountains, Nev. and Elk 
 Mountains, Col. The term dolerite refers to the coarse- 
 crystalline state, anamesite to the medium- to fine-crystalline 
 state, and basalt to the microcrystalline to compact (see 
 later under " Feldspar-basalt "). Nepheline is usually well 
 crystallized and apparent in dolerite, but only (m) in basalt. 
 In some cases nepheline forms a granular and sometimes an 
 irregular interstitial amorphous filling in which the other 
 minerals appear, as in phonolite, and it readily alters to 
 zeolites. The other minerals appear as in basalt (p. 227). 
 The principal accessories are leucite, hauyne, and melilite. 
 These sometimes preponderate to form their own types of 
 basalt. Plagioclase can enter in a slight amount without 
 placing the rock among the basanites ; a withdrawal of both 
 feldspar and feldspathoids makes it a limburgite, and a loss 
 of olivine forms nephelinite. 
 
 (a) Nephilinitoid Basalt (Boricky) is a basalt in whose (m) 
 groundmass, instead of nepheline, is seen a colorless, gray- 
 ish white, or yellowish white substance, which reacts like 
 nepheline by polarized light, but is otherwise unlike it and 
 greatly altered. In Bohemia. (This is a (m) distinction 
 and cannot be made (M ). 
 
PRIM A RY RO CKS. 2 1 9 
 
 (b) Noseanite (Boficky). A nosean-rich nepheline-basalt 
 with coarse, medium, and fine states. In Bohemia, the Eifel, 
 -etc. 
 
 2. LEUCITE-basalt, Anamesite, and Dolerite. 
 A usually dark-gray, sometimes (M) fine-crystalline, 
 rarely coarse-grained, usually microcrystalline to 
 compact and slaggy groundmass composed of (m) 
 leucite, augite, magnetite, and olivine, with or without 
 glass base, and carrying (m) and sometimes (M) pheno- 
 crysts of augite and olivine, and rarely leucite. 
 Silica 40-47 ; Gr. 2.84-2.94. 
 
 It occurs as necks and lava-streams, especially devel- 
 oped and studied in the Eifel, Erzgebirge, about the lake of 
 Laach, and in Hesse, Bohemia, Sardinia, Algiers, Persia, 
 Australia, and New Zealand. As stated above, the doleritic 
 state is rare, the anamesitic uncommon, and the basaltic 
 cannot be readily told by inspection from feldspar-basalt, as 
 leucite retreats to the (m) groundmass, which is rarely coarse 
 enough to be resolved with the lens. Leucite occurs some- 
 times well crystallized, but usually irregular and rounded. 
 In the groundmass it is ill defined, and thus differs (m) from 
 its habit in tephrite. Augite and olivine occur as in other 
 basalts. Nepheline, melilite, and haiiyne are in varying 
 amounts, and form transitions into the other basalts of the 
 group. Samdine and plagioclase cannot be very abundant 
 without forming either \euc\te-phonolite or basanite. Biotite, 
 apatite, and hornblende also occur (the last abundant in a 
 few localities). 
 
 (a) Leucitoid Basalt (Boficky). A companion to nephelini- 
 toid basalt. Here leucite is not sharply defined, but seems 
 to be present in irregular colorless patches in the interstitial 
 spaces. In Bohemia. 
 
 (b) Peperin-basalt (Boficky). A reddish brown to brown- 
 
22O MANUAL OF LITHOLOGY. 
 
 ish gray clayey or weathered groundmass composed (m) of 
 augite, leucite, nepheline, magnetite, and rarely olivine, 
 carrying large well-defined phenocrysts of augite, horn- 
 blende, and rubellan. It is found at Kostenblatt, Bohemia, 
 and in a few neighboring localities. It is probably a 
 hardened mud-tuff (whence the name). 
 
 3. MELILITE-basalt (Stelzner). 
 
 A usually greenish black (sometimes grayish black or 
 grayish blue) fine-crystalline to compact groundmass, 
 composed of (m) melilite, augite, and olivine, and 
 carrying phenocrysts of (M) olivine and augite, rarely 
 of melilite, and (m) of the same, with nepheline, mag- 
 netite, and apatite. 
 
 Silica 34-36 ; Gr. 2.89-3.04. 
 
 It occurs in small bosses ; in dikes of small and medium 
 size ; in streams and tuffs. It is especially developed in 
 Swabia ; also in Bohemia, Saxony, Sweden, the Transvaal, 
 etc., and in America at Ste. Anne, Canada, Manheim, N. Y., 
 and Uvalde county, Tex. The honey-yellow melilite is gen- 
 erally well crystallized, and is sometimes large enough to be 
 distinguished by the lens, but it is usually (m) and forms one- 
 third of the whole rock. Augite and olivine as in the other 
 basalts, and frequently the latter is the only (M) visible phen- 
 ocryst. It is sometimes altered to serpentine. As acces- 
 sories occur (m) a scattering of biotite laminae ; nepheline 
 usually rare, but abundant in the Canadian rock ; native 
 copper is found now and then ; picotite, hauyne, and horn- 
 blende are rare. This ultra-basic rock is found breaking 
 through granite and other rocks of high acidity, so that it 
 has not lost any acidity in so doing. It is sometimes drusy. 
 Rosenbusch has named the dike-forms on the island of Alno, 
 Sweden, alnoite. Their mica (anorhite) is arranged parallel 
 to the selvages, as in cases already noted in micaceous 
 
PRIMARY ROCKS. 221 
 
 dikes. The Canadian rock also has anomite, and much 
 nepheline and perofskite. 
 
 (There are no intrusives to this group.) 
 
 ALKAU-LIME-SODA SECTION. 
 
 GROUP 19. TEPHRITE-BASANITE. 
 Ha. TEPHRITE-BASANITE-THERALITE EXTRUSIVES. 
 
 (Necessary minerals: Feldspathoids, plagioclase, pyroxene, with or 
 without olivine.) 
 
 (a) Without olivine, the tephrites (v. Fritsch). 
 
 1. Pyroxene, plagioclase, and nepheline, Nepheline-te^h.- 
 rite. 
 
 2. Haiiyne, Haiiyne-tephrite. 
 
 3. Pyroxene, plagioclase, and leucite, Leuctte-tephrite. 
 
 (b) With olivine, the Basanites (Brongniart). 
 
 1. Pyroxene, plagioclase, olivine, and nepheline, Nepheline- 
 basanite. 
 
 2. Pyroxene, plagioclase, olivine, and leucite, Leucite- 
 basanite. 
 
 ai. NEPHELINE-tephrite 
 
 A generally fine-crystalline to compact (but sometimes 
 coarse crystalline-granular and porous) groundmass, 
 sometimes basaltic, and sometimes of greasy luster ; 
 light gray, grayish green, brownish gray ; composed 
 of (m) plagioclase, augite, and nepheline (sometimes 
 with leucite), and more or less glass base. This is 
 
222 MANUAL OF LITHOLOGY. 
 
 sometimes clear of phenocrysts, and sometimes ex- 
 hibits them of (M) size, of the components, with ac- 
 cessory hornblende, biotite, sanidine, and hauyne. 
 Augite is green and brown, the former in the ground- 
 mass and the latter as phenocrysts. Hornblende and 
 biotite are sometimes abundant and (m) ; sanidine is 
 rare and scarce ; hauyne is blue and yellow. 
 Silica 49-57 ; Gr. 2.62-2.75. 
 
 It occurs as lavas-streams, sheets, plugs, in Germany,. 
 Bohemia, Africa, Asia, the Canaries, Cape Verdes, and in 
 the Peloncello Mountains, Ariz. 
 
 (a) Buchonite (Sandberger) is a variety with a (m) nephe- 
 line-plagioclase groundmass containing microlites of augite,. 
 carrying abundant long black prisms of hornblende, nephe- 
 line with greasy luster, (M) biotite and plagioclase, and 
 sometimes orthoclase. Silica 54-84; Gr. 2.85. From the 
 Rhone district (Buchonia). A hornblende-nepheline-teph- 
 rite. 
 
 (b) Phono lit e-te^\irite. A compact glimmering ground- 
 mass with greasy luster, composed of a moderate amount of 
 plagioclase, considerable sanidine, scanty augite and horn- 
 blende, and carrying phenocrysts of sanidine and hauyne. 
 
 (c) Tephritoid (Bucking). A plagioclase-augite rock 
 without olivine, in which nepheline cannot be recognized as 
 a distinct mineral, but whose base seems to carry it, from 
 its high soda content and its gelatinizing with acids. 
 
 a2. HAUYNE-tephrite. 
 
 A dark-gray to black groundmass carrying phenocrysts 
 (visible with lens) of labradorite, acicular hornblende, 
 augite, dark-blue hauyne, or waxy-yellow nosean 
 grains. The groundmass contains (m) augite in abun- 
 dance, with titanite and apatite, seldom olivine. From 
 La Banne d'Ordenche, and near the lake of Gury, 
 France. 
 
PRIMARY ROCKS. 22 $ 
 
 a$. LEUCITE-tephrite. 
 
 A structure like nepheline-tephrite. Fresh and weath- 
 ered, and altered to analcime. In a light-gray, bluish, 
 or greenish gray groundmass (fine-grained to compact, 
 and rich in glass base or without it) composed of (m) 
 plagioclase (sometimes sanidine), small amounts of 
 leucite, and sometimes nepheline, augite, magnetite, 
 and apatite, are phenocrysts of leucite (sometimes of 
 large size, and sometimes altered to analcime), plagio- 
 clase, sanidine, augite, nepheline, hauyne, hornblende,, 
 and quartz, and (m) melanite. 
 Silica 46-58; Gr. 2.57. 
 
 It occurs in lava-streams infrequently in dikes in Ger- 
 many, Bohemia, Italy, East Indies. The leucite is usually 
 in well-defined individual grains no matter how minute it 
 may be, and in this respect it differs from its habit in the 
 basalts, where it is much more irregular and fills interstitial 
 spaces in the groundmass. 
 
 (Hussak places here the rocks of Brazil, Cape Verdes^ 
 and at Deckertown, N. J., which carry large folia of biotite, 
 and rounded bodies which are sometimes distinguished as 
 analcime and sometimes as calcite. All of these rocks seem 
 to have been metachemized, as the augite has uralitized, and 
 the above rounded bodies are probably altered leucites.) 
 
 bi. NEPHELINE-basanite. 
 
 This rock varies between nepheline-basalt and nepheline- 
 tephrite. It resembles basalt, and has a groundmass of 
 (m) plagioclase in varying proportions, nepheline, 
 augite, and olivine, and carries phenocrysts of the 
 same. The groundmass may be (i) basaltic and black 
 or brown, composed of much plagioclase, black augite, 
 nepheline, and olivine, with small amounts of glass,. 
 
224 MANUAL OF LITHOLOGY. 
 
 and not many accessory minerals, or (2) tephritoid and 
 greenish, through change in augite, with magnetite 
 and small amounts of feldspar, and carrying an abun- 
 dance of accessories, as hornblende, biotite, titanite, 
 hauyne, and sometimes sanidine, so that it becomes 
 phonolite. 
 
 Silica 40-51; Gr. 2.90-3.15. 
 
 It occurs in the Eifel, in Bohemia, Cape Verdes, Canaries, 
 South Africa, Japan, Uvalde County, Tex., Elk Mountains, 
 Col., etc., in lava-flows, and weathers to a yellowish crust 
 (somewhat like that of phonolite), and gelatinizes with 
 HC1. 
 
 Basanitoid (Bucking). A compound of plagioclase, oli- 
 vine, and augite, and with no perceptible nepheline, but 
 with a base that gelatinizes with acids, like nepheline com- 
 pounds, and has a high soda content. It occurs along the 
 Rhone and south of the Thuringian Forest. 
 
 b2. LEUCITE-basanite, Leucitophyre (in part). 
 A similar rock with leucite replacing nepheline. In a 
 glass base is a combination of (m) leucite, plagioclase, 
 olivine, and magnetite. Leucite alone is commonly 
 (M), sometimes green or black augite; the others 
 rarely, and nepheline never. The texture varies from 
 coarse-granular to compact in the same lava. This 
 was formerly included with leucite-phonolite under 
 the name leucitophyre. 
 
 Silica 47.64; Gr. 2.77-2.81. 
 
 It is the lava of Vesuvius, and also found in the Eifel, 
 Brazil, Java, and lower California. 
 
PRIMARY ROCKS. 22$ 
 
 GROUP 20. THERALITE. 
 
 Ha. TEPHRITE-THERALITE INTRUSIVE. 
 
 (Necessary minerals : Feldspathoids, plagioclase, and pyroxene.) 
 
 THERALITE (Rosenbusch). 
 
 A granitoid to compact compound of augite, plagioclase, 
 and nepheline, with olivine as accessory. 
 Silica 43. 17; Gr. 2.93. 
 
 This occurs in dikes, bedded sheets, and laccoliths in 
 the Crazy Mountains, Mont., and is the intrusive state of 
 the tephrites that was looked for, and the name is given 
 from the Greek verb " to be sought for." The augite is in 
 prisms up to \ inch ; biotite in sharp hexagonal tables ; an- 
 orthoclase and nepheline in coarse-grained aggregates; 
 olivine is (M) and rust-brown. In the largest laccolith the 
 texture was granitoid in the middle and became compact at 
 two feet from the walls, with columnar-jointed structure 
 normal to them. There are porphyritic states of a dark 
 green with phenocrysts of black augite, and abundant olivine 
 and biotite. A similar rock has been noted on the Elbe. 
 
 Teschinite. Rosenbusch places this rock here as the leu- 
 cite equivalent of theralite, as the analcime is its representa- 
 tive ; but the microscope shows that this mineral has been 
 formed at the expense of labradorite. For the description 
 of the rock see under " Diabase." 
 
 GROUP 21. Ilia. BASALT-GABBRO EXTRUSIVES. 
 
 ///. LIME-SODA SECTION. 
 (Necessary minerals; Plagioclase, pyroxene, olivine, magnetite.) 
 
 Following the analogy of the former divisions, this group 
 will be separated, according to the predominant member of 
 the necessary minerals, as follows : 
 
226 MANUAL OF LITHOLOGY. 
 
 1. Predominant plagioclase, Plagwclase-bzs&lt, or basalt. 
 
 2. Predominant olivine, Limburgite, or magma-basalt. 
 
 3. Predominant pyroxene, Augitite. 
 
 DOLERITE (Haiiy), " Deceptive." 
 ANAMESITE (v. Leonhard), " Intermediate." 
 
 BASALT (Agricola), Feldspar-basalt. (From the 
 
 Latin basaltes.) 
 
 (M) dolerite is the coarse-grained, anamesite the 
 medium fine-grained, and basalt the microcrystal- 
 line to compact state of a compound of (M) plagio- 
 clase and augite, with (m) magnetite, and olivine (M) 
 and (m) ; also with neither nepheline nor leucite. All 
 the states exhibit pores and vesicles, but the last is 
 highly vesicular and amygdaloidal. 
 
 Silica, dolerite, 48-57 ; anamesite, 47-52 ; basalt, 
 
 40-51. 
 Gr. dolerite, 2.7-3'; basalt, 2.9-3.1 ; average, 2.87. 
 
 The compound occurs widely distributed through the 
 world as a basic lava, in surface and intrusive sheets, lava- 
 streams, plugs, and dikes. In North America it covers ex- 
 tensive areas, and especially on the Pacific border, where it 
 forms many " table mountains " and surface sheets many 
 square miles in area. Basalt especially, and anamesite to a 
 much less degree, are traversed by planes causing columnar 
 and tabular jointing. This is especially the case near the 
 margins of the flows. The columnar structure is well de- 
 veloped near Orange, N. J., on the Columbia River, Ore., 
 and abroad at Fingal's Cave, the Giant's Causeway, in 
 Australia, etc. The columns are straight or curved, and 
 horizontal, vertical, or inclined, dependent on the direction 
 of the flow, as the jointing is normal to the cooling surface, 
 
PRIMARY ROCKS. 22/ 
 
 whether that be the air or the dike- or bed- walls. This 
 structure is caused by the contraction of the cooling mass, 
 and is met with in dike-rocks and their walls. The tabular 
 structure is similarly caused, and divides the columns near 
 the selvages of the dikes. This is sometimes of " ball 
 and socket " form, which is shown on a grand scale near 
 San Francisco, Cal. This last is probably due to the 
 same forces that cause spheroidal weathering. The number 
 of sides to a column varies from three to eight. The 
 " plugs " above mentioned are the filled up flues of extinct 
 volcanoes. 
 
 The adjective " feldspar " is applied by many authorities 
 to this mineral combination, to show that it does not contain 
 nepheline nor leucite. In case a distinct comparison is made 
 between the basalts, this may be necessary ; but, as the 
 original " basalt " contains that mineral, it can be termed 
 " basalt," as the hornblende-syenite is simply " syenite.'* 
 The other basalts are then &^*/*#i-basait, &V*-basalt, etc. 
 The varying states (dolerite, anamesite, basalt) are due 
 solely to differences in the rapidity of cooling, analogous to 
 the differences in the crystalline texture of slowly and rap- 
 idly cooled abyssals. In a thick effusion of the mixture the 
 interior will show the very coarse " dolerite," which will 
 change through the medium grain of the same to the fine- 
 grained " anamesite," and thence, as we near the top of the 
 flow or the selvage of the dike, we find the grain becoming 
 microcrystalline, and finally reach compact " basalt," where 
 cooling was most rapid. The surfaces of lava-flows are 
 characterized by vesicular, slaggy, and pumiceous states, as 
 already noted ; but the fluidity of the effused basalt is so 
 great that some of the vesicles are large enough for the tall- 
 est man to stand erect and extend his arms without touching 
 the interior, as in some Hawaiian flows. The lining of 
 vesicles and the selvages of dike-basalt show vitreous states 
 
22% MANUAL OF LITHOLOGY. 
 
 (tachylite, hyalomelane), and infiltration into the vesicles of 
 old lavas forms amygdaloidal structures. 
 
 As dolerite is coarse- to medium-grained, the principal 
 components can be recognized (M\ The fresh fracture 
 shows a brilliant surface. The plagioclase is usually fresh and 
 white or light gray, and occurs in tables, blades, irregular 
 .grains, and rarely in prisms. It is found as phenocrysts 
 in the principal mass and in the cavities, and is usually 
 labradorite, but varies more frequently to the bytownite- 
 .anorthite end of the series than to andesine. As phenocrysts 
 it is sometimes an inch long. Sanidine occurs sporadically 
 at times, generally (m), but sometimes (M), and half an inch 
 long by one quarter wide (Lowenberg, where the transition 
 between andesite and basalt has been noted). Augite occurs 
 in stout brownish black columns or grains, sometimes in 
 laths. It is brown, brownish red, and rarely green by trans- 
 mitted light. In the groundmass it is seldom well crystal- 
 lized. Olivine is rarely present in the well-crystallized states, 
 -except in Iceland, where it is reported to be occasionally as 
 abundant as the augite, and of a semimetallic luster and 
 .greenish brown color. Magnetite is rarely visible to the eye 
 in any ofthe rock states, but titaniferous magnetite appears 
 {M) in large black folia, in some Hungarian rocks, and half 
 a foot across. Apatite (m) is rare ; large greenish-yellow or 
 light brownish-yellow crystals of hornblende infrequent, and 
 quartz rare. 
 
 As anamesite the components are generally fine-grained 
 and require a lens for distinction. The same minerals occur, 
 and in about the same proportion, except that olivine be- 
 comes more apparent (m) in the groundmass. We can 
 detect the compound character by the naked eye, but find it 
 ihard to resolve it. 
 
 In basalt the conditions are different. The fresh rock 
 is microcrystalline (with the recognized glimmer on a 
 
PRIMARY ROCKS. 22$ 
 
 fresh fracture) to compact and homogeneous. The color is 
 generally grayish to bluish black, seldom greenish black, 
 dark green, or dark brown. In the South Mountain, on the 
 border of Pennsylvania and Maryland, the ancient basalts 
 are now pale green, and have been sheared into rocks which 
 were thought to be slates until the late Dr. G. H. Williams 
 demonstrated their igneous origin. The fracture is uneven, 
 splintery, and coarse-conchoidal in the compact states. It 
 often carries (M) phenocrysts of olivine, plagioclase, augite, 
 and magnetite in crystalline grains, on fresh fractures the 
 last shows metallic reflections of extreme minuteness. The 
 groundmass varies from holocrystalline to a half-glassy 
 state, and carries few phenocrysts in all the variations be- 
 tween granular and glassy. The altered augite forms green 
 earth, chlorite, and calcite. Olivine is oil-green and in 
 angular (M) and round grains. Hornblende generally as 
 phenocrysts and (M), (sometimes f inch), and yellowish 
 brown (brown by transmitted light) ; this has already been 
 noted in the description of other rocks as " basaltic horn- 
 blende." Biotite is (M) in phenocrysts. Some authorities 
 note " hornblende " and " mica " varieties of basalt. Quartz 
 is in (M) grains in Europe and most notably in the western 
 United States, where many authorities have commented 
 upon it. All agree that it is primary. In the " quartz- 
 basalts " of this locality it is one of the oldest crystalliza- 
 tions, both (M) and (m), and is milk-white. Among the (M) 
 accessories are zircon, bluish sapphire, blue cordierite in 
 granular masses over two inches long, metallic iron (at 
 Mount Washington, N. H., Isle of Disko (150 Ibs.)), and 
 an olivine compound, in irregular shapes and varying 
 sizes, called " bombs." These last are peridotites, and are 
 thought by some to be segregations of the magma, and by 
 others to be pyroclasts, as they frequently exhibit sharp 
 re-entering angles. They contain nepheline in nepheline- 
 
230 MANUAL OF LIT HO LOG Y. 
 
 basalts. In the cavities, cracks, and interior vesicles of 
 basalt are numerous secondary minerals from metachemism, 
 as quartz, chalcedony, hyalite, fire-opal, semi-opal, zeolites, 
 carbonates, of lime, magnesia, iron, etc., barite, green earth, 
 delessite, and chlorophseite. Epidote is rare. Native copper 
 is found at Lake Superior and in the South Mountain of 
 Pennsylvania and Maryland. The rock weathers to a rusty 
 crust of lighter color than the interior, and the angular 
 edges round by spheroidal weathering. This sometimes 
 proceeds regularly inwards to form concentric shelly crusts 
 when the rock is compact and not much jointed, and these 
 can be separated with a hammer ; sometimes weathering 
 enters along the joint planes so as to form irregular poly- 
 hedra, that fall apart on fracturing, after the analogy of ball 
 and socket jointing. In this case the weathering is uniform 
 throughout. The state thus produced by the variations in 
 color is called " spotted " or " granular " basalt. The first 
 chemical change is in the formation of carbonate and 
 oxide of iron, which, by loss of carbonic acid, become 
 ferruginous tuffs and red clays. The varieties are: 
 
 1. Quartz-basalt (Diller), with large percentage of free 
 quartz. From Lassens Peak, Cal., the Eureka district, Nev., 
 Tewan Mountains, N. M., Santa Maria basin, Ariz., Anita 
 Peak, Col., with a few localities in Europe where small 
 amounts are found. The quartz is in milk-white grains with 
 plagioclase, augite, and olivine. Iddings reports them as 
 distinctly rounded, and suggests that they are the un- 
 absorbed portion of the original mass, in which they were 
 formed by the action of moisture. In the Tewan locality 
 both quartzose and quartzless forms agree closely, with 
 silica 52 ; the Lassens Peak variety shows silica 57.25. 
 
 2. Hyper sthene-bviS&lt (Diller). From Mount Thielson, 
 Ore. A porous basalt with a groundmass rich in (m) 
 dark-brown glass, and consisting of (m) plagioclase, augite, 
 
PRIMARY ROCKS. 
 
 magnetite, and apatite, carrying great phenocrysts of 
 plagioclase, hypersthene, and olivine. Similar rocks are 
 reported from Mount Pitt, Ore., and from San Salvador. A 
 fironzite-basalt is reported from Greenland. Silica 55.68; 
 Gr. 2.64-2.88. 
 
 3. Parabasalt (Zirkel), Olivineless Basalt. Carrying mono- 
 clinic and rhombic pyroxene and plagioclase, but without 
 olivine, nepheline, or leucite. It occurs as dolerite, aname- 
 site, and basalt, in Germany, Sardinia, Madagascar, etc. 
 
 4. Analcimite (Gemellaro). A highly vesicular basalt 
 with large cavities and clefts in which analcime has been 
 deposited through alteration in the rock, so that the greater 
 portion of the mass is of this mineral. From the Cyclopean 
 Islands. 
 
 BASALT GLASS. 
 
 Here are grouped together all the glassy states of all the 
 basalts noted, and of any mixture. 
 
 BASALT GLASS (Judd and Cole). 
 Tachylite (Breithaupt). An extrusive basic glass with 
 conchoidal fracture, readily soluble in HC1 (whence the 
 name). 
 
 Hyalomelane (Haussmann). A similar glass not so 
 .affected by acids. 
 
 Both types are found in glassy states of all the basalts, 
 so that they cannot be divided between them with 
 any regularity. The names are valueless, except as 
 showing that the glass sometimes dissolves, and some- 
 times resists the effect of the acid. 
 
 Silica 44-54; Gr. 2.5-2.7; water 6-7. 
 
 They form thin linings to vesicular cavities, thin crusts on 
 lava-flows, and seldom occur in large masses, except in the 
 Kilauea lavas, where owing to the enormous extent of the 
 crater the cooling is exceptional, and it is there in quite 
 
232 MANUAL OF LITHOLOGY. 
 
 thick crusts as pumice. In one instance it is a dike one 
 inch thick. The color varies from grayish white to black 
 through olive-green and greenish black, blue to bluish black, 
 or shades of brown. The structure is compact ; it occurs 
 only in small pieces, porous, slaggy, pumiceous, hairlike, 
 perlitic, and porphyritic ; when the last, the phenocrysts are 
 (in). The fracture is conchoidal ; fuses easily to a slaggy 
 glass ; hardness less than that of obsidian ; magnetic, and 
 generally opaque in the thinnest splinters. Owing to the 
 failure to divide the basalt vitrophyres between tachylite 
 and hyalomelane, Judd and Cole suggest " basalt glass" for 
 all such states. 
 
 1. Hydrotachylite (Petersen). From Rossberg, Darm- 
 stadt. A somewhat weathered bottle-green to black glass, 
 with greasy luster, conchoidal fracture, and usually clear 
 of phenocrysts. Easily soluble in concentrated HC1 ; easily 
 fusible. Silica 47.8; Gr. 2.103; H. 3. This is a state of 
 nepheline-basalt which had silica as low as 40.53 ; Gr. 2.524; 
 H. 5-6; and difficultly soluble in concentrated HC1. 
 
 2. Leucite-basanite-perlite, Obsidian, and Pumice. The 
 Vesuvian lavas are crusted with these states. The glass is 
 black and vitreous or pitchy, and yellowish brown by trans- 
 mitted light, carrying spherules and phenocrysts of (M) 
 leucite and augite. Porous white pumice comes from 
 Monte Somma and Pompeii. Silica 47.8 ; Gr. 2.77. It is 
 found in Italy, Java, Lower California. 
 
PRIMARY ROCKS. 2$$ 
 
 LIMBURGITE (Rosenbusch), Magma-basalt (Bo- 
 
 ficky). 
 
 A microcrystalline to compact basaltic groundmass carry- 
 ing usually only (M) phenocrysts of olivine, some- 
 times of augite and hornblende, and composed of oli- 
 vine, augite, and magnetite, with more or less glass 
 base. As accessories occur nepheline, leucite, and 
 plagioclase. 
 
 Silica 40-43 ; Gr. 2.83-2.97; water 2-5. 
 
 A rock, first found near Limburg, without a feldspathic 
 mineral, which occurs like basalt extensively in Germany,. 
 Bohemia, Spain, Cape Verdes, South Africa, Portugal, 
 Brazil, Greenland, etc. The augite is large and green, or 
 small and light brown to yellow ; hornblende is large ; olivine 
 is of the hyalosiderite type, with metallic luster and yel- 
 lowish green to golden yellow color; the amount of glass 
 varies ; secondary minerals are carbonates, zeolites, chal- 
 cedony, and hyalite. There are two types : 
 
 1. /Wdfr/tfr-magma-basalt, where the rock is not much 
 affected by acids ; is almost holocrystalline with a small 
 amount of brown glass, and forms hyalomelane glass, 
 analogous to the basalts. 
 
 2. Feldspathoid Magma-basalt, with abundant clear glass 
 base ; gelatinizes with HC1 to form much NaCl on evap- 
 oration ; forms glass of the tachylite type, and is analogous 
 to the nepheline-basalts. 
 
 Verite (Osann), Mica-magma-basalt. From Vera, near 
 Cabo de Gata, Spain, where it occurs as a lava-stream. (M) 
 a black lava with pitchy luster; often amygdaloidal; carry- 
 ing phenocrysts of brown mica in folia, visible (M) and 
 readily with the lens. The groundmass is a glass rich in 
 mica, olivine, diopside-like pyroxene, and some apatite. 
 Silica 55.17. 
 
234 MANUAL OF LIT HO LOG Y. 
 
 AUGITITE (Doelter). 
 
 A black compound of augite, magnetite, and glass base. 
 Silica 41-45. 
 
 This was first found as a lava in the Cape Verdes, and 
 also occurs occasionally in Bohemia, Venezuela, France, 
 Portugal, Brazil, etc. The glass base is either brown or 
 yellow, and is soluble in HC1 with slight difficulty ; or it is 
 colorless and readily soluble. Augite rarely forms large 
 phenocrysts, but is usually a confused mixture of small yel- 
 lowish or reddish prisms. Haiiyne is sometimes accessory ; 
 plagioclase, nepheline, biotite, hornblende, apatite, specular 
 hematite, ind magnetite occur. It readily forms zeolites. 
 
 1. Haiiynetachylite (Mohl), is a brown glass from the South 
 Sea Islands, carrying the above, and is a glassy augitite. 
 
 2. Ehrwaldite (Cathrein). A greenish to grayish-black 
 microcrystalline groundmass with black lustrous augite f to 
 i J inches ; brown biotite to f inch ; brownish to dark-green 
 phenocrysts of bronzite turned to bastite. The ground- 
 mass (m) is doleritic, and carries much basaltic hornblende, 
 augite, rhombic pyroxene, biotite, apatite, and magnetite. 
 It weathers to carbonates and zeolites. There is neither 
 olivine nor nepheline. 
 
 GROUP 22. GABBROS. 
 
 Ilia. BASALT-GABBRO INTRUSIVES. 
 
 (Necessary minerals : Plagioclase, olivine, pyroxene, magnetite.) 
 
 These may be arranged according to the predominant 
 mineral : 
 
 1. Plagioclase series, Gabbros. 
 
 2. Olivine series, Peridotites. 
 
 3. Pyroxene series, Pyroxenites. 
 
 4. Magnetite series, Magnetites. 
 
PRIMARY ROCKS. 335 
 
 GABBROS. 
 
 Combinations, varying from coarse granitoid to compact, of predom- 
 inant plagioclase, a pyroxene, olivine, and magnetite in varying propor- 
 tions. They can be divided, according to the size of their crystals, and 
 their predominant mineral, into : 
 
 I. GRANITOID GABBROS : 
 
 a. Plagioclase and diallage, Gabbro ; with olivine, <9//-z//>z<?-gabbro. 
 
 b. Plagioclase and rhombic pyroxene, Norite ; with olivine, OK- 
 
 c. Plagioclase, Anorthosites ; with olivine, Troctolite 
 
 II. GRANULITIC GABBROS : 
 
 a. Plagioclase and augite, Diabase ; with olivine, 
 
 III. GABBRO-PORPHYRITES : 
 
 a. Plagioclase and rhombic pyroxene, ./V0r//<?-porphyrite. 
 
 b. Plagioclase and augite, Dzafrase-porphyrite. 
 
 c. Plagioclase, Labrador porphyrite. 
 
 d. Augite, ^4z^7/<?-porphyrite. 
 
 IV. MlCROCRYSTALLINE GABBROS I 
 
 a. Without olivine, Aphanite. 
 
 b. With olivine, Melaphyre. 
 
 V. GABBRO GLASS: 
 
 a. Gabbro glass. 
 
 b. Diabase glass. 
 
 c. Variolite. 
 
 \a. GABBRO (Breislak), Diallagite (Descloiseaux), 
 
 Granitone. 
 
 A holocrystalline, granitoid, equidimensional mixture of 
 plagioclase and diallage, with magnetite, titanite, 
 apatite, and olivine. 
 
 Silica 43-54 ; Gr. 2.8-3.2. 
 
 It occurs as masses, bosses, intrusive sheets, dikes, and 
 surface sheets in Saxony, Silesia, the Harz, the Rhone dis- 
 trict, Bohemia, the Alps, Italy, Spain, France, Great Britain, 
 Norway, Sweden, Iceland, Japan, Africa, Australia, South 
 America, Massachusetts, New Hampshire, Delaware, Mary- 
 
236 MANUAL OF LITHOLOGY. 
 
 land, New York, Colorado, about Lake Superior, California, 
 The typical gabbro is very coarse-grained and granitoid, 
 with predominant plagioclase. It also has fine-grained tex- 
 tures, seldom amorphous, and exhibits parallel (banded,, 
 striped, schistoid), fluidal and somewhat centric structures. 
 Plagioclase is labradorite or anorthite (sometimes oligoclase, 
 and even orthoclase with quartz), and is usually in isometric 
 crystalline grains (sometimes two inches) of a grayish white 
 color (sometimes brownish and bluish violet). The feldspars 
 sometimes change to saussurite, as stated under the minerals, 
 though it is also a compact zoisite or a form of garnet. 
 Diallage is bladed, in irregular tables or in grains, colored 
 gray, brown, oil-green, with strong metallic-pearly luster. 
 The plates are sometimes three inches broad. It alters to 
 grass-green smaragdite with pearly luster. Judd thinks 
 diallage only a " schillered " augite, and the augite and 
 rhombic pyroxene (enstatite) the primary forms of the 
 group. Hornblende, rhombic pyroxene, and mica are fre- 
 quent essentials and ( M) ; as accessories are garnet, zircon 
 (sometimes one inch long), pyrrhotite (not pyrite), and 
 secondary calcite. The minerals crystallized at the same 
 time and are generally hypidiomorphic. Olivine occurs 
 (M) and is sometimes very abundant. It usually alters to 
 other minerals (serpentine and chrysotile). The rock is 
 usually poor in accessories. With predominant hornblende 
 the rock is diorite ; with rhombic pyroxene, a norite ; with 
 augite, a diabase. It cannot be traced into hypocrystalline 
 nor porphyritic varieties, nor is it accompanied by tuffs. 
 
 i. Zobtenite (J. Roth). From the Zobtenberg, Silesia. A 
 schistoid gabbro, which also has an olivine variety. A coarse- 
 to fine-grained rock, also found on the selvages of gabbro 
 eruptions, as is usually the case with mixtures of highly 
 unequiaxial black minerals, and with parallel arrangement 
 to the dike-walls. 
 
PRIMARY ROCKS, 237 
 
 2. Beerbachite (Chelius). A fine-granular dike-gabbro 
 which also carries olivine, from the Melibocus, with silica 
 47. Hornblende sometimes replaces diallage. 
 
 3. Odinite (Chelius). From near Darmstadt in a dike, with 
 silica 52. A gray groundmass carrying plagioclase and 
 green to colorless augite with mica in the center of the 
 dikes, which are coarse-grained there. 
 
 Hypersthene-gabbro, Gabbro-granite (Chester). From 
 Delaware, where it contains accessory quartz, basaltic horn- 
 blende, and biotite. Hypersthene-gabbros also occur in 
 the Odenwald, at Monzoni, etc. 
 
 Hornblende-gabbro (Chelius). From the Odenwald, 
 Black Forest, Alsace, etc., with scanty diallage and abun- 
 dant hornblende (J to 2 inches). This is like diorite. In 
 some of the localities the diallage has altered to hornblende 
 by paramorphism. 
 
 i. Smaragdite-gabbro, with diallage altered to smarag- 
 dite, with grass-green color and pearly luster, and plagio- 
 clases not much changed to saussurite. At Mittleberg, etc. 
 
 (Some authorities place here the alteration products 
 from diallage to hornblende, as the so-called " hyperite-dio- 
 rites," etc. These have been described under " Diorite.") 
 
 Mica-gabbro. From the Brocken, Harz. A fine-grained 
 rock rich in biotite and augite and poor in olivine. Quartz 
 appears more frequently than in normal gabbro, as would 
 be the case with micaceous rocks. It is found elsewhere 
 as a variety in gabbro formations. 
 
 Orthoclase-gabbro (Irving). From Lake Superior, with 
 orthoclase, oligoclase, apatite, diallage, and much basaltic 
 hornblende. It is generally free from olivine and carries 
 secondary quartz. 
 
 Saussurite-gabbro, Euphotide (Haiiy). A rock from 
 Italy, France, Sweden, etc., where plagioclase is altered to 
 
238 MANUAL OF LITHOLOGY. 
 
 saussurite and diallage to smaragdite, with titanite, chro- 
 mite, pyrite, serpentine, and carbonates. Silica 43-50 ; Gr. 
 2.65-3.69 ; H. 2.5-3 I fusibility 3-3.5, and more or less at- 
 tacked by acids. The euphotide of Mont Rosa has Gr. 3.65 ; 
 from Sweden, 3.60 ; from France, 2.69. As they have their 
 diallage more or less changed, they are classed as saussurite- 
 diallage-gabbro and saussurite-smaragdite-gabbro. 
 
 Olivine-gabbro (G. Rose). A gabbro containing (M) 
 olivine in small blackish green grains, or its weathered 
 equivalent (serpentine or chrysotile). It occurs in Scandi- 
 navia, Great Britain, Japan, Waterville and Mount Washing- 
 ton, N. H., Cortlandt, N. Y., Maryland, Minnesota, Iron 
 Mountain, Col, St. John, N. B. 
 
 i. Olivine-enstatite-gMoro. From the Western Isles of 
 Scotland, carrying olivine and enstatite. 
 
 U. NORITE (Esmark). 
 
 A usually coarse- to fine-grained (sometimes granitoid, 
 porphyritic, and ophitic) compound of plagioclase 
 and a rhombic pyroxene (hypersthene, enstatite, 
 bronzite), with diallage, hornblende, orthoclase, il- 
 menite, and magnetite, also olivine and quartz. 
 Silica 43-65; Gr. 2.8-3.1. 
 
 It occurs in widely extended masses in Laurentian for- 
 mations especially in Scandinavia and North America ; 
 also in dikes. It is found in New York, Pennsylvania,, 
 Delaware, Maryland, North Carolina. It is associated with 
 beds of titaniferous magnetite, and some authorities see in 
 this a segregation from a gabbroitic magma. The minerals 
 appear as in gabbro, and orthoclase is sometimes two inches 
 long. The typical norite has a highly basic plagioclase 
 with enstatite or hypersthene, and with little diallage, horn- 
 blende, or biotite. A high percentage of quartz forms 
 
PRIMARY RGCKS. 239 
 
 quartz-norite, and of olivine, olivine-uorite. A quartz-norite 
 from Mount Hope, Md., carries orthoclase and blue quartz. 
 
 Hypersthene-norite, when hypersthene is the predomi- 
 nant mineral. This is found about Lake Superior, the 
 Adirondacks, in Delaware, etc. Some authorities call this 
 "hyperite," while others use that term for "augite-norite." 
 This is a misnomer, as it is only a norite. 
 
 Monzonite. A variety of the above from Monzoni in 
 the Tyrol. Name no longer used. 
 
 Bronzite-norite. A variety with bronzite, now em- 
 braced under the general term. From Finland. 
 
 Augite-norite. A compound of hypersthene, augite, 
 biotite, reddish brown feldspar, fibrous diallage, with the 
 first two equally prominent. Cortlandt, N. Y. Silica 55. 
 
 Mica-norite. A compound of magnetite, hypersthene, 
 biotite (bent and twisted about large portions of feldspar), 
 broken and bent plagioclase, and garnet. Schistoid by 
 selvage action at Cortlandt, N. Y. 
 
 Hornblende-norite. A transition between norite and 
 diorite. From the Alps. 
 
 Spheroidal Norite, Ball Gabbro, " Potato-stone." From 
 Romsas, with thick-shelled greenish brown concretions (up 
 to six inches diameter) of biotite flakes and hypersthene, in a 
 light-colored ground mass of labradorite, oligoclase, biotite, 
 and magnetite ; also at Cortlandt, N. Y. 
 
 Ic. ANORTHOSITE (F. D. Adams). 
 A gabbro with predominant feldspar (anorthite) to the 
 almost entire exclusion of all other ingredients. 
 
 The plagioclase is frequently 95 per cent of the rock, and 
 none of the essentials or accessories are ever abundant, such 
 as hyperite, augite, hornblende, biotite, titanite, and magne- 
 tite. It occurs extensively in the Laurentian of New York, 
 Canada, about Lake Superior, Labrador, and Newfoundland. 
 
240 MANUAL OF LITHOLOG F. 
 
 1. Forellenstein, Troctolite (Bonney). A gabbro com- 
 posed of olivine and plagioclase. The olivine is altered to 
 serpentine. There is little or no diallage. From the vicinity 
 of Neurode, where it has the local name given above ; but 
 the contrast of the spots of blackish green serpentine grains 
 against the snow-white feldspar led Bonney to call it as 
 above given from its resemblance to the sides of a trout. 
 The plagioclase is always like anorthite. Silica 41.13; Gr. 
 2.88. Found in Canada. 
 
 2. Ossipyt (Hitchcock) is a similar rock from Ossipee, 
 N. H., with labradorite, olivine, magnetite, and an amphibole. 
 
 (This series is the " complement " of magnetite in the 
 differentiation of a gabbroitic magma.) 
 
 GRANULAR GABBRO. 
 
 \\a. DIABASE (Haussmann). 
 
 A coarse- to fine-grained and usually compact and ophitic 
 greenish compound of plagioclase, augite, and gener- 
 ally viridite, with specks of ores and accessory bio- 
 tite, rhombic pyroxene (usually (m)\ olivine as in 
 gabbro ; quartz occasionally (m). 
 
 Silica 43-56; quartz-diabase 53-58; Gr. 2.8-3. 
 
 It occurs as surface and intrusive sheets and beds, and as 
 dikes, and joints and weathers like basalt. A locality on the 
 shore of Lake Superior in a width of 14 inches exhibits 28 
 intrusions of diabase into granite ; so that 27 granite plates, 
 varying in thickness from J inch to 8 inches, lie between 
 them. It is abundantly developed throughout the world, 
 and especially in the Trias of the Atlantic border of the 
 United States. It is usually fine-grained and frequently 
 aphanitic and porphyritic ; also schistose ; parallel struc- 
 tures; variolitic, and amygdaloidal. The cavities of the rock 
 in the last state are filled with quartz, actinolite, asbestus, 
 
PRIMARY ROCKS. 24! 
 
 pistacite, cat's-eye, axinite, calcite, dolomite, native copper, 
 and zeolites. The diabase-/w/ hy rites are in small dikes or 
 the selvages of great ones. It also shows tuffs. Olivine is 
 variable. Plagioclase is oligoclase, labradorite, bytownite, 
 and anorthite ; tabular, lath-shaped, and regular ; white, 
 grayish white, and greenish white. Augite is brownish to 
 brownish black as idiomorphs, irregular grains, and slender 
 laths ; quartz and orthoclase are (m) ; biotite is usually in 
 the hornblendic varieties of coarse grain. Augite alters to 
 chlorite, serpentine, and uralite. Viridite occasionally is in 
 (M) folia. It colors the rock. Epidote is also a secondary 
 product. The color is usually green. The Washoe diabase 
 is blue when freshly blasted ; in a minute it shows brownish 
 shades, and in five minutes it is entirely brown. When in 
 dikes and masses, diabase is frequently altered to schists by 
 squeezing. Barus fused a diabase with Gr. 3.0178 to a glass 
 with Gr. 2.717, and argues that the original density is due 
 to pressure during solidification. 
 
 1. Leucophyre (Gumbel). From the Fichtelgebirge. A 
 light-colored saussurite-like rock with green augite, colored 
 by viridite, and carrying titanite, plagioclase, piedmontite, 
 augite (either green or brown), scanty hornblende. Silica 71. 
 
 2. Proterobase (Gumbel). From the same locality, and 
 meaning an older rock than the others. It carries primary 
 basaltic hornblende. A later rock is called hysterobase. 
 
 3. Algovite (Reiser). A granular to compact dark-green 
 to reddish brown amygdaloidal and porphyritic rock with 
 great plagioclases. The only (M) minerals are plagioclase 
 and light-brown augite. 
 
 4. Diabase-pegmatite (Brogger). From Brandbokampus, 
 Norway, and composed of augite, basaltic hornblende, and 
 titanite in large grains, with very basic plagioclase, in dikes 
 where large crystals are formed like pegmatite, of plagio- 
 clase with hornblende and augite playing the role of quartz. 
 
242 MANUAL OF LITHOLOGY. 
 
 5. Calcareous Diabase. This is no longer known as a 
 separate rock, as the calcite, in any case, is a secondary 
 product. There were states of this called calcareous apha- 
 nite and schalstein. 
 
 Sahlite-diabase (Tornebohm). From Sweden, England. 
 Idiomorphic diopside-like augite with frequent quartz. 
 Also in the Trias sandstone of the Connecticut Valley. 
 
 Enstatite (Bronzite)-diabase (Rosenbusch). From Saar- 
 Nahe district, Sweden, England. A hypersthene-diabase is. 
 found in New Jersey, Virginia, etc. 
 
 Uralite-diabase. From the Schwarzwald, Harz, Cyprus, 
 Sweden, the iron region of Michigan. This is distinct from 
 hornblendic proterobase. A medium-grained compound of 
 bytownite, large fibrous prisms of uralitized pyroxene, com- 
 pact grains of hornblende, and biotite. It alters to epidote 
 and chlorite. It is widely scattered throughout the world,, 
 with diabase, but of limited occurrence at any one place. It 
 is accompanied by garnet in Michigan. 
 
 Mica-diabase (Emerson). In dikes at Franklin, N. J. It 
 is spherulitic, with small pyroclasts of fused willemite from 
 the dike-walls through which it broke. It is composed of 
 labradorite, augite, biotite, apatite, and titanite. 
 
 Ophite (Palassou). From the Pyrenees, Spain, Portugal. 
 A coarse-grained to (M) dense and seldom porphyritic rock, 
 light- and dark-green to black. Gr. 2.7-3; silica 49.50. It 
 occurs as dome-shaped masses and dikes. It is a uralitized dia- 
 base with columnar jointing and spheroidal weathering, so- 
 that concentric shells can be removed as in the case of basalt. 
 (M) plagioclase and augite are not abundant ; secondary 
 calcite occurs in veins, and some kinds effervesce with acids. 
 
 Teschenite (Hohenegger). In irregular masses, apophy- 
 ses, and dikes. From eastern Silesia. A felsitic rock with 
 
PRIMARY ROCKS. 243 
 
 intersertal texture in which hornblende forms long black 
 acicular crystals of basaltic type ; apatite the same at times. 
 Named from Austrian Silesia (Teschen). Plagioclase is lab- 
 radorite-bytownite-anorthite ; augite (M)\ ilmenite; scanty 
 biotite. When coarse-grained, hornblende and augite are in 
 (M) individuals. Analcite is abundant, and on this account 
 Rosenbusch places this with theralite, as another combina- 
 tion of plagioclase-feldspathoid rock; but Zirkel states that 
 the microscope shows that the last mineral is formed at the 
 expense of labradorite, and not from a possible nepheline or 
 leucite. It occurs (M). Chlorite and calcite are secondary. 
 
 Olivine-diabase. Silica 48.18 ; Gr. 2.93-3.19. It occurs in 
 dikes in Germany, Sweden, Great Britain, Asia, South 
 Africa, Brazil, in the United States in Minnesota, Deerfield, 
 Mass., Campton, N. H., Kennebunkport, Me., Orange, N. J., 
 Nevada. Olivine is partly fresh and partly opalized and 
 serpentinized ; augite is partly like diallage ; hornblende and 
 biotite are (M) in the coarse-grained states to a higher 
 degree than in diabase ; and much hornblende forms olivine- 
 proterobase. Plagioclase is usually labradorite ; anorthite 
 forms the variety eukrite (with little olivine and biotite, but 
 much magnetite); orthoclase is found in large Carlsbad twins 
 at Falkenstein, Saxony (two inches long). The texture 
 varies from granitoid to ophitic, compact, vesicular, and 
 slaggy ; in beds, extrusive and intrusive sheets, and dikes. 
 
 PORPHYRITES OF THE GABBRO GROUP. 
 
 Ilia. NORITE-porphyrite. 
 
 A half-glassy rock with porphyritic structure ; pitchy 
 luster ; carrying small phenocrysts of rhombic 
 pyroxene and (M) plagioclase ; without quartz, horn- 
 blende, or biotite. 
 
 Silica 56-60 ; Gr. 2.7-3. 
 
 A scarce rock, associated with norite, and only possible 
 
244 MANUAL OF LITHOLOG Y. 
 
 where rhombic pyroxene is abundant. It is called enstatite- 
 porphyrite, ^>'/m/^-porphyrite, etc., as the pyroxenic 
 mineral changes, and 0/zV/W-norite-porphyrite, when olivine 
 also appears as phenocrysts. 
 
 Hyper sthene-quartz-Tpor^\\y rite (Lossen). From Elbin- 
 gerode, as a hornstone-like groundmass with (M) pheno- 
 crysts of plagioclase, hypersthene, small quartzes, and 
 sporadic garnet ; orthoclase is (m) ; also biotite, apatite, and 
 zircon. Silica 69.94. 
 
 lllb. DIABASE-porphyrite (Rosenbusch). 
 A holocrystalline groundmass (///), carrying (M) pheno- 
 crysts of labradorite and augite. 
 Silica 43-58 ; Gr. 2.9. 
 
 The following porphyrites occur in dikes, as selvages to 
 diabases, in Saxony, Thuringian Forest, Harz, Nassau, Saar- 
 Nahe district, Vosges, Greece, Bulgaria, Switzerland, Italy, 
 Great Britain, Sweden, Asia, Egypt, Victoria, in United 
 States about Lake Superior. They joint and weather like 
 diabase and basalt. Plagioclase is white to greenish white, 
 usually J inch long (rarely i inches), and generally altered 
 and stained with chlorite and epidote; augite is in stout 
 prisms, greenish, greenish brown, and black, and pitch-black 
 (all in the same fragment) ; quartz (;). The groundmass is 
 greenish gray to blackish green ; seldom brownish black or 
 reddish violet; when fresh gives the microcrystalline 
 glimmer; sometimes there is a small amount of (m) glass 
 base ; drusy, amygdaloidal (filled with calcite, quartz, 
 chalcedony, cat's-eye, epidote, axinite, and zeolites). 
 
 Black Porphyry (Streng). From Elbingerode, Harz, 
 with a black groundmass carrying (M) phenocrysts of labra- 
 dorite and small prisms of augite, with accessory mica in 
 brownish black folia, pyrite, and magnetite. The ground- 
 mass is seen to be crystalline by the lens. 
 
PRIMARY ROCKS. 24$ 
 
 lllc. LABRADOR Porphyrite (Delesse). 
 A compact grayish green, dark-green, even reddish-violet 
 ground mass, with phenocrysts of greenish labradorite 
 in tables from one-third to two-thirds of an inch long, 
 and rarely small augites. 
 
 Silica 54 ; Gr. 2.77 ; water 2.5. 
 
 The general occurrence and character are as described 
 under " Diabase-porphyrite." It is found at Duluth, Wis., 
 and Taylor's Falls, Minn. The varieties are : 
 
 1. Cuselite (Rosenbusch), with bluish gray groundmass 
 carrying -J inch plagioclase and chloride grains. Silica 58.02. 
 
 2. Porfido-verde-antico. From Laconia, Greece, Great 
 Britain, etc. An olive-green groundmass which becomes 
 lighter on heating, carrying dark-green augite and greenish 
 white labradorite phenocrysts. Silica 53 ; Gr. 2.91. Epi- 
 dote, chlorite, and quartz are secondary. 
 
 \\\d. AUGITE-porphyrite. 
 
 A compact dark-green matrix carrying phenocrysts of 
 augite of inch and over. 
 Silica 42-49 ; Gr. 2.9. 
 
 Abundant as dikes and lava-streams in the Alps, with 
 vesicular and amygdaloidal states common. There are 
 placed as varieties : 
 
 1. Uratite-porphyry (G. Rose). First described from the 
 Urals, with a dense greenish gray groundmass (sometimes 
 blackish gray carrying phenocrysts of plagioclase from i to 
 i| inch, and uralite). Silica 61 ; Gr. 3. 
 
 2. 3/z^-augite-porphyrite. From England, with abun- 
 dant folia of mica and augite. Silica 48-51 ; Gr. 2.57. 
 
246 MANUAL OF LITHOLOGY. 
 
 MICROCRYSTALLINE GABBROS. 
 
 I Va. APHANITE (" Unresolvable "). 
 This is a compact state of the gabbro group, and in hand 
 specimens can only be divided into the diabase and other 
 forms by the presence of a few phenocrysts, which are not 
 sufficiently important to form a porphyrite. It may be 
 taken as the groundmass of the porphyrites, and varies from 
 microcrystalline to compact (m), but with small amount of 
 glass base. When it becomes glassy, it falls under the next 
 division of the group. We can distinguish only norite and 
 diabase-aphanites, as gabbro cannot yet be reported in com- 
 pact or porphyritic states, and norite rarely. 
 
 I. Norite-aphanite is reported from Fifeshire, Scot- 
 land. A compact grayish-black rock associated with 
 norite there. 
 
 II. Diabase-aphanite. 
 
 A (M) compact diabase without phenocrysts, forming 
 an apparently homogeneous mass, dark green to black, 
 as hard as feldspar ; dull luster, subconchoidal frac- 
 ture ; sometimes slightly porphyritic, vesicular, 
 amygdaloidal, and slaty. 
 Silica 43-58 ; Gr. 2.6-3. 
 
 This is associated with diabase ; joints and weathers like 
 basalt. Phenocrysts of augite or plagioclase in predomi- 
 nance form those varieties of porphyrite. It bears to 
 diabase the relation that felsite does to granite. Some au- 
 thorities see in this a highly devitrified diabase glass. 
 
 j. Calcareous Aphanite, Kalkaphanit. An aphanitic mass 
 carrying abundant spherules of calcite, which are not the 
 fillings of amygdules. 
 
 . 2. Amygdaloidal Aphanite, Spilite, where the calcite, 
 quartz, or other minerals are the filling of amygdules. The 
 French geologists call this spilite. 
 
PRIMARY ROCKS. 247 
 
 (NOTE on diabase rocks. Many geologists make no dis- 
 tinction between diabase and dolerite, other than that of 
 color and difference in age. They both contain the same 
 mixtures and appear in the same states. The color is said 
 to be due to the formation of viridite, and the greater abun- 
 dance in amygdaloidal states in diabase is due to greater age 
 and exposure to metachemic agents. Others note that there 
 are diabases without viridite, which seem to be older forms 
 of augite-andesite. There is also a difference in texture in 
 diabase and dolerite, which may be due to longer exposure 
 to the above-named agencies. At any rate, both are placed 
 in the group of gabbros, and are most intimately associated.) 
 
 IVb. MELAPHYRE (Brongniart). 
 
 A compact half-pitchy black, green, red, brown, bluish 
 purple groundmass, weathering to brown, red, and 
 green, composed of (m) plagioclase, pyroxene, and 
 olivine, and carrying at times phenocrysts, which are 
 usually olivine (sometimes ^ inch, and usually visible 
 with a lens). It is associated in Scotland with augite- 
 andesites, and is thought by some to be an olivine 
 variation of them ; by the majority of petrographers, 
 as an oiivine variation of basalt and aphanite. 
 Silica 51-57; Gr. 2.68-2.85. 
 
 It occurs in beds, sheets, dikes, bosses, and pyramidal 
 masses in Silesia, Thuringian Forest, Saxony, Bohemia, Great 
 Britain, France, Hungary, the Alps, Spain, Greece, South 
 Africa ; in the United States at Keweenaw Point, Lake 
 Superior, Nevada, Kennebunkport, Me. It joints irregularly 
 in columns, tables, etc., and when weathered is full of 
 ferrite, epidote, calcite, etc. A number of varieties are 
 made on (m) variations of groundmass. 
 
 With this rock, when amygdaloidal, are associated native 
 copper (Lake Superior), silver (the same), zinc ores, jasper, 
 
248 MANUAL OF LITHOLOGY. 
 
 chalcedony, agate, amethyst, calcite, etc., in abundance, 
 never with zeolites, so that the Oberstein rock was worked 
 for agate till exhausted. Epidosite is an epidotized variety. 
 Navite (Rosenbusch) is a red groundmass carrying 
 phenocrysts of plagioclase and olivine. From Ober- 
 stein. 
 
 V. GABBRO GLASS. 
 
 With the exception of diabase, these are not very abun- 
 dant, as the rocks are very basic and do not easily form such 
 states, as their low heat content, in proportion to their great 
 fluidity, allows them to form stony states under conditions 
 where the acid rocks would only form glasses. The occur- 
 rence of gabbro is given as a probable gabbro glass. No 
 norite-glass is reported as yet. 
 
 (a) Gabbro Glass. From Carrock Fell, England, in a dike 
 one inch thick, traversing gabbro, and reported as probably 
 part of it, as shown by its high specific gravity (2.99). A 
 greenish to purplish glass, weathering yellowish brown ; 
 waxy luster ; slightly magnetic ; H. 6.5 ; silica 51-53 ; fuses to 
 a black enamel on thin splinters. 
 
 (ft) Diabase Glass. In some cases this is simply the ex- 
 tension of the glass base that is found in some diabases ; in 
 others it is a regular glass, with greasy luster, occurring with 
 diabase, and forming pitchstone, pitchstone-porphyry, and 
 obsidian states. Silica 44-55 ; Gr. 2.4-2.6. Near Quotshau- 
 sen the diabase stream (extrusive) is fresh and has a glass 
 crust with phenocrysts of altered olivine. It is also found 
 on the selvages of dikes in Scotland, and in one or two in 
 stances in America; also in Sweden (see below). 
 
 i. Wichtisite (Tornebohm). From Finland, in consider- 
 able masses ; black ; slight luster ; conchoidal fracture ; 
 hardness 6.5 ; Gr. 3.03 ; fusible to a black enamel ; silica 
 54-56 ; in a dike 4-5 inches wide at Wichtis. 
 
PRIMARY ROCKS. 249 
 
 2. Sordawalite (Tornebohm). From Sordawala, in inch 
 selvages to a narrow dike in hornblende-schists. It is 
 black, like anthracite ; vitreo-greasy luster. H. 4-4.5 ; Gr. 
 2.55-2.62 ; silica 47-49. 
 
 (c) Variolite, Jadeglanduleux (Brongniart). A light- to 
 dark-green devitrified spherulitic gabbro glass, with silica 
 52.79 ; Gr. 2.896. Found in England, Ireland, Sweden, Silesia, 
 Siberia, France, Thuringian Forest, Fichtelgebirge, Italy. 
 Weathers and joints spheroidally; carries abundant greenish 
 white to violet-gray spherules with radial-fibrous and con- 
 centric-shelly structure of a silicate which are so firmly 
 intergrown in the mass that they do not separate on weather- 
 ing, but, being more resistant than the groundmass, are left 
 projecting above the surface as brown pustules (whence the 
 name). Cole and Gregory on studying the occurrence at 
 Mount Genevre decided that the rock was a devitrified 
 tachylite with spherules. This rock must not be confused 
 with amygdaloidal forms of aphanite, where the spherules 
 are calcite ; nor with the amygdaloidal forms of melaphyre, 
 where they are silica. 
 
 BASALT-GABBRO INTRUSIVES. 
 
 II. O LI VINE SERIES. 
 (Necessary mineral : Olivine.) 
 
 PERIDOTITE (Rosenbusch). 
 
 These massive holocrystalline rocks are plagioclaseless 
 gabbros with predominant olivine. Silica 26-45. Zirkel 
 objects to the name " peridotite," as in some cases the min- 
 eral is not olivine, but one of its varieties ; but the term is 
 in general use, and is understood as a series with an olivine 
 mineral predominant. According to the other component 
 or components, the rocks are called : 
 
250 MANUAL OF LITHOLOGY. 
 
 (a) Dunite (v. Hochstetter). An olivine rock, generally 
 with chromite. From Dun Mountain, New Zealand. An al- 
 most pure aggregate of olivine of characteristic color, angu- 
 lar grains, splintery fracture, and vitreo-greasy luster. 
 Silica 42-43; Gr. 3-3.3. This is also found in Japan, the 
 Western Isles of Scotland, and in a dike near Willard, Ky., 
 with abundant garnet. It serpentinizes. 
 
 (b) Picrite (Tschermak). A compound of olivine and 
 augite, named from the abundance of magnesia (" bitter ") 
 salt in it (Greek pikros). In dikes and beds in Austria, 
 England, Scotland ; in United States in Arkansas (Murfrees- 
 borough), Deer Island, Maine, Cortlandt, N. Y. In England 
 it is reported as passing into diorite. It is mainly of olivine, 
 and the rest a compound of augite, hornblende, and mag- 
 netite ; blackish green in many cases, and almost compact 
 with olivine in phenocrysts half an inch long. Olivine 
 serpentinizes, as usual, in many cases. Silica 38.9 ; Gr. 2.96. 
 It forms porphyritic states. Kimberlite (Carvall-Lewis) is a 
 similar rock from Kimberly, South Africa, at the diamond 
 mines ; and palceopicrite (Gumbel) (" old picrite ") is a serpen- 
 tinized form with abundant chlorite in the Fichtelgebirge. 
 
 (c) Eulysite (Erdmann). A probably metamorphic com- 
 pound of fayalite (iron-olivine) green augite, and pyrope, in 
 lenticules in granulite near Tunaberg, Sweden ; with thin- 
 jointed structure. It is of limited extent. 
 
 (d) Wehrlite (v. Kobell). A dark-colored, coarse-grained 
 mixture of fresh olivine and green diallage, with abundant 
 basaltic hornblende and titaniferous magnetite. From Hun- 
 gary, Bosnia, Finland, Scotland, Borneo, Japan. 
 
 (e) Saxonite (Wadsworth). A compound of serpentinized 
 olivine and rhombic pyroxene (enstatite or bronzite) ; also 
 called " schiller rock," from the alteration of the pyroxene 
 to bastite. Silica 41.48. It is rarely found with fresh olivine. 
 It occurs from the Baste, near Harzburg, and obtained the 
 
PRIMARY ROCKS. 2$ I 
 
 name " harzburgite " from Rosenbusch, which is later than 
 that given above. It is found in the Alps, Sweden, Borneo, 
 New Zealand, and in the United States in Maryland with 
 bronzite. Silica 43, and Gr. 3.022. Buchnerite (Wadsworth) 
 is a similar compound with additional augite. 
 
 (/) Lherzolite (de Lametherie). From L'herz in the 
 Pyrenees. A coarse- to fine-grained and compact compound 
 of olivine, diopside (grass-green and like diallage), enstatite, 
 and accessory picotite. Silica 40-44 ; Gr. 3.3-3.4. In some 
 cases it is so compact as to appear as a monotonously colored 
 serpentine. Diopside in grains ; enstatite yellowish brown 
 to greenish gray with fibrous cleavage ; picotite is small 
 and black. It occurs in great sheets in the Pyrenees, Italy, 
 Norway, Tyrol, Spain, Maryland, and at Mont Diablo, Cal. 
 In Italy and Norway it is fresh ; in Germany, France, and 
 -Cornwall more or less completely altered to serpentine, the 
 olivine going first, enstatite next, diopside last. 
 
 (g) Cortlandtite (G. H. Williams). This is Bonney's 
 " hornblende-picrite," and is a compound of olivine, horn- 
 blende, and augite, and is named from Cortlandt, N. Y., 
 where it occurs in dikes. It also is found in Australia, 
 Sumatra, Custer County, Col. G. H. Williams sug- 
 gested that the previous name " hudsonite " (Cohen) be 
 given to the augite-picrite type, while " cortlandtite " be 
 used for the hornblende variety, and Rosenbusch and Zirkel 
 have adopted the same. 
 
 (It) Scyelite (Judd). From Loch Scye, Scotland, is a 
 mixture of (m) olivine-green hornblende and biotite. 
 
 (z) Biotite-olivine Rock (Koch). A compound of fresh 
 olivine and great folia of biotite, rounded grains of spinel 
 -of dark bluish green, titaniferous-magnetite, accessory 
 apatite and plagioclase. Silica 33-35 ; Gr. 3.27. From. 
 Crittenden County, Ky., DeWitt, Ithaca, N. Y. 
 
MANUAL OF LITHOLOGY. 
 
 BASALT-GABBRO INTRUSIVES. 
 
 ///. PYROXENE SERIES. 
 (Necessary mineral : Pyroxene.) 
 
 PYROXENITE (Hunt), a general name for an eruptive 
 granular rock consisting of one or more members of this 
 mineral group, and equivalent to a gabbro without plagi- 
 oclase or olivine. Silica 50-55 ; Gr. 3-3.4. The name has 
 nothing to do with the pyroxenite of Coquand, which 
 refers to a malacolite rock in granular limestone, and is 
 wholly metamorphic. Rocks of this group are reported from 
 Maryland, North Carolina, and elsewhere. That from 
 Maryland consists of diallage and bronzite. 
 
 The late G. H. Williams suggested the following classifi- 
 cation : 
 
 With augite, Pyroxenite. From Cortlandt, N. Y., Sierra 
 Nevada, Cal. 
 
 With diallage, Diallagite. (See p. 235.) 
 
 With bronzite, Bronzitite. 
 
 With enstatite and diallage, Websterite. From North 
 Carolina, Italy, etc. 
 
 IV. MAGNETITE SERIES. 
 (Necessary mineral : Magnetite.) 
 
 While magnetite is generally placed as a metamorphic 
 rock from contact action, there are many cases where it is 
 a distinct differentiation of a gabbro magma with or without 
 other typical minerals as accessory. Many authorities hold 
 that, as magnetite loses its magnetism at high temperatures, 
 it could not thus be formed. It may be answered that there 
 would be the same argument against its presence in basalt 
 
PRIMARY ROCKS. 
 
 and other truly eruptive rocks. This series does not pro- 
 pose to claim for all magnetites an eruptive origin, but many 
 of them have a decided one, as the differentiation of a 
 gabbro magma that has its antithesis in anorthosite. 
 Magnetite and anorthosite are therefore " complementary " 
 rocks. The variations thus far noted are : 
 
 (a) Magnetite-olivenite (Sjogren). From Taberg, Sweden, 
 composed of magnetite and olivine with a small amount of 
 plagioclase, with accessory mica and apatite. Here it is a 
 distinct differentiation of a hypersthene-gabbro. 
 
 (b) Plagioclase-pyroxene-rc\a.gnetite. Similar differentiations. 
 From the Odenwald, Frankenstein, etc. 
 
 (c) Plagioclase-olivine-m&gnetite, Cumberlandite (Wads- 
 worth). From Cumberland, R. I.; with silica 21; with 
 feldspar as phenocrysts. 
 
 (d) Pyroxene-magnetite, Jacupirangite (Derby). 
 
 (e) Nep/ietme-0tivtne-isicupira.ngite. Both from Brazil, as 
 differentiations of dikes. 
 
254 MANUAL OF LITHOLOGY. 
 
 APPENDIX TO GABBRO. 
 SERPENTINE. 
 
 Here are assembled entirely altered rocks which may 
 have originally consisted of olivine, diorite, or gabbro, as 
 these rocks pass (including all their ingredients) into this 
 mineral, as seen along the juncture of the hornblendic gneiss 
 and Potsdam quartzite at South Bethlehem and at Easton 
 on the northern border of the South Mountain in Pennsyl- 
 vania. It is therefore found in beds where it has formed 
 from metamorphic rocks, and in dikes where it comes from 
 those decidedly eruptive. Under the olivine series are given 
 a number of instances of the latter change. 
 
 SERPENTINE. 
 
 A compact rock, dull in fresh fracture, soft, with greasy 
 feel ; usually dark green or brown. 
 Gr. 2.5-2.7. 
 
 It occurs compact, porphyritic (with crystals of pyrope),. 
 slaty, and veined. As accessories occur pyrope, talc, bronzite, 
 chlorite, mica, magnetite, etc. Serpentine is classed among 
 the peridotites from their habit of weathering, though it is 
 derived from augitic and hornblendic rocks through a 
 similar process. The serpentine-quartz rock at South 
 Bethlehem, Pa., between the gneiss of the South Mountain 
 and the overlying Potsdam quartzite, has been derived from 
 the lower rock through change in the hornblende. 
 
SECONDARY ROCKS. 
 
 In contrast with primary rocks, which have been formed 
 by one continuous process from a fluid magma, secondary 
 rocks are those which have been formed from pre-existing 
 rocks, and which show by texture or structure, or both, such 
 a derivation ; or they are aggregates of chemical or organic 
 forces through which the weathered or soluble portions of 
 older rocks are gathered into masses. All of these can 
 be distinguished from the rocks already described by the 
 microscope, if not by the eye, though there are transitions 
 in certain cases that will be impossible to classify without 
 the microscope. 
 
 The tendency in nature is to stable compounds. The 
 rotting of vegetation and the decay of nitrogenous bodies 
 are paralleled in the " weathering " of rocks. In all these 
 there is a change from a less to a more stable compound, 
 and, be the process short or long, there will ultimately be 
 reached a compound stable under a continuation of the cir- 
 cumstances which formed it. These circumstances do not, 
 however, remain continuous, and the constant variations in 
 nature tend to new combinations. A good example is seen 
 in the action of the oxides of iron. Most waters after soak- 
 ing through the earth's crust, especially in volcanic regions, 
 have minute percentages of sulphuric acid, which dissolves 
 whatever protoxides of iron are met with and carries the 
 solution into the bodies of water on the earth's surface. 
 The protoxide at the surface of the water becomes hy- 
 
 255 
 
256 MANUAL OF LITHOLOGY. 
 
 drated sesquioxide, which is no longer soluble in the acid, 
 but falls to the bottom of the liquid to take oxygen to what- 
 ever organic bodies may be there, and, being reduced, is 
 again soluble and brought to the surface, to renew the oper- 
 ation. This is but a short cycle of changes ; others may 
 require centuries to complete. In the previous pages min- 
 erals have been noted as undergoing " alteration " and form-- 
 ing " secondary " minerals, and these, in their turn, have 
 been broken up to make more stable forms as the black 
 bisilicates pass through viridite, epidote, carbonates, opa- 
 cite, or ferrite, to form ferruginous clays ; while feld- 
 spars, through other lines of alteration, form lighter clays. 
 Quartzose rocks, after the weathering and levigation of 
 their unstable compounds, are reduced to " granular" quartz 
 sand. When weathering outstrips denudation, the rocks 
 will have made these changes, or have lost their cementing 
 media to great depths, as in Brazil, where the elder Agassiz 
 reported weathering at a depth of 150 feet. Incipient 
 weathering proceeds to great depths even in temperate lati- 
 tudes, as Gallon states that in Europe it is usually necessary 
 to strip away 80 feet of slate outcrop before finding work- 
 able stone. This is for unglaciated regions ; but in the slate 
 belt of Pennsylvania, which was covered by the furthest 
 and earliest of the ice advances, the average of " mucking " 
 is but 10 feet, and near Treichler's, Pa., workable slate lies 
 directly underneath glacial gravel. Other good examples 
 of the slowness of weathering are shown in the anthracite- 
 coal basins around and south of Hazelton, which were also 
 covered by the earliest ice advance. It is only in these 
 regions that it is profitable to " strip " the surface, and 
 throughout these regions anthracite coal is mined and sold 
 with no covering but glacial gravel. On the other hand, 
 the loss of cementing material proceeds to great depths. 
 In the iron (limestone) ores of the Clinton formation, north 
 
SECONDARY ROCKS. 
 
 of Danville, Pa., the cementing calcite has been removed 
 over large areas for 500-700 feet from the outcrop of the 
 beds, and deeper along the numerous faults that intersect 
 the region. The slight variation in dip of surface and bed 
 makes this average 40-60 feet below the surface, and the 
 removal has been so complete that the bed can be worked 
 with an ordinary pick or hoe, and the overlying shales have 
 lost their consistency and are readily cut with a pick, unless 
 extremely siliceous. We thus see that weathering pro- 
 duces large masses of decomposed rock in place, and a 
 comparison of fresh and weathered rock shows us that the 
 primary rocks have lost their alkalies and soluble acids ; 
 while the quartz and aluminous silicates remain. We must 
 be prepared, therefore, to find these stable compounds pre- 
 dominant in secondary rocks, unless changes have formed 
 new compounds. Denudation tends to remove these ac- 
 cumulated masses and distribute them under water in lakes 
 or along seaboards. The study of orogenic movements 
 shows us that these sediments may be transformed into a 
 new series of " metamorphic " rocks, and that, by similar 
 movements, the primary rocks may be similarly changed 
 without undergoing weathering and denudation. A third 
 class of rocks is formed by chemical precipitates from sat- 
 urated solutions ; but this is inconsiderable in varieties of 
 rocks or bulk. A fourth class is due to the secretive power 
 of organisms ; a fifth to the forces acting on the country- 
 rocks during eruption or orogenic movements, by which 
 comminution is produced, etc. All of these can be grouped 
 under two heads, whether the masses retain their original 
 state of aggregation (subject to minor changes that do not 
 constitute metamorphism), or whether they have been meta- 
 morphosed, as: 
 
 I. Automorphic Aggregates. 
 II. Metamorphic Aggregates. 
 
258 MANUAL OF LITHOLOGY. 
 
 I. AUTOMORPHIC AGGREGATES. 
 
 In this group the changes subsequent to aggregation 
 must be simple and due to pressure without great heat 
 or other non-metamorphic agencies of consolidation. The 
 causes of aggregation are mechanical, chemical, and organic. 
 In each of the classes the predominant force will be one of 
 these three ; but this does not presuppose that either or 
 both of the others cannot enter in a subordinate manner. 
 
 Mechanical Aggregates, Fragmental Rocks. These are 
 formed and gathered by the mechanical forces of nature 
 from the broken (clastic) fragments of older rocks, without 
 predominant chemical or organic action. The forces pro- 
 ducing the comminution and, to a great extent, the aggre- 
 gation are : 
 
 (A) Hydrogenic, or due to water in forcing apart (through 
 frost) the rocks and comminuting the fragments : grinding 
 these during transportation and sorting them. 
 
 (B) Pyrogenic, or due to the eruptive forces which act 
 upon the walls of fissures, or which produce finely commi- 
 nuted fragments of primary rocks. 
 
 (C) Orogenic, or due to the crushing effect of earth 
 movements. 
 
 (A) Hydrogenic Aggregates. 
 
 These can be divided according to the manner in which 
 they were assembled by water, whether by the liquid or 
 solid state, as : 
 
 i. Aqueous, where the assemblage was caused by rain, 
 streams, etc.; and 
 
 (a) Unsorted Debris, where the aggregation is due to 
 rain, melting snow, or the undermining of areas through 
 solution ; 
 
 (b) Stratified Deposits, where the sorting and transport- 
 ing power of water have assembled the mass. 
 
SECONDARY ROCKS. 2$9 
 
 2. Glacial, where the assemblage was caused by ice in 
 the form of glaciers, and by its ablation. 
 
 (NOTE. With the aqueous rocks will be noted the simi- 
 lar forms produced by ^Eolian forces, as they resemble 
 them lithologically.) 
 
 (B) Pyrogenic Aggregates. 
 
 1. Pyroclasts, when the fragments have been torn from 
 the sides of the fissures through which the eruption was 
 made, or formed from the eruptive itself. 
 
 2. Tuffs, when consisting of eruptive ash, which has 
 been subsequently compacted to a greater or less degree, 
 and more or less altered. 
 
 (C) Orogenic Aggregates. 
 
 Oroclastic Breccias, when formed by orogenic move- 
 ments. 
 
 UNSORTED DEBRIS. 
 
 The want of stratification that characterizes these depos- 
 its is also possessed by glacial aggregates, especially the 
 stranded lateral moraines on the sides of valleys, which are 
 accumulations of the same ultimate origin that have been 
 moved further down the valley. The ordinary moraine-stuff 
 can be distinguished from these deposits by the presence of 
 rocks foreign to the neighborhood in the absence of distinct 
 marks of glaciation in the mass. Another unfailing dis- 
 tinction is in the relative freshness of the mass from top to 
 bottom of aj vertical section. Unsorted debris is most 
 weathered at the surface, where atmospheric agents have 
 unrestrained action, and possesses greater freshness towards 
 the bottom of the section, where the solid rock is met with. 
 Glacial accumulations, on the contrary, have been turned 
 over and thoroughly mixed, and the time of accumulation 
 has been small with respect to the rate of weathering of 
 
26O MANUAL OF LITHOLOGY. 
 
 rocks; so that the close of the accumulation finds the mass 
 quite uniformly weathered on a vertical section. If, how- 
 ever, there should have been a long interval between the 
 beginning and end of the aggregation, we shall find the 
 above order reversed, and the freshest material on top. 
 This last state of affairs can be met with in ordinary aggre- 
 gation on a steep hillside, where the " creep " produced by 
 rains or melting snows brings down the slope fragments re- 
 cently riven by frosts to cover older deposits, and there will 
 be a transition from a solid and fragmental top to a softer 
 and more uniform bottom ; but the rough, subangular out- 
 lines of the fragments in a " creep " aggregation cannot be 
 mistaken for the glaciated rocks of a terminal moraine. An 
 old terminal moraine would weather like any other accumu- 
 lation of material ; but on reaching its bottom we should 
 not find the gradual transition to solid rock of similar char- 
 acter, and all the material of the lower layer would not be 
 equally fresh. The study of these varying deposits will soon 
 allow the observer to distinguish between them. According 
 to the amount of movement in gathering the mass, we can 
 distinguish: 
 
 I. Debris in Place. In this case there has been no 
 movement ; the rock has weathered above its own outcrop, 
 and at a rate greater than that of denudation, so that accumu- 
 lation has taken place. The results of such are : 
 
 (a) Sands, as in the case of quartzose rocks. These sand 
 accumulations are of varying values, dependent on the 
 ipurity of the mineral that composes them. Decomposed 
 quartziferous schists, gneisses, etc., are frequently screened 
 to furnish sand for building purposes. The Oriskany sand- 
 stone of eastern Pennyslvania furnishes abundant sands of a 
 high character; the calciferous sand-rock of Chester County 
 in the same State furnishes a milk-white sand ; the Potsdam 
 of New York, and the St. Peter's of the northern Mississippi 
 
SECONDARY ROCKS. 26 1 
 
 basin, also furnish on weathering sands excellent for glass- 
 making. 
 
 Arkose (Brongniart) is a sandstone formed in place 
 from the debris of granite, and is styled " granitic sand- 
 stone," as it contains quartz, feldspar, and mica in clastic 
 grains, and solidified by pressure. It was originally noted 
 in France, and is found on the borders of granitic masses. 
 The Potsdam sandstone at South Bethlehem, Pa., rests 
 against the hornblendic gneiss and granulite of the South 
 Mountain, and its lowest layer shows (for a few inches) 
 an abundance of feldspar. 
 
 (b) Clays, when argillaceous or feldspathic rocks weather. 
 Granites form a sandy kaolin that can be levigated for pot- 
 tery-making; argillaceous limestone loses its calcite and 
 forms brick and terra-cotta clay if quartzose or flinty, it 
 furnishes a poorer article; slate rots to bluish or reddish 
 clays which make good pressed brick ; ferruginous bands in 
 slates and shales are fired for "metallic" paint; the under- 
 shales of the coal beds of the Appalachian area furnish ex- 
 cellent clay for fire-brick. Special varieties of clays have 
 been thus named: 
 
 Bituminous Clay is the decomposed shales of the Trias 
 and Tertiary coals of Europe. Of bluish or blackish gray 
 to black color; it smolders when fired, and burns red. 
 
 Saliferous Clay is from salt shales or marls, and contains 
 much chloride of sodium, often in crystals, as in the Salina 
 formation of the United States, and elsewhere in salt-for- 
 mations. 
 
 Alum Clay is a decomposed " alum shale," and formed 
 by the weathering of the shale and its pyritiferous con- 
 tent. It is common about coal outcrops that are '* bony" 
 and pyritiferous. 
 
 "Mining" is an earthy clay highly charged with carbon 
 that forms when a. coal-bed weathers. The name is a 
 
262 MANUAL OF LIT HO LOG Y. 
 
 miner's term. The same term is also used for any 
 weathered soft clayey rock that can be readily worked 
 with a pick underground. 
 
 Soft Ore is the miner's name for the leached limestone 
 ore of the Clinton formation in the eastern United States. 
 Atmospheric waters have removed the carbonate of lime, 
 and left the iron as a mixture of carbonate, clay and lim- 
 onite which is soft enough to be dug out with the fingers. 
 It extends generally above water-level, and in some cases 
 to one hundred feet below it, in the vicinity of Danville, 
 Pa. 
 
 The secondary rocks formed from debris in place are 
 numerous. All the primary rocks of any great development 
 have their clays and earths formed from the weathering of 
 their masses, and in this earthy or clayey matrix are held 
 angular and rounded pebbles to form their breccias. These 
 latter will be treated later under the head of " Megaclastic 
 Aggregates," as there is very little difference, if any, in the 
 appearance of a breccia formed in place, and inclosed in a 
 matrix of its own rock, and the same when moved a short 
 distance. The rocks forming in place are all characterized 
 by a freedom from inclusions. In many cases the weathered 
 tuff-conglomerates and breccias resemble the debris states 
 of the same rock, as do the weathered tuffs the equally 
 weathered debris ; but the tuffs usually contain bombs, la- 
 pilli, and organic inclusions, especially if they have been 
 aggregated by heavy rains or meltings of large snow masses, 
 while the debris rocks fall over the outcrop and remain free 
 from intermixtures with foreign substances. The following 
 conditions of weathering have been given special names : 
 
 (c) Laterite. This term was originally given to the weath- 
 ering in tropical lands of a primary rock to form a highly 
 ferruginous clay that was soft when dug, but hardened on 
 exposure to the air, and was used, like adobe, for brick- 
 
SECONDARY ROCKS. 263 
 
 making. The tropical climate induces a higher degree of 
 oxidation than does the more northern and cooler one, so 
 that all rocks in hot countries tend to form debris character- 
 ized by ferric rather than ferrous oxides. This has recently 
 been noted in a comparison of the soils in the northern and 
 southern States of the Union. The above term has been 
 extended to include all weatherings in place attended by a 
 high oxidation of the iron content and a further impregna- 
 tion with the same, and we now have the terms sandstone- 
 laterite, granite-laterite, tuff-laterite, etc., for the above 
 conditions in these rocks. In Hungary trachyte-laterite is 
 known by the local name nyirock. 
 
 (d) Wacke. This was formerly used to denote the weath- 
 ered state of a rock poor in silica, and was afterwards ex-, 
 tended to cover all weathered states of rocks by means of 
 the adjective " wackenitic." In Europe this survives in 
 "graywacke," but the term is obsolete here, and Dana ex- 
 presses the state of opinion in saying in his last edition of the 
 41 Manual " " which used to be called gray wacke" 
 
 2. Debris Slightly Moved. These accumulations are 
 found on moderate slopes, and are usually of medium-sized 
 fragments, more or less mixed with local foreign material of 
 different origin, as : 
 
 (a) Loam. A mixture of clay and sand with more or less 
 organic matter (humus) of a loose and earthy nature, and 
 formed from the washings of higher lands through the action 
 of rain or melting snow. In some countries the " black soil " 
 is twenty feet deep, as India less so in eastern Kansas and 
 Nebraska. 
 
 (b) Forest Soil. Here the loam is mixed with stumps and 
 limbs of trees, and accumulations of whatever animals in- 
 habited or died in the region. The amount of humus is 
 much greater than in loam, and the material more porous 
 and irregular in size and character. 
 
264 MANUAL OF LITHOLOGY. 
 
 (c) Dirt-bed. A buried and " fossilized " forest soil, which 
 is distinguished from the sedimentary beds with which it is 
 intercalated by the absence of stratification and the remains 
 of land animals only. 
 
 3. Agglomerated Debris. These accumulations are 
 found at the bottom of high cliffs, near the bottom of steep 
 slopes, and where the tops or sides of openings have fallen 
 from weathering, or been crushed by the removal of their 
 supports, as : 
 
 (a] 6Yz^"-agglomerate, where the scaling of cliffs has heaped 
 at their foot (either above or below water) an aggregate of 
 material of all sizes, from the largest masses to the finest 
 clay. The interstices are filled by subsequent rains and 
 melting snows, so that the lower part is a " giant breccia." 
 This is especially the case where the fall has taken place into 
 water of considerable depth, and thus unaffected by wave 
 action. 
 
 (If) 5/^-agglomerate, where the material has slid down 
 a steep slope gradually. Here the descent has been gradual, 
 and the material is generally of smaller sizes and more uni- 
 formly compact. 
 
 (c) dw-agglomerate, where rubbish has accumulated 
 in a cavern by the gradual falling of the roof, and has been 
 mixed with washings into the cavern, as well as cemented 
 by whatever was held in solution by percolating waters. 
 Under this German authorities name especially 
 
 Haselgebirge. In the salt region of the northern Alps, 
 where agglomerates have been formed with a clay matrix 
 by the caving in of caverns washed out of the rock salt. 
 
 (d] Eruptive-agglomerate, where large blocks have fallen 
 into an old crater or on its slopes, and have been cemented 
 by a new flow from the same crater or an adjacent one. In 
 this case the cemented fragments are universally formed by 
 the weathering of an old lava, and are not pyroclasts. 
 
SECONDARY ROCKS. 265 
 
 STRATIFIED AQUEOUS DEPOSITS. 
 These are accumulations which have been transported and 
 sorted by water, and which are more or less homogeneous 
 in composition. According to the size of the particles, they 
 can be divided into : 
 
 1. Aggregates whose particles can be suspended in or 
 pushed by water moving with slight rapidity, as a river 
 after it leaves the piedmont portion of its course ; or micro- 
 clastic. 
 
 2. Aggregates whose particles are too large to be so 
 suspended or moved ; as megaclastic. 
 
 I. Microclastic Aggregates. These are loose or solid, 
 and may be divided, according to the chemical composition 
 of the materials into : 
 
 (a) Argillaceous. 
 
 (b) Mixed. 
 
 (c) Quartzose. 
 
 ia. LOOSE ARGILLACEOUS AGGREGATES. 
 
 CLAY. 
 
 A compound of kaolin (hydrated silicate of alumina) with 
 silica, iron, lime, magnesia, potash, soda, and varying 
 amounts of impurities, among which may be noted 
 mica and partly decomposed feldspar. It is white 
 when pure, but is colored in shades of yellow and 
 red through brown to black. Pure kaolin and dry 
 clay are not plastic, but generally fall to an impal- 
 pable powder ; when moistened with water, it is more 
 or less plastic ; when fired, it becomes hard and stony : 
 when dry and breathed upon, it gives a characteristic 
 odor (whence the term "clayey " odor), and it adheres 
 to the tongue. 
 
 Silica 40-90; Gr. 1.75-2 ; when heated at 100 C. f 
 2.44-2.47. 
 
266 MANUAL OF LITHOLOG Y. 
 
 These compounds are valuable on account of their plas- 
 ticity, and this, as shown by Cook, depends on their fineness. 
 After strong heating the combined water is driven off and 
 the plasticity is lost, unless finely ground and allowed to 
 stand with water. The color of clay is due to the impuri- 
 ties chiefly iron in the form of protoxide, which is con- 
 verted to the higher oxide by firing. Calcite neutralizes the 
 coloring effect of iron, so that a marly clay will burn to a 
 " cream " color instead of red. Sedimentary clays are found 
 scattered throughout the world wherever deep water and 
 gentle currents prevail. They can be told from glacial 
 clays by their stratification, and the arrangement of their 
 foreign burden in parallel lines and with the longer axes (if 
 unequiaxial) parallel to the stratification. Glacial clays are 
 generally more siliceous, and usually abound in foreign ma- 
 terial of all sizes, and this is arranged haphazard, with no 
 attempt at what has just been described. Clays joint on dry- 
 ing and become friable. A " fat " clay is tough and plastic, 
 and with not much foreign matter ; a " lean " clay is sandy, 
 and therefore " loose " and with little plasticity. We can 
 distinguish : 
 
 1. Kaolin (see under " Minerals as Rocks"). 
 
 2. Pipe-clay, Plastic Clay. A white clay (therefore free 
 from iron) of nearly pure kaolin. 
 
 3. Brick-clay, Tile-clay. An impure clay with a high per- 
 centage of iron (6-8 per cent) used for brick, tiling, terra- 
 cotta. Clay with 90 per cent of silica has been used for mak- 
 ing brick. 
 
 4. Paint-clay. The washings from limonite ores are now 
 used for burning to make " metallic" paint. This is a highly 
 ferruginous clay and is accumulated in settling ponds to 
 which the wash-waters from limonite workings run. It also 
 deposits from mine water. 
 
 5. Fire-clay, with little iron and but traces of the alkalies 
 
SECONDARY ROCKS. 267 
 
 and lime. When the impurities run above 4 per cent, it 
 loses its refractory nature. Silica average 72. 
 
 6. Fuller s-earth. A somewhat greasy, earthy, and soft sub- 
 stance with greasy streak, with light shades of green and 
 brown, that falls to mud on placing in water and is not plas 
 tic. It is found on the Rhine, in Belgium, Saxony, and 
 England, usually as a formation in the Jurassic and Creta- 
 ceous ; but in some cases it is the result of the weathering of 
 gabbro-, hornblende-, and greenstone-schists. 
 
 \b. LOOSE MIXED AGGREGATES. 
 MUD. 
 
 An indefinite term applied to microclasts of varying 
 composition when mixed with much water. In gen- 
 eral it may be defined as an impure clay with abun- 
 dant proportions of fine sand, and whatever material 
 happens to be abundant at the place where it forms. 
 It occurs at the surface of the earth after rain, be- 
 hind dams, in the mouths of rivers that empty into 
 sounds, and where the tide has little scouring effect, 
 etc. When compact, it forms " mudstone." 
 
 In general, this compound has little claim for a place in 
 lithology, but it has been found in the " Bad Lands " of 
 South Dakota, filling dikes by injection from below, as in 
 the case of igneous rock. This is shown by the unstratified 
 state of the filling and the want of arrangement of unequi- 
 axial particles relative to the dike-walls. A mixture of pure 
 clay with much water is also called " mud," as is, in fact, 
 any similar mixture of fine earthy materials. Under this 
 can be placed : 
 
 1. Alluvium. The earthy, clayey deposit from flooded 
 rivers upon low lands, which varies in size of grains with 
 the velocity of the waters. 
 
 2. Silt is the same in origin, but mixed with the finer 
 
268 MANUAL OF LITHOLOGY. 
 
 material carried by low water and deposited on a small scale 
 behind dams, and on a larger one in the mouths of rivers 
 and over broad bays into which they empty. We speak of 
 the " silting " of a river or bay, and refer to the filling of the 
 muddy bottom, and the encroachment of the muddy shores. 
 This is shown on a grand scale along the Atlantic coast of 
 the United States, where the rivers empty behind sandy 
 barriers and where there are broad sounds between the 
 ocean and the land from New Jersey to Georgia. 
 
 3. Loess. An earthy, clayey deposit (frequently cal- 
 careous, with marly nodules) forming unstratified layers in 
 valleys, but, unlike alluvium, of wind-drift origin. This is 
 included with aqueous deposits from its association with 
 and its likeness to them. 
 
 4. Adobe. A similar deposit in the arid regions of the 
 western States of the Union, consisting of calcareous clay 
 mixed with angular quartz grains of great fineness, and folia 
 of mica arranged haphazard. Of wind origin ; unstratified, 
 and used for the making of brick ; hence the names " adobe " 
 brick, " adobe " house. The winds from the Mojave Desert 
 in California bring to the coast an abundance of this fine 
 dust, so that the sun is almost obscured. Similar accumula- 
 tions of wind and muddy wagon-wheels are seen in the 
 buried cities of the East, old Rome being twenty feet below 
 the present city level from this cause. The American 
 " adobe " deposit is from 2000 to 3000 feet thick. 
 
 ic. LOOSE QUARTZOSE AGGREGATES. 
 SAND. 
 
 An aggregate of loose mineral grains (usually of quartz) 
 varying in size from impalpable dust to an eighth of 
 an inch. With the quartz are associated feldspar, 
 mica, dolomite, calcite, magnetite, and (less frequently) 
 other minerals. 
 
SECONDARY ROCKS. 269 
 
 This is the accumulation of the last states of the stable 
 mineral components of rocks, and, though the accumulations 
 are mainly due to water, a large number are due to wind, as 
 in deserts and along sandy shores. The shape of the grains 
 varies, but it can generally be said that the most angular 
 grains are found nearest the origin of the sand, and that at- 
 trition and transportation round the edges rapidly, so that 
 in studying the grains of sand of a peculiar nature from its 
 origin to varying distances along a given line it was found 
 that the greater the distance from the origin the more 
 round the form. In general, it can be said that sands due to 
 weathering and denudation of rocks by ordinary processes 
 are by no means so sharp and angular as those due to glacial 
 action ; and in the case of fine sands and clays of glacial 
 origin there is a decided glimmer to the cloud obtained bv 
 stirring in water that is absent in those of ordinary origin, 
 unless they happen to be quite micaceous, and then the 
 glimmer is pearly rather than vitreous. The following are 
 .some of the more important mineral varieties of sand : 
 
 i. Magnetite-sand. Found in rivers and along the coasts 
 of regions where primary rocks exist. In many cases the 
 sands are worked by magnetic separation for the mag- 
 netite. 
 
 2. Gold-bearing Sand. Found where rocks containing gold 
 have weathered. California, Australia, the Urals, etc., are 
 historical for the amounts of the precious metals thus 
 found. 
 
 3. Diamond-sand. From Brazil, and formed of the debris 
 of itacolumite. This contains also topaz, hyacinth, garnet, 
 -emerald. 
 
 4. Tin-sand is the debris of greisen, and is found most 
 extensively formed at Banca and Billeton, in the Straits of 
 Malacca, and less extensively in Cornwall and other tin* 
 bearing regions, as the Dakota Black Hills. 
 
2/0 MANUAL OF LITHOLOG Y. 
 
 5. Crystal-sand, where the original clastic grains have 
 been built upon by quartz from solutions until a crystal out- 
 line has been formed by what Dana styles crystallinic meta- 
 morphism. This is occasionally found in loose sand, but the 
 process usually compacts the mass into sandstone. 
 
 6. Calcareous Sand is formed on coral reefs and other cal- 
 careous formations, and is usually soaked in so strong a 
 cementing material that, though it can be readily dug with 
 a spade and cut into various shapes, it soon hardens to a 
 solid and somewhat friable rock. 
 
 7. Anthracite-sand. For a short time after the wreck of 
 one of the Philadelphia & Reading colliers north of Minot's 
 Ledge, on the Massachusetts coast, the beach was lined with 
 anthracite sand and gravel, but the wave action soon re- 
 duced it to impalpable powder and it disappeared. It fur- 
 nished a good example of the " rolling " power of water. 
 
 8. Pumice-sand is found on the shores of the volcanic 
 regions of south Italy, the Island of Teneriffe, the lake of 
 Laach, and in other volcanic regions bordering on the water, 
 where the waves can work over the debris and tuffs to form 
 sand. 
 
 (Blown Sand bears to ordinary sand the same relation 
 that loess does to clay, as it is a wind accumulation, and 
 found in deserts and along shores. These are sometimes 
 called jEolian formations.) 
 
 SOLID MICROCLASTIC AGGREGATES. 
 
 These can be grouped under two general heads : those 
 with predominant clay, and those with predominant quartz. 
 The claystones and mudstones gradually shade into one 
 another, and are distinct from the sandstones. These rocks 
 have been cemented together by various media : pressure 
 (with or without heat and moisture), solutions of various 
 compounds siliceous, calcareous, ferruginous, etc. They 
 
SECONDARY ROCKS. 
 
 may be of any color from white to black through yellows, 
 reds, blues, and browns, less frequently greens, depending 
 on the presence of iron, manganese, carbon, etc. 
 
 I. CLAYSTONE. 
 
 A compact and tolerably solid mass consisting of clay, 
 not cleavable, and fracturing readily in any direction ; 
 variously colored. 
 
 This is the hardened sediment called " clay," and not the 
 weathered aggregate of pyroclasts called " tuff." It is dis- 
 tinguished from the slates and shales by its want of regular 
 fracture, as well as its inferior hardness and lower content 
 of foreign admixtures. 
 
 II. SHALE, Argillaceous Shale. 
 
 A claystone which cleaves readily along its planes of 
 stratification, but which shows no slaty cleavage. It 
 is a consolidated clay or mud, and usually gray to 
 black in color, with infrequent greenish, reddish, or 
 purplish shades. 
 
 This is a softer rock than clay slate, owing to the absence 
 of the pressure which in the latter produced cleavage. It- 
 frequently contains folia of mica, abundance of quartz sand, 
 and other impurities that form the varieties named below. 
 It shades into clay-slate in some localities, and into flagstone 
 (by predominance of quartz). The varieties are : 
 
 1. Schieferletten, Rcthelschiefer (Gumbel). This is a 
 variegated shale with a greasy feel ; easily fractured, and 
 carrying a good deal of water, so that it is still somewhat 
 plastic. It is an imperfectly solidified claystone. 
 
 2. Bituminous Shale, with a small amount of bitumen ; 
 of a dark-brown color. This will not burn by itself, and is 
 thus distinguished from the " Brandschiefer," which will. 
 
2/2 MANUAL OF LITHOLOGY. 
 
 3. Carbonic Shale, with more or less carbon intimately 
 mixed with it ; of medium fine-grain ; bedding-cleavage ; 
 shelly, splintery fracture across the cleavage ; black color, 
 and considerable percentage of iron, through the increase in 
 which .it shades into " black-band " ironstone. It occurs as 
 41 partings " in coal-beds, and burns fiercely in culm-banks, 
 as its porosity furnishes sufficient air for combustion. When 
 the " cut-off " was dug to isolate the fire in the Butler mine, 
 near Pittston, Pa., the traces of a previous fire were found 
 that had left the masses of the coal pillars intact, but had 
 burned to ash the partings formed of coal shale throughout 
 a large area, and on an average of eight to ten feet from the 
 air. 
 
 4. Micaceous Shale. A sandy shale with abundant flakes 
 of mica found in the coal measures. 
 
 5. ^/ww-shale. A pyritiferous shale associated with the 
 coal, and wherever organic accumulations were sufficiently 
 abundant to reduce the iron slimes in waters carrying sul- 
 phuric acid, by combining their oxygen with the organic 
 carbon or hydrogen. It is usually dark-gray to black, and 
 the pyrite is interlaminated with the clay or aggregated in 
 masses from the size of peas to several feet in diameter. 
 This is readily weathered to form alum-clay. 
 
 III. CLAY-SLATE. 
 
 A compact fissile claystone usually colored dull blue 
 or bright red (also purple, green, brown, and black) 
 with occasional admixtures of quartz and other min- 
 erals. The cleavage is quite perfect with respect 
 to a plane which may or may not correspond to that 
 of deposition, and may be produced by pressure, or 
 by the arrangement of abundant unequiaxial minerals 
 parallel to the plane of deposition. 
 
 Silica 40-75 (average 60) ; Gr. 2.5-2.85. 
 
SECONDARY ROCKS. 2/3 
 
 According to whether the cleavage is irregularly ar- 
 ranged with respect to the bedding plane, or generally 
 follows it, we can arrange the above rocks into two general 
 groups : 
 
 I. ARGILLITE, Clay-slate. 
 
 A rock with composition as above stated, but with few 
 impurities, and with well-developed slaty-cleavage at 
 any angle to the bedding plane. 
 
 This is the ordinary clay-slate, and is generally found in 
 the older formations where beds of clay have been subjected 
 to high pressures. In some cases, and generally in the 
 harder slates, the pressure has destroyed the bedding- 
 cleavage, but in the softer varieties it remains highly devel- 
 oped. In this rock there are few inclusions, and the hard- 
 ness is due solely to pressure. The binding material is 
 usually a small amount of carbonate of lime. 
 
 (a) Roofing Slate. This is dark-colored from carbon, or 
 red from ferrite. It should be free from inclusions, from 
 admixtures of pyrite and other efflorescent minerals, and 
 from sand. 
 
 (b) Ordinary Clay-slate. A variety of the above without 
 the high degree of cleavage necessary for roofing purposes, 
 and with abundant inclusions of other minerals. 
 
 (c) Pinsill, Pencil Slate. This soft variety retains the 
 bedding-cleavage, and breaks readily into long slender 
 prisms used for slate-pencils (whence the Welsh name) ; 
 also found in the Thuringian Forest. 
 
 (d) Black Chalk. A soft and highly carbonaceous clay 
 slate used for marking purposes. Found associated with 
 clay-slate in the Thuringian Forest, Spain, etc. 
 
 (e) Carbonaceous Clay-slate is a transition into the above 
 and into alum shale. 
 
274 MANUAL OF LITHOLOGY. 
 
 (f) Calcareous Clay-slate, where the cementing medium 
 is highly prominent, and forms nodules in the mass, as well 
 as lighter bands. 
 
 The argillites are found in the regions of metamorphic 
 rocks, and pass by regular gradations into the crystalline 
 schists. In the United States roofing slates are found in 
 Vermont and Pennsylvania. In the latter State they occur 
 in the Hudson and Marcellus formations ; mainly in the 
 former. 
 
 2. PHYLLITE. 
 
 A clay-slate with abundant mica, a greater tendency to 
 a crystalline texture, a greater luster, and a larger 
 proportion of microcrysts uniformly scattered 
 throughout the mass ; with cleavage sometimes 
 parallel to the bedding-planes, and due solely to 
 sedimentation. 
 
 This variety includes two dissimilar types : 
 
 (a) Micaceous Clay-slate. A slate cleavable parallel to the 
 bedding planes due to the pressure of the superincumbent 
 mass and to an abundance of folia of mica arranged parallel 
 to the bedding, as is shown by the intercalation of strata of 
 grits and sands in the slate measures. 
 
 (b) Phyllite Proper. A highly crystalline slate ; with 
 perfect cleavage normal to the pressure (or inclined to it, 
 see Becker's experiments) ; with a higher content of mica 
 than that possessed by argillite, and much quartz, chlorite, 
 feldspar, and rutile, and yet retaining the evidences of 
 sedimentation, and not subjected to either regional or 
 contact metamorphism, as far as the formation of " contact " 
 minerals. The foreign minerals may have entered the mass 
 as sediments from older rocks, or as crystallizations due to 
 the pressure which produced cleavage. Argillite shades 
 
SECONDARY ROCKS. 
 
 into phyllite, and the latter may be taken as the intermediate 
 state between argillite and argillaceous mica-schist. In 
 general phyllite can be told from argillite by its higher 
 luster. Many authorities class phyllite with the meta- 
 morphic schists on account of the content of crystalline 
 minerals ; but Geikie states that no line can be drawn be- 
 tween them, and Dana places them together. 
 
 SOLID QUARTZOSE MICROCLASTIC AGGREGATES. 
 SANDSTONE. 
 
 A rock composed of consolidated sand of any kind. Ac- 
 cording to the predominant mineral, we may have 
 siliceous, granitic, micaceous, feldspathic, calcareous, 
 etc., varieties. 
 
 Sandstones vary in regard to their cementing medium. 
 It is generally siliceous or argillaceous ; but, as in the Oris- 
 kany sandstone of eastern Pennsylvania, it is calcareous, and 
 a short exposure to the weather causes the bands with this 
 cement to crumble to sand. In many cases beach sands with 
 a large content of shell fragments are more or less con- 
 solidated from the solution of the shells by meteoric water. 
 Infiltrations of ferruginous solutions usually cement the 
 lower layers of sand that rest against a non-porous medium 
 with hydrated sesquioxide of iron, to form a ferruginous 
 sandstone, in case the amount of iron is small ; if large, a 
 siliceous limonite is the result. As sandstones are sediment- 
 ary deposits, they are stratified ; but the conditions of 
 deposit may have been such as to permit one series of forces 
 to act during a long period, so that the deposit for the 
 period was uniform, and the layer of rock of great thickness. 
 A succession of long and uniform intervals will produce a 
 thick-bedded rock; of short periods, a thin-bedded rock; and 
 of very short periods, a laminated rock. Sandstones, accord- 
 
276 MANUAL OF LITHOLOGY. 
 
 ing to the nature and strength of the cementing medium, are 
 compact, friable, and incoherent. Some of the varieties are : 
 
 1. Ferruginous Sandstone, where the cementing medium 
 is iron with a varying amount of clay. According to the 
 form of this element we have : 
 
 (a) Red Sandstone, where the anhydrous oxide is pres- 
 ent. Dana says that this form of oxide is due to the 
 heated condition of the waters in which the sediments 
 were deposited. 
 
 (b) Yellow Sandstone, where the hydrous oxide is pres- 
 ent. Both of these are taken as evidence of scarcity of life 
 in the area of deposition, or the organic aggregates would 
 have been oxidized at the expense of the sesquioxides, and 
 they would have been reduced to protoxides, and, as such, 
 would not have colored the stone. 
 
 2. Argillaceous Sandstone is where the cement is clay, and 
 this can be recognized by its odor, as stated under " Clay. " 
 
 3. Calcareous Sandstone, where the cement is carbonate 
 of lime, as in some bands of the Oriskany sandstone, noted 
 above. 
 
 4. Siliceous Sandstone, where the cement is silica. 
 
 5. Grit A sandstone where the grains are sharp and of 
 the largest size (one-eighth of an inch). 
 
 6. Flagstone. A thin-bedded stone easily capable of being 
 split parallel to the bedding, and furnishing large slabs for 
 paving and flagging. This is sometimes called laminated, 
 and some authorities state that the tendency is due to minute 
 particles of mica. The slabs have evidently possessed an 
 incipient tendency to separate in the mass, as their faces are 
 frequently covered with dendritic markings, as are the joint 
 faces of other rocks. 
 
 7. Micaceous Sandstone. A rock with much mica. The 
 micaceous sandstones of the anthracite-coal measures of 
 Pennsylvania carry a large mica content, as well as a large 
 
SECONDARY ROCKS. 2/7 
 
 percentage of carbon, and their tendency to split in thin 
 laminae is due to the mica, which shows readily in silvery 
 folia against the black background. It is also called fissile 
 sandstone. "Ganister" belongs here. 
 
 8. Freestone. This term is applied by quarrymen to any 
 stone that breaks equally well in all directions. The " brown- 
 stories " used in facing buildings in the eastern United States 
 are examples of this variety. 
 
 9. Kaolin-sandstone, with kaolin as a cementing medium. 
 A rare stone, found in the Thuringian Forest, and from its 
 refractory nature used for lining furnaces. 
 
 10. Asphaltic Sandstone, where asphalt is a cementing 
 medium. Of limited occurrence in Europe. 
 
 11. Crystal-sandstone, where the grains have been fur- 
 nished with crystal planes and terminations by crystallinic 
 metamorphism. These occur in the older sandstones. 
 
 12. Buhrstone. A highly siliceous and cellular rock 
 found in the Tertiary of Paris, and extensively worked for 
 millstones. Also found in South Carolina. 
 
 13. Dike-sandstone. This is the unstratified filling of 
 dikes in various rocks which have been filled in the usual 
 way by injections from below, as the unequiaxial minerals 
 are arranged haphazard without any relation to the dike- 
 walls or the horizontal plane. 
 
 14. Feldspathic Sandstone is found near granitic out- 
 crops. The lower portion of the Potsdam sandstone at 
 South Bethlehem is somewhat feldspathic. A greater 
 amount of this mineral would form arkose. 
 
 SAND-ROCK (Dana). 
 
 A rock made of sand of any kind, especially if not sili- 
 ceous or granitic. 
 
 In this rock the predominant mineral is not quartz, but 
 
278 MANUAL OF LITHOLOGY. 
 
 .a small amount of quartz may enter without placing the 
 compound among the sandstones. As varieties are : 
 
 1. Calcareous Sand-rock is made of comminuted corals, 
 shells, etc. 
 
 (a) Coquina (Spanish local name) is the shell rock of 
 Florida, which is soft when excavated, but soon hardens, 
 as seen in the old walls and buildings of St. Augustine, Fla. 
 
 2. Glauconite Sand-rock, when composed of grains of 
 green earth and quartz. 
 
 3. (Arkose has already been noted on p. 261. It is a com- 
 pound of feldspar, quartz, and varying amounts of mica, and 
 is found at or near the outcrops of granite or gneiss.) 
 
 4. Serpentine Sand-rock is found on the Isle of Rhodes, 
 as the result of the alteration and weathering of a basic vol- 
 canic rock. 
 
 MEGACLASTIC STRATIFIED DEPOSITS. 
 
 These deposits are composed of materials usually greater 
 than \ inch, and are collected by flooded and torrential 
 streams, and energetic wave action. The deposits are dis- 
 tinguished by the shape of their materials, and upon this 
 shape depends the length of time during which they were 
 being assembled and the name by which they are known, as : 
 
 Breccia. 
 
 Angular fragments of minerals or rocks firmly ce- 
 mented together by some matrix or binding medium. 
 Brecciola (Brongniart). 
 
 A breccia composed of small fragments. 
 Conglomerate. 
 
 A rock composed of rolled pebbles or stones cemented 
 
 in any manner. 
 Pudding-stone. 
 
 A conglomerate with rounded stones (Dana). 
 
SECONDARY ROCKS. 
 
 Gravel. 
 
 A loose and uncemented accumulation of rolled stones 
 
 and sand of moderate sizes. 
 Shingle. 
 
 An accumulation similar to gravel, but of larger stones 
 
 and without sand. 
 Hard-pan. 
 
 An accumulation of any of the above forms sufficiently 
 cemented to break in masses, but readily broken up 
 with the pick or bar. 
 
 The above rolled varieties are mainly of quarts, as no 
 other mineral can last under the strong grinding induced by 
 such powerful and long-continued forces. The breccias may 
 be formed of any of the foregoing rocks. Conglomerates 
 are consolidated shingles and gravels, and the latter are 
 found where strong currents would sweep away the sands 
 and roll the larger fragments. Breccias are found near the 
 outcrops of the rocks from which they have been broken. 
 The greater the distance of transportation the greater the 
 loss of angular contour and the more the rounding, as well 
 as the greater per cent of loss from abrasion, so that only the 
 hardest rocks reach the accumulations of gravel and shingle, 
 or remain there long, and the quartz rocks and siliceous 
 porphyries alone resist the combination of grinding and 
 weathering to which such aggregates are subjected. The 
 classification of conglomerates and breccias has been 
 abandoned by most authorities on the ground that both the 
 material of the angular or rolled fragments and of the ce- 
 menting matrix should be considered. The latter may be 
 argillaceous, calcareous, ferruginous, or siliceous, and the 
 fragments of any rock may be bound by any one of the 
 above, or by a weathered portion of the same rock. These 
 rocks will be distinguished from pyroclastic and oroclastic 
 breccias and conglomerates by their cementing media. It 
 
28O MANUAL OF LITHOLOG Y. 
 
 is proposed to classify all conglomerates and breccias, ac- 
 cording to the cementing media and the material of which 
 they are composed, as follows : 
 
 I. The cementing medium is of the same nature as the 
 included fragments (either fresh or weathered) and formed 
 by ordinary agencies. For such rocks the terms " quartz" 
 conglomerate, " quartz " breccia, " trachyte " breccia, " por- 
 phyry " conglomerate, " slate " breccia, " limestone " con- 
 glomerate, will be used. These are <#m-breccias and 
 conglomerates. 
 
 II. The cementing medium is different from the inclosed 
 fragments, and may be : 
 
 (a) Siliceous. A breccia with this matrix and trachyte 
 fragments will be a " siliceous " trachyte breccia, etc. 
 
 (b) Calcareous. A conglomerate with this matrix and 
 diabase fragments will be a " calcareous " diabase conglom- 
 erate. 
 
 (c) Argillaceous. This will furnish " argillaceous " lime- 
 stone conglomerate, etc. 
 
 (d} Ferruginous. This will give " ferruginous " quartz 
 conglomerate, etc. 
 
 GLACIAL AGGREGATES. 
 I. MEGACLASTIC. 
 
 There is but one group under this head where all the 
 fragments are of large size, and that is of 
 
 ERRATICS, Perched Blocks. 
 
 Large masses of rock moved from their original position 
 by a glacier, and left by its ablation scattered over 
 mountain and valley along the line of its motion. 
 
 These are found abundantly over New England, and the 
 upper tier of the middle and western-central States. In some 
 places they are as large as a house, and are left, in many 
 
SECONDARY ROCKS. 28 1 
 
 cases, so delicately poised on top of other rocks (on which 
 they are ''perched") that they can be moved by the hand. 
 They can be distinguished from the country-rock by their 
 difference in composition. In the preceding pages notes 
 have been made of the occurrence of varieties of rocks as 
 " bowlders," " blocks," etc., of this origin. 
 
 II. MIXED Glacial Aggregates. 
 
 The majority of glacial deposits due to ice alone are 
 found under this head ; the distinguishing characteristic 
 being a heterogeneous unstratified mixture of all sizes of 
 material from the finest rock-meal to fragments as large as 
 a house. This is generally termed moraine-stuff, and it can 
 be separated according to its origin and mode of formation 
 into : 
 
 i. Lateral Moraine-stuff. This was originally a " cliff " or 
 " slope agglomerate " which had settled on the side of the 
 moving glacier, and was transported with little or no abra- 
 sion ; so that its particles are as angular as when they reached 
 the ice. In the event of the stagnation and ablation of the 
 ice this fringing string of material will rest along the flanks 
 of the mountain or across the valley where the edge of the 
 ice formerly existed, and it can only be told from local cliff- 
 or slope-agglomerates by the finding of rocks moved out of 
 place, as sandstone resting on granite, granite on limestone, 
 uniformly red rocks resting on uniformly white ones, etc. 
 In a valley its detection is easier. If, however, the material 
 reach'ed the ice-front, it became intermingled with the ma- 
 terial brought in and under the ice. Two glacial affluents 
 meeting in the central glacier would have their adjacent 
 lateral moraines unite in a medial moraine, which, under 
 similar circumstances, would be found along or across the 
 valleys traversed by the ice, and parallel to the lateral 
 moraines. 
 
282 MANUAL OF LITHOLOG Y. 
 
 2. Ground Moraine. This material is formed under the 
 glacier by the grinding- effect of the rocks frozen into its 
 lower portion on the surfaces traversed. The result is the 
 grooving and polishing of both rocks and surface, and the 
 formation of " rock-meal." The ablation of the ice leaves 
 this as the lowest of the glacial formations, and on this falls 
 whatever is carried in or on the ice. This is also called sub- 
 glacial moraine. It usually has a cement of dense clay or 
 rock-meal that incloses rounded and glaciated fragments 
 torn from outcrops covered by the flow of the ice. In case 
 the fragments are unequiaxial they are arranged with their 
 longer axes parallel to the motion of the glacier. Like the lat- 
 eral stuff, it is unstratified and quite compact from the press- 
 ure of the mass of ice. This is also called " bowlder clay." 
 
 3. Terminal Moraine. This is the heterogeneous material 
 brought in any way by the glacier and heaped at its front. 
 It contains all the material described above, and in some 
 cases forms a hill more than 100 feet high and over a mile 
 wide. For a description of the great terminal moraine of 
 the Glacial period see the works of Lewis, Wright, Chamber- 
 lain, Salisbury, and others. (Kames, drumlins, etc., belong 
 to geology, and- not lithology.) 
 
 III. MEDIUM to MICROCLASTIC Glacial Aggre- 
 gates. 
 
 These are caused by the ablation of the ice. It can melt 
 under two general conditions : on a surface that will allow 
 ready discharge of the water, or against a slope that will 
 hold it in a body of varying dimensions ; or, again, it can 
 reach the sea or a lake, and " calve " its bergs upon the 
 surface with their burden of material. The two last cases 
 are practically the same, if we eliminate the distributing 
 effect of tides ; but with tides or currents the results are 
 quite similar. We distinguish: 
 
SECONDARY ROCKS. 283 
 
 1. Aprons, where the ablation is above water, and where 
 the water from the melting ice flows away with its burden 
 down a slight slope. The large fragments remain at the 
 ice-front; but the smaller are distributed in a succession of 
 increments that produce stratification in case the flows vary, 
 or an unstratified aggregate if they remain constant. This 
 gradually thins out on going away from the ice-front, and 
 passes from coarse to fine material, and finally dies out. The 
 characteristic of this formation is the uniformity of the mass 
 on a vertical section. 
 
 2. Slack-water Clay. This is formed by the discharge of 
 the sub-glacial streams into a lake or quiet sea, so that 
 the burden of fine rock-meal is distributed over the bottom, 
 to form a deposit of extreme fineness at a distance from the 
 front, but becoming more sandy and gravely near it. The 
 bergs from the ice-front sail away with their burden of the 
 varying kinds of moraine-stuff described, and, as they melt, 
 they drop into the water their clay, sand, gravel, and 
 bowlders. These in their descent arrange themselves so as 
 to offer the least resistance to the water, and enter the clay 
 at all angles ; so that we can readily distinguish this forma- 
 tion from the " bowlder clay " or "till "-by the want of 
 arrangement of the burden, as well as by the looser state of 
 .aggregation, there being no ice-pressure to consolidate. 
 The Packer clay of the Lehigh Valley, Pa., of this formation, 
 and during the earliest of the ice advances, is in some cases 
 Jifteen feet thick. 
 
 PYROGENIC AGGREGATES. 
 
 (A) PYROCLASTS. 
 
 Fragments formed in any way during any portion of an 
 eruption, and remaining loose or cemented by the 
 eruptive magma. 
 
284 MANUAL OF LITHOLOGY. 
 
 These fragments may be taken from the country-rock in 
 which the fissure was made, from the eruptive rock itself, 
 or from any other eruptive rock. According to their state 
 of aggregation, we can distinguish : 
 
 1. Loose Aggregates, where the fragments after ejec- 
 tion have fallen in loose masses and have not been cemented 
 by any medium. According to their size, we find : 
 
 (a) Blocks. Large and generally solid masses (sometimes 
 eight feet in diameter) ejected from volcanoes. Sometimes 
 these are compact inside and slaggy outside, as if torn from 
 the walls and partly fused ; generally they are angular or 
 subangular, and if round become bombs. 
 
 (b) Bombs, where the fragments are of considerable 
 size, and have been somewhat fused and rounded before 
 ejection, or during their ejection, from their plasticity and 
 the rotatory motion to which they were subjected. Promi- 
 nent among these are the " basaltic " bombs noted in the 
 treatment of primary rocks, which consist almost wholly of 
 olivine or a mixture in which it is predominant. Stelzner 
 reports obsidian bombs from Australian volcanoes i inches 
 in diameter. Masses of slag as large as the head have been 
 discharged from Vesuvius during an eruption. 
 
 (c) Lapilli. Fragments of slag as large as a walnut, and 
 thence to minute sizes, and of various shapes. They are 
 portions of the vesicular mass blown up by the force of 
 eruption, and exhibit a vesicular structure within. 
 
 (d) Ash, Sand, when smaller than lapilli. It consists of 
 the finest dust, as well as megascopic sizes, and (m) shows 
 microliths, glass fragments, and minute crystals. The sand 
 is coarser than the ash, and the series from coarse to fine 
 would read : blocks, bombs, lapilli, sand, and ash. Pozzulana 
 is a loosely coherent sand useful for hydraulic mortar. 
 
 2. Pyroclastic Breccias, Friction Breccias (in part). 
 These can be divided according to the origin of the frag- 
 
SECONDARY ROCKS. 28$ 
 
 merits included, but the matrix in every case is eruptive. 
 These breccias can be distinguished from ordinary ones by 
 the matrix, as in the former the result of aqueous action is 
 here replaced by that of fire. The breccias are named by 
 stating- both fragments and matrix, as before noted, with the 
 exception that the fragments of a rock cemented by a 
 matrix of the same are distinguished from the similar breccia 
 formed by water by prefixing " pyroclastic " (see under (b\ 
 below). The varieties are : 
 
 (a) Where the country-rock is different from the eruptive 
 magma. Here fragments of phyllite or sandstone cemented 
 by eruptive basalt would be " phyllite-basalt " breccia, 
 " sandstone-basalt " breccia. In the same way we would 
 have " granite-quartz-porphyry " breccia, etc. 
 
 (b) Where the first outrush of the magma had its selvages 
 chilled against the walls, and portions of these are torn off 
 by the following rush and solidified with it. Here frag- 
 ments and magma are alike, and we would have a " quartz- 
 porphyry-quartz-porphyry " breccia, or, briefly, as stated 
 above, a " pyroclastic quartz-porphyry " breccia, in distinc- 
 tion from a " quartz-porphyry " breccia formed from debris. 
 
 (c) Where the same or previous eruptions have formed a 
 cone of vesicular lava, lapilli, etc., and subsequent extrusions 
 have filled the crater and burst through the walls to form a 
 breccia with the cinders, lapilli, etc. In this case the name 
 would be as in the last, but the character of the breccia 
 would be different, as the fragments would be more vesicular. 
 
 (ff) TUFFS. 
 
 Aggregates of volcanic ejectamenta of varying size, more 
 or less firmly compacted by the agency of water, and 
 therefore more or less weathered. 
 
 These ejectamenta are the blocks, bombs, lapilli, sands, and 
 ashes just described. On being thrown into the air they 
 
286 MANUAL OF LITHOLOGY. 
 
 fall at distances from the volcano dependent on the force 
 and direction of discharge and the velocity of the wind,, 
 which sorts the material, and carries the particles to dis- 
 tances dependent on their fineness. The classic eruption of 
 Krakatoa sent its fine dusts 50,000 feet into the air, so that 
 they encircled the globe, and remained suspended long 
 enough to produce the peculiar appearances at sunset dur- 
 ing the following autumn. An examination of the deep-sea 
 deposits shows us that volcanic ashes are distributed every- 
 where. This sorting causes a gradual transition from the 
 coarse material at the foot of the volcano to the finest mate- 
 rial at a distance, with a corresponding diminution in amount 
 of sediment, and a corresponding increase in the proportion- 
 of foreign admixtures. The ejectarnenta may fall under two- 
 general conditions : on land or into water. Falling on 
 land they may accumulate as a dry, loose dust, or may be- 
 come mixed with the condensed moisture that follows an 
 eruption, and fall to the earth as a muddy rain, which will 
 accumulate as a flow of mud that covers the low lands at 
 the mountain foot, as was the case with Pompeii. The dry 
 dusts remain until a heavy rain or the melting of deep snows 
 forms with them a thin mud which flows in a similar man- 
 ner, but, in this case, bears with it whatever may have accu- 
 mulated on the surface during or since the deposit ol the 
 dust, such as portions of vegetation, etc. In either case 
 these flows form regular strata and exhibit a " pseudo- 
 fluidal" structure (the migration structure of Giimbel), and a 
 section will exhibit compact, sandy, conglomerated, and 
 brecciated states, with inclusions of foreign organic and in- 
 organic material (leaves, stems, trunks, pebbles, etc.). In 
 case the volcano be near a lake or the sea the ejectamenta 
 will form a uniformly pure stratified deposit on and below 
 the adjacent shore, and this will become intermixed with 
 foreign sediment at greater distances, so as to form a gradual 
 
SECONDARY ROCKS. 28/ 
 
 transition from tuff to sediment, and both would inclose fos- 
 sils of the period. Miigge proposes the term tuffite for 
 automorphic tuff sediments, and tuffoid for similar regional 
 metamorphic sediments (provided that it is regional and not 
 contact metamorphism). Weathered tuffs resemble, when 
 of fine grain, weathered debris in place, but a distinction 
 can be made, as with tuffs foreign inclusions just noted, and 
 bombs, lapilli, etc., are the rule ; with debris in place, the 
 exception. Laterites form from tuffs as from rock in place, 
 and through the same causes. As tuffs are peculiar to vol- 
 canic rocks, their association with old eruptives, which are 
 now known as intrusives, proves that they reached the sur- 
 face, and that their surface deposits were similar to those of 
 active volcanoes. Separating these into tuff, tujfite, and 
 tuffoid, the following varieties have been noted : 
 
 I. TUFF. 
 
 Accumulations of volcanic ejectamenta on land, more or 
 less solidified by rain and surface water. 
 
 (a) Quartz-porpkyry-tuft, Porphyry-tuff, Felsite-tuff, Feld- 
 spathic Ash (Jukes). An earthy, clayey, and usually com- 
 pact " claystone," colored from snow-white through shades 
 of yellow and green to brown and bluish, and inclosing 
 crystals of quartz and mica, and fragments of organic 
 bodies. Silica 75-80 ; Gr. 2.62-3.02. Found in Alsace, 
 Saxony, China, and abundantly in Wales. It passes over 
 into the debris conglomerates and breccias of the rock. 
 
 (b) Rhyolite-tuft. is abundant in Hungary and Nevada. 
 
 (c) Rhyolite-perlite-tuft is found with rhyolite-tuff. 
 
 (d) Rhyo lite-pumice-tuft is extensively developed with 
 rhyolitic extrusions. 
 
 (e) Trachyte-iuft. occurs as a fine earthy mass of light 
 colors in Hungary, Italy, and other trachyte regions, and 
 
288 MANUAL OF LITHOLOGY. 
 
 carries impressions of plants, etc., and as secondary products 
 wood- and precious opal. 
 
 (f) Trass (Rhine), Pausilippo (Sicily), Tosca (Teneriffe), 
 Moja (South America), are tuffs formed from mud-streams 
 due to rain and melting- snow, and contain a high content 
 of foreign inclusions. They are all rhyolitic or trachytic in 
 their composition, and are local names of the same forma- 
 tion. 
 
 (") PhonoKte4.\& is found in France, Bohemia, etc., near 
 the phonolite extrusions, and /?#te-phonolite-tuff occurs at 
 the lake of Laach. 
 
 (h) Andesite-\.\&. From Santorin, the Andes, etc. 
 
 (i) Mica-porphyrite-\.\& is reported from Italy. 
 
 (/) Diorite-tuft, or what seems to be such, is reported in 
 one extended locality near Badmannsdorf. 
 
 (k) Basalt-\.\&. This is a dirty gray to yellowish brown 
 aggregate of small particles of basalt. It is full of the 
 alteration products from basalt green earth, calcite, zeo- 
 lites, etc., and is extensively developed in basaltic regions. 
 
 (I) Peperino is an ash-gray tuff from the Alban Hills of 
 Italy. The grayish matrix incloses folia of black mica, 
 grains and phenocrysts of augite, leucite, and magnetite, 
 with fresh and weathered olivine. 
 
 (m) Palagonite-\u& (v. Waltershausen). First noted at Pala- 
 gonia, Sicily. It is a glassy basalt with much included 
 water, and is caused by the action of hot water on the 
 molten rock. Some authorities describe the rock as due to 
 a discharge under water. It is compact and amorphous, 
 with pitchy luster ; color yellow to black ; conchoidal to 
 splintery fracture; H. 4.5; Gr. 2.4-2.6, and chemical com- 
 position of basalt. The action of the water has con- 
 verted all the iron present as protoxide to sesquioxide. 
 Rosenbusch has found that the interior of the palagonite 
 fragments, which the original investigator named siderome- 
 
SECONDARY ROCKS. 289 
 
 lane, is a highly ferruginous and waterless tachylite. Palag- 
 onite is found extensively in Iceland, and with it hyalome- 
 /a tie-tuft. 
 
 (n) Mefapkyre-toS. is reported from Germany and Greece. 
 
 (o) Augite-porphyrite-\.\& is reported from the Tyrol and 
 elsewhere. 
 
 (p) Dia&ase-tuR is extensively developed in the Voigt- 
 land, Harz, England, etc. ; of gray to brownish green 
 color. 
 
 All of the above rocks are characterized by the presence 
 of inclusions that point to an origin on land. In 1861 
 v. Richthofen was the first to attempt to separate tuffs 
 according to their manner of deposition and subsequent 
 treatment ; but Miigge, as stated above, was the first to 
 propose names for the varieties formed under water and 
 afterwards metamorphosed, as : 
 
 II. TUFFITE (Miigge). 
 
 A tuff that has accumulated under water and has inclu- 
 sions of marine life, but which has been consolidated 
 by pressure alone, and has not undergone " meta- 
 morphism." 
 
 Not very many types of this rock have, thus far, been 
 reported, as the majority of observers have directed their 
 attention elsewhere, and it is by no means the most easy 
 matter to form the necessary distinction without the exami- 
 nation of a considerable area. Tuffites of quartz-porphyry 
 are reported from Wales, of augite-porphyrite from the 
 Tyrol, and the following rock is probably of this group : 
 
 Pietra Verde. This is found in Italy, southern Tyrol, the 
 Balkans, etc. It is a rock like hornstone, with silica 50-69 ; 
 Gr. 3 ; colored green to dark-green, and splintery fracture. 
 It can just be scratched by steel, and is found among the 
 Mesozoic sediments of the southern Alps. 
 
2QO MANUAL OF LITHOLOGY. 
 
 III. TUFFOID (Miigge). 
 
 A tuff or tuffite altered by regional metamorphism. 
 
 This can only be told from the foregoing by the micro- 
 scope in hand specimens ; but in the field it will be found 
 associated with metamorphic rather than sedimentary rocks* 
 Under this seem to fall 
 
 (a) Schalstein. This is a metamorphosed diabase-tuffite, 
 and is found extensively developed in Nassau, Devonshire, 
 etc. Silica 17-44; Gr. 2.63-2.85. The base looks like a 
 diabase-tuff ; but it is mottled with greenish, gray, and 
 spotted layers of calcite. It is sometimes amygdaloidal, and 
 sometimes contains brecciated fragments of argillite and 
 chlorite-schist. 
 
 (U) G^^-schalstein is reported from the upper island 
 of Japan (Hokkaido). 
 
 IV. SILICIFIED Tuffs, Breccias, etc. 
 
 Tuffs, etc., with their original materials replaced by 
 . silica. 
 
 These are rare occurrences, and have thus far been re- 
 ported from the Black "Forest, Odenwald, in Europe; Sau- 
 gus, Mass., where quartz-porphyries have been thus far 
 found in this state, and in the Sudbury district of Canada 
 in a band of silicified breccia more than forty miles wide. 
 
 OROCLASTIC (CATACLASTIC) BRECCIAS. 
 
 These rocks have been formed on immense scales by the 
 crushing of rocks during orogenic movements. They can 
 be divided into two general classes : 
 
 I. SHEAR-ZONE Breccias, Friction Breccias (in 
 part). 
 
SECONDARY ROCKS. 
 
 Breccias produced by crushing of rocks along fractures, 
 either directly or aided by a lateral movement, and 
 cemented by the comminuted portions formed during 
 the movement, and washed into the interstices; or by 
 infiltration of aqueous solutions, either with or with- 
 out metamorphism of a slight character produced 
 by the heat developed during the shear. 
 
 In many cases, as along the shores of Avalanche Lake, N. 
 Y., the rock of the shear-zone has been metamorphosed ; but 
 where the fragments retain their angularity, the class can 
 be distinguished from other breccias, as follows : 
 
 From pyrogenous breccias of the walls of the country- 
 rock by the nature of the matrix, which is eruptive in the 
 latter and aqueous in the former. 
 
 From pyrogenous breccias of the tuff type by the dif- 
 ferences in the included fragments. 
 
 From debris breccias by the greater angularity of the 
 fragments. 
 
 From stratified breccias by the absence of sand and 
 gravel and the general uniformity of the fragments. 
 
 II. REGIONAL Breccias. 
 
 Breccias produced by the crushing of extensive areas of 
 the solid rocks during orogenic movements, with little 
 or no displacement of the crushed portions, and a 
 cementing by infiltration of aqueous solutions, and 
 generally of a calcareous or siliceous nature. 
 
 These are found bordering the regions of mountain ele- 
 vation. A good example is seen in the Siluro-Cambrian sandy 
 limestone of eastern Pennsylvania, along the north flank of the 
 South Mountain, as it exhibits large areas of rock crushed 
 into fragments of all sizes, which have not moved from their 
 places, and retain their lines of sedimentation, but which have 
 
292 MANUAL OF LITHOLOGY. 
 
 been firmly cemented by calcite infiltrations. The spaces be- 
 tween the fragments are usually thinner than a sheet of writ- 
 ing-paper, and the contrast between the various colors and 
 textures of the limestone and its white cement is strong. 
 
 AUTOMORPHIC CHEMICAL AGGREGATES. 
 
 These are the results of the solution of minerals and their 
 deposition by the drying or cooling of the liquid. The sol- 
 vents are waters charged with various acids and of varying 
 temperatures. The theories of the formation of these de- 
 posits belong to geology ; the results can be grouped under 
 two heads. 
 
 I. Aggregates from drying or oxidation. 
 
 II. Aggregates from cooling or saturation. 
 
 1. This class of deposits is by far the greater in number 
 of species and extent of formations. The process has been 
 going on since the beginning of the accumulation of water 
 on the earth's surface. The materials held in solution are 
 various ; but the bulk of the deposits are found to belong to 
 these groups. 
 
 i. Calcareous; 2. Haloidal ; 3. Ferruginous; 4. Aqueous. 
 
 CALCAREOUS DEPOSITS. 
 
 These are mainly of two salts, the carbonates and the 
 sulphates. Under the former are the limestones deposited 
 during early times ; but as these cannot be now told from 
 highly metamorphosed later sediments, there will be no at- 
 tempt to separate the two forms. The other form of lime- 
 stone is shown in stalagmite and stalactite, formed at the 
 (present day wherever caverns exist. The sulphates are due 
 to the drying of saline solutions and the deposit of the lime 
 :salts at an early period, as the solubility of gypsum is very 
 slight. 
 
SECONDARY ROCKS. 2$$ 
 
 (a) STALACTITE and STALAGMITE. 
 
 Stalactites are formations found on the roofs of caverns 
 or other places composed of limestone, or containing lime- 
 stone, as on the under sides of bridge-arches of limestone, 
 or even of sandstone cemented with ordinary mortar. They 
 resemble icicles, and are caused by the percolating water 
 running preferably down certain spots with not too high 
 velocity, The dropping water loses its carbonic acid and 
 also dries, so that its soluble salts are added to the icicle-like 
 form, and it increases in length till it sometimes, as in the 
 Mammoth and other caves reaches many feet. The stalag- 
 mite is formed underneath the stalactite, where the drops 
 have reached the floor, and is an icicle reversed, and growing 
 upwards. The terms do not presuppose that the material is 
 carbonate of lime, as stalagmites and stalactites are found in 
 similar positions and formed of fluorite, barite, chalcedony, 
 limonite, etc., and only the form of the deposit is indicated ; 
 but, as they are found of this composition many times more 
 abundantly than of all the others combined, the terms without 
 other limitations' are usually referred to formations of lime. 
 A section of either shows concentric rings, formed by dis- 
 tinct layers of material, which sometimes vary considerably 
 in color. 
 
 (b) GYPSUM. 
 
 An aggregate of hydrous sulphate of lime ; usually 
 crystalline ; sometimes compact or fibrous ; white 
 when pure, but gray, yellow, brown, and red when 
 impure. 
 
 Gr. 2.32 ; H. 1.5-2. 
 
 Its softness, high content of water, and sulphur reaction 
 distinguish \it from similar-appearing rocks. The gray 
 varieties are contaminated with bitumen, and the other colors 
 are due to iron. As accessories occur pyrite, chalcopyrite, 
 
294 MANUAL OF LITHOLOGY. 
 
 quartz, mica, boracite, sphalerite, galena, halite, dolomite, 
 sulphur, and other minerals to a less degree. Alabaster is 
 a white, granular gypsum, sometimes semitranslucent. 
 
 (c) ANHYDRITE. 
 
 An aggregate of anhydrous sulphate of lime. 
 Gr. 2.8-3 : H. 3-3.5- 
 
 This is told from calcite and dolomite by its failure to 
 effervesce with acids, and from gypsum by its absence of 
 water. It occurs with gypsum. 
 
 Both of these occur with beds of rock salt in lenticular 
 masses. They occur to great thickness (600 feet) in the 
 United States, and gypsum is mined in Michigan, Kansas, 
 New York, Iowa, Virginia, Ohio, Utah, Colorado, California, 
 Wyoming, South Dakota and Texas. From Utah come crys- 
 tals of gypsum weighing hundreds of pounds. An alterna- 
 tion of light and dark layers of gypsum is called tripestone. 
 
 HALO I DAL AGGREGATES. 
 ROCK-SALT. 
 
 An aggregate of chloride of sodium ; when pure, per- 
 fectly transparent and clear as water ; variously col- 
 ored by impurities ; crystalline, fibrous, granular, 
 foliated. 
 
 Gr. 2.1-2.2. 
 
 As a rock, salt is usually impure from gypsum, chlorides 
 of lime and magnesia, clay, etc. The thickest beds of the 
 world are at Stassfurt (1800 feet) and Sperenberg, near 
 Berlin (3600 feet). In the United States rock-salt is found 
 at the island of Petit Anse, La. ; in the region of Wyoming, 
 Genessee, and Livingston counties, N. Y. ; and in Kan- 
 sas, Nevada, Utah, and California. As salt-marls it is 
 found in the Salina formation through New York, Ohio, 
 
SECONDARY ROCKS. 
 
 Indiana, Michigan, and western Ontario. The salt lakes of 
 the United States are noted especially the Great Salt 
 Lake of Utah, which is 75 miles long by 40 wide. Other 
 lakes occur in Utah, Nevada, California, and Texas with 
 salt-formations in their vicinity. 
 
 CARNALLITE. 
 
 An aggregate of chloride of potassium and magnesium 
 with conchoidal fracture and red color. 
 Gr. 1.6. 
 
 In a bed at Stassfurt 100 feet thick overlying the salt, 
 and associated with it at other places. 
 
 FLUORITE, Fluor Spar. 
 
 A crystalline rarely compact aggregate of fluoride of 
 calcium. 
 
 Gr. 3.1-3.2; H. 4. 
 
 This occurs in beds in a few cases ; generally in veins in 
 gneiss, mica-schist, clay-slate, both crystalline and uncrys- 
 talline limestones, and in sandstones. It is often the gangue 
 of metallic ores. It occurs in Cumberland and Derbyshire, 
 England, Saxony, Norway, and Baden. In the United 
 States it is found in the adjacent counties of Pope and 
 Harden in Illinois, and Livingston, Crittenden, and Cald- 
 well, Ky., where it occurs as a vein associated with galena 
 and other minerals. 
 
 CRYOLITE. 
 
 A coarse-grained and thick-bedded aggregate of the 
 fluorides of sodium and aluminium. 
 Gr. 2.95 ; H. 2.5-3. 
 
 This occurs in a huge bed overlaid by granite at Ivigtut, 
 Greenland, in snow-white masses partially transparent and 
 
296 MANUAL OF LITHOLOGY. 
 
 with vitreous luster. It is open-worked, and the opening in 
 1892 was 600 feet long and 200 feet wide and over 185 feet 
 deep. 
 
 FERRUGINOUS AGGREGATES. 
 IRON ORES. 
 
 As the majority of these have been subjected to meta- 
 mo'rphism, and all cannot be grouped under this head as far 
 as origin is concerned, they will be treated under the head 
 of " Minerals as Rocks." In this place it will be only noted 
 that siderite is deposited as carbonate, and in many cases is 
 intimately mixed with limestones and dolomites. The spots 
 of iron soon become oxidized and are deposited as hydrated 
 sesquioxide mud with other sediments, or accumulate in 
 shallow ponds near the sea or lakes, and form lenticular 
 masses of limonite. These by loss of water become hema- 
 tite, or, by partial reduction through organic aggregates, 
 become magnetic oxides. At any rate, the ores as a body 
 are held to have an origin as given, and some authorities 
 state that it is the sole origin. In the first part of this book 
 (under " Gabbro") the ideas of other authorities were given 
 that the primal source of the iron was through igneous in- 
 jections and extrusions from abyssal sources. 
 
 AQUEOUS AGGREGATES. 
 ICE. 
 
 An aggregate of frozen (crystalline) water, granular, 
 compact, schistose. 
 
 It may be formed by the solidification of the atmospheric 
 moisture, as snow, and thence compressed to ice ; or it may 
 form on the surface of water immediately. We can distin- 
 guish : 
 
 (a) Ndvt, Oolitic Ice. A granular aggregate of ice 
 formed on the tops of peaks, where there is a considerable 
 
SECONDARY ROCKS. 
 
 variation in temperature, by the rounding of the individual 
 grains of crystalline snow and their gradual aggregation to 
 form the oolitic grains of the ne've' t or firn, as it is called. 
 
 (b) Glacier Ice. A consolidated neve by compression 
 and the infiltration of water, as the ne"v slides down the 
 sides of the hills. The interior of the glacier ice is crystal- 
 line, in distinction from the granular character of the firn 
 or neve. It is filled with air-bubbles when in small masses,, 
 and these may be full of mud. In large masses it is fre- 
 quently an alternation of white layers full of vertical air- 
 bubbles and blue, dense, and clear layers. 
 
 (c) Water Ice. Formed on the surface of water, and 
 compact ; white or greenish. It may be formed from fresh 
 or salt water. 
 
 (d) Ground Ice. This is where shallow water freezes to 
 the bottom, and thus incloses the stones and finer material 
 of that bottom. It sometimes forms in deep water by the 
 freezing of the lowest layer of water during very cold 
 weather. 
 
 AUTOMORPHIC ORGANIC AGGREGATES. 
 
 I. ZOOGENIC. 
 
 Aggregates produced by animal agency, and accumulated me- 
 chanically by any of the aeollan or aqueous forces. 
 
 II. PHYTOGENIC. 
 
 Aggregates produced by vegetable agency, either grown in place 
 or accumulated as above stated. 
 
 (A) CALCAREOUS. 
 i. LIMESTONE Group. 
 
 A compact uncrystalline aggregate of carbonate of lime ; 
 massive, concretionary, earthy, or hypocrystalline ; 
 colored white, whitish, grayish, bluish, blue, brown- 
 ish, black ; usually with accessory clay or sand, or 
 both. Gr. 2.6-2.8 ; H. 3. 
 
298 MANUAL OF LITHOLOG Y. 
 
 Here will be classed all forms of limestone, whether of 
 chemical or organic origin, as already stated. Most lime- 
 stones are of organic and zoogenic origin, though some are 
 phytogenic. Chemical and zoogenic limestones will be 
 noted together. 
 
 I. ZOOGENIC SECTION. 
 (a) LIMESTONE. 
 
 A compact rock with conchoidal to splintery fracture ; 
 dull ; color generally gray or yellowish blue, green, 
 red, brown, or black. 
 
 It is rare that pure carbonate of lime is found in nature. 
 The iron salts give the rocks red colors; carbonaceous im- 
 purities make them dark ; clay and silica alter their hard- 
 ness and change them from ordinary to hydraulic varieties. 
 The ordinary limestones are compact, especially the recent 
 geological ones ; the older ones are frequently coarse-crys- 
 talline. It is often associated and mixed with magnesian 
 limestone (dolomite), and in some cases the fossils will be 
 dolomite and the inclosing rock calcite (Hunt). Limestone 
 can be told from dolomite by its lower specific gravity, its 
 greater effervescence with acids, and its action when pow- 
 dered and heated on platinum foil (limestone powder heat- 
 ing quietly, glowing, and adhering together ; dolomite 
 powder swelling and becoming loose, or fusing to a slag if 
 clayey). Many limestones appear to be compact rocks and 
 non-fossiliferous on a fresh fracture, but on exposure to 
 weathering the less soluble fossils remain (while the matrix 
 decomposes), and thus obtain a high relief. Other limestones 
 show at once their origin, and are almost entirely composed 
 of fossils, which may be cemented by a compact matrix, or 
 may be loosely held together by porous material washed 
 into their interstices. Pure limestone contains 56 per cent 
 
SECONDARY ROCKS. 299 
 
 of lime. When metamorphosed, limestone becomes marble 
 (q. v.). The inclusions in limestone are varied and numer- 
 ous. The fossils are generally removed in the older rocks 
 by infiltrations which have entirely replaced the body of the 
 fossil, or have more or less fully filled the cavity with crys- 
 tals of different minerals. As accessories are found com- 
 monly quartz, mica, pyrite, lead, sphalerite, chalcopyrite, 
 and sulphur. These occur sometimes scattered through the 
 mass, but usually in nests, strings, druses, geodes, etc., in 
 the cavities, cracks, etc., in the rock. The fact that lime- 
 stone was deposited as a calcareous mud in layers has al- 
 lowed drying and consolidation to form joint planes normal 
 to the bedding planes ; and the further fact that it is readily 
 soluble in water charged with carbonic acid has allowed its 
 ready solution and etching by surface waters, which have 
 thus hollowed it along joint and bedding planes, to form 
 gashes and caverns of varying sizes, and in which the ac- 
 cessory minerals especially the ores noted above could be 
 deposited. Its impregnation by solutions of magnesia has 
 produced many dolomites, and solutions containing sul- 
 phuric acid have formed some gypsums and anhydrites. 
 The varieties are : 
 
 Dolomitic Limestone. This is a porous yellowish to 
 dark-gray stone with considerable carbonate of magnesia in 
 its composition, but not enough to make a pure dolomite. 
 Its specific gravity is higher than that of limestone in pro- 
 portion to the amount of the dolomitic contamination. It 
 is found associated with limestone, and in some quarries the 
 infiltrating solution that has produced the dolomitization 
 has proceeded irregularly downwards, so that portions of a 
 stratum are limestone and other adjacent portions contain 
 magnesia. In the Silurian limestones of Pennsylvania 
 alternate layers in a quarry consist of pure and dolomitic 
 limestone. 
 
300 MANUAL OF LITHOLOG Y. 
 
 Siliceous Limestone. This may have the silica scat- 
 tered throughout the mass to form a harder stone, or it 
 may occur in nests, strings, etc. It sometimes occurs in 
 nodules of chert or hornstone, that appear after slaking 
 the lime, as lumps and sands. This variety is called 
 cherty limestone. It is common in the Siluro-Cambrian 
 limestones of eastern Pennsylvania, near the base of the 
 measures. 
 
 Bituminous Limestone, Fetid Limestone, Swinestone, 
 Stinkstone. This is generally dark-colored, and emits a 
 bituminous odor when struck, heated, or rubbed. Some 
 stones do not show this discoloration when fresh, as the 
 limestone of northern Illinois, which is light-colored when 
 quarried, but after exposure to air and dust becomes 
 mottled with blackish patches. On treating with HC1 a 
 scum of bitumen is left. It belongs to the older geological 
 formations, and is not found later than the Lias. 
 
 Argillaceous Limestone, Marly Limestone, Clayey 
 Limestone. A usually gray rock with light-reddish and 
 yellowish shades ; of dull fracture almost earthy ; some- 
 times splintery ; leaving considerable clay after treatment 
 with HC1. Pyrite is abundant. These are transitions 
 between limestone and marl, and are found on the border- 
 lines between calcareous and argillaceous areas of sedi- 
 ments. In the great valley between the Kitatinny and 
 South mountains in eastern Pennsylvania, the border be- 
 tween the slates of the north and the limestones of the south 
 is occupied by a belt of argillaceous limestone, much of 
 which is 
 
 Hydraulic Limestone. This contains from 10 to 50 per 
 cent of silica, alumina, and iron oxide ; does not slake at 
 all under water, or at least very slowly, and its " setting " 
 is due to a chemical combination of lime and magnesia 
 with silica and alumina. It is always a transition between 
 
SECONDARY ROCKS. 3OI 
 
 a calcareous and an argillaceous formation, and partakes 
 of the characteristics of both, being fine-grained, frequently 
 cleavable, with greater tendency to splintery fracture 
 (like shale), and with an effervescence to show its calca- 
 reous nature. It resembles the shales more than the lime- 
 stones. 
 
 Lithographic Limestone is a slightly argillaceous and 
 siliceous limestone, with an eminently uniform and fine 
 grain ; breaking with a subconchoidal fracture, and ex- 
 hibiting, as a rule, a gray, drab, or yellowish color. It 
 must be porous enough to absorb the greasy compound 
 which holds the ink ; soft enough to work under the en- 
 graver's tool, and homogeneous throughout ; without veins, 
 nests, cracks, or irregularities or impurities of any kind, 
 so that the reagents will act on all parts with equal force. 
 The best lithographic limestone is at Solenhofen, Bavaria ; 
 'but stones are used from many other countries. In the 
 United States it has been reported in Arizona, Alabama, 
 Arkansas, Indiana, Illinois, Iowa, extensively in Kentucky, 
 Missouri, Tennessee, Texas, Utah, and Virginia ; but while 
 small pieces may be found at these localities, the value 
 of the stone is its possessing the above requirements, and 
 its formation in masses of sufficient size. The Arizona 
 stone seems to promise the largest and most uniform 
 pieces. 
 
 Sandy Limestone is a transition between sandstone and 
 limestone which, by weathering, leaves the sand in masses. 
 This is common in the transition beds between the Potsdam 
 sandstone and the Silurian limestone of Pennsylvania, and 
 especially in Center County, where the weathering of the 
 rock has left great depths of sand over the " sandy barrens." 
 The fractured surface of this rock feels harsher than that of 
 limestone, and the sand is left as a sediment on treating 
 with HC1. 
 
3O2 MANUAL OF LITHOLOGY. 
 
 Ferruginous Limestone. A compound of ferric, or hy- 
 drated ferric, oxides and limestone. The iron gives red 
 or brown shades to the rock, dependent on the amount* 
 It is also sandy or clayey. It is not peculiar to any forma- 
 tion, and is found most commonly in the " marbles " of the 
 United States. 
 
 Rotten Stone. A sandy and ferruginous limestone that 
 has lost its lime from leaching, so that the ferruginous fine 
 sand remains. It is used for polishing purposes. It is a 
 porous rock, light, and found associated with sandy lime- 
 stones. The loose calcareous mica-schists of Vermont are 
 sometimes low in lime and mica and high in silica, and these 
 weather to a coarse rotten-stone. 
 
 Glauconitic Limestone. A greenish limestone with abun- 
 dant grains of glauconite. It is found in Europe in for- 
 mations extending from the Trias to the Tertiary, in limited 
 localities. 
 
 Slaty Limestone. This must not be confused with the 
 argillaceous variety, which acquires a cleavage from the 
 clay. In this case the slaty cleavage is due to pressure. 
 It can only occur in fine sediments that have been strongly 
 compressed, and is therefore rare. It occurs at Solenhofen, 
 where the fine-grained rock cleaves so readily that it is used 
 for slating purposes. It is sometimes associated with mar- 
 ble, and formed at the same time, but without the action 
 that metamorphosed the latter. 
 
 Limestones may also be porous, nodular, geodic, cellular, 
 fibrous, stylolitic, brecciated, conglomerated, and earthy ; as 
 well as characterized by the fossiliferous life from which 
 they were formed by comminution of the remains, as num- 
 mulite, ostaea, hippurite, ammonite, encrinite, terebratula, 
 muschelkalk, coral-rag, etc. In distinction from the com- 
 pact forms just noted, these last, characterized by the 
 varieties of animal life, are called shell limestones, coralline 
 
SECONDARY ROCKS. 303 
 
 limestones, encrinal limestones, as they are composed of the 
 remains of mollusca, corals, or crinoids. 
 
 (6) CHALK. 
 
 An earthy limestone, rough to the feel, friable, white 
 (sometimes gray and light shades of other colors), 
 imparting its color to whatever it is rubbed against; 
 of minutely fine and even grain, irregular fracture, and 
 dull surface. 
 
 This is the result of an extensive aggregation of minute 
 animal organisms in the form of oozes at the bottom of the 
 deep seas, so that one million of them are required to form 
 a cubic inch of the rock (Ehrenberg). It is usually pure 
 carbonate of lime, but is frequently marly, and intermixed 
 with the shells of larger animals that have dropped into it, 
 as well as abounding \\\ flints, which will be described later. 
 In some localities on coral reefs the holothurioids and other 
 animals that inhabit the reef form, by digesting the coralline 
 fragments, a fine calcareous dust which solidifies, to make 
 coral chalk. 
 
 II. PHYTOGENIC LIMESTONES. 
 (c] TRAVERTINE. 
 
 A somewhat cellular, and concretionary limestone formed 
 by calcareous waters flowing over a surface, mainly 
 through the agency of conferva-like plants. 
 
 This is the method of origin of a good many travertines ; 
 though there are some due entirely to chemical action, as in 
 the case of stalagmite and stalactite. Travertine is found 
 wherever waters highly charged with carbonate of lime flow 
 over the earth's surface, and sometimes in great masses, as at 
 Tivoli, near Rome, and in this country about the lakes of 
 the Great Basin. The hot springs of the Yellowstone Park 
 
34 MANUAL OF LITHOLOGY. 
 
 have been used as illustrations in all the standard geologies. 
 The travertines can be divided into the shelly or loose sorts, 
 which are almost entirely due to life, and the compact kinds, 
 that are frequently of purely chemical origin. They are of 
 light colors of red and usually yellow, and the dense kinds 
 have a splintery fracture. St. Peter's at Rome is built of 
 travertine. Under this rock come : 
 
 1. Thinolite (King). A crystalline travertine of unknown 
 origin found in the Mono and Lahontan basins of the western 
 United States. It is pseudomorphed after Gay-Lussite. 
 
 2. Mexican Onyx. This is a beautiful compact travertine 
 in soft colors and clouded masses. H. 3.5 ; Gr. 2.75. This 
 misnamed stone was first imported from Algiers; but the 
 exhibit of the Mexican government at Philadelphia in 1876 
 called attention to the great extent of the stone in that 
 country, so that in the United States it goes by the name at 
 the head of the section. It occurs in bowlders of varying 
 size from a few inches up to twelve feet in a tough reddish 
 or dark-brown clay. In one instance (Antigua Salines) it is 
 found in a hard flintlike country-rock that resembles " bastard 
 jasper," in " veins varying from one inch to twelve inches in 
 width" (Merrill). 
 
 (d) TUFA, Kalktuff. 
 
 A light, porous, cellular, earthy, friable limestone, formed 
 by plant-life, and carrying an abundance of foreign 
 inclusions, as leaves, sticks, moss, etc. 
 
 This is of the same nature as travertine, but of still more 
 porous structure. In the Great Basin of the West it forms 
 large masses. 
 
 (NOTE. The names " tuff," " tufa," are variously used by 
 different authorities. They both designate a light, porous, 
 friable aggregation, and some authorities use one word to 
 designate all such, using the adjectives " volcanic " and 
 
SECONDARY ROCKS. 30$ 
 
 " calcareous " to distinguish the two general kinds. In this 
 book the " tuffs " are volcanic, and the " tufas " organic). 
 
 (e) OOLITE, Roestone. 
 
 A limestone composed of minute concretionary spherules 
 from the size of millet-seed to that of a small pea, and 
 resembling the roe of a fish (whence the name). 
 
 This rock was formerly thought to have been formed by 
 concretionary action about grains of sand of any sort in 
 waters charged with lime salts ; but they are now thought to 
 be the result of algae. In the Great Salt Lake of Utah they 
 are now forming as a scum along the shores, though no traces 
 of lime are detected in the waters. It has been found that few 
 of the waters of the earth's surface no matter how high the 
 temperature are without minute forms of life, and to these 
 is due the aggregation of various chemical compounds, the 
 groups above named, for instance, and the similar siliceous 
 ones that will be noted later. The grains of oolite are vary- 
 ing in structure : compact, radial-fibrous, concentric-crys- 
 talline, etc. Oolitic limestone is sometimes composed 
 entirely of these grains, and sometimes they are sporadically 
 scattered through an otherwise compact matrix. The lime- 
 stones of Bath, Portland, Caen, etc., are good examples of this 
 stone in Europe, and in England the Upper Jurassic is called 
 4t Oolite." A larger size of grain makes pisolite, or peastone, 
 where the spherules are as large as peas, or larger. These 
 are found in hot springs carrying a large proportion of sol- 
 uble salts, as at Carlsbad, where the " sprudelstein " forms. 
 
 2. DOLOMITE, Magnesian Limestone. 
 
 A granular, compact, or earthy aggregate of dolomite 
 (with more or less calcite) ; slightly effervescent with 
 cold acid. Gr. 2.87-2.89 ; H. 3.5. 
 
 Pure dolomite or bitter-spar carries 54 per cent of car- 
 
306 MANUAL OF LITHOLOGY. 
 
 bonate of line, and the rest carbonate of magnesia. It 
 usually varies by having a much greater proportion of lime,, 
 and containing a variety of ingredients similar to those in 
 limestone. The differences between the two rocks have 
 been given under " limestone " ; in addition it can be stated 
 that calcite slakes quickly, to form a" hot" lime, while dol- 
 omite slakes slowly, to form a " cold " lime. Many authori- 
 ties hold that all dolomites are alterations in limestones 
 through infiltrating solutions of magnesia. This may be the 
 case, as we do not find travertine or tufa-formations in dol- 
 omite, but oolite is of both. In the Silurian of Pennsylvania 
 alternating limestones and dolomites are found in the same 
 quarry, and Hunt states that dolomite fossils are found in 
 limestones, while v. Richthofen notes that the dolomites of 
 the southern Tyrol are from reef-building corals. It is prob- 
 able that many dolomites are due to the action of magnesia in 
 solution and otherwise, while an equally large number were 
 formed directly from the sea water by animal life, after the 
 analogy of limestone. They occur in all of the older geolog- 
 ical ages, and have many names that do not distinguish more 
 than the fossils. As a rock it exhibits granular, compact, 
 earthy, porous, cellular, brecciated, concretionary, and other 
 forms. In the last the concretions are sometimes as large as 
 cannon balls. It does not exhibit, or, at least, it exhibits 
 very rarely, oolitic, slaty, fibrous, and stylolitic states. 
 
 3. MARL. 
 
 A compound of clay and calcite, or dolomite ; compact, 
 earthy, fissile, usually soft ; crumbles on exposure to 
 the air ; effervesces with acids ; hardness under 3. 
 The proportion of lime salts varies from 20 to 60 per 
 cent. Beyond these on either side the rock does not crum- 
 ble on exposure, and is either clay or one of the limestones. 
 It is usually gray, but also yellow, brown, greenish, bluish, 
 
SECONDARY ROCKS. 3O/ 
 
 violet, and red. It may be named after the geological forma- 
 tion in which it is found, from the fossils it carries, from its 
 states or its impurities. Under the next to the last we have 
 compact, earthy, and shaly marl ; under the last calcareous, 
 dolomitic, argillaceous, sandy, micaceous, bituminous, gyp- 
 seous, glauconitic, shelly, and oolitic. The copper-slate of 
 Mansfield is a bituminous marl carrying chalcopyrite. 
 
 (B) SILICEOUS ORGANIC AGGREGATES. 
 
 I. ZOOGENIC SECTION. 
 I. FLINT, Feuerstein. 
 
 A gray to black, compact, and intimate mixture of amor- 
 phous and crystalline silica ; hardness of quartz ; frac- 
 ture conchoidal ; translucent on thin edges ; occurs 
 principally as nodules in the upper chalk of Europe, 
 where it has been formed by organic agencies. 
 
 The first aggregates are the spiculse of glass sponges, 
 echini, and brachiopods. These on becoming triturated 
 form aggregations into which siliceous solutions penetrate 
 to consolidate them ; or form around them by direct pre- 
 cipitation. 
 
 Chert, Phthanite, is an impure flint which consists 
 sometimes of an aggregate of quartz and feldspar, and some- 
 times of silica alone. It is found especially, though not 
 wholly, in limestones, where it has been formed by similar 
 agencies, as shown by microscopic sections. It is also called 
 hornstone, and much resembles felsite, but is distinguished 
 by its infusibility. It is variously colored, and shows oolitic 
 states. By a considerable admixture of iron it passes into 
 jasper, and, with the addition of clay, to clay ironstone. In 
 both the above the mixture of amorphous and crystalline 
 silica can be detected by treatment with caustic potassa. 
 
308 MANUAL OF LITHOLOGY. 
 
 2. RADIOLARIAN OOZE. 
 
 A deep-sea deposit formed on the bottom of certain re- 
 gions in the western and middle Pacific Ocean by 
 minute animals that secrete silica probably from the 
 clay in suspension in those waters. 
 
 The deepest dredgings (five miles) show that the bottom 
 of this ocean is covered with the skeletons of these animals, 
 mixed with fragments of the spiculas of sponges. Their size 
 is as minute as in the oozes forming the chalk, already noted. 
 
 3. NOVACULITE, Whetstone. 
 
 A probable aggregation of calcareous ooze where silica 
 has replaced the original calcite. 
 
 While some forms of whetstone are slaty from metamor- 
 phic action, and are highly siliceous argillites or phyllites, 
 the novaculite of Arkansas is a microcrystalline aggregate 
 of quartz sand ; porous, and, according to Rutley, formed 
 by replacement of calcite by silica, as the structure (m) is 
 like flint. The Arkansas variety is" snow-white, with con- 
 choidal fracture, and the hardness of quartz. The whet- 
 slates of Europe are either siliceous phyllites of whitish to 
 greenish color (in some localities owing its value to minute 
 crystals of manganese garnet, of which it carries a predom- 
 inant portion of its bulk), or they are siliceous argillites. 
 They occur in Wales, Devonshire, the Thuringian Forest, 
 etc., but in none of these localities do they resemble the 
 novaculite of Arkansas. A coarser oil-stone is found in 
 Orange County, Ind. 
 
 II. PHYTOGENIC SECTION. 
 
 I. DIATOM-EARTH, Infusorial Earth. 
 
 An aggregate of the skeletons of the microscopic plants 
 called diatoms ; whitish, yellowish, light-brown. 
 
SECOND AR Y ROCKS. 309 
 
 This is forming now in the south Pacific Ocean at great 
 depths. It occurs in beds near Bilin, Bohemia, where 
 Ehrenberg estimated that 41,000,000,000 of skeletons ex- 
 isted in one cubic inch. It is also found near Richmond,, 
 Va., Monterey, Cal., Yellowstone Park, etc. As varieties 
 are : 
 
 (a) Tripoli, Polishing Slate. This is a soft rock easily 
 pulverized, and with slaty structure, formed of diatom earth. 
 It is extensively used for polishing purposes, and is divided 
 in Bohemia into two varieties polirschiefer, soft, friable, 
 not adhering to the tongue, and saugschiefer, more solid 
 (from opalizing), and adherent to the tongue. It is found in 
 Nevada. 
 
 (b) Kieselguhr, Infusorial Meal, Diatom Mud (Naumann). 
 This is a finer grained aggregate than the last, and is used 
 as the " dope " for dynamite. It formed great deposits in 
 the Tertiary period, and is found from Chesapeake Bay to 
 Richmond, Va.; also in Nevada, California, Oregon, and 
 Utah. Randanite is the same rock from Algiers and France, 
 as named by Salvetat. 
 
 2. FIORITE, Geyserite, Siliceous Sinter. 
 
 An aggregation of opal silica through the action of con- 
 ferva-like algse. 
 
 At one time the formation of sinter was thought to be 
 due to the drying of the solution ; at another, to its cooling. 
 Through the researches of W. H. Weed it is found that the 
 aggregation is due to a plant that grows an inch in about 
 ten weeks and secretes silica. The deposits are beautifully 
 exhibited on a grand scale in the Yellowstone Park. The 
 rock is of two kinds sinter, compact and hard ; siliceous tufa, 
 less compact. It also forms stalactites on the edges of the 
 basins ; spheres and other forms under the escaping waters; 
 
3IO MANUAL OF LITHOLOGY. 
 
 covers leaves and twig's with incrustations, etc. The color 
 is usually snow-white, also yellowish, grayish, reddish, and 
 bluish, according to the impurities contained. The surface 
 of the deposit is wrinkled, smoothly irregular, etc. The 
 mass is cheesy when first formed, but hardens on exposure 
 to the air. It is found with geysers and silicated springs in 
 Iceland, New Zealand, in great profusion, and as above 
 stated, in the Yellowstone Park. 
 
 (C) PHOSPffATIC ORGANIC AGGREGATES. 
 
 The chief source of organic phosphates is zoogenic, as 
 the amount of phosphoric acid secreted in plants is incon- 
 siderable, and its aggregation is under conditions that de- 
 stroy all traces of its origin. Plants are an ultimate source 
 of the element, as they furnish food for animals, and thus 
 permit the concentration of phosphorus in their bones and 
 excrements, shells, integuments, etc. These during all geo- 
 logical time have been triturated and buried under con- 
 ditions favoring the formation of concretions of phosphoric 
 acid with lime and clay, so that from the beginning of animal 
 life on the earth to the present day there have been aggre- 
 gations of phosphates as impregnated sediments, as nodules, 
 as fresh or fossilized remains, and as excrements. We can 
 distinguish : 
 
 I. PHOSPHORITE (Kirwan). 
 
 An aggregate of phosphate of lime ; compact ; whitish, 
 yellowish, grayish, or brownish. 
 
 Gr. 3-3.2 ; H. 5 and less. 
 
 The " phosphorite " of Kirwan, which included all apa- 
 tites, has been extended to include all compact aggregates 
 of phosphoric acid of any origin. They occur as uniformly 
 disseminated sediments, as nodules in various cements, and 
 
SECOND A R Y ROCKS. 3 I I 
 
 as metamorphosed crystalline aggregates. Here will be 
 treated " apatite," though its origin may be inorganic. 
 
 (a) Apatite. A crystalline, cleavable, granular-massive 
 aggregate of phosphate of lime with either chloride or 
 fluoride of lime. H. (crystal) 5, (massive) 4.5 ; Gr. 2.92-3.25. 
 Luster vitreous-subresinous ; streak white ; color sea-green, 
 bluish green, violet-blue, sometimes white, occasionally yel- 
 low, gray, red, brown usually dull colors; transparent to 
 opaque ; brittle. It occurs most extensively in metamorphic 
 rocks of all ages, and especially in metamorphic limestone. 
 It occurs massive in large veins in limestone of the Lauren- 
 tian near Ottawa, Perth, and Kingston, Canada, where it is 
 mined for fertilizing purposes. A massive, impure, altered 
 apatite, earthy, whitish to grayish color, and resembling 
 lithographic stone, is called osteolite, as its composition is the 
 same as that of bone. It is found in fissures and cavities in 
 dolerite, etc., in Bohemia, the Fichtelgebirge, etc. 
 
 (b) Phosphate Rock. An aggregate of phosphate of lime, 
 with calcite, clay, and other impurities, occurring in beds, 
 and enclosing fragments of shells, bones, etc., in small 
 amounts. It occurs in beds in the Bala limestones of Wales, 
 in the Jurassic of Bavaria, and elsewhere in Europe, and in 
 the Devonian of Tennessee under the Chattanooga shale. 
 The last is bluish black, yellowish, light-gray, full of 
 nodules, shell impressions, arid in some cases resembling 
 air-dried coquina. It also occurs in South Carolina and 
 Florida. 
 
 (c) Phosphatic Chalk. A series of brownish layers in the 
 chalk of Belgium, France, and England where there is a 
 concentration of phosphate, which has replaced the shells 
 of foraminifera. The proportion of phosphate of lime runs 
 as high as 45 per cent. 
 
 (d) Pebble Phosphate. This is a concretionary aggregate 
 extensively developed from South Carolina to Florida as 
 
312 MANUAL OF LITHOLOGY. 
 
 pebbles of varying sizes imbedded in limestone, clay, or 
 sand. The limestone is white and phosphatic ; the clay is 
 marly, and contains, with the nodules, the teeth of sharks 
 and bones of animals, land and marine. The concretions 
 are called by the miners " hard rock," the inclosing lime- 
 stone " soft rock "; " land pebble " is the concretional deposit 
 on land, but when the rock weathers and the concretions 
 are washed into the rivers with sand and clay, the aggrega- 
 tion is called " river pebble." It contains about 26 to 34 
 per cent of phosphoric acid, and is found near the surface 
 in the river beds, and in Florida under a thin covering in 
 the swamps, and is recovered by dredging. The land de- 
 posits are mined and treated by washing. 
 
 2. BONE-BRECCIA. 
 
 An aggregate of fragmentary bones of extinct or living 
 animals, more or less mixed with earth, sand, or lime. 
 
 The "breccia" refers to the fragmentary state of the 
 bones. This is formed on the floors of limestone caverns, 
 either through their having been used as dens by animals, 
 or through the accumulation of bones and other rubbish 
 by streams flowing through the caves or by floods. The 
 dropping waters from the roof furnished lime as an ad- 
 mixture in case the cave was continually inhabited for 
 the accumulations, or, in the event of its remaining vacant 
 for long periods, covered the accumulations with a layer 
 of stalagmite. In a slight degree the cave earths formed by 
 the accumulations in caves through human habitation can 
 be classed here. They will be distinguished by the ad- 
 mixture of charcoal, portions of weapons and utensils, and 
 other indications of human residence. As caves are favorite 
 habitations for bats, their bones are found in the loose 
 calcareous tufas forming in caves of the present period in 
 America. 
 
SECOND AR Y ROCKS. 3 * 3 
 
 3. BONE-BEDS. 
 
 Aggregates of the bones 01 land and marine animals in 
 the older geological formations. 
 
 This is a geological term for the limestone beds of the 
 Rhastic formation in Swabia, Franconia, Thuringia, etc., and 
 in England geologists note the " Lias bone-bed " and the 
 " Ludlow bone-bed." These beds are largely made up of 
 the bones of animals. The South Carolina and Florida beds 
 are also called " bone-beds." 
 
 4. COPROLITE-BEDS. 
 
 Aggregates of the fossilized excrement of vertebrated 
 animals. 
 
 These begin in the Carboniferous formation, with the 
 aggregates of fossil excrement of ganoids, with their scales 
 and bones. The beds become more important as we go 
 higher, and in the Cretaceous they are worked for 'manure. 
 These beds are noted especially in England and Europe. 
 Logan reports a possible occurrence in the Lower Silurian 
 of Canada. 
 
 5. GUANO. 
 
 An aggregate of the excrement of sea-fowl formed on 
 islands in the rainless tracts off the western shores of 
 South America and Africa. 
 
 This is an earthy, white, gray, or yellowish brown ac- 
 cumulation of unpleasant odor. The absence of erosive 
 agents allows the accumulation to reach over 100 feet in 
 many cases, and with it are found inclusions of animal and 
 vegetable life. The islands are the roosts of sea-fowl, and 
 where they form their nests. 
 
MANUAL OF LITHOLOGY. 
 
 (D) CARBONIC ORGANIC AGGREGATES. 
 
 These are all vegetable aggregates, and have generally 
 grown in place, but in some cases have accumulated 
 through other influences. They can be divided into rocks 
 forming a regular series from plant to mineral. All are com- 
 bustible, black or brown, and can be divided as follows : 
 
 Peat, or vegetable matter that has undergone little al- 
 teration. 
 
 Lignite, Brown Coal, containing much bitumen. 
 
 Coal, Soft Coal, Stone Coal, containing much less bi- 
 tumen. 
 
 Anthracite, containing little or no bitumen. 
 
 Graphite, without bitumen, and only combustible under 
 the blowpipe. 
 
 Semibituminous coal and semianthracite are transitions 
 between bituminous coal and anthracite, and meta-anthra- 
 cite is a transition between that rock and graphite. 
 
 In examining the geological record we find that the 
 recent formations are of peat, and the oldest are of graphite. 
 The peats have undergone little consolidating pressure 
 the graphites have been highly metamorphosed. 
 
 I. PEAT, Turf. 
 
 A yellow, brown, or black aggregation of vegetable mat- 
 ter, varying from light and fibrous interwoven states 
 to compact and clayey ones. 
 
 This is a more or less decomposed and chemically altered 
 accumulation of vegetation, dependent on its position in the 
 mass and the age of the same. In old peat bogs that have 
 been undisturbed there is a gradual transition from the light- 
 yellowish or brownish yellow fibrous aggregate of growing 
 moss, through the dead and brown fibrous aggregate slightly 
 below the surface ; the still lower and more compact mass 
 
SECOND A R Y ROCKS. 3 1 5 
 
 with brownish fibers and generally blackish color ; the lower 
 black and still more compact mass with few shreds of fibers, 
 to the compact and creamlike black mass that may be more 
 or less earthy or clayey, from admixtures of sand or clay. 
 The preglacial beds are covered with gravels, and com- 
 pressed into compact and cheesy masses that are compressi- 
 ble with the fingers when fresh, but fracture with a pitchy 
 luster when suddenly strained, and dry to a hard mass with 
 .strong luster. The ordinary peats resemble, when perfectly 
 decomposed, black clays when wet, and varieties of brown 
 coal when dry. Peat can be divided according to the plants 
 from which it was formed, as moss-peat, heath-, grass-, leaf- 
 peat, etc. The states near the bottom of the beds are called 
 mud-peat and pitch-peat, according to their state of ag- 
 gregation, while paper-peat has been compressed strongly 
 enough to cleave readily. As accessories are found limonite, 
 infusorial earth, gypsum, pyrite, and vivianite. The'weather- 
 ing of pyrite forms an iron vitriol, and makes the variety 
 w/r*0/-peat. Peat burns with a strong pyroligneous odor, 
 and gives a brown coloration when boiled with caustic 
 potassa, from the presence of cellulose. When subjected to 
 a pressure of 6000 atmospheres, peat entirely loseslts organic 
 structure, and forms a coal-like mass with brilliant luster, 
 .black color, and great brittleness. 
 
 II. LIGNITE, Brown Coal. 
 
 A brown or black earthy mass, with brown streak, highly 
 inflammable, compact or earthy. 
 
 This is a partially altered vegetable aggregate, com- 
 pressed strongly. It shows traces of vegetation at times, such 
 .as stems with woody fiber, etc. Its specific gravity varies 
 from 0.5 to 1.5, and its carbon content from 55 to 75 per cent. 
 As accessories are found amber, asphalt, gypsum, calcite, 
 pyrite, sphaerosiderite, and numerous organic compounds. 
 
MANUAL OF LITHOLOGY. 
 
 This differs from "soft" coal by its greater content of 
 bitumen, by its pyroligneous odor and its brown coloration 
 of boiling caustic potassa, as well as by its lower specific 
 gravity and hardness. As varieties are: 
 
 (a) Pitch Coal. A brown coal with pitchy or waxy lus 
 ter ; black, compact, and exhibiting the greatest hardness of 
 all the varieties ; without traces of woody structure ; of the 
 highest density and carbon content of the lignites. It occurs 
 in Bavaria. 
 
 (b) Dysodile, Leaf Coal, Paper Coal. Yellowish brown, 
 saddle-colored laminas of the thinness of paper from com- 
 pression, or the presence of numerous leaves from which it 
 was formed. It carries bitumen, infusorial earth, and clay. 
 It occurs near Bonn and elsewhere. 
 
 (c) Moor Coal is a feltlike aggregate resembling turf. 
 
 (d) Bituminous Wood retains the texture of the wood 
 from which it was formed. 
 
 (e) Pyropissite (Kengott), Wax Coal, forms the upper 
 bench (3$- feet) of certain brown coals in Saxony. It is a 
 dark grayish yellow T to yellowish brown plastic mass, with 
 greasy, smirchy character ; easily breaking with earthy 
 fracture ; lustrous streak ; Gr. 0.9 ; lights in the flame of a 
 candle and burns with a clear flame (giving off much 
 steam), and forms a black pitchy mass. 
 
 (/) Needle Coal, from Alsace and elsewhere, is an aggre- 
 gate of acicular elastic blackish-brown particles with greasy 
 luster on fracture. The " needles " are often over seven 
 inches long. 
 
 (The Tertiary lignites of Brandon, Vt., have long been 
 noted for their vegetable remains and especially the fossil 
 fruits. Brown coal is found generally in the Tertiary, and 
 is a transition between peat and coal.) 
 
SECOND A R Y ROCKS. 3 1 7 
 
 III. COAL, Soft Coal, Stone Coal, Pit Coai, Bitumi- 
 nous Coal. 
 
 A compact mass, usually brittle, sometimes with distinct 
 jointing or cubical cleavage, sometimes with con- 
 choidal fracture ; colored shades of black ; streak 
 grayish black to brown ; burns less readily than brown 
 coal, but gives a clear flame ; no pyroligneous odor, 
 but strong bituminous smell ; usually friable. Gr. 
 1.2-1.35. 
 
 This is distinguished from brown coal by its smell and 
 its failure to afford a brown color when boiled with caus- 
 tic potassa. It contains less bitumen than brown coal, but 
 shows in many places aggregates of a charcoal-like substance 
 retaining the texture of wood, and called by the miners 
 " mother of coal." It contains from 75 to 90 per cent of 
 carbon, and carries as accessories pyrite and marcasite 
 {which are seldom absent, and give the red and pink colors 
 to the ash), pyrophyllite as linings of the joints, and others 
 sporadically distributed. This is found extensively devel- 
 oped throughout the world, and especially in the Appala- 
 chian coal-field that stretches from Pennsylvania to Alabama 
 and Ohio, and in large areas, elsewhere noted, in the United 
 States. It has the following varieties : 
 
 (a) Caking Coal, where the mass (whether solid or in 
 powder) fuses and runs together in the fire to form coke. 
 
 (b) Splint Coal, Hard Coal, Non-caking Coal, breaks with 
 conchoidal fracture and in large masses ; is not friable, nor 
 so easily inflamed as the caking coal, but leaves a loose ash. 
 It adheres while burning, but does not leave a strong coke, 
 nor does it fuse together. 
 
 (c) Cherry Coal, Soft Coal, Sand Coal, is a softer coal 
 than the last, and when powdered and inflamed its grains 
 
MANUAL OF LITHOLOGY. 
 
 burn separately and do not coalesce. It has a high resinous 
 luster, is easily friable, and readily inflames. 
 
 The first two form the gas coals, as they are extensively 
 used for its production, and are found abundantly in the 
 Appalachian coal-field. This form of coal can still further 
 be divided, according to texture or other variations, as fol- 
 lows: 
 
 1. Cannel Coal, Candle Coal, Parrot Coal. This is a dull 
 coal at times appearing like black claystone that burns 
 witfi a clear flame like a candle. In Scotland it is called 
 " parrot," from the chattering noise caused by its cracking 
 when inflamed. It breaks with a shaly to even fracture. 
 The more lustrous varieties leave little ash, the duller ones 
 a larger amount. This is found in Ohio. 
 
 2. Torbanite, Bog-head Coal, was a formation (now ex- 
 hausted) in Scotland that carried a large amount of ash and 
 of volatile matter, and was extensively used for gas-making. 
 
 3. Jet is a black variety of brown coal, compact, appear- 
 ing like asphalt, taking a high polish, readily cut and 
 worked, and extensively used for jewelry and ornament. 
 It occurs in small isolated masses in formations later than 
 the Carbonic in Franconia, France, Yorkshire, etc. 
 
 IV. SEMIBITUMINOUS Coal. 
 
 A coal of general appearance like the last, but differing 
 in chemical composition and density. 
 
 It varies from 1.3 to 1.45 in Gr., and has but 12 to 20 per 
 cent of volatile constituents ; while bituminous coal has Gr. 
 1.2-1.35, as above given, and carries more than 20 per cent 
 of volatile matter. Both of these coals smoke when burn- 
 ing, especially at the beginning of the inflammation, and in? 
 this respect differ from anthracite, which burns without 
 smoke or smell. This coal is a transition between the 
 
SECOND AR Y ROCKS. 319 
 
 bituminous and semianthracite coals. In Virginia and 
 North Carolina. 
 
 V. SEMIANTHRACITE. 
 
 A coal with but 6 to 11 per cent of volatile matter, and 
 with Gr. 1.4-1.5 ; luster dull, angular fracture, and 
 hardness less than anthracite. In Pennsylvania, Ar- 
 kansas, etc. 
 
 VI. ANTHRACITE (v. Haidinger). 
 
 An iron-black to velvet-black coal with vitreo-metallic 
 luster; hard and brittle; Gr. 1.5-1.7; conchoidal frac- 
 ture ; volatile matter under 5 per cent. 
 
 This coal is " hard " anthracite, in distinction from the 
 semianthracite. It burns with a short flame, does not 
 easily inflame, and gives no smoke. It is found in south 
 Wales with semianthracites ; but the greatest development 
 is in the Carbonic of Pennsylvania, where it covers large 
 areas, and is worked in fourteen named beds, and many 
 " leaders " of varying thinness. The " anthracites " usually 
 mentioned in other countries are more of the semianthra- 
 cite type. There is no general distinction for this coal, as 
 it varies in appearance in each bed, and in the same bed in 
 different districts, and even in the same mine. The " Mam- 
 moth," " Baltimore," " Jugular," or other names for the (E) 
 or largest bed of the measures, generally maintains an aver- 
 age thickness of 8 yards, and sometimes reaches 38 yards. 
 It has a high luster, and the middle " benches " break with 
 a conchoidal fracture, but the upper bench will frequently 
 exhibit as high a degree of cubical cleavage as in caking 
 coal. The (B) bed, which lies upon the Pottsville conglom- 
 erate, sometimes is a bed 8 yards thick (Nanticoke), with 
 high luster and no partings of slate ; twenty miles to the 
 north it is a 4-yard bed so entirely without luster that its 
 
320 MANUAL OF LITHOLOG Y. 
 
 shipment with other coals has condemned the mixture as 
 " slaty." In this respect it resembles cannel coal in having 
 a high per cent of ash. The principal accessories are 
 pyrite, marcasite, and pyrophyllite, and the presence or 
 absence of the pyrites grades the coals as red or white ash, 
 the former burning to a free ash, the latter to a slaggy 
 mass. The bottom clay of the (F) bed is frequently a 
 " black-band ironstone." 
 
 VII. META-anthracite. 
 
 A metamorphosed anthracite occurring in regions of oro- 
 genic movements; Gr. 1.8-1.9; luster higher and hard- 
 ness greater than in anthracite. 
 
 This occurs in the Rhode Island (Carbonic) coal-field and 
 is found in regions of greatest disturbance. The coal has 
 become partially turned to graphite and will only burn with 
 forced draught. All of the Rhode Island coal is harder and 
 denser than that of Pennsylvania, as it has undergone a cer- 
 tain amount of metamorphism. 
 
 VIII. GRAPHITE, Black Lead. 
 
 A grayish black aggregate of nearly pure carbon ; flaky 
 to granular and compact ; soft, with greasy feel ; in- 
 flammable under the blowpipe ; with metallic luster ; 
 black streak (like lead pencil). Gr. 1.9-2.2. 
 
 This occurs entirely in metamorphic rocks. As acces- 
 sories are silica, clay, oxide of iron, hornblende, mica, apatite, 
 pyrite, rutile, corundum, etc. It is found in Siberia, Bo- 
 hemia, Austria, etc., and in the United States along the 
 Archaean area from New York to Alabama, and in the same 
 area in Massachusetts and Michigan. The principal place 
 is near Ticonderoga, N. Y., where it occurs in a graphite 
 schist, containing 8 to 15 per cent of graphite. It is also 
 worked at Cranston, R. I., in connection with the meta- 
 
SECOND AR Y ROCKS. 32 1 
 
 anthracite coal just mentioned. In the Rocky Mountains 
 graphite beds occur in Albany County, Wyo., Gunnison 
 County, Col. (where it forms beds two feet thick, and very 
 impure), Humboldt County, Nev., Beaver County, Utah, 
 and in the Black Hills of South Dakota. Graphite schist 
 is metamorphic, but it is closely connected with the fore- 
 going, and as it is sometimes found with phyllites, it can be 
 placed with them. 
 
 (E) HYDROCARBONIC ORGANIC AGGREGATES. 
 
 I. ASPHALT, Mineral Pitch. 
 
 A brownish black to black amorphous opaque mass ; 
 strongly smelling of petroleum ; when cold, smooth, 
 brittle, resinous luster and conchoidal fracture ; melts 
 at 90 to 100 C., and burns with a bright flame, with 
 bituminous odor and much smoke ; plastic at ordinary 
 (summer) temperatures; Gr. 1-1.68 ; streak paler than 
 the fractured surface. 
 
 It occurs associated with petroleum as its hardened 
 form, as impregnations in rocks (already noted under lime- 
 stones, sandstones, marls, etc.), and as independent beds. 
 At Seyssel, France, it forms a large deposit, but the most 
 important deposit in the world is the asphalt lake of the 
 island of Trinidad, ij miles in circumference. It also 
 exudes from the ground on the borders of the Dead Sea 
 and in Sicily. In the United States liquid asphalt is found 
 in Ventura County, Cal. An exceptionally pure form is 
 found near Fort Duchesne, in the Uintah Reservation of 
 Utah, under the name of gilsonite or uintaite, which is used 
 almost entirely for varnish. Bituminous sandstones are 
 found in California, Colorado, Kentucky, Utah, and lime- 
 stones in the last State and Texas. The liquid bitumen is 
 full of vegetable remains ; and also carries varying propor- 
 
322 MANUAL OF LITHOLOGY. 
 
 tions of earthy contaminations. It is extensively used for 
 paving and forming the matrix for bricks formed of lime- 
 stone breccia. 
 
 II. OZOKERITE, Mineral Wax. 
 
 A white (when pure), leek-green, yellow, brownish yel- 
 low, or brown amorphous mass ; translucent ; greasy ; 
 melts at 56 to 100 C. ; Gr. 0.85-0.95 ; ordinarily it 
 is soft and plastic and with fibrous fracture. The 
 greenish shades are due to dichroism. 
 
 Its name refers to its waxlike appearance and its foul 
 odor, but some varieties are odorless. It occurs principally 
 in Galicia in Austria-Hungary, and in the United States 
 near Thistle, Utah. The European product is valued at 
 from $800,000 to $1,000,000 per annum. Occurs with 
 bituminous clay, coal, etc. 
 
 III. PETROLEUM, Mineral Oil, Kerosene. 
 
 A thick to thin fluid ; colorless, yellow, or brown ; trans- 
 lucent to transparent. Gr. 0.7-0.9. 
 
 It occurs in rocks of all ages from the Lower Silurian to 
 the present epoch ; most commonly with argillaceous shales 
 and sandstones, but sometimes with limestones. It is found 
 along the western shores of the Caspian Sea, in Italy, Sicily, 
 in mid-Europe, at Rangoon, Birmah, and in the United 
 States in New York, Pennsylvania (especially), Ohio, In- 
 diana, Virginia, Kentucky, Illinois, Colorado, and California. 
 Oil, gas, and salt water are found together in the wells, and 
 when first struck the oil is forced out to great heights by 
 the pressure within, and flows for varying lengths of time 
 till the pressure is exhausted. At the present time the old 
 fields are becoming exhausted. 
 
S CONDA RY RO CKS. 3 2 3 
 
 IV. BITUMINOUS SHALE, Oil Shale, Brand- 
 schiefer. 
 
 Shale containing sufficient oil to allow economic distilla- 
 tion ; pitch-black to brownish black ; affording some- 
 times a greasy streak ; burning in the fire with a 
 bluish flame when lit with a match. 
 
 These shales are filled at times with the remains of fish, 
 and thus show the origin of the oil. They probably repre- 
 sent the shales from which the petroleum now flows, and 
 when that shall have lost its ability to flow the reservoirs 
 will resemble the above shales. These are extensively mined 
 for distillation, though by no means so extensively as before 
 the discovery of petroleum, but after its exhaustion their 
 value will return again. They are found in Scotland, Ger- 
 many, and in the United States, as stated under " Asphalt," 
 especially in California, Colorado, Kentucky, and Utah. 
 
 (F) FERRUGINOUS ORGANIC AGGREGATES. 
 
 NOTE. Microscopic examination shows that many lim- 
 onites and sphaerosiderites are aggregated by diatoms and 
 confervid algae, which separate the iron from the water to 
 form oolite or a fine powder. Some iron ores are, therefore, 
 of organic origin, but, as stated on p. 295, all the ores will 
 be treated as " minerals as rocks," and found on p. 371. 
 
METAMORPHIC ROCKS. 
 
 GENERAL REMARKS. 
 
 Metamorphism is a change in rocks of so incomplete a 
 nature that there remain some traces of the original or in- 
 termediate conditions. Had the change been complete 
 there would be nothing to indicate its occurrence, and we 
 would be justified in calling the rock a primary one. Meta- 
 morphism may be further defined as a change in form, 
 nature, or constitution, or all of them, through combinations 
 of heat, pressure, or interstitial water (with the possible 
 presence of " mineralizing agencies " accompanying intru- 
 sives), and is called local or regional, as it is applied to a large 
 or small area. As far as their results are concerned they 
 are much the same thing (Barrois). Local metamorphism 
 occurs near and is caused by the intrusion of a hot fluid 
 magma. The altered area is called the aureola. On exam- 
 ining it from its contact with the intrusive, where the great- 
 est metamorphism has taken place, to its edge, where it 
 gradually shades into the unaltered rock, we find no sudden 
 changes in alteration where lines of demarkation can be 
 drawn ; but rather a gradual shading of one part into an- 
 other by differences that are less perceptible in the broader 
 than the narrower aureolae. These vary in width from a 
 few inches to four miles, and can be usually divided into a 
 series of bands or zones, which occupy quite proportionate 
 widths of the general belt, and which are characterized by 
 peculiar minerals or forms of alteration. While these 
 aureolae are generally proportionate in width to the bulk of 
 
 324 
 
ME TA MORPHIC ROCKS. 325 
 
 the intrusive, they are not wholly so, as metamorphism has 
 been found to be a matter of heat, and the substances from 
 which the new minerals have been taken are generally 
 grouped within a small fraction of an inch of the spot where 
 the reconstruction has taken place, so that bulk analyses of 
 unaltered and altered rocks show differences mainly due to 
 loss of water and carbonic acid. The heat of intrusive 
 masses of the same mixture may and does vary, as shown 
 by variations in breadth of aureolse ; and while large masses 
 may show them only on one side, a small dike in Bretagne 
 is reported (but four inches wide) of well-crystalline granite 
 and well-defined aureolas. Here the heat increment was 
 supplied by a long flow through the dike-walls. We must 
 place duration of flow, therefore, as a principal agent in the 
 case, as well as bulk of intrusive, and we must not expect to 
 find the most decided metamorphism ahvays about the 
 largest masses of intrusive, but it will vary with the heat of 
 the intrusive, its bulk, the duration of its flow, the composi- 
 tion of the walls, their bedding with respect to the intrusive, 
 and (from these last two) the rate of heat-transmission of the 
 walls. Other metamorphic effects are the bleaching of 
 rocks, their coloration, induration, and the changing of 
 clastic to crystalline texture, while the structure becomes 
 foliated and sometimes parallel-columnar. These can be 
 grouped as mineralizing and caustic. As both are due to 
 heat, their extent is a measure of heat, and the great width 
 of mineralized aureolae about granite is as truly a sign of 
 heat though there be no fusing of dike-walls as the indu- 
 ration of sandstone for a mile from a basalt dike, though 
 there be little or no mineralizing. We all assent to the 
 eruptive nature of basalt ; most authorities to that of gran- 
 ite. The only refuge for those who deny it is to claim the 
 region as a shear-zone, where the shear has furnished heat 
 enough to metamorphose the country-rocks and render the 
 
326 MANUAL OF LITHOLOGY. 
 
 granite fluid ; but this would destroy the dike-walls, and 
 cause that shading of sedimentary to primary which is 
 never found in nature. Granite in dikes is, therefore, erup- 
 tive if it shows a metamorphic aureola and possessed a cer- 
 tain amount of heat, but the valuation of that amount is 
 differently reported. When it was thought that mineralizing 
 was due to the introduction of new elements, it could be 
 claimed that granite was cooler than basalt when erupted, 
 but now that heat does the work, and as all eruptions carry 
 " mineralizing " agencies, it becomes necessary to study the 
 effects of heat on the vapors accompanying eruptions, and 
 the temperatures necessary to fuse the rock classes. Barus 
 finds that basalt fuses at 2250 F., while rhyolite (granite 
 mixture) is viscid still at 3100 F. All authorities agree 
 that the lower temperatures of volcanic effusion are charac- 
 terized by steam, carbonic acid, etc., while the higher ones 
 have HC1, fluoric and boric acids. Steam becomes wetter 
 at low than at high temperatures. Dana well observes that 
 dry heat never could indurate sandstone, but the moisture 
 in the cooler flow of basalt would have its dissolving effect, 
 while the hotter and, perhaps, somewhat disassociated steam 
 of the hotter granitic flow would tend to desiccate rather 
 than fuse, as wood has been charred by impinging steam. 
 It may further be said that granitic outpourings were so far 
 in the past that the internal heat of the earth had desiccated 
 the sediments and rocks, so that there was less interstitial 
 water than in the more recent sediments and rocks through 
 which basalt extruded, and as moisture is a great heat-car- 
 rier, the extent of induration is due to this fact. It is gen- 
 erally allowed that the eurites are a granitic mixture, and 
 the temperature of their fusion is that of granite and rhyo- 
 lite (3100 F.). Cole reports a eurite dike cutting an an- 
 desitic country-rock (fusing at 2520 F.) and melting a few 
 inches of the walls by its greater heat (?), and sending into 
 
ME TAMORPHIC ROCKS. Z 2 7 
 
 this melted selvage a few of its own intratelluric pheno- 
 crysts of pink feldspar, so that the cooled selvage presents 
 the anomaly of a basaltic andesite carrying phenocrysts of 
 pink orthoclase. A reversed example is where granite pyro- 
 clasts are included in eruptive gabbro, and the granophyre 
 fused to a rhyolite with flow structure and spherulites. 
 Here the cooler (?) rock fuses the one solidifying at a 
 greater heat. The results of the study of the action of 
 included fragments seems to show that the amount of solu- 
 tion depends on the dissimilarity of the rocks. Acid mag- 
 mas have little or no effect on acid sediments or acid rocks, 
 basic magmas on basic aggregates; but basic magmas will 
 dissolve acid rocks, and vice versa. We may conclude, 
 therefore, that acid magmas are hotter than basic, have their 
 volatile components heated to the point of association as 
 mineralizers, form large mineralized aureolas, and exhibit 
 little or no dissolving effect because the accompanying vapor 
 is too highly heated for fusion, and further because the 
 ordinary sediments are aggregations of quartz mainly, and 
 with more acid than basic accessories, and therefore are not 
 readily acted upon by acid magmas. Basic magmas, on the 
 contrary, are cooler, have wetter steam and more HC1 than 
 fluoric or boric acids, mineralize slightly, and indurate read- 
 ily, both from their acting upon more moist aggregates, and 
 from the acid character of those aggregates. Owing to the 
 greater exhibition of these effects along the line of contact 
 of intrusive and country rock, local metamorphism is called 
 contact metamorphism, and the same adjective is applied to 
 the results of the change, as contact rocks, contact minerals, 
 contact induration. 
 
 Regional or dynamo metamorphism, on the other hand, is 
 the change produced over wide areas through pressure, 
 heat, and moisture, irrespective of the presence or absence of 
 intrusives. In equally numerous cases these latter may have 
 
328 MANUAL OF LITHOLOGY. 
 
 added their increment (locally) to the change, or have been 
 involved in it. The pressure is dynamic, and not superin- 
 cumbent, and has usually been the cause of the heat. The 
 moisture has been usually interstitial. As the definition of 
 metamorphism requires the retention of some trace of ihe 
 original structure, or some evidence of a change, we must 
 be able to trace these rocks to their original conditions, or 
 find the evidences of alteration. The former is possible in 
 many cases in the field ; the latter is possible sometimes only 
 through the microscope. With a ready escape for water, 
 and with limited heat and pressure, the rocks are freed from 
 volatile components, as gases from soft coal, CO 2 from car- 
 bonates, moisture from sediments, while the particles of the 
 rock are forced nearer one another. Moisture allows crys- 
 tallinic changes, as the rebuilding of the faces on clastic 
 grains, so that sandstone becomes quartzite and limestone 
 marble. Metachemism (Dana) allows the formation of new 
 minerals from aggregates of varying composition in the im- 
 mediate neighborhood. Loss of bedding structure follows 
 and " foliation " is induced, so that the rock is no longer a 
 sediment, but a crystalline schist. These are the same changes 
 that have taken place in contact metamorphism, but applied 
 on a grander scale, by lower heat and therefore during a 
 longer period. Following Dana, the changes may be 
 grouped as follows : 
 
 1. By small amounts of heat: discoloration, drying, con- 
 solidation. 
 
 2. By increasing amounts : crystallization of sediments. 
 
 3. By greater amounts : mineralization. 
 
 These are followed by incipient and (in regional meta- 
 morphism) complete fusion, with results that cannot be told 
 from fusion due to other agencies. The resulting rocks 
 depend on the composition of the mass acted upon as well 
 as its inclosed moisture. Heating dry quartz would make 
 
METAMORPHIC ROCKS. 
 
 no change, but moist sand would become quartzite. Alu- 
 minous sediments from which the alkalies have been leached 
 form aluminous silicates (cyanite, garnet, andalusite), but 
 cannot form mica, which requires alkalies, as does feldspar. 
 Crystallinic" metamorphism has already been noted as re- 
 building the faces of clastic grains. This is shown on a 
 grand scale in the change of clastic limestone to crystalline 
 marble. 
 
 Another series of similar rocks may form on varying 
 scales through the crushing of solid rocks, as shown in a 
 series of gneisses and other crystalline schists on the north 
 shore of Lake Superior. From all these causes there arise 
 rocks metamorphosed from older sediments or solid rocks. 
 Some of them are crystalline ; others crystalline and schist- 
 ose ; others still (as eruptive gneiss) have been heated suffi- 
 ciently to become fluid, but not homogeneous, and have 
 been erupted in this state, as shown by their aureolae. All 
 are equally metamorphic rocks, but there are two grand 
 divisions the schistose, and those merely crystalline and fused* 
 We can, therefore, divide this class into : 
 
 I. Metamorphic crystalline rocks. 
 II. Metamorphic crystalline schists. 
 
 I. METAMORPHIC CRYSTALLINE ROCKS. 
 
 
 
 These are the results of incipient and (generally) of con- 
 tact metamorphism, and begin with the caustic effects of 
 burning coal-beds and of dikes, and extend through the 
 beginning of a crystalline texture in slates to the complete 
 crystallization of limestone through regional metamorphism^ 
 The caustic effects and incipient crystallization Avill be noted 
 in Division (\a\ and the complete crystallization in (I) and 
 Part II. 
 
33O MANUAL OF LITHOLOGY. 
 
 la. CAUSTIC EFFECTS. 
 
 PORCELLANITE, Porcelain Jasper. 
 
 A baked clay, blue, gray, yellow, brown, and red ; spotted, 
 streaked, clouded ; compact, coarse-schistose, slaggy ; 
 conchoidal fracture ; translucent on thin edges ; dull or 
 slightly greasy luster. 
 
 Most authorities describe this as the result of the burning 
 of a clay-bed rich in feldspar by intrusions of trap or the 
 heat from burning coal-beds. Geikie seems to place here the 
 hornstone-like product of an intrusion in argillite. Porcel- 
 lanite is distinguished from both jasper and hornstone by its 
 ready fusibility, and its forming glass when heated with soda. 
 
 METAMORPHIC ARGILLITE. 
 
 The rocks produced by the variations in metamorphism 
 are found most closely associated in contact effects, as in 
 regional metamorphism wide areas are occupied by a 
 variety which may be found occupying a zone of moderate 
 width about an intrusive. Quite similar results are found 
 about various intrusives along the outer zones, the great 
 differences being [found along the immediate contact. This 
 is the case in the examples of metamorphism in other rocks 
 that follow, and in this and the following descriptions the 
 results with a highly acid magma (granite) will be followed 
 by those of a highly basic (diabase) one. The varieties 
 found near the contact are peculiar to contact metamor- 
 phism ; those due to heat alone (moist heat) are found in 
 regional metamorphisms also. Beginning with the outer 
 extremity of the aureola, in this and the following cases, 
 we find in acid contacts : 
 
 (a) Knotty Slate. This has the color of argillite, but in it 
 are small darker knots or spots with indistinct margin which 
 are shown (m) to be incipient staurolites and andalusites. 
 This shades into one of the following : 
 
METAMORPHIC ROCKS. 331 
 
 (b) Staitroltte-s\ate, where the more micaceous slate shows 
 staurolite ; ckiastolite-sl&te, when it exhibits that mineral ; 
 vttrelite slate, with ottrelite ; dipyre slate, with phenocrysts of 
 dipyre. These shade into 
 
 (c) Leptinolite. Here the texture changes and the rock is 
 like hornstone. (m) it is an aggregate of andalusite, stau- 
 rolite, colorless mica, and other minerals dependent on the 
 composition of the intrusive. With intrusive granite this 
 rock shades into 
 
 (d) Cornubianite (of Bonney), when it is a fine-grained and 
 gneissoid compound of quartz, mica, and tourmaline ; or 
 
 (e) Proteolite (of Bonney), when it is a similar compound 
 of quartz, mica, and andalusite. (d] and (e) are hard, com- 
 pact rocks and with their ingredients entirely (m), so that 
 they resemble (M) hornstone, and fall under Geikie's "por- 
 cellanite " above. When andalusite is predominant, these 
 are called andalusite hornstone. In none of these last is there 
 the perfect foliation of gneiss, so that they are better treated 
 here than with that rock. 
 
 In basic contacts the outer zones are similar to the above, 
 but the inner ones are different. As they are alike in 
 phyllites and some shales, all will be described here, and 
 references made under the other rocks to this description. 
 Instead of the leptinolite, above noted, there are two rocks 
 which vary in the arrangement of the minerals, as: 
 
 (c') Spilosite (Zinken). Gr. 2.78. A fine-grained to com- 
 pact and sometimes schistose, feldspathic mass, greenish, 
 with gray or grayish green scales as large as flax-seeds, and 
 weathering to a rusty brown color, scattered through it. 
 The similar state called 
 
 (d r ) Desmosite (Zinken) differs in its density (Gr. 2.81), 
 and in the arrangement of the fresh or weathered spots in 
 distinct bands and layers, so that there is an alternation of 
 white and colored bands. These shade into 
 
33 2 MANUAL OF LITHOLOGY. 
 
 (e f ) Adinole (Lessen). This differs from the above in its 
 possessing a less strongly marked flat-parallel structure. It 
 much resembles halleflinta, but it is much more fusible. It 
 has Gr. 2.71 ; silica 65-80 ; soda 4-10. It is a very compact, 
 felsitic, hornstone-like rock, with conchoid al fracture, and is 
 (m) fine-crystalline. It is colored green, red, and gray, and 
 with the colors banded as in halleflinta. All of these are 
 varieties of " whet-slates." 
 
 These states of metamorphism are found as follows: 
 Knotty slate, chiastolite-, and other slates in New England, 
 Scotland, Wales, Bretagne, Pyrenees ; spilosite, desmosite 
 and adinole in the Harz, and the last also in Bretagne and 
 Wales. 
 
 METAMORPHIC PHYLLITE. 
 
 Taking a similar example of a granite-phyllite contact,, 
 we will find similar zones characterized by similar rocks, the 
 difference being in the greater proportion of mica. Begin- 
 ning with the outer edge, as above, we find 
 
 (a) <Fri**/-slate. This differs from knotty slate in the 
 brownish concretions resembling grains of corn, dried cur- 
 rants, etc. (hence the name). They have a slightly higher 
 luster and seem to be made of talc or mica. The slate itself 
 seems to have a higher luster, or rather glimmer, from the 
 creation of a higher mica content. This shades into a fruit- 
 slate with more mica and chlorite, and this into 
 
 (b) Mica-andalusite-s\2ite, like a similar argillite reaction, 
 but with more mica. This shades into the rock named above 
 
 (c) Proteolite (of Bonney), which is a compound of quartz, 
 mica, and andalusite. 
 
 Some of the stages of metamorphism are represented by 
 other rocks called sericite-phyllite (Lossen), which is a (m) 
 compact, greenish, reddish, or violet sericite-schist ; and mica- 
 phyllite, which is a similar aggregate of mica, compact and 
 
METAMORPHIC ROCKS. 333 
 
 with silky luster. Some granite-phylhte contacts are 
 strongly tourmalinized to form tourmatme-hornstone, and 
 Joiirmatine-schist, which is a schistose state of the tourmaline 
 rock noted under " Granite." The basic contacts with 
 phyllite show somewhat similar states, and with similar 
 names to c r , d 1 ', and e r , under " Argillite," above. Adinole is 
 also a state of metamorphism in shales, and is found as such 
 in the Harz and the Taunus. 
 
 METAMORPHIC SANDSTONE. 
 This is first indurated. The basic intrusives form green- 
 ish colorations ; the granitic whiten and mineralize, so that 
 with the latter we find, as we approach the contact, biotite- 
 quartzite, which shades into sillimanite-biotite-qua.rtz\te, and 
 that to feldspar-biotite-qu.a.r\.z\ie, and these frequently contain 
 garnet. Quartzite and its varieties will be fully described 
 later. Argillaceous sandstones form porcellanite on diorite 
 contacts. The diabase-sandstone (Trias) contact of Rocky 
 Hill, N. J., shows tourmaline. 
 
 METAMORPHIC LIMESTONE. 
 
 The first step is the formation of marble (" marmarosis," 
 Geikie). The crystalline product then acquires lime sili- 
 cates in ordinary limestone, and additional magnesia sili- 
 cates in dolomitic varieties ; such as garnet, vesuvianite, 
 wollastonite, and the others noted under " Marble." At the 
 contact is formed a calcareous variety of the hornstone-like 
 rock above noted, with similar appearance and fracture, 
 called time-st/icate-hornstone. Some included pyroclasts 
 have been altered to a crystalline-granular aggregate of the 
 above minerals with abundant olivine. 
 
 METAMORPHOSED SCHISTS, etc. 
 These are schists and primary rocks that have been met- 
 amorphosed, and not metamorphosed sediments. Dependent 
 
334 MANUAL OF LITHOLOGY. 
 
 on the similarity or dissimilarity of the intrusive, slight or 
 quite extensive changes take place. Acid intrusives make 
 little change, beyond slightly increasing the prominence of 
 certain minerals in acid rocks; while basic intrusives in 
 basic rocks have still less effect. Intrusives of different 
 composition impose on the country-rock slight changes, such 
 as alteration of pyroxene to hornblende in granite-dolerite 
 contacts ; while basic-acid contacts show fusing effects. 
 
 Ib. METAMORPHIC CRYSTALLINE ROCKS. 
 CALCAREOUS. 
 
 MARBLE, Granular Limestone. 
 
 A crystalline-granular aggregate of calcite in equidimen- 
 sional coarse to fine saccharoidal grains intergrown 
 together without druses or pores; variously colored, 
 and with or without accessories. 
 H. 3 ; Gr. 2.7-2.8. 
 
 Marble occurs in beds and lenticular masses between 
 metamorphic schists and as contact deposits with intrusives 
 into limestone. In some cases the process of metamorphism 
 has softened the mass, so that its beds become swollen and 
 appear like dikes, or are squeezed like apophyses into the 
 fissures and cracks of the inclosing schist. The best statuary 
 marbles come from southern Europe, but very good stone 
 is found at Rutland, Vt. The trade name " marble " differs 
 from the above definition in including any limestone of any 
 texture which is susceptible of a high polish and desirable 
 for ornamental purposes. True marbles are found in Canada, 
 New England, eastern New York and Pennsylvania, New 
 Jersey, eastern Maryland, Pickens County, Ga., and Cali- 
 fornia, which are mainly white. Red and reddish marbles 
 are found in east Tennessee, Vermont, Arkansas, Alabama, 
 
METAMORPHIC ROCKS. 335 
 
 Maryland, Missouri, New York, where it has been quarried, 
 especially in the first two states, and is reported from 
 Georgia, Colorado, North Carolina, and Wyoming. Black 
 marble is found in Vermont, New York, Williamsport, Pa., 
 California, Arkansas, and is reported as occurring in Colo- 
 rado, Illinois, Tennessee, and West Virginia. Gray marbles 
 occur in New York, Virginia, Tennessee, and Arkansas. 
 When the great West has been fully explored, there will 
 probably be deposits of this stone in the metamorphic areas. 
 In addition to the colors already noted there are found yellow 
 and yellowish shades, and blue and bluish varieties. The 
 purest white and finest grained marbles in the world come 
 from Carrara, Italy, and Paros, Pentelicon, and neighboring 
 localities in Greece. As accessories in the United States and 
 (J/) are : (i) common accessories, muscovite, serpentine 
 (especially about New Haven, Conn.), scapolite, spinel, talc, 
 titanite, and wollastonite ; (2) less common, in northeastern 
 New York, apatite, corundum, epidote, bronzite, hypersthene, 
 rutile, graphite, chondrodite, tourmaline, actinolite, vesu- 
 vianite, and zircon. At Muscalonge Lake fluorite crystals 
 measuring one foot on a side have been found. These and 
 a few others are found in New England and the eastern part 
 of the Middle States along the regions of uplift. Freedom 
 from, or mixtures with, these form the following varieties : 
 i. More or less free from accessory minerals : 
 (a) Statuary Marble. A pure white variety, fine-grained 
 and firm-textured. The Parian marbles come from the island 
 of Paros, Pentelican from near Athens, Carrara from Modena, 
 Italy, Luni from the Tuscan coast. These are the best exam- 
 ples of the variety, though here and there in the quarries 
 about Rutland, Vt., are found quite good kinds, their chief 
 fault being too great softness. 
 
 (&) Giallo-antico is the beautiful Italian variety with 
 ocher-yellow to cream-yellow color with whitish mottlings. 
 
MANUAL OF LITHOLOGY. 
 
 (c) Sienna Marble is another yellow Italian kind, with 
 veins and mottlings of bluish red and (less frequently) of 
 purple. 
 
 (d) Red Marbles. The Mandelalo is an Italian kind, with 
 yellowish white spots on a light red ground. Tiree marble, 
 from Scotland, exhibits light shades to rose-red. Tennessee 
 marble shows brownish and purplish shades, and in this 
 background the whitish fossils stand out prominently. This 
 last is only partially metamorphic. The " Winooski " red 
 marble is one of the most handsome variegated marbles of 
 the world. It is found along the eastern shore of Lake 
 Champlain, and is harder than the Tennessee variety. 
 
 (e) Snowflake Marble is found at Pleasantville, N. Y. It 
 is composed of snow-white crystals, some of which are over 
 an inch long. It is reported as the strongest, most durable, 
 and purest in composition and color of any marble in the 
 United States. 
 
 (/) Blue Marbles. A turquois-blue variety is found at 
 Seravezza, Italy, a dark blue at Gouverneur, N. Y., and a 
 blue black at Glens Falls in the same State. 
 
 (g) Anthraconite (v. Moll), Lucullite, Nero-antico. A 
 black marble found in nests and veins in other rocks, and 
 (infrequently) in beds. Its color is due to carbon, as is 
 shown by its burning white. Black marbles are reported 
 (see above) in the United States, but there are no extensive 
 workings. Anthraconite in beds is found near Christiania. 
 
 2. With accessory minerals : 
 
 (a) Cipolino. An easily weathering white marble with 
 abundant pale greenish mottlings and shadings from talc and 
 mica. These accessories become so abundant as to impart 
 a distinct cleavage to the rock, and an increase in mica forms 
 a transition to calcareous mica-schist. It is found in Sax- 
 ony, Piedmont, Greece, and along the Green Mountains of 
 Vermont. 
 
METAMORPHIC ROCKS. 337 
 
 (b) Ophicalcite (Brongniart), Verde Antique, is a white 
 marble clouded with green from serpentine. It also exhibits 
 yellowish and bluish shades. The serpentine is in grains, 
 nests, and stains, thoroughly intermixed with the calcite. 
 This is interesting as being the home of Eozoon. It is found 
 in Canada and New England (especially about New Haven, 
 Conn.), and in Warren County, N. Y. 
 
 (c) Calciphyre (Brongniart) is a marble porphyritic from 
 phenocrysts of garnet, vesuvianite, and augite. 
 
 (d) Hislopite (Haughton), from Talki, in the East In- 
 dies, is a highly glauconitic marble. 
 
 (e) Predazzite is a compound of marble and brucite, and 
 occurs at Predazzo, Tyrol. 
 
 In addition to the above, marbles may carry so high an 
 amount of certain minerals as to be styled tremolitic, gra- 
 phitic, chloritic, chondroditic, etc. 
 
 Dolomite also forms a marble, but it crumbles from 
 weathering, as the calcite content dissolves faster than the 
 other and undermines the structure. 
 
 II. METAMORPHIC CRYSTALLINE SCHISTS. 
 
 In this division are included rocks with but slight schist- 
 ose structure, as they are found associated geologically with 
 the schists rather than with the contact formations. At times, 
 however, some of their varieties may be found in small zones 
 in contact aureolae. Under the various rock classes will be 
 found all variations in metamorphism, from the state where 
 the original bedding and fossiliferous content can be dis- 
 tinctly traced, to the almost M^ta-granites, which retain slight 
 evidences of their metamorphism, but have lost all traces of 
 original condition. All of these are more or less foliated, 
 and shade from the highly developed foliation of the general 
 body of the group towards the failing of foliation through 
 
MANUAL OF LITHOLOGY. 
 
 its shading into bedding, on the one hand, and through its 
 obliteration from almost perfect fluidity of the highly meta- 
 morphic mass, on the other. We thus find schists varying 
 from the incipient cleavage of claystones through slates, 
 crystalline and foliated phyllites, to mica-schist and fine- 
 grained gneiss. The foliation of these rocks is usually 
 curved and crumpled, but in the less altered rocks it is flat- 
 parallel, with the layers unlike the laminae of strata in being 
 flat-lenticular instead of flat-plane. In cases of a secondary 
 metamorphism imposed on schists there is a secondary folia- 
 tion that can be readily distinguished. New England is an 
 excellent field to study metamorphism, and especially 
 along the Green Mountains, where sediments can be traced 
 into schists within limited areas, and secondary foliation is 
 noted in Berkshire County, Mass. 
 
 The term " schist " is sometimes loosely used to describe 
 coarse elastics which have been more or less bent, but which 
 have not become crystalline-granular. It is not so used in 
 these pages, but refers only to those crystalline-granular 
 rocks which are foliated. All crystalline rocks without foli- 
 ation are " rocks.'' This has already been stated, but it is 
 repeated here, as the following pages will contain descrip- 
 tions of crystalline rocks (so called) which are found with 
 schists, but are unfoliated, or but slightly crumpled. It re- 
 mains to say that cleavage is not taken as foliation. Both 
 may be due to the same or similar causes, but the argillites 
 and phyllites will be classed with the " rocks," and the mica- 
 schists, into which they shade by regular gradations, will 
 fall into " schists/' In German the same word (sckiefer} is 
 used for schists, slates, and shales, though they are separated 
 in classifying rocks, and occasion some trouble to the begin- 
 ner who consults books in that language. 
 
 Summing what has been said of the origin of schists and 
 adding thereto, we find that they may come : from the origi- 
 nal crust (?) of the molten globe ; as true eruptives in the 
 
METAMORPHIC ROCKS. 339 
 
 early geological ages ; as tuff states (?) of old eruptives : or 
 as sediments altered by deep burial, metachemism, or oro- 
 genic action. The results will be so similar that no division 
 can be made from hand specimens, and the eruptive origin 
 can only be seen in the contact aureola of the rock. We can 
 divide them roughly according to the mineral components, as 
 in the eruptive rocks, but less closely, as there is a broader mix- 
 ture of minerals, owing to the varieties of origin and amounts 
 of metamorphism. Those having predominant quartz and 
 with silica over 55 per cent will be classed as acid, while 
 those with a lower silica content will be grouped as basic. 
 
 ACID SERIES. 
 
 The rocks of this series are more or less foliated, crystal- 
 line-granular, generally (M) compounds of quartz, 
 feldspar, mica, with various accessories ; coarse and 
 fine-grained and (M) compact ; massive or fissile ; 
 variously colored. 
 
 Silica 55-82; Gr. 2.6-3.2. 
 
 They can be divided, according to the predominant minerals, as follows. 
 QUARTZ GROUP : 
 
 Quartzite, quartz-schist, itacolumite, Lydian stone. 
 QUARTZ-MICA GROUP. 
 
 Mica-schist and its varieties. 
 QUARTZ-TOURMALINE GROUP. 
 
 Tourmaline-schist, tourmaline-hornstone. 
 QUARTZ-IRON GROUP: 
 
 Itabarite, micaceous iron-schist. 
 QUARTZ-FELDSPAR GROUP: 
 
 Granulite, gneiss and its varieties. 
 QUARTZ-FELDSPAR-MICA GROUP: 
 
 Halleflinta, porphyroid, (adinole). 
 FELDSPAR-MICA GROUP : 
 
 (Cornubianite). 
 
 Adinole and cornubianite have already been described, and are in- 
 cluded in the above to show where they would come in the series if their 
 connection with contact products did not place them in a previous series. 
 
34 MANUAL OF LITHOLOG Y. 
 
 QUARTZ GROUP. 
 
 QUARTZITE. 
 
 A granular to compact aggregate of quartz with coarse- 
 splintery, conchoidal, and vitreous fracture, and with 
 few or no signs of foliation. 
 
 This occurs in beds with crystalline schists, and in some 
 cases hundreds of feet thick. It also occurs in regions of 
 sediments where crystallinic metamorphism has filled the 
 interstices of a sandstone to form a compact rock. Both 
 kinds are generally associated with the oldest formations. 
 Quartzite is found along the Appalachian region of the 
 eastern United States. It is generally white, sometimes 
 yellowish white, yellow, red, and blue. The grains can 
 generally be distinguished (M) ; but sometimes the rock is 
 so fine that they can only be seen (m), and it resembles the 
 Arkansas novaculite when white, and some flints when 
 colored. It is a true sediment, and retains its bedding and 
 other characteristics. The quartzite of South Bethlehem, 
 Pa., has almost lost its original habit, and breaks with a 
 conchoidal fracture, while its lower portion is porphyritic 
 with feldspar phenocrysts. The same rock twenty miles to 
 the southwest, at Fleetwood, Lyons, etc., is the crumbly 
 Potsdam sandstone with unchanged bedding planes and 
 riddled with casts of scolithus. The South Bethlehem rock 
 is light or dark gray ; the Fleetwood rock white, yellowish, 
 or reddish. Quartzite also occurs as a contact formation 
 with intrusive dikes, and forms a zone of a few feet in thick- 
 ness. In still further cases the rock seems to be solid (M) 
 quartz, of great purity and high translucence almost be- 
 coming subtransparent, and exhibits a highly developed 
 flat-parallel cleavage. It frequently shows well-developed 
 cubical jointing. As accessories occur (abundantly) chlorite, 
 magnetite, pyrite, and specular hematite. The last occurs 
 
METAMORPHIC ROCKS. 34 * 
 
 in hand specimens in Virginia in thin plates parallel to the 
 cleavage of the quartzite. Other accessories are carbon,, 
 graphite, rutile, apatite, tourmaline, garnet, cyanite, mica,, 
 ottrelite, etc. The last occurs in a fine blue quartzite near 
 Rutland, Vt, the color showing strongly when the rock is 
 wet, and fading when dry. As varieties are : 
 
 (a) Oolitic Quartzite. In concretions weighing several 
 hundredweight in the " sandy barrens " of Center County, 
 Pa., in the limonite mines. The same form is reported from 
 Sumatra. The variety shows spheroidal grains one-twelfth 
 of an inch in diameter. The Center County variety may be 
 a replacement of calcite by silica, as the " barrens " are 
 formed by the leaching of the former mineral from the 
 calciferous sand-rock. 
 
 (b) Buhrstone (Hitchcock) is a similar rock as far as origin 
 is concerned, and forms a compact quartzite with irregular 
 pores that occurs in Berkshire County, Mass., and along the 
 Appalachian border from South Carolina to Georgia. The 
 rock is more mineralogical than economic, as it is not 
 worked, the best millstones of the United States being from 
 the Berea (O.) grit. The best buhrstones come from France. 
 
 These two varieties have been described under organic 
 aggregates of silica, but are again noted, as their organic 
 origin is only probable. The various accessories named 
 above are frequently predominant enough to form varieties 
 bearing their names, as tourmatme-quartzite, etc. 
 
 QUARTZ-SCHIST. 
 
 A foliated quartzite, usually with some mica. 
 
 This may be taken as a mica-schist with the silica in ex- 
 cess of 82 per cent, but with sufficient mica to impart a 
 schistose structure. A failure of the mica places the rock 
 in " quartzite," and an increase of the mineral in " mica- 
 schist." Geikie notes large tracts in the Scottish Highlands 
 
34 2 MANUAL OF LITHOLOGY. 
 
 where the rock is a transition between quartzite and mica- 
 schist, and varies from one extreme to the other the mica 
 allowing the rock to be split into flagstones. In the Green 
 Mountains of Vermont quartz-schist occurs, and with a 
 further change (by the entrance of calcite) into calciferous 
 quartzite and calciferous mica-schist. In the same region 
 also occurs : 
 
 Conglomerate Schist. This is a transition between a 
 quartz conglomerate and a gneiss. The pebbles of the con- 
 glomerate are sometimes only slightly flattened, and may 
 reach several inches in diameter. They are then inclosed 
 in a schistose matrix, so that they can be readily distin- 
 guished from an unaltered conglomerate. In other cases 
 the rock has been so strongly compressed that the pebbles 
 are flattened to long lenticules with rounded ends, and still 
 further metamorphism changes them to lenticular folia of 
 crystalline quartz, with no traces of their original shape. 
 This is reported from the Alps, Saxony, Norway, France, 
 Ireland, Scotland, and the Green Mountains. 
 
 ITACOLUMITE (v. Eschwege), Flexible Sand- 
 stone. 
 
 A fine-grained and schistose aggregate of quartz, 
 
 dered flexible, when in moderately thin plates, by 
 parallel laminae of mica, talc, chlorite, and sericite. 
 
 This was first described at the mountain Itacolumi in 
 Brazil, where the formation is of great thickness and extends 
 several miles the mountain being 5400 feet high. It also 
 occurs in the Southern Atlantic States of the Union and in 
 Pennsylvania. Some authorities class this as a sandstone. 
 As accessories are micaceous hematite, magnetite, martite, 
 native gold, and diamond. 
 
METAMORPHIC ROCKS. 343 
 
 LYDIAN STONE, Siliceous Schist, Phthanite 
 (Haiiy), Touchstone. 
 
 A cryptocrystalline aggregate of quartz, with clay, car- 
 bon, and oxide of iron ; black or dark-colored ; hard ; 
 infusible ; with splintery fracture. 
 
 This occurs in thin bands in, and later than, the Silurian, 
 and appears to be an original and not a metamorphic rock, 
 as the beds with which it is intercalated are not altered. It 
 also abounds in fossils (graptolites, for example) ; but its 
 general appearance is that of a schistose rock. It can be 
 placed here or with sandstone with equal propriety. It is 
 reported from the Carbonic of the Appalachian area. It 
 was formerly used in distinguishing native metals and their 
 alloys by their streaks on the fine dark surface. 
 
 QUARTZ-MICA GROUP. 
 
 MICA-SCHIST, Mica-slate. 
 
 A schistose aggregate of quartz and mica in widely vary- 
 ing proportions. 
 
 Silica 55-82; Gr. 2.7-3.17. 
 
 It occurs in extensive formations in the metamorphic 
 areas of the world, and as inner contact zones of great width 
 about bosses of granite, and is found in the Archaean forma- 
 tions throughout the world. It is always crystalline and 
 foliated, but varies in almost every other character, as the 
 mica varies from the condition of an accessory to that of 
 being almost the sole ingredient. The texture sometimes 
 becomes so slightly foliated that the rock becomes almost 
 wholly granular-massive. The two ingredients frequently 
 are not equally mixed, but aggregate, in folia of varying 
 thickness, to form a flat-parallel structure. At times the 
 mica is in knots of varying size which are connected in the 
 quartz matrix by strings of mica. In other varieties the 
 
344 MANUAL OF LITHOLOGY. 
 
 quartz forms large plates, strings, or segregations about 
 which the mica is grouped. There are few rocks in which 
 so great a variety of arrangement of ingredients and of 
 structures exist. The mica is usually muscovite or biotite 
 more generally the former, which is of white color. The 
 greasy varieties (formerly thought to be talc) were found 
 by Dewey to be damourite, and varieties carrying them 
 were named by Dana /*jj>dfo?mica-schists. It happens fre- 
 quently that both biotite and muscovite are together, to 
 make a mottled rock. The quartz is in grains or larger 
 aggregates, as already noted. As accessories occur abun- 
 dantly calcite, feldspar, garnet, tourmaline, hornblende, 
 andalusite, iolite, staurolite, chlorite, rutile, graphite, iron 
 ores, talc, and cyanite, so that varieties are formed through 
 them. In the contact zones about granite occur also silli- 
 manite, fibrolite, and epidote. The various textures and 
 structures form another class of varieties, so that from the 
 above many are noted by various authorities. Especially 
 prominent are : 
 
 (a) Damourtte-schist, //^fo?mica-schist (Dana). This is 
 a soft rock with damourite or one of the hydromicas re- 
 placing mica. It occurs as alterations of older rocks, such 
 as crushed diorites, and as beds in slightly metamorphic 
 sediments. In eastern Pennsylvania there are two damour- 
 ite beds, the lower being between the Potsdam sandstone 
 and the gneiss, and the other between the Hudson slates and 
 the Silurian limestone. This forms the matrix of the sub- 
 glacial till along the northern border of the South Moun- 
 tain, at Bethlehem, Pa. It also is found along the Taconic 
 region, in Canada, and along the Laurentian of the Atlantic 
 States. It is usually in light colors, that just noted being 
 shades of cream. The compact state is called agalmatolite. 
 It occurs in the Alps as paragonite-sc\\\st, when this form of 
 mica is predominant. 
 
METAMORPHIC ROCKS. 345 
 
 (b) Calcareous Mica-schist. A fissile, crystalline-granular 
 aggregate of quartz, mica, and calcite, of all degrees of 
 coarseness, and all extents of variation in the proportions of 
 the components. The variety from the Erzgebirge is a 
 foliated limestone, and a transition between cipolmo and 
 mica-schist. In the eastern Alps the rock consists of alter- 
 nate layers of mica-schist and limestone. The varieties of 
 central Vermont are a most intimate mixture of the ingre- 
 dients in variable proportions. At times there is a fine- 
 granular and slightly foliated mixture in which quartz is 
 predominant, so that it resembles a slightly micaceous cal- 
 ciferous sand-rock on a fresh fracture, but the weathered 
 specimens show the difference in composition to a high 
 degree, as they lose their calcite and leave the quartz deeply 
 rusted from the decomposed mica, so that the weathered 
 stone can be readily crumbled with the fingers, and forms 
 " rotten stone." Other varieties in the same region consist 
 almost entirely of mica (predominant), and large knots or 
 concretions of cream-colored calcite or dolomite, drawn out 
 to form " eyes " in the dark mass. A third variety shows 
 predominant quartz with calcite and subordinate mica. The 
 calcite exhibits cleavage surfaces on a fracture, some of which 
 are inch across. The variety at Woodstock, Vt., abounds 
 in garnet ofAll sizes up to that of the fist. Other accessories 
 are tourmaline, hornblende, epidote, magnetite, graphite, and 
 talc the last sometimes replacing mica to form calcareous 
 taic-schist. 
 
 The following varieties are also worthy of note: chlorit- 
 oid, from the Alps ; tourmalinic, from Saxony, the Green 
 Mountains, etc. ; double mica, nacritide (Schill), with both 
 micas, from Saxony, Pike's Peak, Kansas ; gneissic, from the 
 Erzgebirge; garnetiferous, a common variety; graphitic, 
 from Saxony, the Pyrenees, Norway, etc. ; andalusitic, from 
 Sweden, Spain, Ireland, Tyrol, etc. Many of these are 
 
34-6 MANUAL OF LIT HO LOG Y. 
 
 found in New England. Hornblendic mica-schist will be 
 noted later under " Hornblende-schist." An epidote-glauco- 
 is reported from the island of Celebes. 
 
 QUARTZ-TOURMALINE GROUP. 
 
 TOURMALINE-SCHIST. 
 
 A foliated granular aggregate of quartz and tourma- 
 line. 
 
 This is not the schistoid state of the compound of quartz 
 and tourmaline noted under " Granite," but a contact product 
 of granite. In this rock the tourmaline is in granules and 
 acicular crystals, and the rock as a whole is fine-granular 
 and black. While tourmaline-quartzite and tourmaline rock 
 are formed from the granite by the influence of the boric 
 and fluoric acids, this and the next rock are formed by simi- 
 lar agents from the country-rock. Tourmaline-schist occurs, 
 therefore, as an inner contact zone of an intrusive granite 
 with phyllite and similar rocks, and is found in Cornwall, in 
 the Erzgebirge, and elsewhere. 
 
 TOURMALINE-hornstone. 
 
 A (M) compact aggregate of quartz and tourmaline with 
 mica, staurolite, iron ores, etc. ; with splintery frac- 
 ture ; slight foliation ; grayish color. 
 
 This is the tourmaline representative of the ordinary 
 hornstone formed in granite contacts without exhalations of 
 the above-noted mineralizing acids, and the similar lime- 
 siiicate-hornstone of the contacts with limestone. (M) it 
 cannot be told from the above when compact, and it is only 
 by following it into parts of the aureola where tourmaline 
 appears (M) that the variety can be known. It is readily 
 told when examined (m). It is found in Cornwall, Saxony, 
 Bretagne, Norway, and at Mount Willard, N. H. 
 
METAMORPHIC ROCKS. 347 
 
 With this formation of tourmaline there is also a growth 
 of topaz, so .that in the breccias of tourmaline-quartz-schist 
 there occur nests and veins of topaz (crystal, granular, com- 
 pact), as on the granite-phyllite contact of the Schnecken- 
 stein in the Voigtland, to form " topasbrockenfels." 
 
 QUARTZ-IRON GROUP. 
 
 ITABIRITE (v. Eschwege). 
 
 A granular to compact aggregate of quartz, micaceous 
 hematite, and magnetite. 
 
 It appears to be a highly ferruginous mica-schist, and 
 "with itacolumite forms Mount Itabtra in Brazil. It is also 
 found in the Carolinas, at Sutton, Canada, Norway, and on 
 the Gold Coast of Africa. It is black and violet in color, 
 and has the iron ores as predominant minerals, with quartz 
 sometimes quite an unimportant ingredient, while at other 
 localities the quartz forms white lenticular strings, so that 
 the mass has a decided schistose appearance. As accessories 
 occur talc, chlorite, hornblende, biotite, garnet, gold, epidote, 
 .and feldspar. On weathering it forms a sand called jacottnga. 
 
 MICACEOUS IRON-SCHIST. 
 
 A granular schistose aggregate of quartz and micaceous 
 iron. 
 
 It occurs in beds in metamorphic regions, and is found 
 In Brazil, Hungary, South Carolina, etc. The quartz is in 
 white grains (usually grayish white), scattered between the 
 folia of micaceous hematite. These latter are black, and so 
 evenly arranged that the rock seems dotted with white in 
 .stripes. In the iron region of Virginia, near Lynchburg, a 
 similar rock appears with the two minerals in masses, the 
 quartz being predominant and the hematite forming plates 
 an inch broad, so as to impart a somewhat flat-parallel struc- 
 ture to the rock. 
 
34^ MANUAL OF LITHOLOGY. 
 
 QUARTZ-FELDSPAR GROUP. 
 
 GRANULITE (Weiss), Leptynite (Haiiy). 
 
 A slightly foliated fine-grained aggregate of granular 
 quartz and feldspar, usually with small garnets. 
 Silica 70-80 ; Gr. 2.6-2.7. 
 
 This is a gneiss without mica, and occurs locally in Ar- 
 chaean formations. It is especially developed in the eastern 
 part of North America. In Canada it is known locally, 
 north of Lake Ontario as " huckleberry rock." The Second 
 Geological Survey Reports of Pennsylvania place here the 
 non-garnetiferous mass of the South Mountain at its eastern 
 extension between the Delaware and Schuylkill rivers. At 
 times the foliation is so indistinct that it might be called 
 aplite, were it not for the presence of garnet. The quartz is 
 white, and occurs in grains and strings, which give a 
 schistose appearance to the mass. The feldspar is usually 
 orthoclase (microcline, microperthite) of pale reddish, yel- 
 lowish, or white color; or plagioclase (oligoclase) in rare 
 cases. Garnet is red, and from (m) proportions to the size 
 of peas, rounded or roughly crystal, sometimes flattened like 
 the quartz till as thin as a sheet of paper, and forming red- 
 dish specks on a fracture parallel to the foliation. Among 
 the accessories is biotite, which makes transitions to gneiss, 
 so -that we can have the two intermediate rocks biotite- 
 granulite and ^wm-granulite. The following accessories 
 are frequently so abundant as to form rocks with similar 
 names, as ^/^^/V^-granulite, garnet-granulite, tourmatine-gran- 
 ulite. The variety in eastern Pennsylvania can be called 
 ^07-^/^/z^-granulite, as it varies between that rock and horn- 
 blende-gneiss. Pyroxene-grauulite, /lyfierstkene-granulite, and 
 ^^//dg^-granulite are basic forms occurring in Saxony. If 
 mica occurs, it is usually dark brown to black (Zirkel) ; 
 "usually a white variety of mica, seldom black" (v. Cotta). 
 
METAMORPHIC ROCKS. 349 
 
 The ordinary granulite is white, yellowish, or flesh-red, with 
 garnet and cyanite (Rossw r ein, Saxony); striped granulite 
 has the components in parallel stripes (on the Zschopau, 
 Saxony) ; black granulite, from iron (Penig, Saxony). The 
 rock is characterized by regular jointing parallel to the 
 foliation, and an irregular cross-jointing with smooth part- 
 ings. The Pennsylvania rock shows abundant slickensides 
 as large as the palm of the hand. 
 
 QUARTZ-FELDSPAR-MICA GROUP. 
 
 GNEISS (old miner's term for the rock containing 
 the ore). 
 
 A schistose granular aggregate of quartz and feldspar 
 (potash, soda, or lime-soda) with one of the black bi- 
 silicates, preferably the micas. A foliated granite. 
 Silica 56-75 ; Gr 2.6-2.8. 
 
 It occurs in widespread masses in the Archaean forma- 
 tions of the earth, especially in Scandinavia, Scotland, and 
 the eastern part of North America, where it forms a V-shaped 
 area extending from Labrador to New York, and thence by 
 the north shore of Lake Superior to the Arctic Ocean, with 
 a narrow tongue southward from New York to Alabama 
 along the Atlantic coast. There are extensive masses in 
 New England also. The Adirondacks and White Mountains 
 abound in varieties. The great seaboard cities of the eastern 
 coast New York, Philadelphia, Baltimore, and Richmond 
 are built on gneiss. In the western part of the Union it 
 forms the axes of extensive mountain chains, and the centers 
 of raised regions. Gneiss is generally a highly metamorphic 
 sediment that has sometimes become eruptive (Scottish 
 Highlands), and exhibits contact aureolae ; also metamor- 
 phosed states of crushed granites and other acid rocks 
 (Alps, north shore of Lake Superior, etc.). It differs from 
 
35 MANUAL OF LITHOLOGY. 
 
 granite in its foliation and in the more granular texture of 
 the ingredients, which are not interlocked into one another, 
 but are more distinct, and occur in banded and foliated 
 structures, the mica laminae and other unequiaxial minerals 
 (tabular feldspars, tourmaline, hornblende, lenticular aggre- 
 gations, concretions, etc.) having a parallel arrangement 
 which allows cleavage along the foliation, and more readily 
 along the layers of mica. The feldspar is usually orthoclase 
 in crystalline grains of the lighter colors of the granitic 
 mineral, except the decided red, which is only found when 
 it is stained with ferric oxide. It frequently occurs as 
 phenocrysts to form porphyritic gneiss, and in some cases is 
 in twinned forms half a foot in length. Microcline is of fre- 
 quent occurrence, and sometimes microperthite. Plagio- 
 clase is sometimes greenish from epidotizing of pyroxenic 
 ingredients. Oligoclase and albite are common, but usually 
 as phenocrysts and not in the general mixture ; labradorite is 
 very rare. Quartz occurs in grains and lenticular strings, 
 which latter sometimes form bands of great purity one foot 
 wide, with parallel folia of mica scattered through them. 
 As inclusions in quartz occur feldspar, biotite, fine acicular 
 rutile, epidote, zircon, graphite, etc. Pegmatitic structures 
 occur which vary from the ordinary in being poikilitic, as 
 feldspar is highly predominant. As in granite, the mica is 
 muscovite and biotite in irregular folia, but of more rounded 
 contours. Biotite is green, with inclusions of garnet, epi- 
 dote, zircon, etc., and alters to chlorite and epidote. Musco- 
 vite is colorless or light shades of green and gray. As stated 
 under the description of minerals, the two are intergrown 
 as alternate laminae of an aggregation, or as parts of the 
 same folia. As essentials occur tourmaline in prisms and 
 acicular crystals, single or aggregated, and sometimes four 
 inches long ; occasionally in rounded grains. Hornblende 
 occurs in biotite gneiss, and is associated with that mineral 
 
METAMORPHIC ROCKS. 35 I 
 
 as in granite. It is generally of light colors, or not of very 
 dark ones. Sometimes glaucophane is found. Pyroxene 
 occurs under the same conditions as in granite, and is found 
 in plagioclase- gneiss accompanied by few accessories. 
 Hypersthene sometimes occurs with labradorite and biotite* 
 lolite is found in bluish grains and forms the variety " cor- 
 dierite "-gneiss. Garnet is one of the most common acces- 
 sories, and is more abundant (M) than in granite, but much 
 less so than in mica-schist. It shows red and brown colors.. 
 Sillimanite, fibrolite, andalusite, and staurolite are abundant 
 in micaceous gneiss, but less so than in mica-schist. Less 
 frequently occur epidote, apatite, zircon, titanite, magnetite, 
 graphite, chlorite, etc. Lenticular aggregates of orthoclase 
 or microcline alone, orthoclase with mica coating, tourma- 
 line and quartz, glaucophane in dark blue knots, etc., also 
 occur. The varieties are : 
 
 (a) Typical Gneiss, Mica-gneiss. In this the black bisili- 
 cate is one or both of the micas. Variations are muscovite-, 
 biotite-, and muscovite-biotite-gneiss. Predominant mica of 
 either kind forms micaceous gneiss. Variations in the text- 
 ure and structure of the mica varieties form the states 
 known as granite-gneiss, where the foliation is so indistinct 
 as to be almost lost ; porphyritic- or augen-gneiss, where 
 phenocrysts or eye-shaped kernels of feldspar are scattered 
 through the mass ; wood-gneiss, where the ingredients are 
 arranged in fibrous-parallel structure, as in wood, so as to 
 supersede the schistose structure ; slate-gneiss, where the 
 texture is fine and mica is predominant, so that a decided 
 cleavage is formed ; ribbon gneiss, where quartz, feldspar, 
 and mica are aggregated in thin and mutually alternating 
 layers, which give, on a cross-section, the striping of a rib- 
 bon ; giant gneiss is the schistose form of giant granite, 
 where the ingredients are respectively an inch in size ; red 
 gneiss, with silica 74-76, feldspar orthoclase and predomi- 
 
352 MANUAL OF LITHOLOG Y. 
 
 nant, mica always white and not abundant ; sometimes 
 eruptive ; gray gneiss, with silica 64-67, mica dark and pre- 
 dominant, feldspar orthoclase and oligoclase. 
 
 (ft) Cordterite-gneiss is a variety of biotite-gneiss where 
 iolite (cordierite) is abundant with gray quartz and much 
 feldspar. It is usually of dark color. It occurs in Saxonv, 
 France, Scandinavia, etc., and at Guilford, Conn. 
 
 (c) Granule-gneiss has little mica, and that usually white. 
 V. Cotta states that it always belongs to the red gneiss. 
 
 Other varieties of the mica-gneisses are made by pre- 
 dominant fibrolite, garnet, graphite, epidote, talc, and iron 
 ores. Where the mica is more or less replaced by other 
 minerals, other variations of greater value and extent occur, 
 as: 
 
 (d) Sericite-g\\Q\ss is an aggregate of quartz, albite, and 
 sericite, with now and then white or black mica in small 
 amounts, and a chloride mineral. It occurs in the Taunus, 
 in Japan, etc. 
 
 (e) Protogme-gneiss is a decidedly schistose state of the 
 schistoid protogine-granite already noted. It consists of an 
 aggregate of white or reddish orthoclase, greenish white 
 plagioclase, and quartz with a talclike mineral. A variety 
 of this is chloritic gneiss. It is widespread in the Alps, and 
 was called " alpenit " by Simler. 
 
 (/) Hornblende-gneiss, Syenite-gneiss, etc. This is a 
 gneiss with hornblende more or less replacing mica, which 
 is biotite rather than muscovite. The feldspar also changes, 
 and instead of predominant orthoclase, oligoclase and other 
 plagioclases appear. With orthoclase we have " syenite "- 
 gneiss, with plagioclase " diorite "-gneiss, and with plagio- 
 clase and mica " tonalite "-gneiss. Pyroxene appears in this 
 variety and alters to chlorite and epidote. The varieties of 
 hornblende-gneiss are very abundant in the Archaean areas, 
 and the Pennsylvania gneiss of the eastern middle part of 
 
METAMORPHIC ROCKS. 353 
 
 the State is granulite-hornblende-g\\eiss y with accessory allan- 
 ite, molybdenite, and considerable magnetite, which forms 
 extensive ores in New Jersey. Anthophyllite and glauco- 
 phane are frequently abundant enough to form varieties. 
 
 (g) Pyroxene-gneiss. This is an aggregate of predomi- 
 nant plagioclase(albite, oligoclase, labradorite, and anorthite) 
 with some orthoclase and quartz and a light-colored pyrox- 
 ene. As accessories are wollastonite, scapolite, occasional 
 calcite, biotite, garnet, titanite, and frequently hornblende. 
 Occasional combinations are omphacite and bronzite, saus- 
 .suritic feldspar, etc. This variety can be called from its 
 feldspar plagioclase-gueiss and anvrt kite-gneiss, and when the 
 pyroxene is hypersthene it may be called " norite "-gneiss ; 
 when diallage, " gabbro "-gneiss ; when augite, " diabase "- 
 gneiss ; or all the minerals can be used as a prefix, as hyper- 
 sthene-anomiteplagioclase-giiQiss, diallage-gneiss, augite-gneiss, 
 wollastonite -augite- gneiss, scapolitic augite-gneiss. Augite- 
 gneiss is found in Scandinavia, Spain, Bretagne, Vosges, 
 etc., and in Minnesota, Wisconsin, and New York. 
 
 QUARTZ-FELDSPAR-MICA GROUP. 
 
 HALLEFLINTA. 
 
 A (M) compact homogeneous rock with an appearance 
 like hornstone, a splintery to conchoidal fracture, and 
 color varying in bands of gray, green, yellow, dark 
 brown, to black. It fuses only on thin edges. It may 
 be considered, in some cases, as a compact gneiss, in 
 others as a devitrified rhyolite. 
 Silica 61-83 5 Gr. 2.65-2.78. 
 
 This occurs in Sweden with granulite and gneiss, into 
 which it can at times be traced, but Nordenskiold has re- 
 cently described occurrences of it as a devitrified rhyolite, 
 where it exhibits the flow structure, lithophysas, etc., of that 
 
354 MANUAL OF LITHOLOGY. 
 
 rock. It is fine-crystalline (m), and shows an intimate mix- 
 ture of quartz and feldspar, with scales of mica and chlorite. 
 We have, therefore, two origins for the same rock the 
 metamorphic form of fine sediments which have become 
 a compact gneiss, and the devitrified form of an extrusive 
 glass. Halleflinta much resembles adinole and porphyroid. 
 A porphyritic halleflinta was found to be a devitrified quartz- 
 porphyry. It is also found in Bavaria, Baden-Baden, and 
 the northwestern part of South America. 
 
 PORPHYROID. 
 
 A rock with felsitic groundmass; somewhat schistose 
 from the development of micaceous scales, and exhib- 
 iting sporadic phenocrysts of quartz and feldspar. 
 Silica 75-83 ; Gr. 2.6-2.75. 
 
 It is found among the schistose rocks of Saxony and in 
 the Paleozoic areas of other parts of Europe, and is thought 
 to be an orogenic product from extensive shearing and sub- 
 sequent rearrangement of material. It resembles a schistose 
 and micaceous quartz-porphyry, and is like adinole in its 
 appearance and behavior. The feldspar is orthoclase or 
 albite in quite perfect crystals, and the quartz is frequently 
 in double pyramids. The mica is paragonite or sericite 
 (both belonging to muscovite). With a coarser grain the 
 rock would become a highly crystalline gneiss. It so much 
 resembles the rock last noted that some authorities call it a 
 " porphyritic" halleflinta. It occurs in the northern penin- 
 sula of Michigan in the Huronian formation, and in Nevada. 
 
METAMORPHIC ROCKS, 35 S 
 
 BASIC SERIES. 
 
 The rocks of this series are more or less foliated, crystal- 
 line-granular, generally (M) compounds of pyroxene, 
 amphibole, garnet, talc, chlorite, serpentine, with 
 feldspar (usually plagioclase), quartz, and various ac- 
 cessories ; coarse- and fine-grained, and (M) compact ; 
 massive or fissile ; variously colored. 
 Silica 26-58 ; Gr. 2.7-3.5. 
 
 They can be divided, according to the predominant min- 
 erals, as follows : 
 
 MARGAROPHYLLITE GROUP: 
 
 Talc-schist, calcereous talc-schist, listwenite, dolerine, renssel- 
 
 aerite, steatite, potstone, chloride potstone. 
 Chlorite-schist, uralite-schist, chloritoid-schist. 
 Pyrophyllite-schist. 
 
 EPIDOTE GROUP : 
 
 Epidosite, epidote-schist. 
 
 GARNET GROUP : 
 
 Garnet rock, eclogite, cyanite rock, kinzigite. 
 
 AMPHIBOLE GROUP : 
 
 Amphibolite, hornblende-schist, actinolite-schist, glaucophane- 
 schist, green schist. 
 
 PYROXENE GROUP : 
 
 Pyroxene rock, pyroxene-schist, erlan. 
 
 OLIVINE GROUP : 
 
 Olivine rock, olivine-schist, eulysite. 
 
 MARGAROPHYLLITE GROUP. 
 
 TALC-SCHIST. 
 
 A schistose aggregate of talc with quartz and (less fre- 
 quently) feldspar, and other accessories, the talc is 
 predominant in yellowish or greenish scales ; soft ; 
 with pearly luster and greasy feel. J^ vt^/ 
 Silica 27-62 (average 50-55) ; Gr. 2.6-2.8. 
 
MANUAL OF LITHOLOGY. 
 
 This occurs in beds of considerable size, but not very 
 widely spread, and is found in the Urals, Alps, Apennines, 
 in Brazil, Canada, New England, and along the Archaean 
 formation of the Atlantic coast. Quartz occurs in grains, 
 lenticules, and strings parallel to the foliation. Other acces- 
 sories are micas, chlorite, actinolite, calcite and other car- 
 bonates, magnetite, pyrite, and, less commonly, garnet, 
 olivine, tourmaline, asbestus, rutile, cyanite, staurolite, and 
 others. It is a metamorphosed sediment, and shades into 
 protogine-gneiss, chlorite-schist, clay-slate, mica-schist, and 
 similar rocks. As varieties are : 
 
 (a) Calcareous talc-schist. This bears to this rock the 
 same relation that calcareous mica-schist bears to mica- 
 schist. It is a less common rock, but is found in similar 
 formations, as along the Green Mountains, in New England, 
 etc. 
 
 (b) Listwenite is a granular talc-schist, with yellowish 
 greenish color, from the Urals, and carrying much quartz 
 and calcite, so that it shows a fine-granular-slaty structure. 
 With the calcite is dolomite, and sometimes siderite. In 
 some varieties the quartz fails. This is the rock penetrated 
 by beresite. 
 
 (c) Dolerine (Jurine) is a talc-schist from the Pennine 
 Alps with essential feldspar and chlorite. 
 
 (d) Rensselaerite (Emmons) is a pseudomorph of talc after 
 pyroxene that is found in northern New York and Canada, 
 especially at Hermon, N. Y. It is associated with crystal- 
 line limestone, and shades imperceptibly into serpentine. It 
 is seldom found in large masses : they are irregular and up 
 to 900 to 1000 feet long. It is cryptocrystalline and waxlike 
 in composition, with colors whitish, yellowish, gray, green- 
 ish, and pearl-white. 
 
 (e) Steatite, Soapstone, is a massive talc, coarse-granular, 
 grayish green, gray, and brownish gray. This frequently 
 
METAMORPHIC ROCKS. 357 
 
 contains chlorite, and then forms what some authorities call 
 " talcose potstone." One of the principal quarries in the 
 United States is a few miles northwest of Easton, Pa.; an- 
 other is near Philadelphia in the same State. 
 
 (/) Potstone is a soft, sectile, greenish gray aggregate of 
 talc, chlorite, and serpentine in a feltlike web. It is rarely 
 foliated. It is infusible, and frequently carries as accessories 
 mica, calcite, dolomite, magnetite, and pyrite. These some- 
 times cause effervescence with acids. It is an impure stea- 
 tite, and is found in New England, Canada, and New York. 
 It is used for making cooking-pots, and was so used by the 
 Indians. 
 
 (g) Chloritic Potstone is a variety that carries predomi- 
 nant chlorite, and is therefore a transition to that mineral. 
 It is found with steatite. 
 
 CHLORITE-SCHIST. 
 
 A granular to schistose aggregate of scaly chlorite with 
 quartz, and sometimes feldspar, talc, mica, epidote, 
 and magnetite. 
 
 Silica 26-50; Gr. 2.7-3. 
 
 This occurs with gneiss and other schists in bedded 
 masses, arid is found in Austria, the Alps, Tyrol, Italy, Asia 
 Minor, the Urals, Brazil, Transvaal, and in the Southern 
 Atlantic States. The chloritic mineral is one of that group, 
 and is predominant. It gives the green or blackish green 
 color and grayish green streak to the rock. It is usually 
 soft and coarsely foliated, and with little quartz. Abundant 
 quartz forms a more granular rock with greater hardness, 
 and sometimes occurs in folia, lenticules, irregular strings, 
 or thin veins that traverse the rock in all directions. It 
 shades into talc-schist, protogine-gneiss, argillaceous mica- 
 schist, and slaty serpentine. The coarser schistose states 
 
35$ MANUAL OF LITHOLOGY. 
 
 are sometimes called chloritic gneiss, while the finer and more 
 even and silky kinds are chlorite- slate. 
 
 (a) Uralite-schist (Kantkiewicz) is a coarse-schistose aggre- 
 gate of (m) fine-grained chlorite and epidote with accessory 
 quartz and biotite, and with (M) phenocrysts of augite-like 
 uralite. It alters to a green chloritic mineral. It is found 
 in the Urals. 
 
 (b) Chloritoid Schist (Sterry Hunt) is a dark- colored schist 
 of considerable extent in Canada, composed of a chloritoid 
 mineral allied to chlorite and to ottreiite. It also occurs 
 near Salzburg, and in Roumania. 
 
 PYROPHYLLITE-SCHIST. 
 
 A compact and but slightly schistose aggregate of pyr- 
 ophyllite. 
 
 Silica 65.93 ; Gr. 2.82-2.91. 
 
 This is a rare occurrence as a rock, and is found thus in 
 North and South Carolina, Georgia, and Arkansas, where it 
 forms schistose to compact beds of greenish to yellowish 
 white color, resembling in appearance and feel a slaty soap- 
 stone. It is generally free from accessories, and forms a 
 smooth and evenly soft rock, microcrystalline to aphanitic, 
 that is extensively worked for slate pencils. 
 
 EPIDOTE GROUP. 
 
 EPIDOSITE (Pistacite Rock). 
 
 A yellowish green, light green, to dark green aggregate 
 of predominant epidote and quartz, with an amphi- 
 bole, mica, or chlorite, and, less frequently, feldspar 
 and pyroxene ; hard ; massive to schistose ; granular 
 to compact ; tough. 
 
 Silica 62 ; Gr. 3-3.4 ; H. 7. 
 
 It occurs associated with crystalline schists, and also as 
 an alteration product from an eruptive, and is found in 
 
METAMORPHIC ROCKS, 359 
 
 Brazil (?), at several localities in Canada (St. Joseph, Grand 
 Manatee River, Melbourne), Greece, island of Anglesea, etc., 
 and as the alteration product of a melaphyre in northwestern 
 South America. It is also reported from Portage Lake, 
 Wis., as a similar product. The Canadian textures are com- 
 pact to coarse-grained. The varieties are : 
 
 (a) Gtaucofl/iane-epidosite. From the island of Syra, with 
 a yellowish white principal mass of fine epidote, with zoisite, 
 mica, and chlorite, in which are somewhat stout glauco- 
 phanes. 
 
 (b) Omphacite-zoisite Rock, from the same island, has the 
 principal mass of grains of zoisite with phenocrysts of 
 omphacite, and as accessories are leaves of talc, grains of 
 epidote, stout prisms of tourmaline, folia of chlorite and 
 biotite, and (ni) rutile and calcite. 
 
 EPIDOTE-SCHIST. 
 
 A schistose aggregate of the above minerals with similar 
 silica, specific gravity, and other characteristics. 
 
 This is associated with the above rock, and forms transi- 
 tions into it. The variety of the island of Timor shows as 
 accessories sericite, magnetite, quartz, calcite, plagioclase, 
 and specular hematite, and has a greenish color and silvery 
 luster on the foliation surfaces. As varieties are : 
 
 (a) ffvrnbtende-epidote-schist. From the phyllite forma- 
 tion of the peninsula of Chalcidice. It is a fine-grained 
 aggregate of coarse epidote, bright green hornblende, and 
 tufts of chlorite. 
 
 (b) Mtca-epidote-schist, in dark-green thin foliated struc- 
 ture, with predominant epidote, quartz, green biotite, and 
 iron ores, with variations where quartz and mica were each 
 predominant. 
 
 (c) Calcareous Epidote - schist, " Kalkpistacit " - schist 
 (Forth). From northeast Bohemia, with a principal mass 
 
MANUAL OF LITHOLOG Y. 
 
 of calcite, epidote, and mica, with accessory albite, quartz, 
 iron ores, and pyrite. This is the parallel of calcareous 
 mica-schist, etc. 
 
 (d) Murasaki (Koto), Manganese-epidote-schist, from the 
 island of Shikoku, Japan, is a violet rock of small quartz 
 grains with phenocrysts of epidote f inch long, with acces- 
 sory sericite, greenish yellow garnet, rutile, orthoclase, and 
 blood-red specular hematite. These are called also " pied- 
 montite "-schists, from the name of the manganese-epidote, 
 
 GARNET GROUP. 
 
 GARNET ROCK, Garnetyte (Dana). 
 A crystalline-granular aggregate of predominant garnet 
 with an amphibole, augite, epidote, quartz, and mag- 
 netite ; variously colored. 
 
 Silica 44.85 ; Gr. 3.3-3.54. 
 
 It is a rare rock, and occurs in a few irregular beds and 
 lenticular masses in mica-schist and gneiss, and is found in 
 Bohemia, Saxony, Silesia, Tyrol, France, the Urals, Belgium, 
 Canada, and Nevada. With the failure of garnet this be- 
 comes amphibolite. In addition to the above minerals there 
 are also found with garnet in smaller proportions and less 
 frequently micas, iron ores, serpentine, apatite, olivine, 
 vesuvianite, calcite, pyrite, and now and then feldspar. 
 Zirkel notes the infrequency of the latter as peculiar. Owing 
 to the great variety of its mixtures the color varies widely. 
 Sometimes the brown or yellowish garnet (aplombe) pre- 
 dominates, so that the rock consists almost wholly of that 
 mineral. It is usually of that color, buff, or greenish white ; 
 tough ; fine-grained. The stone of that color from Viel 
 Salm, Belgium, forms the best oil-stone in the world. It is 
 there a spessartite (manganese-garnet). At Orford, Canada, 
 a white lime-alumina-garnet (grossularite) forms with a little 
 
METAMORPHIC ROCKS. 361 
 
 serpentine a whitish rock. At St. Frangois, Canada, the 
 same garnet forms with an almost equal proportion of pyr- 
 oxene a yellowish white to greenish white rock. At Hohen 
 Waid in the Odenwald a beautiful brown garnet forms a 
 rock with quartz, calcite, actinolite, and epidote. At Big 
 Cottonwood Canon, Utah, a similar rock is formed of brown 
 garnet, quartz, (m) epidote, and folia of iron. 
 
 ECLOGITE (Hauy). 
 
 A coarse- to fine-grained (seldom compact) crystalline- 
 granular aggregate of grass-green omphacite (or 
 diopside) and red garnet with frequent blue cyanite 
 and white mica. The first occurs as a crystalline 
 matrix, usually slaty or fibrous, in which the garnets 
 appear as phenocrysts. 
 
 Silica 45-57; Gr. 3.20-3.50. 
 
 This occurs in quite extensive lenticular beds in gneiss, 
 granulite, serpentine, and mica-schist, and is found in the 
 Erzgebirge, Fichtelgebirge, Austria, Baden, Scotland, the 
 western Alps, Norway, Sweden, Servia, the island of Syra,. 
 Japan, the Orange Free State, at Cape Horn, and a some- 
 what similar rock is found in the Sierra Nevadas. Ompha- 
 cite is found in short, thin leek-green or grass-green prisms, 
 which are sometimes serpentinized. The garnet is almandite 
 with variations in the proportions of the ferrous and ferric 
 oxides. It occurs in rounded phenocrysts. Cyanite is 
 usually (M) ; sometimes only (m) ; frequently so predominant 
 that it forms the following variety. Quartz is generally 
 allotriomorphic, and sometimes as large as peas. Black 
 hornblende is usually present, and sometimes exceeds the 
 omphacite and garnet, so as to form an eclogitic amphibolite. 
 In some varieties grass-green smaragdite appears with 
 omphacite, and alters to chlorite. The silvery mica is mus- 
 covite. Biotite now and then occurs. Zoisite, rutile, apa- 
 
362 MANUAL OF LITHOLOGY. 
 
 tite, magnetite, pyrite, pyrrhotite, and zircon also occur 
 quite predominantly. This rock is a hard and dense mix- 
 ture that resists weathering better than its surroundings, 
 and projects from them in prominent knolls. 
 
 (a) Cyanite Rock is a variety of the above where cyanite 
 is predominant. It consists of an aggregate of cyanite and 
 white mica, and also occurs as an offshoot of mica-schist. 
 As the latter it is common in the Green Mountains of Ver- 
 mont. The cyanite is of varying color, from fine blue to 
 white, and usually occurs in long, flat, bladed crystals, and 
 so predominant that the rock is almost entirely composed 
 of it. As accessories occur garnet, calcite, and occasionally 
 tourmaline. 
 
 KINZIGITE (Fischer). 
 
 A crystalline-granular schistose aggregate of garnet, 
 biotite, and oligoclase ; coarse to compact. A garnet- 
 gneiss. 
 
 Silica 44.53; Gr. 3. 
 
 This occurs associated with gneiss and crystalline schists 
 in the Black Forest (where it was first noted at the Kinzig), 
 the Odenwald, and in Italy. The first is coarse-schistose, 
 and the ingredients of large size. Oligoclase is white and 
 grayish green, and frequently half an inch in size. It is 
 sometimes accompanied by orthoclase and microcline. 
 Garnet is sometimes as large as peas. Biotite is black, and 
 when quartz appears it forms a garnetiferous biotite-gneiss. 
 Quartz is not common, and occurs in grains and flat lenti- 
 cules. As accessories occur graphite, apatite, pyrite, mag- 
 netite, iolite, sillimanite, fibrolite, and rutile. 
 
METAMORPHIC ROCKS. 363 
 
 AMPHIBOLE GROUP. 
 
 AMPHIBOLITE. 
 
 A granular aggregate of dark green to black hornblende 
 with more or less quartz, and sometimes chlorite. 
 Silica 47-50 ; Gr. 2.9-3.1. 
 
 This occurs in beds and flat lenticular masses with gneiss, 
 mica-schist, and phyllite, and is found in Saxony, Silesia, 
 Japan, New England, Nevada, etc. The hornblende is fre- 
 quently the sole ingredient. As accessories in addition to 
 those given are biotite, orthoclase, plagioclase, garnet, pyr- 
 oxene, zoisite, and iron ores. These tend to form variations 
 from the schistose variety, and from hornblende-gneiss. In 
 amphibolite there is no tendency to foliation, and the in- 
 gredients are arranged irregularly throughout the mass. 
 
 /v/^r/ar-amphibolite, Plagioclase-amphibolite, is a vari- 
 ety with considerable plagioclase (and some orthoclase), 
 so that it forms a ^ta-diorite (Dana). It is not common 
 without foliation. Other varieties noted by different 
 authorities are quartz-, epidote-, garnet-, and tf/V^-amphibolite. 
 The last has been already described under its original name, 
 Jiemithrtne. 
 
 HORNBLENDE-SCHIST. 
 
 A granular and schistose aggregate of the above min- 
 erals with similar silica and specific gravity. 
 
 This is a more widespread rock than the former, as it is 
 associated with schists and partakes of their foliation. It is 
 common in western New England, and the garnetiferous 
 variety of the region running north and south along the 
 Connecticut River between Norwich, Vt., and Hanover, 
 N. H., has been well known for many years as furnishing 
 transparent garnet fit for jewelry. Coarse garnets much 
 fissured are found as large as filberts, but with bright red- 
 
364 MANUAL OF LITHOLOGY. 
 
 dish brown color. The garnetiferous mica-schist of the 
 Green Mountains frequently contains a considerable amount 
 of calcite intimately mixed with it, so that the rock weathers 
 to a rough surface, and the imperfect garnets in spheroids 
 of the size of French peas, or smaller, project, to give the 
 rock a pitted appearance. Other accessories are epidote, 
 biotite, scapolite, and zoisite, as well as those named above. 
 In some cases the quartz and hornblende are aggregated in 
 flakes or patches, so that the rock has a beautifully mottled 
 appearance. The appearance of feldspar forms a transition 
 to hornblende-gneiss. The hornblende-granulite of the 
 South Mountain in eastern Pennsylvania abounds in segre- 
 gations of this rock with predominant hornblende, and 
 also intercalated masses of hornblende-gneiss. In the Lake 
 Superior region and in the Alps are dikes of diabase altered 
 to this rock by squeezing, and in Calaveras County, Cal., 
 olivine extrusives have been altered in a similar manner to 
 form ta/-amphibole-schist. Much oligoclase forms diorite- 
 schist. 
 
 ACTINOLITE-SCHIST. 
 
 A schistose aggregate of actinolite, either alone or with 
 other minerals. 
 
 Silica 52-55 ; Gr. 2.95-3.05. 
 
 This occurs like hornblende-schist, and is found in the 
 Fichtelgebirge, the Alps, Italy, and along the Green Mount- 
 ains. The accessories are generally subdominant to actino- 
 lite. They are quartz, feldspar, epidote, garnet, biotite, 
 muscovite, chlorite, monoclinic pyroxene, rhombic horn- 
 blende, zoisite, olivine, the iron ores, zircon, and pyrite. 
 Ollenite is an ^akte-actinolite-schist that forms at Monte 
 Rosa a large mass, which varies from schistose to compact. 
 
METAMORPHIC ROCKS. 365 
 
 GLAUCOPHANE-SCHIST, Glaucophanyte (Dana). 
 
 A schistose aggregate of glaucophane with accessory 
 epidote and muscovite. 
 Silica 55-57; <J r - 3- 
 
 This occurs in thin lenticules with other schists, and is 
 found in the island of Syra, Switzerland, Piedmont, New 
 -South Wales, Bretagne, and California. The glaucophane 
 is in blue acicular crystals with parallel arrangement, so 
 that the mineral has been taken for cyanite. As accessories 
 occur green mica, hornblende, zoisite, quartz, plagioclase, 
 arfvedsonite, rutile, chlorite, and iron ores. A fourchite- 
 sandstone contact near San Francisco, CaL, formed glauco- 
 phane-schist. 
 
 j/z#0te-glaucophane-schist is a variety where epidote is 
 predominant. It is found in Switzerland, Piedmont, Croatia, 
 Spain, Greece, and in Asia Minor. Predominant epidote 
 forms glaucophane-epidote-schist. 
 
 (NOTE on Amphibole-schists. These are thought by 
 many authorities to have been basic intrusions in the rocks 
 where they are found, and that they have been altered with 
 those rocks to their present state. It may also be noted 
 that in some localities garnet, when finely crystalline, is in 
 trapezohedra rather than dodecahedra. 
 
 GREEN SCHIST (Kalkowsky). 
 
 A green, grayish green, to greenish black schistose ag- 
 gregate of quartz and feldspar in varying proportions, 
 with changeable amounts of hornblende, epidote, and 
 chlorite. 
 
 This is held by many authorities to be a squeezed dia- 
 base. It is found in regions of erogenic movements with 
 phyllite, and sometimes in considerable masses, and is found 
 in the Alps, Silesia, Saxony, Lake Superior, etc. Feldspar 
 
366 MANUAL OF LITHOLOGY. 
 
 and quartz are the predominant minerals, and form a closely 
 intercrystalline background for the other minerals. The 
 hornblende is light green, greenish blue, and blue, and forms 
 long thin prisms. Epidote is usually a secondary form of 
 hornblende and chlorite. With these occur black augite 
 (sometimes altered to viridite and epidote), calcite, and the 
 ores* 
 
 (a) Prasinite (Kalkowsky) is a similar aggregate of horn- 
 blende, epidote, and chlorite 6f intensely green color,. 
 whence the name. 
 
 (b) Amphibole-adinole-sc\\ist is a granular to compact felsitic 
 rock like adinole, with a light green to greenish gray color 
 and schistose structure, from Saxony. It is Credner's 
 " hornschiefer." The composition is (m) generally, as it is 
 seldom that it is coarse-grained enough to distinguish the 
 ingredients without a strong lens. It is formed of quartz, 
 plagioclase, hornblende, epidote, and magnetite. 
 
 PYROXENE GROUP 
 
 PYROXENE ROCK. 
 
 A granular to compact aggregate of predominant pyrox- 
 ene without schistose structure, with or without 
 accessories. Silica and specific gravity are as in the 
 mineral group, with variations on both sides. 
 
 This occurs with the crystalline schists with changeable 
 character (from variation in the predominant mineral). It 
 never plays as large a part as the corresponding amphibole 
 rock. The varieties are : 
 
 (a) Enstatite Rock. From Bavaria, the Transvaal, and in 
 Delaware and Lancaster counties, Pa. As accessories are 
 magnetite, picotite, olivine, diopside, rnagnesite, and mono- 
 clinic pyroxene. Silica 53-55 ; Gr. 3.22. 
 
METAMORPHIC ROCKS. 
 
 (b) Sagvandite (Pettersen) is a similar rock from Norway 
 composed of enstatite and magnesite. Silica 55 ; Gr. 3.22. 
 
 (c) Diallage-hypersthene Rock is a fine-grained aggregate 
 from Madagascar. 
 
 (d) Augite Rock forms a granular green and yellow ag- 
 gregate in the mica-schist of western Massachusetts. It 
 occurs also in Scandinavia and Canada. 
 
 (e) Malacolite Rock forms a white granular and almost 
 compact rock, with splintery to earthy fracture, in a bed in 
 the granular limestone of the Riesengebirge and in Sweden. 
 This is the " pyroxenite " of Coquand. It affords silica 55. 
 
 (/) Omphacite Rock, in large irregular grains, with spo- 
 radic grains of olivine and rutile, is found in the Sierra 
 Guadarrama. 
 
 (g) Diallage Rock is a light-green, compact aggregate of 
 diallage, with columnar jointing, from Cyprus, where it is 
 associated with gabbro and serpentine. The diallage is 
 visible with a lens, and is associated with talc, serpentine, 
 and tremolite. 
 
 (Ji) 0&&*-diallage Rock, from the peninsula of Chalcidice, 
 is an aggregate of dark-colored diallage and white lustrous 
 grains of zoisite. As accessories are a talcose mineral and 
 a monoclinic feldspar. It forms a beautiful rock with coarse 
 granitic structure. The diallage is somewhat altered to 
 green fibrous hornblende. 
 
 PYROXENE-SCHIST. 
 
 A similar aggregate to pyroxene rock with a schistose 
 structure. 
 
 This is somewhat more rare than the pyroxene rock, as 
 the alterations that produce foliation generally alter the rock 
 to hornblende, so that the altered states are found under the 
 amphibole-schists. The silica and specific gravity are as 
 above given. The varieties noted are : 
 
368 MANUAL OF LITHOLOGY. 
 
 (a) Augtte-schist is a fine-grained schistose aggregate of 
 pale or dark green augite, Avith sometimes quartz, plagio- 
 clase, magnetite, and chlorite, of rare occurrence in the crys- 
 talline schists. In some cases they are compact, soft, and 
 readily scratched with the finger-nail. They are so com- 
 pact that only augite can be noted with a lens. Much pla- 
 gioclase forms diabase-schist. 
 
 (b) Gtauctf/iane-augite-schist, which varies between dial- 
 lage and omphacite in its augite content is reported from 
 the island of Syra. 
 
 (c) Vesuvtamte-augite-schist is reported from Elster as a 
 thick-banded dirty green or dirty white rock, in lenticules 
 in gneiss, composed of quartz, garnet, and augite, with vesu- 
 vianite, plagioclase, apatite, titanite, and pyrite. Generally 
 <). 
 
 (d) Egeran-schist, Vesuvianite-schist, is a schistose aggre- 
 gate of vesuvianite, augite, tremolite, and quartz. This 
 occurs near Eger, Bohemia, and was first thought to be 
 eclogite. It consists of predominant vesuvianite which ob- 
 tained its name " egeran " from this locality, where this rock 
 lies in an isolated mass in granite. 
 
 ERLAN (Breithaupt). 
 
 A crystalline-granular aggregate of almost colorless 
 pyroxene in irregular grains or fibers, with colorless 
 and limpid feldspar, vesuvianite (m), quartz, epidote, 
 rutile, titanite, biotite, and muscovite. 
 Silica 53.16; Gr. 3--3.I. 
 
 This occurs an beds in gneiss, and is found at Erla 
 (whence the name) near the Schwarzenberg. It is usually 
 a compact felsitic mass with light greenish gray color, ap- 
 pearance like saussurite, and fine-splintery fracture. It was 
 thought by Breithaupt to be of an entirely different compo- 
 sition. 
 
METAMORPHIC ROCKS. 369 
 
 OLIVINE GROUP. 
 
 OLIVINE ROCK. 
 
 A yellowish green to dark green aggregate of granular 
 olivine irregularly arranged, and with or without 
 accessories, but without foliation. 
 Silica 29-41 ; Gr. 2.7-3.3. 
 
 This occurs in many varieties interlaminated with gneiss, 
 mica-schist, hornblende-schist, talc-schist, granulite, etc. 
 It is a rare combination and usually altered to serpentine. 
 The bands and masses are irregular and of subordinate ex- 
 tent, and, as stated by Geikie, were " probably eruptive 
 masses contemporaneous with or subsequent to the sur- 
 rounding gneisses and schists." Olivine rarely occurs alone, 
 but is combined with one of the pyroxenes. It alters to ser- 
 pentine and talc. The varieties are : 
 
 (a) Enstatite-Q\\vi\\Q Rock, with diopside, green clino- 
 chlore, and magnetite, in a bed in the Fichtelgebirge with 
 hornblende-gneiss. It alters to talc-schist. It is also found 
 in Austria and Sweden. 
 
 (b) Bronzite-oliv'me Rock, from Austria, between diorite- 
 schist and biotite-gneiss, consisting of olivine and actinolite 
 in which the bronzite occurs as phenocrysts. Spinel, ser- 
 pentine, magnetite, and chlorite also occur. 
 
 (c) Amphibole-o\i\\nQ Rock, from Himberg, Austria, with 
 olivine forming one third of the mass, the rest being actino- 
 lite, hypersthene, dark green spinel, clinochlore, and talc. 
 The weathered crust shows amphibole and anthophyllite. 
 It occurs also in Sweden. 
 
 (d) Garnet-Q\\v'me Rock, in granulite of the Kampthal, 
 Austria, is composed of olivine, picotite, pyrope, bronzite, 
 hornblende, and scanty diallage in a coarse mixture. 
 
 (e) Chromite-olivine Rock. This is like dunite, but carries 
 actinolite, pearly mica, sporadic diopside, and pyrrhotite. 
 
370 MANUAL OF LITHOLOG Y. 
 
 It is found at the Eulengebirge in Silesia, where it forms a 
 dark green lenticule, thirty feet long, in amphibolite. A 
 serpentinized variety is found in Steiermark, and in Norway 
 (in quartzite and mica-schist) is a similar greenish fine- 
 grained aggregate of light olivine, colorless pyroxene, mica, 
 and chromite. 
 
 OLIVINE-SCHIST. 
 
 A schistose aggregate of predominant olivine, fresh or 
 serpentinized, and with or without accessories. Silica 
 and specific gravity as above. 
 
 This occurs to a slightly less extent than the " rock," as 
 the imposition of foliation induces changes to serpentine or 
 talc. There is not so much of a tendency towards predomi- 
 nant minerals associated with olivine as in the last variety. 
 As accessories are smaragdite in prisms, light brown en- 
 statite, chromite, bronzite prisms, black hornblende, acicular 
 tremolite, augite, gold, garnet, talc, chlorite, and magnetite. 
 It is found in Sweden, Greenland, Africa, and in a widely 
 developed zone between the Blue Ridge and the Great 
 Smoky mountains in North Carolina. At the last locality 
 the olivine is fresh and oil-green, and varies from a distinct 
 schist to a rock with slight foliation. 
 
 EULYSITE (Erdmann). 
 
 A thin-plated aggregate of fayalite, omphacite, and 
 brownish red garnet, with some apatite and magnetite, 
 and (sporadically) smaragdite-like hornblende and 
 mispickel. 
 
 This occurs near Tunaberg, Sweden, in a thin lenticular 
 bed in granulite (or gneiss) about 30 feet thick and 350 to 
 500 feet long. 
 
MINERALS AS ROCKS. 
 
 Under this division it is proposed to discuss the iron ores, 
 serpentine, kaolin, bauxite, magnesite, barite, the iron sul- 
 phurets, and sulphur. Some of these might have been in- 
 cluded under the previous groups if their origin had been 
 a single one, but as they have been formed in a number of 
 ways, they must be placed by themselves, rather than split 
 among the various classes according to the forces that pro- 
 duced each portion. The others are simple minerals and 
 only of local occurrence, so that their bulk is inconsiderable 
 in comparison with the simple minerals noted in the previous 
 pages. They will be described without further discussion, 
 and those of similar composition will be grouped together. 
 
 THE IRON GROUP. 
 
 LIMONITE (Beudant, not of Hausmann, as the latter 
 was for bog ore only), Brown Hematite (Jameson), 
 Brauneisenstein (Ullman, not of Werner nor Haus- 
 mann, as they included more than this rock), Bog- 
 iron ore (Kirwan). 
 
 A compact, earthy, porous, fibrous, scaly, oolitic aggre- 
 gate of hydrated sesquioxide of iron ; yellowish 
 (through brown) to black ; yellowish brown streak ; 
 with accessory manganese, clay, and silica. 
 
 Iron 59.89; water 14.44; H. 1-5.5 < Gr. 3.4-3.95. 
 
 It occurs at the bottom of marshes (whence the name), 
 ponds, and lakes, where it has settled from chemical precipi- 
 
 371 
 
3/2 MANUAL OF LITHOLOGY. 
 
 tation or the action of organisms on the solutions in which 
 it is held ; as a matrix of the lower layers of porous strata 
 resting against impervious ones ; as mixed with drift when 
 aggregated from old surfaces by glacial action ; as replacing 
 silica in chert or limestone (dolomite) in beds and oolitic 
 aggregations ; as alterations of hematite or siderite ; as rust- 
 ings and weatherings of ferruginous minerals (magnetite, 
 pyritiferous aggregates, black bisilicates, etc.), or teachings 
 from ferruginous soils and clays, 'it is thus aggregated with 
 clay, sand, gravel, and other impurities in more or less com- 
 pact forms. It forms purer concretions of varying form 
 from shot and pea sizes to aggregates weighing several hun- 
 dredweight. It is always forming and quite rapidly, as the 
 clays from limonite washings that have been emponded 
 form strata of considerable depth, which have along their 
 lower layers incipient aggregations of a soft nature, and in 
 several cases the writer has found shelly concretions about 
 discarded track-spikes that have lain in moist places the 
 spike being reduced to a skeleton of the impurities in the 
 iron. The wooden boxes leading water from coal mines in 
 a short time are lined with a layer of limonite, and whatever 
 impurities may have been in suspension, as a compact and 
 hard rock. The places where the aggregations take place 
 are generally hollows in the surface rocks, or in beds where 
 replacement is in progress. In some cases the cavities are 
 caverns hollowed by subterranean solutions whose roofs 
 have fallen in or been removed by glacial action. It is 
 found in surface hollows mixed with clay, drift, etc., along 
 the Archaean area of the Atlantic border of the United 
 States ; as cement for sands, etc., in Lehigh, Northampton, 
 Columbia, and (extensively) Center counties, Pa. ; as replac- 
 ing silica and calcite in beds from Virginia to Georgia, 
 Texas, Vermont, and elsewhere. These can be divided 
 into two general varieties : 
 
MINERALS AS ROCKS. 373 
 
 (a) Bedded, where the aggregates are replacements or 
 concretions in definite beds. Here the impurities are those 
 of the original bed, and the iron is more generally dissemi- 
 nated through the mass than assembled at definite points. 
 Here also are placed the fillings of veins, cracks, etc., in 
 other rocks. 
 
 (b] Loose, where the ore is in aggregates distributed 
 through surface accumulations, and can be readily worked 
 by pick and shovel. 
 
 As far as general appearance of the individual particles 
 is concerned, there is little difference in appearance between 
 these two divisions, and in each are found particles from 
 shot sizes up to many feet in diameter which may be clayey, 
 soft, and impure, showing the lighter colors noted above, or 
 comparatively pure, dark-colored, and hard. The shapes 
 may also vary from massive to reniform, stalactitic, oolitic, 
 scaly, pisolitic, concretionary (solid or hollow), in the last 
 case called " ore-pots," or the ore may be a coloration of 
 clay, sand, etc., either loose or hard ; if the former, it is 
 yellow ocher. 
 
 RED HEMATITE, Specular Iron. 
 
 A compact, earthy, fibrous, scaly, oolitic, and sometimes 
 crystalline aggregate of anhydrous sesquioxide of 
 iron ; red to black ; streak red ; with accessory man- 
 ganese, silica, and clay ; sometimes magnetic, and 
 magnetipolar. 
 
 Iron 70; H. 2-6.5 ; Gr. 4.5-5.2. 
 
 This occurs like limonite, but under conditions that 
 favored the formation of anhydrous sesquioxide, such as the 
 deposition of iron oxide in heated waters, die replacement 
 of silica and calcite in beds in hot climates; r*nd, unlike lim- 
 onite, it may have had an eruptive origin It is found in 
 
374 MANUAL OF LITHOLOGY. 
 
 beds and lenticular masses in the crystalline schists, and 
 frequently with the crystal (specular) form. It also is found 
 as original or replacement formations in oolitic aggregations, 
 as in the beds of the Clinton formation from New York to 
 Alabama, and in Wisconsin, Illinois, and Kentucky. In 
 many cases this is a replacement, as the fragments of shells 
 are turned to ore, and in the interiors of many of the un- 
 changed ones are specular crystals from the intruding solu- 
 tions. The extensive beds of the Penokee-Gogebic region 
 are also replacements ; the immense beds of the Marquette- 
 Menominee region are thought by some to be eruptive, and 
 the Mesabi beds to be precipitates from a heated ocean as 
 are the clay ironstones, which are mixtures with clay. 
 There are decided varieties of this rock, as follows : 
 
 (a) Red Hematite. This is the common kind, and is com- 
 pact, earthy, fibrous, and oolitic. It breaks with an earthy 
 to silky luster. 
 
 (b) Micaceous Hematite. This is a variety in thin folia. 
 In some cases it is interbedded with chlorite schist, as in 
 Hungary. At the Republic mine in Michigan the immense 
 bed is formed of a fine micaceous aggregate with metallic 
 luster and somewhat fissile structure. 
 
 (c) Specular Hematite. This occurs in crystalline aggre- 
 gates. The island of Elba affords fine examples. It is also 
 found at Pilot Knob, Mo., in the Lake Superior region, New 
 York, and Canada. 
 
 As an example of parallel beds of varying ores the 
 Lynchburg region of Virginia is remarkable, as there one 
 /finds limonite, red hematite, and magnetite in parallel con- 
 torted beds between chlorite-schists, limestones, and sand- 
 :stones. When the inclosing rocks are both limestone, the 
 bed is limonite ; when limestone on one side and sandstone 
 oDr schist on the other, red hematite ; when sandstone and 
 
MINERALS AS ROCKS. 375 
 
 schist, magnetite. The following varieties are due to ad- 
 mixtures with other minerals: 
 
 (d] Siliceous Hematite. This is a replacement of silica 
 by hematite to form a jasper, thence a jaspery hematite, 
 thence a hematite. All variations can be found in the many 
 workings of Center County, Pa. 
 
 (e) Black Hematite is a manganiferous variety with a 
 black color and streak. 
 
 (/) Menaccanite, Ilmenite, Titaniferous Iron Ore, occurs 
 in beds or veins in diorite at Krageroe, Norway, and in 
 masses at Bay St. Paul, Canada, in syenite. It also occurs 
 as sands, and is called iserine. 
 
 MAGNETITE. 
 
 A granular, compact, and schistose aggregate of a com- 
 pound of protoxide and sesquioxide of iron ; black 
 color and streak ; metallic luster ; magnetic and 
 magnetipolar. 
 
 Iron 72.41 ; H. 5.5-6.5 ; Gr. 4.9-5.2. 
 
 This occurs in beds and lenticular masses of great size in 
 gneiss, mica-schist, chlorite-schist, hornblende-schist, and 
 granular limestone, and is found in the Archaean formations 
 of the world, and especially in Scandinavia, the Urals, east- 
 ern North America, and the Lake Superior region. Its 
 origin is either eruptive or metamorphic. As the former it 
 occurs in gabbro regions, and in Rhode Island is a titan- 
 iferous magnetite eruptive (cumberlandite). It sometimes 
 seems to be a metamorphosed limonite ; in north Wales it 
 is a metamorphic replacement of oolite. Among large 
 masses is the iron mountain of Gellivara in Lulea-Lappmark 
 which is over 500 feet high, i^ miles wide, and 3 miles 
 long. The accessories are numerous, as would become a 
 metamorphic rock, and are hematite, chromite, chlorite, 
 
t MANUAL OF LITHOLOGY. 
 
 titanite, pyrite, chalcopyrite, quartz, apatite, hornblende, 
 augite, garnet, feldspar, etc. The varieties are : 
 
 (a) Catawbirite (Lieber). From South Carolina, where it 
 occurs in great abundance. It is an intimate aggregate of 
 magnetite and talc. 
 
 (b) Chromic Magnetite, where chromite is the sole acces- 
 sory, and is predominant in the mixture. 
 
 (c) Garnetiferous Magnetite. This occurs near garnet 
 rock, and passes into it. 
 
 SIDERITE (Haidinger), Spathic Iron. 
 
 A granular to compact aggregate of carbonate of the 
 protoxide of iron ; yellowish white, gray, or yellowish 
 brown ; streak white ; darkens to brown or black on 
 exposure to the air ; effervesces with acids. 
 Iron 48.22; H. 1-4.5; G"r. 2.5-3.9. 
 
 This occurs in beds and masses of varying dimensions, 
 but not so large as in the ores already described, in gneiss 
 and the crystalline schists, and as beds (with clay) in recent 
 formations also ; in veins in the oldest rocks, and in the Erz- 
 berg in Styria forms a mountain 2700 feet high. As black- 
 band and clay ironstone it occurs in beds in various forma- 
 tions. As spathic ore it is found at Roxbury, Conn. ; as 
 clay ironstone, in the Carbonic of the Appalachian area, and 
 as a bed extending under Chesapeake Bay. As black-band- 
 it is found in the coal measures of the United States - 
 though not worked, owing to the abundance of better ores. 
 As varieties are : 
 
 (a) Spharosiderite, Clay Ironstone, is a dull brown to 
 black compact form of siderite, with a variable mixture of 
 clay and some organic matter. It occurs in the Carbonic 
 and other formations in the form of nodules gathered about 
 some object (pebble, leaf, fossil), or as beds interstratified 
 with shales and coals. 
 
MINERALS AS ROCKS. 377 
 
 (b) Black-band. A compact and frequently siliceous 
 clay ironstone rendered black by a large proportion of car- 
 bon, and with so much of it that it will inflame in heaps 
 without admixture with coal. 
 
 FRANKLINITE (Berthier). 
 
 A massive, coarse- to fine-granular and compact aggre- 
 gate of protoxides of iron, zinc, and manganese, com- 
 pounded with sesquioxides of iron and manganese; 
 iron-black ; streak dark reddish brown ; luster metal- 
 lic ; acts slightly on the magnet. 
 
 Iron 45-48; zinc 9-20; manganese 8-12; H. 
 5.5-6.5; Gr. 5.07. 
 
 This may be called a manganese-zinc-magnetite. It oc- 
 curs at Franklin and Sterling Hill, N. J., where it forms 
 large beds in granular limestone, and is associated with 
 massive zincite and willemite. This is its only occurrence 
 as a rock. 
 
 SERPENTINE ("Ophites," Pliny). 
 
 A massive, fine-granular to cryptocrystalline and com- 
 pact rock, sometimes slaty, soft, with greasy feel ; 
 dark green to brown ; usually with accessory min- 
 erals. 
 
 Gr. 2.5-2.7; H. 2.5-5.5. 
 
 This occurs in many ways, as already described in the 
 foregoing pages, and is the alteration product from many 
 minerals. The varieties with calcite have been noted. It 
 frequently is porphyritic from phenocrysts of pyrope, and 
 often slaty. The accessories that form varieties are olivine, 
 amphibole, pyroxene, garnet, chlorite, talc, and the iron 
 ores ; less frequently quartz, and opal. As variations 
 in texture and structure are: (massive) retinalite, por- 
 cellophite, and bowenite ; (lamellar) antigorite, from 
 
37 8 MANUAL OF LIT HO LOGY. 
 
 Piedmont; williamsite, from Texas, Pa.; (foliated) mar- 
 molite, from Hoboken, N. J., Blandford, Mass. ; ther- 
 mophyllite, from Hopansuo, Finland ; (fibrous) chrysotile, 
 picrolite both abundant. Admixture with opal forms 
 silicophite (Schrauf) ; with garnet, ^or^-serpentine ; with 
 bronzite, bronzite-serpentine, etc. It joints irregularly (ex- 
 ceptionally it is columnar, frequently tabular). It is most 
 frequently found in irregular and subordinate beds between 
 crystalline schists, and also forms the necks of altered erup- 
 tives. It occurs massive and in workable quantities in New 
 England and along the Atlantic States. 
 
 BARITE, Barytes, Heavy Spar. 
 
 Sulphate of barium; Gr. 4.3-4.7; 11.2.5-3.5; white to 
 black usually white, gray, or blue (the last two 
 being transparent). 
 
 It occurs as a gangue in metal-bearing veins throughout 
 the world, and in veins and pockets in limestone. It is 
 found in bowlders and nodules in clay in Virginia, between 
 slate and limestone, and in surface clay in Missouri. The 
 supply in the United States comes from the last two States, 
 though small amounts are found in North Carolina, Illinois, 
 and New England. 
 
 MAGNESITE (Brongniart). 
 
 Carbonate of magnesia ; Gr. 3-3.2 ; H. 3.5-4.5 ; white to 
 brown (according to the amount of iron). 
 
 It occurs associated with serpentine, talc-schist, and other 
 magnesian rocks, and is found at Veitsch (Styria), Austria; 
 near Frankenstein (Silesia), Prussia ; Mantoudi (Euboea), 
 Greece ; and Child's Valley, Cal. The Austrian de- 
 posits are beds conformable to Silurian strata ; those of 
 Greece are in large veins in serpentine. Magnesite has also 
 been reported from Bolton, Canada. 
 
MINERALS AS ROCKS. 379 
 
 KAOLIN, Porcelain Clay. 
 
 Hydrous silicate of alumina ; Gr. 2.4-2.63 ; H. 1-2.5 J 
 white when pure, but colored variously by impurities. 
 
 This occurs as the alteration by weathering of aluminous 
 minerals, especially feldspars of granite and gneissoid rocks 
 and porphyries. Where weathering has taken place for a 
 long time, without erosion, there remains a large deposit of 
 kaolin. It is found in the Carbonic measures of the Appala- 
 chian region, and forms extensive beds in the Tertiary for- 
 mation near Richmond, Va. A variety at Lawrence County, 
 Ind., and elsewhere through that State, with a great amount 
 of water, is called indianaite. It is found at Brandon, Vt. ; 
 in the Cretaceous and Quaternary of New Jersey ; in Del- 
 aware, Maryland, Missouri, Oregon, and California. 
 
 BAUXITE. 
 
 Hydrated sesquioxide of alumina with accessory silica 
 and sesquioxide of iron; Gr. 2.55; H. 1-3; whit- 
 ish, yellowish, brown, red, and black, and always 
 more or less stained with iron, manganese, and other 
 minerals. 
 
 This occurs as sediments (in Europe) alternating with 
 sandstones, limestones, and clays ; in pockets and cavities in 
 limestone, and in concretionary grains scattered through 
 the limestones. It is generally oolitic or concretionary. 
 The geological formations where it is found are Trias, 
 Jurassic, and Miocene-Tertiary. It occurs in the United 
 States in residual clays and irregular and ill-defined de- 
 posits, which may be alteration products of underlying lime- 
 stones, as in Europe. The geological horizons of the de- 
 posits are Lower Silurian and Tertiary. It is found in 
 Georgia, Alabama, Tennessee, and abundantly in Arkansas, 
 where it is said to be inexhaustible. It is a source of 
 aluminium. 
 
MANUAL OF LITHOLO^ 
 
 PYRITES. 
 
 Sulphides of iron of varying compositions; Gr. 4.4-5.2; 
 H. 3.5-6.5 ; brass-yellow ; streak grayish black, green- 
 ish black. Under this title are included pyrite, 
 pyrrhotite, and marcasite. 
 
 These occur disseminated in small quantities through the 
 rocks of all ages, and often in large beds of such size as to 
 be called masses. They are found along the eastern slope 
 of the Appalachians from Maine to eastern Alabama. Mines 
 have been worked at Capelton, Canada, Milan, N. H., Staf- 
 ford, Vt, Rowe, Mass., and Tolersville, Louisa County, Va. 
 The 'first and last are the only ones at date affording much 
 of an output. These deposits, though large, are not to be 
 compared with the Rio Tinto deposits that stretch from 
 Spain into Portugal in two vast beds or veins in metamor- 
 phic schists. The southern vein is 300-400 feet wide, and 
 at least 2500 feet long; the northern, 1300-1600 feet wide, 
 and 6000 feet long. At Goslar in the Harz Mountains is 
 a vein ot cupriferous pyrites which is 350 by 1800 feet. 
 At Fahlun, Sweden, is a mass of similar composition in 
 Archaean gneiss and schists. At Agordo, Tyrol, is a mass 
 in talc-schist and clay-slate varying in width from 12 to 250 
 feet. Large desits also occur at Domokos, Transylvania, 
 and Schmollnitz, Hungary. 
 
 SULPHUR. 
 
 Pure sulphur; Gr. 2.072 ; H. 1.5-2.5; color and streak 
 sulphur-yellow. 
 
 This occurs about active volcanoes or associated with 
 beds of gypsum. We can therefore divide the deposits un* 
 der two types : 
 
 (a) The solfatara type, where the mineral is deposited 
 directly from volcanic exhalations (H 2 S and SO 2 ) in cracks 
 
MINERALS AS ROCKS. 38 1 
 
 in the lava and tuffs, or in the clay resulting from their de- 
 composition. 
 
 (b) The gypsum type, where bituminous matter acts on 
 gypsum and reduces it to calcium sulphide and water. The 
 former, being soluble, is affected bythe air, while in solution, 
 to form calcium carbonate and polysulphide of calcium, and 
 the latter breaks up and deposits the excess of sulphur. 
 
 The first type is found in Italy, Japan, southern Utah, 
 and is extensively worked in the- two last the first being 
 somewhat exhausted. The second type is found associated 
 with gypsum in Sicily, France, Spain, northeastern Italy, 
 Greece, and Poland in Miocene-Tertiary formations. Juras- 
 sic beds occur in the Caucasus, and Quaternary deposits in 
 southwestern Louisiana. 
 
SCHEME FOR DETERMINING THE PRINCIPAL 
 
 ROCKS. 
 
 The specimen will fall under one of the four grand divi- 
 sions, according to its TEXTURE. 
 
 (A) Clastic, fragmented, or sedimentary (part), p. 382. 
 
 (B) Compact, dull, or subvitreous. p. 384. 
 
 (C) Compact, vitreous, or resinous, p. 386. 
 
 (D) Crystalline-granular, p. 387. 
 
 It will then be tested to see under which of the following 
 heads it falls : 
 
 I. Untouched or slightly touched by acids. 
 II. Partly attacked by acids. 
 
 III. Completely soluble without effervescence. 
 
 IV. Soluble with more or less effervescence. 
 
 V. Burns more or less readily ; detonates with KNO 8 . 
 
 Having determined under which of the above it falls, it 
 will then be examined regarding its STRUCTURE, whether it 
 be (a) Massive ; (b) Stratified or schistose ; (c] Porphyritic ; 
 (d) Vesicular or amygdaloidal. 
 
 Turning to the following pages, a list of rocks will be 
 found that belong to each group indicated, and the species 
 can be determined by the characteristics there given. 
 
 (A) CLASTIC OR FRAGMENTAL ROCKS. 
 I. UNTOUCHED BY ACIDS. 
 
 (a) Massive or stratified. 
 
 Infusible and insoluble in alkaline solutions. 
 
 Conglomerates and breccias of quartz, jasper, the gran- 
 ites, syenites, etc. 
 
 382 
 
SCHEME FOR DETERMINING THE PRINCIPAL ROCKS. 383 
 
 Sand, gravel, and shingle. 
 Sandstone, grit, and arkose. 
 
 Soluble in alkaline solutions. 
 
 Conglomerates and breccias of opal. 
 Tripoli and tripoli-slate. 
 
 Fusible. 
 
 Conglomerates and breccias of felsite, trachyte, pitch- 
 stone, rhyolite, the mica-traps, porphyrites, etc. 
 
 II. PARTIALLY ATTACKED BY ACIDS. 
 (a) Massive. 
 
 Infusible or slightly fusible. 
 
 Clay and loam, claystone, shale, clay-slate, and the acid 
 tuffs. 
 
 Fusible readily. 
 
 Conglomerates and breccias of dolerite, basalt, phonolite, 
 gabbro, etc. 
 
 The various basic tuffs. 
 
 III. COMPLETELY SOLUBLE IN ACIDS WITHOUT EFFER- 
 VESCENCE. 
 
 (a) Massive or stratified. 
 Give water. 
 
 Gypsum, and the hydrated iron and manganese ores. 
 Without water. 
 
 Anhydrite, and the anhydrous iron and manganese ores, 
 except siderite. 
 
 IV. MORE OR LESS SOLUBLE IN ACIDS WITH EFFERVES- 
 CENCE. 
 
 (a) Massive or stratified. 
 
 The limestones and dolomites, siderite, marl, travertine, 
 and tufa. Conglomerates and breccias of the above, and 
 bone-breccia. 
 
MANUAL OF LITHOLOGY. 
 
 V. BURN MORE OR LESS READILY. 
 (a) Massive or schistose. 
 The carbonic and hydrocarbonic rocks. 
 
 () COMPACT; DULL OR WITH FEEBLE LUSTER. 
 I. UNTOUCHED BY ACIDS. 
 
 (a) Massive. 
 
 Infusible ; insoluble in potash lye ; density 2.6. 
 
 Chalcedony, jasper, Lydian stone, and other crypto- 
 crystalline varieties of quartz. 
 
 Density 2.9 or above. 
 
 Euphotide, the variety containing Saussure's jade from 
 Monte Rosa. 
 
 Soluble in potash lye. 
 
 Semi-opal, siliceous sinter, and other cryptocrystalline 
 forms of opal. 
 
 Fusible. 
 
 Compact mass and hardness 6. Felsite ; fine-grained or 
 microcrystalline mass. Leptinolite, Adinole, Porphyroid. 
 The compact states of the porphyrites. 
 
 (b) Stratified or schistose. 
 
 Fusible. 
 
 Porphyritic. Slaty Porphyry ; not porphyritic. Halle- 
 flinta. 
 
 Infusible. 
 
 Novaculite. 
 
 (c) Porphyritic. 
 
 With quartz. Quartz-porphyry ; with quartz, feldspar, 
 and mica. Granite-porphyry ; without quartz. Feldspar, 
 mica, and hornblende-porphyrite. 
 
SCHEME FOR DETERMINING THE PRINCIPAL ROCKS. 385 
 
 II. PARTIALLY ATTACKED BY ACIDS, 
 (a) Massive, schistose, porphyritic, and amygdaloidaL 
 
 Infusible or slightly fusible. 
 
 Gray mass with crystals of leucite and augite. Leucite- 
 phonolite, and compact forms of leucite-bearing rocks. 
 
 Reddish or grayish porous mass, with bluish crystals of 
 haiiyne. Haiiynophyre. 
 
 Easily fusible. 
 
 Color green rather than black, decolorized by HCL 
 Augite porphyrite, Aphanite. 
 
 Mass like the above with grains, globules, or pustules of 
 a hardness of 6, fusible. Variolite. 
 
 Bluish or grayish black mass, usually with olivine, sel- 
 dom containing quartz, more commonly calcite or zeolites, 
 in amygdaloidal cavities, fuses to black globule, density 
 generally 3. Basalt. 
 
 Compact mass, black on fresh fracture, weathers reddish, 
 fusible to bottle-green globule, never with olivine, fre- 
 quently with quartz in amygdaloids, density generally less 
 than 3. Melaphyre. 
 
 Compact, subgreasy mass, smooth fracture, gray color, 
 density 2.6, easily fusible. Nepheline-basalt. 
 
 Compact, dull, greenish mass, fusible to white globule, 
 yields water when heated, gelatinizes in HC1, with sanidine 
 in crystals. Phonolite. 
 
 III. COMPLETELY SOLUBLE WITHOUT EFFERVESCENCE. 
 
 (a) Massive, stratified, and sometimes porphyritic. 
 Give water. 
 
 Hardness 1.5-2, give sulphur and lime. Gypsum. 
 
 Hardness 3-4, rarely 5, green, red, brown, sometimes is 
 porphyritic from crystals of garnet, blackens before the 
 blowpipe and fuses with difficulty. Serpentine. 
 
386 MANUAL OF LITHOLOGY. 
 
 Give iron or manganese reaction, density 3.5-4.5. Hy- 
 drous ores of iron and manganese. 
 
 Give no water. 
 
 Give sulphur and lime. Anhydrite. 
 
 Give iron or manganese reaction, density 4.5-5.5. An- 
 hydrous ores of iron or manganese. 
 
 IV. MORE OR LESS SOLUBLE WITH EFFERVESCENCE. 
 
 (a) Massive and stratified. 
 
 Hardness under 3, infusible. 
 
 Some limestones, dolomites, and calcareous clay slates. 
 A mixture of calcite and serpentine. Ophiolite. 
 
 (C) COMPACT, VITREOUS, OR RESINOUS. 
 I. UNTOUCHED OR SLIGHTLY TOUCHED BY ACIDS. 
 
 (a) Massive, schistose, and sometimes porphyritic. 
 Infusible, soluble in potash lye, never porphyritic. Opal, 
 
 Siliceous Sinter. 
 
 Fusible. 
 
 Conchoidal fracture, fusible to a blebby globule. Ob- 
 sidian. 
 
 Pearly luster, splintery fracture, gives water in the open 
 tube, frequently containing round grains. Perlite. 
 
 Resinous luster, conchoidal fracture, fuses without in- 
 tumescence to a white vesicular glass. Pitchstone ; with 
 balls of felsite, or crystals or grains of feldspar, and quartz. 
 Pitchstone-porphyry. 
 
 Mass porous, perlitic, sometimes slaty, with crystals of 
 sanidine, mica, or quartz. Rhyolite. 
 
 (b) Vesicular, scoriaceous, pumiceous. 
 
 Perlite and obsidian occur in the first two states ; when 
 in the third, the rock is called pumice. Dark mass, fusible 
 
SCHEME FOR DETERMINING THE PRINCIPAL ROCKS. 387 
 
 to black slaggy globule, heavier than pitchstone, obsidian, 
 or perlite. Hyalomelane. 
 
 II. DECOMPOSED BY ACIDS. 
 
 (a) Massive and vesicular. 
 
 Dark mass, fusible to black slaggy globule, heavier than 
 pitchstone, obsidian or perlite. Tachylite. 
 
 (JD) CRYSTALLINE OR CRYSTALLINE-GRANULAR. 
 I. UNTOUCHED OR SLIGHTLY TOUCHED BY ACIDS. 
 
 (a) Massive, and frequently porphyritic. 
 
 Coarse crystalline-granular or granitoid. 
 
 Quartz, orthoclase, and granite, with mica replaced by 
 talc or chlorite. Protogine ; by tourmaline. Tourmaline- 
 granite ; with tourmaline abundant and flesh-red orthoclase. 
 Luxullian ; mica replaced by epidote. Epidote-granite ; by 
 iolite. Cordierite-granite ; by hornblende. Syenitic Gran- 
 ite. 
 
 With the quartz arranged in layers on the cleavage 
 planes of the orthoclase and white mica. Graphic Granite. 
 
 Like the last, but more coarse and irregular. Pegmatite. 
 
 Quartz and orthoclase. Aplite. 
 
 Quartz and zinnwaldite. Greisen. 
 
 Orthoclase and hornblende. Syenite. 
 
 Oligoclase and hornblende, greenish appearance. Diorite. 
 
 Oligoclase, hornblende, and quartz. Quartz-diorite. 
 
 Oligoclase, hornblende, quartz, and biotite, fusible. 
 Tonalite. 
 
 Oligoclase, orthoclase, hornblende, mica, and quartz. 
 Mica-diorite. 
 
 Cyanite and white mica, with garnets, infusible. Cyanite 
 Rock. 
 
MANUAL OF LITHOLOGY. 
 
 Mica, garnet, and iolite. Kinzigite. 
 Garnet and smaragdite. Eclogite. 
 
 Fine crystalline -granular. 
 
 Rough mass, containing crystals of sanidine and horn- 
 blende, density 2.6, mass fusible to coLorless glass or enamel. 
 The Trachyte group. 
 
 Grayish mass, containing much magnesian mica in 
 laminae, infusible or slightly fusible. Minette. 
 
 Fusible mass, with much magnesian mica in laminae and 
 crystals of hornblende, and oligoclase. Kersantite. 
 
 Reddish mass, hardness 7, attacked by HCi after long 
 heating, density 3.4-4.3. Garnet Rock. 
 
 Diallage and Saussure's jade (compact zoisite) fusible 
 \vith difficulty, gelatinizes after fusion. Euphotide (in part). 
 
 Rough porous mass, gray or black, with crystals of oligo- 
 clase and hornblende. Andesite. 
 
 Like the above, but pyroxene replacing the hornblende. 
 Pyroxene-andesite. 
 
 Grayish, porous, crumbly mass like claystone, oligoclase, 
 hornblende or augite, and dark mica. . (Domite from the 
 Puy de Dome) ; same composition, undecomposed. Domite. 
 
 (b) Stratified or schistose and frequently porphyritic. 
 
 Contain feldspar. 
 
 Orthoclase or oligoclase, quartz and mica. Gneiss ; with 
 talc or chlorite replacing mica. Protogine-gneiss ; with 
 iolite for mica. Dichroite-gneiss ; with hornblende for 
 mica. Syenitic Gneiss. 
 
 Plagioclase and hornblende. Diorite-gneiss, Gabbro- 
 gneiss. 
 
 Orthoclase and black mica, grayish or brownish mass. 
 Schistose Minette. 
 
 Orthoclase and quartz, frequently with garnet and cya- 
 nite. Granulite. 
 
SCHEME FOR DETERMINING THE PRINCIPAL ROCKS. 389 
 
 Without feldspar and with quartz. 
 
 Quartz in crystalline grains. Quartzite, Quartz-schist. 
 
 Quartz and a little white mica, in thin sheets, flexible. 
 Itacolumite. 
 
 Quartz and much mica. Mica-schist. 
 
 Quartz and tourmaline. Tourmaline-schist. 
 
 Quartz, tourmaline, and topaz. Topaz Rock. 
 
 Quartz, in greater or less amount, and talc. Talc-schist ; 
 with pyrophyllite in place of talc, and no quartz. Pyroph- 
 yllite-schist. 
 
 Quartz and . hornblende, sometimes hornblende alone, 
 fusible to black or dark green enamel. Hornblende-schist; 
 an aggregate of actinolite. Actinolite-schist ; with glauco- 
 phane, Glaucophane-schist ; with epidote and glaucophane, 
 either Epidote-glaucophane-schist or the reverse, dependent 
 on which is predominant. 
 
 With much argillaceous matter, Argillite ; with much 
 argillaceous matter and much mica, quite easily fusible, 
 Phyllite ; with ottrelite, Ottrelite-schist ; with chiastolite, 
 Chiastolite-schist ; with decomposed pyrite, Alum-schist; 
 with carbonaceous matter, Black Chalk. 
 
 (c) Vesicular and amygdaloidal. 
 
 Feldspathic mass, density 2.6, rough, and generally more 
 or less fusible. Vesicular Rhyolites and Trachytes. 
 
 II. PARTIALLY ATTACKED BY ACIDS. 
 
 (a) Massive. 
 
 Pyroxene, white or gray labradorite, or oligoclase, and 
 magnetite, sp. gr. 2.9-3, color generally black or gray. 
 When coarse-crystalline, Dolerite ; when fine-crystalline, 
 Anamesite. 
 
 Augite, labradorite, or oligoclase, viridite, and magnetite, 
 color greenish. Diabase. 
 
39 MANUAL OF LITHOLOGY. 
 
 Pyroxene and nepheline, greasy luster, sp. gr. 2.6. Neph- 
 eline-dolerite. 
 
 Pyroxene and leucite, the latter in rounded, indistinct 
 crystals. Leucite-dolerite. 
 
 Pyroxene and hauyne with olivine, mica, and leucite ; 
 porous ; brownish or grayish color. Hauynophyre. 
 
 Pyroxene and hornblende with labradorite and oligo- 
 clase, frequently some mica ; gray or brown ; mass fine- 
 crystalline to compact. Trachydolerite. 
 
 Diallage and plagioclase ; easily fusible ; pearly luster. 
 Gabbro. 
 
 Diallage, plagioclase, and much dark olivine. Olivine- 
 gabbro. 
 
 Plagioclase and hypersthene, or bronzite. Norite. 
 
 Hornblende, labradorite, and oligoclase. Labradiorite. 
 
 Orthoclase, elaeolite, zircon, and hornblende. Elaeolite- 
 syenite. 
 
 Orthoclase, red elaeolite, and hornblende. Foyaite. 
 
 Greenish black hornblende and anorthite. Anorthite- 
 diorite ; if arranged in concentric crystalline rings, alter- 
 nating with one another. Orbicular Diorite. 
 
 Deep green hornblende, white or gray anorthite, and 
 little quartz. Egeran. 
 
 Hypersthene in long black needles, augite, and labrador- 
 ite. Teschinite. 
 
 Pyroxene and anorthite. Eukrite. 
 
 Yellow or green chrysolite (decomp. by H,SO 4 ; sol. in 
 HC1 and chromite). Dunite. 
 
 Fine-grained, greenish gray mass with vitreous feldspar 
 (sanidine); weathers with a sharply denned white crust. 
 Phonolite. 
 
 (b) Stratified or schistose. 
 
 Fine-grained, greenish gray mass, showing cleavage sur- 
 
SCHEME FOR DETERMINING THE PRINCIPAL ROCKS. 3QI 
 
 faces of a vitreous feldspar ; weathers with sharply defined 
 white crust. Phonolite. 
 
 Pyroxene, labradorite, viridite ; color greenish. Diabase- 
 schist. 
 
 Fine-grained, greenish, hardness 2.5-4. Chlorite-schist. 
 
 (c) Porphyritic. 
 
 States of the rocks described under (a) and ^b). 
 
 (d) Vesicular and amygdaloidal. 
 
 The dolerite group, Diabase, Phonolite. 
 Cavities filled with analcite. Analcimite. 
 
 III. COMPLETELY SOLUBLE WITHOUT EFFERVESCENCE. 
 
 (a) Massive. 
 
 The iron and manganese ores. 
 
 White, hardness 2.5 ; completely soluble in H a SO 4 , giving 
 HF. Cryolite. 
 
 IV. MORE OR LESS SOLUBLE WITH EFFERVESCENCE. 
 
 (a) Massive. 
 
 The limestones and dolomites, siderite, and travertine. 
 Greenish felsitic mass with much mica ; iron pyrites fre- 
 quently. Fraidronite. 
 
 (b) Stratified or schistose. 
 
 Quartz, mica, and more or less calcite. Calcareous Mica- 
 schist. 
 
 Calcite and mica. Cipolino. 
 
 Greenish mass, hardness 5 ; contains calcite. Kalk- 
 aphanite. 
 
THE ECONOMIC VALUE OF ROCKS. 
 
 In the previous pages the different rocks of the earth's 
 crust have been described and their accessories given. The 
 latter are sometimes beneficial and sometimes injurious 
 when we examine the variety from the standpoint of value, 
 and that is the reason why long lists of accessory minerals 
 have been noted, when they made no variation in species, 
 and exerted no influence upon the color or general charac- 
 ter. It remains to briefly examine the rocks from another 
 standpoint and to see how they are useful. In this light the 
 majority of them are found to be interesting from their 
 differences, but are either inconsiderable in quantity, or 
 worthless from structural or other defects. The useful rocks 
 that remain are few, and in such quantity that it will pay to 
 assemble the necessary machinery to work them. 
 
 The general value of a deposit depends on its amount, 
 the shape in which it is presented, and its distance from 
 market. The last generally disappears with the advent of 
 civilization, and the market comes to the deposit if it be 
 valuable, as the greater portion of the forces tending to 
 civilize the race had their impetus from a desire to secure 
 lasting temples for their divinities, and to fitly adorn them, 
 so that traffic in stones required roads, and the growth of 
 taste inspired arts of adornment. We can describe the 
 savage as the man of the stone age, where the spallings of 
 nature were utilized, and the civilized man as the man of 
 metals. The second of the above conditions is always an 
 important one, for upon k depends the sizes of the pieces 
 
 392 
 
THE ECONOMIC VALUE OP ROCKS. 393 
 
 obtained and their shapes. A bed ol first-class granite may 
 be so jointed and fissured that it cannot be gotten out in 
 pieces of any size, and can only furnish smaller material, 
 like Belgian blocks for paving. In the same way the acces- 
 sory minerals affect the value of mortars, abrasives, ferti- 
 lizers, lubricants, etc., and injurious ones that cannot readily 
 be removed destroy them entirely ; so that the examination 
 of a deposit should not end with a survey that determines 
 its bulk, but should include an analysis of its surface im- 
 purities and a study of the same at depths, as weathering 
 may have removed harmful portions; and should further 
 determine the purposes for which it is unfit, as well as those 
 to which it is adapted. 
 
 As the principal use of rocks is as materials for construc- 
 tion, those fit for such a purpose will first be considered. 
 They may be utilized as spallings, or in bulk (" dimension 
 stones "). Their value in the latter case depends upon their 
 strength and life, and these vary with the means ot con- 
 solidation, which are : 
 
 1. Intercrystallization of the minerals together without 
 cementing material. 
 
 2. Compression of the clastic grains so that they have 
 been forced to fill the inequalities in those adjacent, and 
 thus approach the intercrystallization of the first case. 
 
 3. A cementing medium, which may be : 
 (a) Silica. 
 
 () Clay. 
 
 (c) Calcite. 
 
 (d) Iron oxides. 
 
 The strength of a rock depends on its compactness, free- 
 dom from a cementing medium, hardness, and position with 
 respect to its bedding planes ; so that rocks formed through 
 the first two means are stronger than those formed through 
 the third if of equal hardness and compactness. 
 
394 MANUAL OF LITHOLOGY. 
 
 The hje of a rock varies with the resistance to weather- 
 ing of its weakest part, so that uniformity of composition is 
 a prime requisite. Conditions that favor weathering are : 
 possessing cements of clay, calcite, and iron oxides ; ad- 
 mixtures with pyritous minerals, or whatever will readily 
 seek more stable forms. In fine, the aggregates of the most 
 stable minerals will live longer that unstable ones. The 
 locality in which the rock is to be used must be considered, 
 as this greatly influences the rock value. A porous rock 
 that would readily scale with frost in the latitude of New 
 York City would weather well in Florida and more tropical 
 regions. Evenness of temperature is a prime factor in lon- 
 gevity, and a stone that would spall under the changes of 
 temperature at New York would last well in the even tem- 
 perature of the Pacific coast from California to Washington. 
 This is the reason why Egyptian monuments have retained 
 their freshness, though exposed to fierce heats ; but have 
 scaled through the variations in temperature when removed 
 to this and other climates. Porosity does not enter here, as 
 so dense a rock as the Potsdam quartzite in a few years 
 takes spheroidal shapes through changes in temperature, 
 while the rock is fresh, as shown in recent railroad cuts. 
 We must therefore consider the region in which the rocks 
 are to be used, and the effects of variation in temperature, 
 as well as changes in atmospheric conditions. Under the 
 latter comes the difference in behavior of the magnesian 
 limestone of which the houses of parliament of Great Britain 
 are built. When used to build country seats, it has lasted 
 for years in pure air, but the gas-laden air of London is 
 surely destroying it. The economic value of a rock, there- 
 fore, depends on many conditions outside of its composition. 
 The different rocks fit for constructive purposes will now be 
 discussed. 
 
 Granite. Under this head will be noted the primary 
 
THE ECONOMIC VALUE OF ROCKS. 395 
 
 rocks and similar crystalline schists. The most durable are 
 'those with fine grain, with small amounts of the black bisili- 
 cates, not too much feldspar, and compact and non-porous 
 structure. The admixture with too many accessories allows 
 too much variation in expansion among the ingredients, and 
 -consequent strain in the mass ; or, with pyritous minerals, 
 carries weathering to its interior ; while porous feldspathic 
 varieties absorb moisture and readily kaolinize. The beauty 
 of a granite is in its uniformity of grain and color ; so that 
 variations in the first, and inclusions of foreign rocks (more 
 or less resolved), such as knots of mica-schist, etc., lower the 
 value. Gneiss is often as good as granite, and generally 
 does not absorb as much heat, so that it cannot be subjected 
 to as sudden strains by changes in temperature, but it is 
 never as uniform in color. Diabase and diorite cannot be 
 compared with the above, as they readily weather; and 
 basalt is inferior from the same cause, as well as from its 
 being fine-jointed, so that it cannot be obtained in large 
 pieces, and its brittleness forbids its ready dressing. For 
 want of a better stone trachyte is sometimes used ; but in 
 competition with granite (under which syenite is included) 
 .and gneiss the porous extrusives are of little value in cli- 
 mates with severe frosts, but can be used in the tropics. 
 The exceptions to this statement are the phonolites which 
 have been rendered slaty, and the devitrified basalts and 
 rhyolites which have been altered and transformed to slates, 
 but these are not used in masses, so that the above rule 
 holds good. 
 
 Sandstone. The nearer this rock comes to the second 
 condition above given, and is free from cementing media, 
 the better it is for building purposes. A small amount of 
 clay will not lower the strength of a fine-grained variety ; 
 but if coarse-grained and porous it will absorb water and 
 cause the rock to swell. Some rather fine-porous stones 
 
396 MANUAL OF LITffOLOGY. 
 
 will be unfit for immediate use if quarried at or near water 
 level, as they will be full of moisture. This will make a. 
 damp wall on the inside, and flake under frost on the out- 
 side ; so that the stone should be well seasoned before being- 
 dressed and used. Calcareous cements in sandstone will 
 invariably and speedily dissolve and allow the rock to- 
 crumble. The best varieties are those purely siliceous, of 
 fine grain, and free from pores, cements, and unstable acces- 
 sories. 
 
 Limestone* This is generally not as fit for exteriors as 
 sandstone, as it weathers more readily, and, as it is not as 
 stable a compound, the accessories form new combinations 
 with it to its disadvantage. Limestones should be as free 
 as possible from all cements, excepting silica. Ferruginous 
 cements are worse here than in sandstone, as they react on 
 the stone, and carry to the interior the process of disintegra- 
 tion. Pyritous aggregates have the same effect. Coarse- 
 crystalline silica unfits the stone for careful working, but 
 fine-crystalline silica adds to its strength. The weathered 
 outcrops will allow us to determine the result of time upon 
 a given stone. The beauty of a stone is frequently destroyed 
 by such an accessory as the mineral oil in the Niagara lime- 
 stone in northern Illinois. When quarried, it is white, but 
 soon becomes smutty in cities, while it remains cleaner in 
 the purer air of the country. As the oil is not evenly dis- 
 tributed, the stainings are irregular, and are thought some- 
 times to add to the appearance of the stone. 
 
 Marble. In the language of the trade any stone that is 
 fine-grained and capable of taking a polish is a " marble," so 
 that many ordinary limestones fall under this designation. 
 The true marbles, will however, occupy the greater part of 
 the material sold under the name. For exteriors dense and 
 strong stones are necessary, while loose and soft ones can be 
 used inside. In any case the stone should not be placed 
 
THE ECONOMIC VALUE OF ROCKS. 
 
 where it will be subjected to strain, or it will crack, if not 
 crush. The modern methods of sawing stone from the solid 
 in the quarry and working the product with the sand-blast 
 allow us to market many brittle stones that formerly could 
 not be used. 
 
 Slate. Not all parts of slate deposits are valuable. 
 .Slates should split readily and into thin and even plates. 
 All seams and streaks of quartz, calcite, and other acces- 
 sories should be avoided, as they condemn the product. 
 Contaminations of pyrites, too much calcite as a cementing 
 medium, and too great porosity shorten the life of slate. 
 Weathering takes place mechanically and chemically. The 
 mechanical part is like the straining already noted from 
 changes in temperature, and slates are more subject to this 
 than other stones, owing to their color and exposure to 
 greater amounts of heat. They are further unfortunate in 
 being placed with the bedding exposed to the weather, so 
 that the strain comes along those planes where cleavage is 
 readiest, and the changes from day to night, or from sun 
 to shower, induce great and sudden strains. The chem-' 
 ical weathering is on a parallel with that in limestones, 
 and is due to the decompositions of the accessories and the 
 attempt to form stable compounds at the expense of the 
 rock. Both forms of weathering are going on at the same 
 time, so that in the purest slates mechanical weathering 
 loosens the outer film in minute folia, and these are knocked 
 off by the impact of rain-drops. The slates free from im- 
 purities and exposed in the purest air will weather rapidly, 
 but the color of the roof will show whether the weathering 
 is mechanical or chemical. Good slate will show dark after 
 3 T ears of exposure, but bleached and mottled slate shows 
 -chemical action on too great an amount of cementing me- 
 dium, or on spots of impurities. Those wishing to study 
 the strength of slates will find Dr. Merriman's discussions 
 
39 8 MANUAL OF LITHOLOGY. 
 
 before the American Society of Civil Engineers of great 
 value. 
 
 Clays. For brick and coarse constructions all clays are 
 more or less useful, but it may be well to bear in mind that 
 alkalies make clay fusible ; and while a small amount may be 
 good, and may render the product denser, too much will 
 make it so fusible that it will warp during firing, or en- 
 danger the strength of a structure during a conflagration, 
 where only a part is on fire. Pottery clays are mixtures 
 of kaolin, as the pure mineral shrinks, cracks, and checks, so 
 as to spoil the product. Silica counteracts this. Iron is the 
 most undesirable accessory under any form, as it destroys 
 the white color. Fire-clays are found as the under-clays of 
 the coal-beds, where vegetation has removed the alkalies 
 and alkaline earths. Any accessories that tend to flux the 
 clay must be looked for in the examination of the deposit 
 for this purpose. Segregations of " giant granite " are 
 valuable for the feldspar, which is ground and used as a flux 
 or admixture in the paste. Flints are used after grinding 
 "for similar mixtures. 
 
 Sands. These are used for glass of varying kinds. 
 Clean sea sand free from iron, or sands from the modified 
 drift of the northern part of the United States, as well as 
 some weathered outcrops of the calciferous sand-rock, are 
 valuable for making ordinary window-glass, but flints are 
 necessary for the whiter and clearer article. For bottles 
 (green) any sand will do, and even granulite is used in 
 abundance, as it contains the necessary ingredients, and can 
 be charged at once into the furnace. It is found in Canada 
 and the eastern part of the United States. Sands for mold- 
 ings must have sufficient clay to keep the form. 
 
 Mortar, Cement. Limestone for mortar should not 
 have more than 8 per cent of silica or similar impurities if 
 first-class mortar is desired. Hvdraulic cements are found 
 
THE ECONOMIC VALUE OF ROCKS. 399 
 
 along the junctions of slates and limestones, but all such 
 junctions are not " hydraulic." Those that " set " under 
 water are called " cements " when they set without first 
 slaking-, but " hydraulic limes " when they slake first. 
 Specimens should be burned and ground to see whether 
 this property is inherent, as without it the deposit is neither 
 limestone nor slate, and of little value. 
 
 Abrasives. For grinding and polishing it is necessary 
 to secure something harder than the body to be treated. 
 It is not always necessary to secure the hardest substance. 
 We can divide the abrasives into the hard, medium, and 
 soft varieties. The hard comprise the corundums, which 
 are found in the Archaean formations, and are separated 
 from the matrix by grinding, and removing the iron ores 
 with the magnet. The medium abrasives are ordinary sand 
 (quartz), garnet, and other minerals of similar hardness that 
 are found in sufficient abundance. The soft abrasives are 
 tripoli and infusorial earth. Tripoli is also used as the dope 
 in dynamite. As compact abrasives the novaculites of Ar- 
 kansas are predominant in this country, though gritty mica- 
 schists and metamorphic phyllite are used for coarse hones. 
 The best and finest oil-stone in the world is the microcrystal- 
 line garnet rock of Belgium. For millstones gritty sand- 
 stones, buhrstones, porous porphyries, etc., are used. 
 
 Lubricants. The minerals used for diminishing friction 
 are graphite, talc, and mica. All of them must be free from 
 grit. It has been found that their value lies in the fact that 
 they are foliated, and the best graphite lubricant is now 
 delivered in flakes rather than in powder. Mica is freed 
 from grit and ground to a flaky impalpable sand. In this 
 way the micaceous segregations in " giant granites " can be 
 utilized. In the same way the foliated varieties of talc and 
 graphite are generally freer from impurities than the crystal- 
 
400 MANUAL OF LITHOLOGY, 
 
 line states, and are more readily and better adapted to the 
 market. 
 
 Fertilizers. For this the phosphorites and guano fur- 
 nish phosphorus, and peat improves the texture and makes 
 the soil warmer. Lime slaked with brine, marl, and gypsum 
 arc generally useful, while carnallite and salt are valuable 
 to furnish potash, soda, and chlorine. 
 
INDEX OF AUTHORITIES. 
 
 Abich, H., 194 
 Adams, F. D., 239 
 Agassiz, L., 256 
 Agricola, G., 226 
 
 Barrois, C., 2, 178, 324 
 
 Barus, C., 104, 241, 326 
 
 Bascom, Miss F., no 
 
 Bayley, W. S., 167 
 
 Becke, F., 178 
 
 Becker, G. F., 94, 130, 208, 274 
 
 Bertels, G. A., 193 
 
 Berghell, H., 217 
 
 Berthier, P., 377 
 
 Beudant, M. F. S., 371 
 
 Blandy, J. F., 89 
 
 Blum, R., 166 
 
 Bolton, H. C., 12 
 
 Bonney, T. G., 82, 126, 240, 251, 331, 
 
 332 
 
 Boricky, E., 12, 218, 219, 233 
 Breislak, S., 235 
 
 Breithaupt, A., 22, 167, 193, 231, 368 
 Brogger, W. C., 21, 136, 151, 152, 153, 
 
 156, 164, 166, 171, 241 
 Brongniart, A., 126, 127, 142, 199, 221, 
 
 247, 249, 261, 337, 378 
 Buch, L. v., 154, 189 
 Bucking, H., 222, 224 
 
 Gallon, J., 256 
 Cathrein, A., 234 
 Chamberlin, T. C., 282 
 Chelius, C., 135, 237 
 Chester, F. D., 237 
 Chrustschoff, K, v., 133, 161 
 Cohen, E., 251 
 
 Cole, G. A., 231, 232, 249, 326 
 Cossa, A., 188 
 
 Cotta, B. v., 124, 131, 135, 136, 142, 
 150, 172, 173, 176, 186, 199, 348, 352 
 Cross, W. C., no 
 
 Dana, E. S., 37 
 
 Dana, J. D., 6, 39, 57, 58, 65, 76, 79, 80, 
 83, 85, 87, 105, 119, 136, 154, 212, 
 263, 270, 275, 277, 278, 326, 328, 344, 
 360, 362, 363, 365 
 
 Daubree, A., 126 
 
 Daubuisson, 142 
 
 Dechen, H. v., 148 
 
 Deecke, W., 216 
 
 Delesse, A., 176, 199, 245 
 
 Derby, O. A., 253 
 
 Descloiseaux, A., 235 
 
 Dewey, C., 26, 344 
 
 Diller, J. S., 230 
 
 Doelter, C., 234 
 
 D'Orbigny, C., 6 
 
 Drasche, R. v., 203 
 
 Dumas, E., 175 
 
 Ehrenberg, C. G., 303, 309 
 
 Elie de Beaumont, 174 
 
 Emerson, B. K., 242 
 
 Emmons, A. B., 205, 209 
 
 Emmons, E., 356 
 
 Erdmann, E., 250, 370 
 
 Esmark, J., 238 
 
 Eschwege, W. L. C. v ., 126, 342, 347 
 
 Fischer, Dr., 362 
 Foerster, H., 184 
 Fouque, F., 8, 21 
 Fournet, J., 132 
 Fritsch, K. v., 221 
 
 Geikie, A., 69, 80, 83, 275, 330, 331, 
 
 333, 341, 369 
 Gemmellaro, C., 231 
 Gerhart, D., 142 
 Gilbert, G. K., 105 
 Gregory, J. W., 249 
 Groth, P., 130 
 Gumbel, C. W., 135, 141, 155, 172, 
 
 173, 188, 201, 241, 250, 271, 286 
 401 
 
4O2 
 
 INDEX OF A UTHORITIES. 
 
 Hague, A., no, 163, 193 
 
 Haidinger, W., 319, 376 
 
 Haiiy, Abbe, 124, 132, 140, 145, 195, 
 
 196, 226, 237, 343, 348, 361 
 Haughton, S., 337 
 Hausmann, J. F. L., 231, 240, 371 
 Hawes, G. W., 130, 153, 211 
 Helmhacker, R., 139 
 Herter, P., 112 
 Hise, G. R. van, r,d, c,$ 
 Hitchcock, C. H., 240, 341 
 Hobbs, W. H., 184 
 Hochstetter, F. v., 250 
 Hohenegger, L., 242 
 Hopkins, W., 67 
 Home, J., 169 
 
 Hunt, T. S., 39, 252, 298, 306, 358 
 Hunter, M., 155, 169 
 Hussak, E., 167, 168, 223 
 
 Iddings, J. P., 4, 12, 57, 83, 93, 95, 97, 
 
 i TO, 230 
 Irving, R. D., 237 
 
 Jameson, R., 371 
 
 feremejew, P. v., 153 
 
 Jenzsch, G., 188 
 
 fohn, C. v., 201 
 
 fudd, J. W., 5, 58, 95, 118, 190, 205, 
 
 231, 232, 251 
 Jukes, J. B., 287 
 
 Kalkowsky, F., 157, 365, 366 
 
 Kantkiewicz, S., 358 
 
 Kemp, J. F., 170, 181, 211 
 
 Keyes, C. R., 40 
 
 Kikuchi, Y., 207 
 
 King, C., 304 
 
 Kittel, M. B., 134, 135 
 
 Kirwan, 310, 371 
 
 Klaproth, M., 158 
 
 Klein, D., 10 
 
 Klement, C., 13 
 
 Kobell, F. v., 250 
 
 Koch, A., 251 
 
 KotO, B., 203, 360 
 
 Lametherie, de, 251 
 Lang, O., 6, 46, 182 
 Lasaulx, A. v., 189 
 Laube, G. C., 163 
 Leonhard, K. C. v., 226 
 Le Conte, J., 67 
 Lenk, C., 161 
 Lessing, F. L., 4 
 Lewis, H. Carvill, 250, 282 
 Lessen, K. A., 155, 244, 332 
 
 Mann, P., 216 
 Marsh, O. C., 63, 71, 72 
 Merrill, G. P., 304 
 Merriman, M., 397 
 Michel-Levy, A., 8, 176, 211 
 Mohl, H., 234 
 Mohs, F., 85 
 
 Miigge, O., 147, 148, 192, 287, 289. 
 2o:> 
 
 Naumann, C., 59, 131, 136, 144, 309 
 Nordenskiold, A., 122, 353 
 
 Orton, E., 89 
 Osann, A., 182, 233 
 
 Pallassou, Abbe, 242 
 Petersen, J., 206, 207, 232 
 Pettersen, K., 367 
 Pichler, A., 129 
 Pisani, F., 126 
 Pliny, 377 
 
 Rammelsberg, C., 216 
 
 Ramsay, W., 217 
 
 Rath, G. vom, 162, 187 
 
 Reiser, K. A., 241 
 
 Richthofen, F. v., 79, 93, 108, no, 
 
 153, 191, 208, 289, 306 
 Riviere, A., 177 
 Rohrbach, C., 56, 57 
 Rose, G., 123, 129, 131, 139, 149, 167, 
 
 238, 245 
 Rosenbusch, H., 21, 34, 39, 46, 56, 57, 
 
 58, 94, no, 121, 122, 123, 124, 126, 
 
 130, 133, 147, 155. 157, 162, 165, 167, 
 
 169-176, 178, 182, 184, 203, 209, 211, 
 214, 215, 2l6, 22O, 225, 233, 242, 
 
 243, 244, 245, 248, 251, 288 
 Roth, J., 108, 190, 191, 203, 204, 236 
 Rutley, F., 78, 83, 115, 142, 308 
 
 Salisbury, R. D., 282 
 Salvetat, M., 309 
 Sandberger, F., 222 
 Sauer, A., 152 
 Schrauf, A., 378 
 Senft, F., 199 
 Simler, R. T., 352 
 Sjogren, H., 253 
 Sorby, H. C., 4, 93 
 Stache, G., 182, 201 
 Steenstrup, K., 167 
 Stelzner, A., 220 
 Streng, A., 244 
 Studer, B., 132 
 Szabo, J., 208 
 
INDEX OF A UTHORITIES. 
 
 403 
 
 Teall, J. J. H., 169 
 
 Tornebohm, A, E., 130, 167, 211, 242, 
 
 248, 249 
 
 Townsend, D., 83. 
 Tschermak, G., 137, 141, 199. 206, 250 
 
 Ullman, J. C, 371 
 
 Vrba, K., 168 
 
 Vogelsang, H., 57, 137, 142 
 
 Wadsworth, M. E., 95, 157, 208, 250, 
 
 251, 253 
 
 Walterhausen, S. v., 288 
 Weed, W. H., 309 
 
 Weinschenk, E., 207 
 
 Weiss, C. E., 348 
 
 Werner, A. G., 126, 371 
 
 Williams, G. H., 4, 57, in, 153, 229, 
 
 251, 252 
 
 Williams, J. F., 148, 168, 170 
 Wright, G. F., 282 
 
 Zinken', 331 
 
 Zirkel, F., 20, 21, 39, 84, 94, 109, no, 
 123, 145, 148, 149, 153, 157, 158, 
 159, 160, 161, 162, 173, 176, 179, 182, 
 183, 185, 194, 198, 201, 203, 204, 208, 
 
 210, 211, 215, 231, 243, 249, 251, 252, 
 
 348, 360 
 
GENERAL INDEX. 
 
 Abrasion, 68 
 
 Accessory ingredients in rocks, 7 
 
 Acid (definition), 4, 85 
 
 extrusives, 107-117 
 
 intrusives, 117-144 
 
 rocks, 4, 85, 99, 107-144 
 
 schists, 354 
 Acmite, 34 
 
 trachyte, 147 
 Actinolite, 36 
 
 schist, 364 
 Adinole, 332, 333 
 Adobe, 268 
 ^Egirite, 34 
 ^Enigmatite, 38 
 Agalmatolite, 26 
 Agate, 15 
 
 Age of rocks (relative), 90 
 Agglomerated debris, 264 
 Agglomerates, 60 
 Akerite, 153 
 Alabaster, 294 
 Albite, 23 
 Algovite, 241 
 Allanite, 40 
 Allotriomorph, 57 
 Alluvium, 267 
 Almandite, 48 
 Alnoite, 220 
 Alpengranit, 132 
 Alpenit, 353 
 Alsbachite, 135 
 Alum clay, 261 
 
 shale, 272 
 Amorphous, 58 
 Amphibole, 35-38 
 
 adinole-schist, 366 
 
 and pyroxene (comparison), 39 
 
 biotite-monchiquite, 170 
 
 fourchite, 170 
 
 monchiquite, 170 
 
 olivine rock, 369 
 
 Amphibole ouachitite, 170 
 
 rocks, 99, 144 
 Amphibolite, 363 
 Amygdaloidal, 79 
 
 aphanite, 246 
 
 porphyry, 140 
 Amygdalophyre, 188 
 Analcime, 47 
 Analcimite, 231 
 Anamesite, 226 
 Andalusite, 49 
 
 hornstone, 331 
 Andesine, 24 
 Andesite, 189 
 
 (hornblende), 191-194 
 
 (pyroxene), 203 
 
 (quartz), 182-185 
 Andesite-diorite group, 189 
 Andesitic glass, 184, 194 
 
 porphyrite, 180 
 
 trachyte, 148 
 Andradite, 48 
 Anhydrite, 294 
 Anisotropic, 57 
 Anorthite, 24 
 
 diorite, 198 
 
 gneiss, 353 
 Anorthoclase, 20, 21 
 Anorthosite, 239 
 Anthophyllite, 35 
 Anthracite, 319 
 
 sand, 270 
 Anthraconite, 336 
 Apatite, 46, 311 
 Aphanite, 246 
 
 (diorite), 202 
 Aplite, 125 
 Apophysis, 105 
 Aporhyolite, no 
 Aprons (glacial), 283 
 Aqueous aggregates, 265 
 Arenaceous rocks, 85 
 
 405 
 
406 
 
 GENERAL INDEX. 
 
 Arfvedsonite, 37 
 Argillaceous, 85 
 
 limestone, 300 
 
 pitchstone, 144 
 
 shale, 271 
 Argillite, 273 
 
 (metam orphic), 330 
 Argillophyre, 139 
 Argiloretinite, 144 
 Arkose, 261 
 
 Arrangement of eruptive rocks, 105 
 
 Asbestus, 36 
 
 Aschaffite, 135, 178 
 
 Ash, 284 
 
 Asphalt, 321 
 
 Augite, 33 
 
 andesite, 204 
 glass, 207 
 
 bearing mica-syenite, 152 
 
 camptonite, 211 
 
 diorite, 210 
 
 free hornblende-andesite, 193 
 
 granite, 131 . 
 
 granitite, 130 
 
 minette, 175 
 
 norite, 239 
 
 porphyrite, 245 
 
 rock, 367 
 
 schist, 368 
 
 soda-granite, 131 
 
 syenite-porphyry, 157 
 
 trachyte, 147 
 Augitite, 234 
 Aureola, 3, 324 
 Automorph, 56 
 Automorphic aggregates, 257-323 
 
 Ball-gabbro, 239 
 
 porphyry, 140 
 Banatite, 186 
 Band porphyry, 139 
 Banded structure, 83 
 Barite, 378 
 Barytes, 378 
 Basalt, 226 
 
 (feldspar), 226 
 
 glass, 231 
 
 leucite, 219 
 
 (magma), 233 
 
 (melilite), 220 
 
 (nepheline), 218 
 
 tuff, 
 
 Basalt-gabbro group, 224-254 
 Basaltic hornblende, 37 
 
 nephenelite, 214 
 Basaltoid leucitite, 215 
 Basanite, 221 
 
 (leucite), 224 
 
 Basanite (nepheline), 223 
 
 Basanitoid, 224 
 
 Basic rocks, 85, 99, 213-254 
 
 schists, 355-370 
 Bastite, 31 
 Bauxite, 379 
 Beach structure, 80 
 Bean-ore, 77 
 
 Bed, 80 
 
 Bedded masses, 80 
 
 sheet, 105 
 Bedding, 80 
 
 - (cloak-like), 81 
 
 (false), 80 
 
 (trough), 8 1 
 Beerbachite, 237 
 Beresite, 139 
 Bergamaskite, 188 
 Biotite, 27 
 
 andesite, 193 
 
 diorite, 199 
 
 gneiss, 351 
 
 granite, 129 
 porphyry, 135 
 
 monchiquite, 160 
 
 olivine rock, 251 
 
 quartzite, 333 
 
 syenite, 152 
 
 porphyry, 157 
 Bituminous clay, 261 
 
 coal, 317 
 
 limestone, 300 
 
 shale, 271, 323 
 
 wood, 316 
 Black (color), 86 
 
 band, 377 
 
 chalk, 273 
 
 granulite, 349 
 
 hematite, 375 
 
 lead, 320 
 
 porphyry, 187, 244 
 Blind joint, 73 
 Blocks, 284 
 
 Blown sand, 270 
 Blue marbles, 336 
 
 porphyry, 185 
 Blumengranit, 124 
 Bog-head coal, 318 
 Bog iron-ore, 371 
 Bombs, 73, 116, 284 
 Bone-beds, 313 
 
 breccia, 61, 312 
 Boninite, 207 
 Borolanite, 169 
 Boss, 104 
 Bostonite, 155 
 Bottlestone, 115 
 Bouteillenstein, 115 
 
GENERAL INDEX. 
 
 407 
 
 Boulder-clay, 61, 282 
 Brandschiefer, 323 
 Breccia, 60, 278 
 
 (bone), 61, 312 
 
 (debris), 262 
 
 (oroclastic), 60, 290 
 
 (pyroclastic), 60, 284 
 Brecciated conglomerate, 60 
 Brecciola, 278 
 Brick-clay, 266 
 Bronzite, 31 
 
 andesite glass, 207 
 
 basalt, 231 
 
 diabase, 242 
 
 limburgite, 207 
 
 norite, 239 
 
 olivine-rock, 369 
 
 trachyte, 148 
 Bronzitite, 252 
 Brown (color), 87 
 
 coal, 315 
 
 diorite, 210 
 
 hematite, 371 
 Buchnerite, 251 
 Buchonite, 222 
 Buhrstone, 277, 341 
 
 Caking coal, 317 
 Calcareous aphanite, 246 
 
 chemical aggregates, 292 
 
 clay-slate, 274 
 
 diabase, 242 
 
 epidote-schist, 359 
 
 mica-schist, 345 
 
 organic aggregates, 297 
 
 rocks, 292 
 
 sand, 270 
 rock, 278 
 
 talc-schist, 356 
 
 tufa, 304 
 Calciphyre, 337 
 Calcite, 53 
 
 Camptonite, 176, 211 
 Camptonitic nephelinite, 214 
 Candle coal, 318 
 Cancrinite, 42 
 
 aegirite-syenite, 167 
 Cannel coal, 318 
 Carbonaceous clay-slate, 273 
 Carbonic shale, 272 
 Carnallite, 295 
 Carvoeira, 126 
 Cataclastic breccias, 290 
 Catawbirite, 376 
 
 Caustic effects, 325 
 Cave-agio merarte, 264 
 
 earth, 312 
 Cavernous, 78 
 
 Cellular, 78 
 Chabazite, 47 
 Chalk, 303 
 Chalybeated, 85 
 
 Chemical aggregates (automorphic), 
 292 
 
 (bulk) analyses, u 
 Cherry coal, 317 
 Chert, 15, 307 
 Cherty limestone, 300 
 Chiastolite, 49 
 
 slate, 331 
 Chlorite, 29 
 
 schist, 357 
 Chloride gneiss, 352, 358 
 
 granite-porphyry, 136 
 
 potstone, 357 
 
 slate, 358 
 Chloritoid schist, 358 
 Chromic magnetite, 376 
 Chromite, 53 
 
 olivine rock, 369 
 Chrysolite, 43 
 Cipolino, 336 
 
 Classification of rocks, 98, 99 
 Clastic, 59 
 
 rocks, 257 
 Clay, 265 
 
 ironstone, 376 
 
 slate, 272 
 
 stone, 77, 138, 271 
 
 porphyry, 139 
 
 Cleat, 73 
 Cleavage, 63 
 Cleaved, 82 
 
 Cliff -agglomerate, 264 
 
 Clinkstone, 158 
 
 Clinochlore, 29 
 
 Cloak-like bedding, 81 
 
 Coal, 317 
 
 Color, 86 
 
 Columnar jointing, 71 
 
 Compact syenite, 157 
 
 Comparison of pyroxene and amphi- 
 
 bole, 38 
 
 Composite rocks, 7 
 Conchoidal fracture, 85 
 Concretion, 76 
 Cone in cone, 72 
 Conglomerate, 60, 278 
 
 schist, 342 
 Contact-metamorphism, 324 
 
 zones, 324 
 Convergence, 69 
 Cooling, 64 
 Copper-slate, 307 
 Coprolite beds, 313 
 Coquina, 66, 278 
 
4 o8 
 
 GENERAL INDEX. 
 
 Coral chalk, 303 
 Cordierite, 47 
 
 gneiss, 352 
 
 granite, 125 
 Cornubianite, 331 
 Corsite, 198 
 Cortlandtite, 251 
 Corundum, 51 
 Cossyrite, 38 
 Crumbly fracture, 86 
 Cryolite, 295 
 Cryptocrystalline, 58 
 Cryptomeric, 61 
 Cryptoperthite, 21 
 Crystal, 56 
 
 sand, 270 
 Crystalline, 58 
 
 granular, 58 
 
 limestone, 334 
 
 rocks, 329 
 
 schists, 337 
 Crystalloid, 58 
 Cumberlandite, 253 
 Current-bedding, 80 
 Cuselite, 245 
 Cyanite, 50 
 
 rock, 362 
 
 Dacite, 182-185 
 
 felsite, 184 
 
 glass, 184 
 
 obsidian, 185 
 
 pitchstone-porphyry, 185 
 
 pumice, 185 
 Damascened, 78 
 Damourite, 26 
 
 schist, 344 
 Debris, 259-264 
 
 breccia, 280 
 
 clays, 261 
 
 in place, 260-263 
 
 sands, 260 
 
 slightly moved, 263-264 
 Desmosite, 331 
 Devitrification, 62 
 Diabase. 240 
 
 aphanite, 246 
 
 glass, 248 
 
 gneiss, 353 
 
 pegmatite, 241 
 
 porphyrite, 244 
 Diallage, 33 
 
 andesite, 206 
 
 granulite, 348 
 
 hypersthene rock, 367 
 
 rock. 367 
 Diallagite, 235, 252 
 Diamond-sand, 269 
 
 Diatoms, 18 
 Diatom earth, 308 
 
 mud, 309 
 Dichroite (iolite), 46 
 
 gneiss, 352 
 
 granite, 125 
 
 Differentiation of magmas, 4, 92 
 Dike, 2, 104, 105 
 
 metamorphism, 325 
 
 sandstone, 279 
 
 (stepped), 105 
 Diopside, 32 
 Diorite, 195-200 
 
 aphanite, 202 
 
 (brown), 210 
 
 glass, 188 
 
 gneiss, 352 
 
 mica - hornblende - pitchstone por- 
 phyry, 189 
 
 mica-pitchstone porphyry, 188 
 
 (orbicular), 198 
 
 porphyrite, 200 
 
 (pyroxene), 209 
 
 (scapolite), 198 
 
 schist, 364 
 
 Diorite-quartzifera-porfiroide, 188 
 Dioritic mica-trap, 176 
 
 lamprophyre, 176 
 Dipyre-slate, 331 
 Dirt-bed, 264 
 Disthene, 50 
 
 rock, 362 
 Ditroite, 168 
 Dolerine, 356 
 Dolerite, 226 
 Doleritic nephelinite, 214 
 Dolomite, 54, 305 
 Dolomitic limestone, 299 
 Domite, 147 
 
 Drusy, 79 
 
 porphyry, 140 
 Drying, 64 
 Dunite, 250 
 Durbachite, 152 
 Dysodile, 316 
 
 Eclogite, 361 
 
 amphibolite, 361 
 Economic value of rocks, 392 
 Egeran-schist, 368 
 Ehrwaldite, 234 
 
 Elaeolite, 41 
 
 syenite, 164 
 
 porphyry, 170 
 
 Elvan, 136 
 Emery, 52 
 Enstatite, 30 
 
 andesite, 206 
 
GENERAL INDEX. 
 
 409 
 
 Enstatite diabase, 242 
 
 olivine rock, 369 
 
 porphyrite, 244 
 
 rock, 366 
 Epidosite, 248, 358 
 Epidote, 39-41 
 
 actinolite-schist, 364 
 
 glaucophane-schist, 365 
 
 granite, 128 
 
 schist, 359 
 
 syenite, 151 
 Epistilbite, 46 
 Erlan, 368 
 Erratics, 280 
 
 Eruptive agglomerate, 264 
 
 rocks, 6, 93, 95 
 
 Essential ingredients (in rocks), 7 
 
 Etched, 59, 65, 73 
 
 Eudyalite-syenite, 168 
 
 Eukrite, 243 
 
 Eulysite, 250, 370 
 
 Euphotide, 237 
 
 Eurite, 142 
 
 External structure, 71 
 
 Extruded sheet, 105 
 
 Extrusive, 95 
 
 rocks, 103 
 Eye-stones, 77 
 
 Fairy stones, 77 
 False-bedding, 80 
 Fat-clay, 266 
 Fault, 64 
 Fayalite, 44 
 Felshe, 142 
 
 porphyry, 137, 141 
 Felsitic, 84 
 
 hornstone, 331 
 Feldspar, 18 
 
 amphibolite, 363 
 
 basalt, 226 
 
 biotite-quarzile, 333 
 
 (decomposition of), 379 
 
 magma-basalt, 233 
 Feldspathic ash, 286 
 Feldspathoid magma-basalt, 233 
 Felsophyre, 57 
 Felsophyric, 85 
 
 Felstone, 142 
 
 porphyry, 139 
 Ferrite, 54 
 
 Ferruginous-organic aggregates, 323 
 Fetid limestone, 300 
 Feuerstein, 307 
 
 Fibrolite, 50 
 Fibrous, 84 
 Filiform, 72 
 Fiorite, 18, 309 
 
 Fire-clay, 266 
 Firn, 297 
 Fissile, 82 
 Fissured, 81 
 Flagband-cleavage, 83 
 Flagstone, 276 
 
 cleavage, 83 
 Flat-parallel structures, 80 
 Flexible sandstone, 342 
 Flint, 19, 307 
 
 Flow-and-plunge structure, 80 
 Fluidal, 83 
 
 Fluorite, 295 
 Fluxion structure, 83 
 Foliated, 82 
 Forellenstein, 240 
 Forest-soil, 263 
 Fourchite. 170 
 Foyaite, 166 
 Fracture, 85 
 Fractured, 82 
 Fragmental rocks, 257 
 Fraidronite, 175 
 Franklinite, 377 
 Free convergence, 69 
 
 stone, 277 
 
 Friction-breccias, 284, 290 
 Fruit-slate, 332 
 Fulgurite, 84 
 
 Fuller's earth, 267 
 
 Fusing point of rocks, 104 
 
 Gabbro, 235 
 
 diorite, 211 
 
 glass, 248 
 
 gneiss, 353 
 
 granite, 130, 237 
 
 schalstein, 290 
 Ganister, 277 
 Garnet, 48 
 
 olivine-rock, 369 
 
 rock, 360 
 
 Garnetiferous magnetite, 376 
 Garnetyte, 360 
 
 Gedrite, 35 
 
 General definitions, 55 
 
 Geodesy, 6 
 
 Geodic, 79 
 
 Geology, 6 
 
 Geyserite, 18, 309 
 
 Giallo-antico, 335 
 
 Giant gneiss, 351 
 
 Gieseckite-porphyry, 171 
 
 Gilsonite, 321 
 
 Glacial aggregations, 75, 280-283 
 
 Glaciated, 59, 68, 74 
 
 Glacier-ice, 297 
 
 Glassy, 61 
 
GENERAL INDEX. 
 
 Glauconitic sandrock, 278 
 Glaucophane, 37 
 
 augite-schist, 368 
 
 epidosite, 359 
 
 schist, 365 
 Globuliferous, 79 
 Gneiss, 349 
 
 (augen), 351 
 
 (chloritic), 352 
 
 (dichroite), 352 
 
 (hornblende), 352 
 
 (mica), 351 
 
 (porphyritic), 351 
 
 (syenite), 352 
 Gold-bearing sand, 269 
 Graniodiorite, 130 
 Granite, 117-134 
 
 gneiss, 351 
 
 laterite, 263 
 
 porphyry, 134 
 Granitell, 125 
 
 Granitic granite-porphpry, 135 
 Granitite, 129 
 Granitoid, 59 
 
 hornblende-andesite, 192 
 
 rhyolite, no 
 Granitone, 235 
 Granophyre, 57 
 Granular, 58 
 Granulite, 348 
 
 gneiss, 352 
 
 (pyroxene), 348 
 Graphic granite, 84, 124 
 Graphite, 320 
 Gravel, 279 
 
 Gray gneiss, 352 
 
 trachyte, 191 
 Green (color), 87 
 
 porphyry, 136 
 Greenstone, 196 
 
 like porphyrite, 177 
 
 trachyte, 208 
 Greisen, 128 
 Grit, 57, 276 
 Grorudite, 136 
 Grossularite, 48 
 Ground-ice, 297 
 
 moraine, 282 
 Groundmass, 57 
 Guano, 313 
 Guinea-quartz, 17 
 Gypsum, 293 
 
 Halbgranit, 125 
 Halleflinta, 353 
 Haloidal aggregates, 293 
 Hard coal, 317 
 Hardness, 85 
 
 Hardpan, 279 
 Harmotome, 47 
 Harzburgite, 251 
 Haselgebirge, 264 
 Haiiyne, 43 
 
 tachylite, 234 
 
 tephrite, 222 
 
 trachyte, 149, 161 
 Haiiynophyre, 216 
 Heavy spar, 378 
 Heat transmission, 53 
 Hemithrene, 199 
 Heulandite, 46 
 Hiortdahlite, 34 
 Hislopite, 337 
 Holocrystalline, 57 
 Hornblende, 37 
 
 andesite, 191 
 . glass, 194 
 pumice, 194 
 
 (basaltic), 37 
 
 epidote-schist, 359 
 
 gabbro, 237 
 
 gneiss, 352 
 
 granite, 131 
 
 porphyrite, 200 
 porphyry, 136 
 
 granitite, 130 
 
 mica-elaeolite-syenite, 168 
 
 minette, 175 
 
 nepheline-tephrite, 222 
 
 norite, 239 
 
 picrite, 251 
 
 porphyrite, 200 
 
 pyroxene-elseolite-syenite, 166 
 porphyry, 171 
 
 quartz-porphyry, 141 
 
 rocks, 144-212 
 
 schist, 363 
 
 syenite, 151 
 
 syenite-porphyry, 156 
 Hornblendite, 212 
 Hornschiefer, 366 
 Hornstone, 15, 307 
 
 (felsitic), 331 
 
 porphyry, 139 
 
 (tourmaline), 333, 346 
 Hudsonite, 251 
 Hyalite, 17 
 Hyalomelane, 231 
 Hyalomicte, 128 
 Hyalosiderite, 44 
 Hyalotourmalithe, 126 
 Hydraulic-limestone, 300 
 Hydrogenic aggregates, 259 
 Hydromica-schist, 344 
 Hydrotachylite, 232 
 Hyperite-porphyrite, 244 
 
GENERAL INDEX. 
 
 411 
 
 Hypersthene, 31 
 
 andesite, 206 
 
 basalt, 230 
 
 diabase, 242 
 
 diorite, 210 
 
 gabbro, 237 
 
 granulite, 348 
 
 hornblende-andesite, 193 
 
 norite, 239 
 
 quartz-porphyrite, 244 
 
 syenite, 153 
 
 trachyte, 148 
 Hysterobase, 241 
 
 Ice, 296 
 Idiomorph, 56 
 liolite, 217 
 Ilmenite, 375 
 Imatra-stone, 77 
 Implication structure, 84 
 Impregnation, 68 
 Indianaite, 379 
 Individualized matter, 55 
 Infusorial earth, 308 
 meal, 309 
 Intermediate rocks, 99, 144 
 
 Internal structures, 78 
 
 Intratelluric crystallization, 58, 94 
 
 Intruded sheet, 105 
 
 Intrusive, 95 
 
 lolite, 47 
 
 Iron ores, 296 
 
 Irregular fracture, 86 
 
 Isenite, 193 
 
 Iserine, 375 
 
 Isotropic groundmass, 57 
 
 Itabarite^ 347 
 
 Itacolumite, 342 
 
 Jacotinga, 347 
 Jacupirangite, 253 
 Jade, 36 
 
 Jadeglanduleux, 249 
 Jasper, 15 
 Jet, 318 
 Jointed, 63, 72 
 
 Kalkaphanit, 246 
 Kalkdiorit, 199 
 Kalkgranit, 129 
 
 pistacit schist, 359 
 
 tuff, 304 
 Kammgranit, 130 
 Kaolin, 379 
 Keratophyre, 141, 155 
 Kerosene, 322 
 Kersantite, 177 
 
 Kersanton, 177 
 Kieselguhr, 309 
 Kimberlite, 250 
 Kinzigite, 362 
 Klein's solution, IO 
 Knotty-slate, 330 
 Kunkurs, 77 
 
 Laacher trachyte, 148 
 Labrador-porphyrite, 245 
 Labradiorite, 199 
 Labradorite, 24 
 Laccolith, 105 
 Laminated, 82 
 Lamprophyre, 172-178 
 Lapilli, 284 
 
 Lateral moraine-stuff, 281 
 Laterite, 262 
 Lathy, 84 
 Laumontite, 46 
 Laurdalite, 164 
 Laurvikite, 152 
 Lava-sperone, 215 
 
 stream, 105 
 Leaf -coal, 316 
 Lean-clay, 266 
 Lenticular masses, 80 
 Lepidolite, 26 
 Lepidomelane, 28 
 Leptynite, 348 
 Leptynolite, 331 
 Leuciite, 198 
 Leucite, 41 
 
 anamesite, 219 
 
 basalt, 219 
 
 basanite, 224 
 
 perlite, obsidian, and pumice, 
 
 232 
 
 dolerite, 219 _ 
 
 elaeolite-syenite, 168 
 porphyry, 171 
 
 nepheline-trachyte, 162 
 
 phonolite, 162 
 pumice. 163 
 
 tephrite, 223 
 
 trachyte, 162 
 Leucitite, 215 
 Leucitoid basalt, 219 
 Leucitophyre, 162, 224 
 Leucophyre, 224, 241 
 Lherzolite, 251 
 Liebnerite-porphyry, 171 
 Lignite, 315 
 Limburgite, 233 
 Lime-granite, 129 
 
 silicate-hornstone, 333 
 Limestone, 297 
 
 (crystalline), 334 
 
412 
 
 GENERAL INDEX. 
 
 Limonite, 371 
 
 Linear-parallel structures, 80, 84 
 
 Liparite, no 
 
 Listwenite, 356 
 
 Litchfieldite, 167 
 
 Lithionite, 27 
 
 Lithographic limestone, 301 
 
 Lithoid, 61 
 
 Lithoidite, no 
 
 Lithology, 6 
 
 Lithopysae, 70, 79 
 
 Lithophysic obsidian, 115 
 
 Lithosphere, 6 
 
 Loam, 263 
 
 Local metamorphism, 324 
 
 Loess, 268 
 
 Lucullite, 336 
 
 Luxullianite, 126 
 
 Lydian stone, 343 
 
 Magma basalt, 233 
 Magnesian limestone, 305 
 Magnesite, 378 
 Magnetite, 52 
 
 olivenite, 253 
 
 rock, 375 
 
 sand, 269 
 
 series, 252 
 Malacolite, 32 
 
 rock, 367 
 Malchite, 182 
 Mamelon, 104 
 Mandelato, 333 
 Manganese-epidote-schist, 360 
 Marble, 334 
 
 Marekanite, 112 
 
 Margarite, 29 
 
 Margarophyllite group (schists), 355 
 
 Marl, 306 
 
 Massive, 78, 80 
 
 rocks, 92 
 
 Mechanical aggregates, 258-292 
 Melanite, 47 
 
 elaeolite-syenite, 169 
 Melaphyre, 247 
 Melilite, 43 
 
 basalt, 220 
 Menaccanite, 375 
 Meta-anthracite, 320 
 Metamorphic argillite, 330 
 
 crystalline-schists, 337 
 
 limestone, 333 
 
 phyllite, 332 
 
 rocks. 324, 337 
 
 sandstone, 333 
 
 schists, 337 
 
 zones, 324 
 Metamorphism, 324 
 
 Metamorphism (contact, or local), 324 
 
 (regional), 327 
 Metamorphosed schists, 333 
 Mexican onyx, 304 
 Miarolite, 132 
 Miarolitic, 59, 133 
 Miascite, 167 
 
 Mica, 25-29 
 
 andalusite-slate, 332 
 
 andesite, 193 
 
 augite-porphyrite, 245 
 
 basalt, 229 
 
 dacite, 184 
 
 diabase, 242 
 
 diorite, 199 
 porphyrite, 202 
 
 elaeolite-syenite, 167 
 
 epidote-schist, 359 
 
 gabbro, 237 
 
 gneiss, 351 
 
 hornblendite, 212 
 
 (hydro-), 26 
 
 leucitite, 216 
 
 magma-basalt, 233 
 
 norite, 239 
 
 phyllite, 332 
 
 porphyrite, 178, 181 
 
 (quartz-), diorite, 187 
 
 rocks, 99, 107 
 
 schist, 343 
 
 slate, 343 
 
 syenite, 152 
 
 trap rocks, 172-178 
 Micaceous clay-slate, 274 
 
 hematite, 374 
 
 iron-schist, 347 
 
 shale, 272 
 Microchemical tests, 12 
 Microclastic, 59 
 Microcline, 20 
 Microcrystalline, 59 
 Microgranitic, 57 
 Micropegmatitic, 57 
 Microperthite, 21 
 Micropoikilitic, 58 
 Microsyenite, 157 
 Migration -structure, 286 
 Mijakite, 206 
 
 Millstone-porphyry, no, 140 
 Mineral oil, 322 
 
 pitch, 321 
 
 wax. 322 
 Mineralizing, 125, 325 
 Minerals as rocks, 371-381 
 
 (necessary) for primary rocks, 98 
 
 (rock-forming), 14 
 Minette, 174 
 Mining, 261 
 
GENERAL INDEX. 
 
 413 
 
 Moja. 288 
 Moldauite, 115 
 Monazite, 51 
 Monchiquite, 169 
 Monzonite, 239 
 Moor-coal, 316 
 Moraine-stuff, 61, 281 
 Mud, 267 
 Mudstone, 267 
 Murasaki, 360 
 Muscovite, 25 
 
 biotite-granite, 123 
 
 gneiss, 351 
 
 granite, 124 
 
 Nacritide, 345 
 
 Nadeldiorit, 198 
 
 Napcleonite, 198 
 
 Natrolite, 47 
 
 Navite, 248 
 
 Necessary ingredients to rocks, 7, 98 
 
 Neck, 103 
 
 Needle-coal, 316 
 
 Nepheline, 41 
 
 anamesite, 218 
 
 basanite, 223 
 
 basalt, 218 
 
 dolerite, 218 
 
 olivine- jacupirangite, 253 
 
 rhomb-porphyry, 171 
 
 tephrite, 221 
 
 trachyte, 158 
 Nephelinite, 214 
 Nephelinitoid basalt, 218 
 Nephrite, 37 
 Nero-antico, 336 
 Nevadite, no 
 
 Neve, 296 
 
 Non-caking coal, 317 
 Nordmarkite, 151 
 Norite, 238 
 
 aphanite, 246 
 
 gneiss, 353 
 
 porphyrite, 243 
 Nosean, 43 
 
 melanite-rock, 162 
 
 phonolite, 161 
 
 trachyte, 161 
 Noseanite, 219 
 Novaculite, 308 
 Nyirock, 263 
 
 Obsidian, 114 
 
 bombs, 116 
 
 perlite, 112 
 
 pumice, 116 
 Odinite, 237 
 Oil-shale, 323 
 
 Oligoclase, 23 
 Olivine, 43 
 
 diabase, 243 
 
 enstatite-gabbro, 238 
 
 gabbro, 238 
 
 kersantite, 178 
 
 less basalt, 231 
 
 leucite-phonolite, 163 
 
 norite, 239 
 porphyrite, 244 
 
 proterobase> 243 
 
 pyroxene-andesite, 206 
 
 rock, 369 
 
 schist, 370 
 
 series, 249 
 Olivineless basalt, 230 
 Ollenite, 364 
 Omphacite, 34 
 
 rock, 367 
 
 zoisite-rock, 359 
 Oolite, 305 
 Oolitic, 76 
 
 ice, 296 
 
 quartzite, 341 
 Opacite, 54 
 Opal, 17 
 Ophicalcite, 336 
 Ophite, 242 
 Orbicular diorite, 198 
 Ordinary clay-slate, 273 
 Ore-pots, 77 
 
 Organic aggregates, 297 
 Oroclastic breccias, 60, 290 
 Orogenic rocks, 289 
 Orthoclase, 18 
 
 gabbro, 237 
 
 monzonite, 152 
 Orthophyre, 153, 154 
 Ortlerite, 201 
 Ossipyt, 240 
 Osteolite, 311 
 Ottrelite, 29 
 
 slate, 331 
 Ouachitite, 170 
 Ozokerite, 322 
 
 Paint-clay, 266 
 Palaeophyre, 188 
 Palaeopicrite, 250 
 Palagonite-tuff, 288 
 Pantellerite, 184 
 
 glass, 185 
 Paper-coal, 316 
 Parabasalt, 231 
 Paragonite, 26 
 
 schist, 344 
 Parallel structures, 80 
 Paramorphs, 8 
 
414 
 
 GENERAL INDEX. 
 
 Pargasite, 37 
 Parorthoclase, 20, 21 
 Parrot coal, 318 
 Pausilippo, 288 
 Peat, 314 
 
 Pebble-phosphate, 311 
 Pegmatite, 124 
 Pele's hair, 72 
 Pelites, 59 
 Pencil slate, 273 
 Penninite, 30 
 Peperin basalt, 219 
 Peperino, 288 
 Peridot, 43 
 Peridotite, 249 
 Perlite, in 
 Perlitic, 79 
 
 dacite, 185 
 pumice, 185 
 
 hornblende-andesite, 194 
 
 pitchstone, 194 
 
 pumice, 194 
 
 pitchstone, 113 
 
 pumice, 116 
 Perthite, 19 
 Petrography, 7 
 Petroleum, 322 
 Petrosjlex, 142 
 Phanerocrystalline, 58 
 Phenocryst, 57 
 Phillipsite, 47 
 Phlogopite, 28 
 Phonolite, 158 
 
 obsidian, 163 
 
 pitchstone, 163 
 
 tephrite, 222 
 Phonolitic trachyte, 148 
 Phosphate rock, 311 
 Phosphatic aggregates, 310 
 
 chalk, 311 
 Phosphorite, 310 
 Phthanite, 307, 343 
 Phyllite, 29, 274 
 
 (metamorphic), 332 
 
 proper, 274 
 Phytogenic limestone, 303 
 
 rocks, 303, 314 
 Picrite, 250 
 Piedmontite, 40 
 
 schist, 360 
 Pietra verde, 289 
 Pilite kersantite, 178 
 Pinsill, 273 
 Pipe-clay, 266 
 
 ore, 77 
 Pisolite, 305 
 Pisolitic, 76 
 Pistacite rock, 358 
 
 Pit-coal, 317 
 Pitch-coal, 316 
 Pitchstone, 143 
 
 felsite, 144 
 
 peperite, 188 
 
 (perlitic), 113 
 
 porphyry, 142 
 
 (rhyolitic), 113 
 
 (trachytic), 113 
 Plagioclase, 21-24 
 
 gneiss, 353 
 
 olivene-magnetite, 253 
 
 porphyrite, 178, 181 
 
 pyroxene- magnetite, 253 
 Plagiophyre, 57 
 
 Plastic clay, 266 
 Plug, 103 
 Poikilitic, 58 
 Polirschiefer, 309 
 Polishing-slate, 309 
 Porcelain, 379 
 
 jasper, 330 
 Porcellanite, 330 
 Porfido rosso, antico, 201 
 
 verde antico, 245 
 Porous, 78 
 
 porphyry, 140 
 Porphyrite, 178, 181 
 Porphyritic, 58 
 
 obsidian, 115 
 
 perlite, 112 
 
 phonolite, 160 
 
 pumice, 116 
 Porphyroid (rock), 354 
 
 texture, 57 
 Porphyry, 57 
 
 like porphyrite, 180 
 Potato-stone, 239 
 Potstone, 357 
 Pozzulana, 284 
 Prasenite, 366 
 Predazzite, 337 
 Preliminary definitions, 6 
 Pressure, 63 
 
 Primary minerals, 8 
 
 rocks, 97 
 
 (general divisions), 106 
 
 Prochlorite, 30 
 Propylite, 208 
 
 porphyrite, 201 
 
 (quartz), 208 
 Proteolite, 331, 332 
 Proterobase, 241 
 Protogine gneiss, 352 
 
 granite, 132 
 Psammites, 59 
 Psephites, 59 
 Pseudochrysolite, 115 
 
GENERAL INDEX. 
 
 415 
 
 Pseudofluidal structure, 286 
 Pseudomorphs, 8 
 Pudding-granite, 133 
 
 stone, 60, 278 
 Pulaskite, 168 
 Pumice, 116 
 
 (basalt), 232 
 
 (leucite-phonolite), 163 
 
 (rhyolite), 116 
 
 sand, 270 
 
 (trachyte), 117 
 Pumiceous, 79 
 
 pitchstone, 114 
 Puy, 104 
 Pyrites, 380 
 
 Pyritiferous porphyry, 139 
 Pyroclast, 60, 283 
 Pyroclastic breccia, 60, 284 
 Pyrogenic aggregates, 283 
 Pyromeride, 140 
 Pyrope, 48 
 Pyropissite, 316 
 Pyrophyllite, 45 
 
 schist, 358 
 Pyroxene, 30-34 
 
 and amphibole (comparison), 39 
 
 andesite, 203 
 glass, 207 
 
 diorite, 209 
 
 gneiss, 353 
 
 granite-porphyry, 136 
 
 granulite, 348 
 
 magnetite, 253 
 
 quartz-porphyry, 141 
 
 rock, 366 
 
 rocks, 99, 213-255 
 
 schist, 367 
 
 syenite, 152 
 Pyroxenite (of Hunt), 252 
 
 (of Coquand), 367 
 
 Quartz, 15 
 
 andesite, 182-185 
 
 augite-andesite, 206 
 diorite, 210 
 
 basalt, 230 
 
 diorite, 186 
 
 hornblende-diorite, 186 
 porphyrite, 187 
 
 keratophyre, 155 
 
 kersantite, 178 
 
 mica-andesite, 184 
 
 mica-diorite, 187 
 prophyrite, 181 
 
 hornblende-porphyrite, 188 
 
 norite, 239 
 
 porphyry, 136-141 
 
 Quartz propylite, 208 
 
 schist, 341 
 
 Buartzite, 340 
 uartzless orthoclase porphyry, 154 
 Quartzophyre, 57 
 
 Radiolarian ooze, 18, 308 
 Randanite, 309 
 Rapakivi, 130 
 Rattle-stones, 65, 77 
 Red gneiss, 351 
 
 hematite, 373 
 
 marbles, 335 
 Regional breccia, 291 
 
 metamorphism, 327 
 Relative age of rocks, 90 
 Rensselaerite, 356 
 Replacement, 88 
 Restrained convergence, 70 
 Retinite, 143 
 
 Rhyolite, 108 
 
 granite group, 107 
 Rhyolitic glass, in 
 
 obsidian, 114 
 
 perlite, in 
 
 pitchstone, 113 
 Rhomb porphyry, 154 
 Ribbon-gneiss, 351 
 Riebeckite, 38 
 Rock, 6, 7 
 
 (composite), 7 
 
 forming minerals, 14 
 
 meal, 282 
 
 salt, 294 
 
 (simple), 7 
 Roestone, 305 
 Rolled, 59, 68, 74 
 Roofing-slate, 273 
 Rottenstone, 302 
 Rubellan, 28 
 
 Sagvandite, 367 
 Sahlite-diabase, 242 
 Saliferous clay, 261 
 Sand, 268 
 
 coal, 317 
 
 rock, 277 
 
 stone, 275 
 
 laterite, 263 
 
 Sandy limestone, 301 
 Sanidine, 19 
 
 bombs, 149 
 
 quartz- porphyry, 141 
 Sanidinite, 149 
 Sanukite, 2^7 
 Sapphire, 51 
 Saugschiefer, 309 
 
4i6 
 
 GENERAL INDEX. 
 
 Saussurite, 39 
 
 gabbro, 237 
 Saxonite, 250 
 Scapolite, 47 
 
 diorite, 198 
 Schalstein, 242, 290 
 
 Scheme for determining the principal 
 
 rocks, 282-391 
 Schieferletten, 271 
 Schist, 82 
 Schistoid elaeolite-syenite, 169 
 
 gabbro, 236 
 
 granite, 133 
 Schistose, 82 
 Scoriaceous, 79 
 Scyelite, 251 
 Seams, 80 
 
 Secondary minerals, 8, 256 
 
 rocks, 6, 255 
 Secretion, 69 
 Sedimentary crystallization, 70 
 
 rocks, 264 
 Sedimentation, 67 
 Segregation, 69, 70 
 Semi-athracite, 319 
 
 bituminous coal, 318 
 Separation of minerals, 9-10 
 Septaria, 77 
 
 Sericite gneiss, 352 
 Sericite-phyllite, 332 
 Serpentine, 44, 254, 377 
 
 sandrock, 278 
 Shale, 271 
 Shaly, 82 
 
 lamination, 83 
 Sharp, 59 
 Shear, 63 
 
 zone breccia, 290 
 Sheet, 105 
 
 Shell limestone, 302 
 Shingle, 61, 279 
 Siderite, 376 
 Sideromelane, 288 
 Sienna marble, 335 
 Siliceous hematite, 375 
 
 limestone, 300 
 
 schist, 343 
 
 sinter, 309 
 
 tufa, 309 
 
 Silicified tuffs, breccias, etc., 290 
 Silicophite, 378 
 Sill, 105 
 Sillimanite, 50 
 
 biotite-quartzite, 333 
 Silt, 267 
 
 Simple rocks, 7 
 Slack-water clay, 283 
 Slate, 272, 274 
 
 Slate gneiss, 351 
 Slaty, 82 
 
 porphyry, 139 
 Slickensides, 63, 81 
 Slope agglomerate, 264 
 Smaragdite, 36 
 
 gabbro, 237 
 Smooth fracture, 86 
 Snow ice, 296 
 Snowflake marble, 336 
 Soapstone, 356 
 Soda-orthoclase-quartz-porphyry, 141 
 
 rhyolite, no 
 Sodalite, 42 
 
 syenite, 167 
 Soft coal, 317 
 
 ore, 262 
 Solution, 65 
 Sordawalite, 249 
 Spathic iron, 376 
 Spectacle-stones, 77 
 Specular hematite, 374 
 
 iron, 373 
 Sperone, 215 
 Spessartite, 48 
 Sphserosiderite, 376 
 Spherical structures, 78 
 Spheroidal, 73 
 
 norite, 239 
 Spherophyric, 79 
 
 granite, 133 
 
 obsidian, 115 
 Spherulitic, 79 
 Spilite, 246 
 Spilosite, 331 
 Splint-coal, 317 
 Splintery fracture, 86 
 Spotted basalt, 230 
 
 phonolite, 160 
 Sprudelstein, 305 
 Stalactite, 72, 293 
 Stalagmite, 293 
 Statuary marble, 335 
 Staurolite, 51 
 
 slate, 331 
 Steatite, 356 
 Stepped dike, 105 
 Stilbite, 47 
 Stinkstone, 300 
 Stone-coal, 317 
 Straticulate, 80 
 Stratified, 68, 80 
 
 aqueous deposits, 265 
 Streaked, 83 
 
 Striped porphyry, 139 
 Structural agents, 61-70 
 Structures, 62-84 
 Stylolites. 63, 71 
 
GENERAL INDEX. 
 
 417 
 
 Subangular, 73 
 
 Sudden changes in rocks, i 
 
 Suldenite, 201 
 
 Sulphur, 380 
 
 Swinestone, 300 
 
 Syenite, 149 
 
 aphanite, 157 
 
 gneiss, 352 
 
 porphyry, 156 
 
 trachyte group, 145 
 Syenitic mica traps, 174 
 
 granite, 131 
 
 lamprophyres, 174 
 porphyries, I53-I57 
 Syenitporphyr, 136 
 
 Tabular fracture, 86 
 Tachylite. 231 
 Taimyrite, 161 
 Talc, 45 
 
 amphibole schist, 364 
 
 schist, 355 
 Tennessee marble, 336 
 Tephrite, 221 
 Tephritoid, 222 
 
 leucitite, 215 
 Terminal moraine, 282 
 Terrane, 6 
 Teschenite, 225, 242 
 Textures, 55-61 
 Theralite, 225 
 Thinolite, 304 
 Tile-clay, 266 
 
 Till, 6t ' 
 
 Timazite, 183, 193 
 Tin-granite, 128 
 
 sand, 269 
 Tinguaite, 167, 171 
 Tiree marble, 335 
 Titaniferous iron-ore, 375 
 Tonalite, 187 
 
 gneiss, 352 
 Topaz, 49 
 
 brokenfels, 347 
 
 rock, 127 
 Topazfels, 127 
 Topazoseme, 127 
 Torbanite, 308 
 Tosca, 288 
 Touchstone, 343 
 Tourmaline, 50 
 
 granite, 126 
 
 hornstone, 333, 346 
 
 quartz ite, 127 
 
 rock, 127 
 
 schist, 333, 346 
 Trachydolerite, 194 
 
 Trachyte, 145 
 
 glass, in 
 
 pumice, 117 
 
 syenite rocks, 145 
 Trachytic obsidian, 115 
 
 perlite, 112 
 
 pitchstone, 113 
 
 pumice, 116 
 Trass, 288 
 Travertine, 303 
 Tremolite, 36 
 Tridyrnite, 16 
 Tripestone, 294 
 Tripoli, 309 
 Troctolite, 240 
 Trough-bedding, 81 
 Trowlesworthite, 126 
 Tufa (calcareous), 304 
 
 laterite, 263 
 
 (siliceous), 309 
 Tuffs, 285 
 Tuffite, 289 
 Tuffoid, 290 
 Turf, 314 
 Typical gneiss, 351 
 
 obsidian, 114 
 
 phonolite, 158 
 
 quartz-porphyry, 138 
 
 trachyte, 147 
 
 Uintaite, 321 
 Unakite, 128 
 
 Unindividualized matter, 55 
 Unsorted debris, 259-264 
 Uralite, 36 
 
 diabase, 242 
 
 porphyry, 245 
 
 schist, 358 
 
 syenite, 153 
 Uvarovite, 48 
 
 Variolite, 249 
 Variolitic granite, 133 
 Veined, 81 
 Verde antique. 336 
 Verite, 233 
 Vesicular, 79 
 
 crystallization, 70 
 
 obsidian, 115 
 
 perlite, 112 
 
 phonolite, 160 
 
 porphyry, 140 
 Vesuvianite, 49 
 
 augite-schist, 368 
 
 schist, 368 
 Viridite, 54 
 Vitreous, 61 
 
4i8 
 
 GENERAL INDEX. 
 
 Vitriol-peat, 315 
 Vhrophyre, 57, 142 
 Volcanic ash, etc., 283 
 
 glass, 114 
 Volcanite, 184 
 Vosgesite, 175 
 
 Wacke, 263 
 Water-ice, 297 
 Wax coal, 315 
 Weathering, 65, 255 
 Websterite, 252 
 Wehrlite, 250 
 Wernerite, 47 
 Whetslate, 308 
 Whetstone, 308 
 White (color), 86 
 
 porphyry, 139 
 Wichtisite, 248 
 
 Wind-drift structure, 80 
 Winooski marble, 336 
 Wood-gneiss, 351 
 
 Xenomorph, 56 
 Yellow (color), 87 
 
 Zeolites, 46 
 Zinnwaldite, 27 
 Zircon, 45 
 
 syenite, 168 
 Zobtenite, 236 
 Zoisite, 39 
 
 diallage rock, 367 
 Zones (metamorphk), 324 
 Zoogenic limestone, 298 
 
 rocks, 297 307, 310 
 Zweiglimmeriger granit, 123 
 Zwitter rock, 128 
 
DESCRIPTION OF THE PLATES. 
 
 The cuts of Plates I, II, and I to 4 of VI are 5/6 natural 
 scale ; 5 and 6 of IV are 3/4 the same ; and 6 of V is 1/20 the 
 same ; the rest are of natural scale. 
 
 PLATE I. 
 
 1. Medium-crystalline-granular (granitoid) porphyritic granite. 
 
 2. Pudding-granite with concretions of predominant mica. 
 
 3. Granitoid olivine-diabase. 
 
 4. Fine-crystalline-granular diabase. 
 
 5. Similar leucite-tephrite, with phenocrysts of leucito. 
 
 6. Fine-crystalline-granular and porphyritic dacite. 
 
 PLATE II. 
 
 1. Porphyritic hornblende-granitite. 
 
 2. Luxullionite. 
 
 3. Coarse-granular elaeolite-syenite. 
 
 4. Porphyritic dolorite. 
 
 5. Oligoclase-porphyrite. 
 
 6. Orthoclase- porphyry. 
 
 PLATE III. 
 
 1. Orbicular diorite. 
 
 2. Pegmatite. 
 
 3. Fine-crystalline hypersthene-andesite (vesicular). 
 
 4. Microcrystalline rhyollte (vesicular and porous). 
 
 5. Microcrystalline limburgite (amygdaloidal). 
 
 6. Microcrystalline quartz-porphyry (vesicular oorous pyroclastic breccia). 
 
 PLATE !V. 
 
 1. Perlite (perlitic). 
 
 2. Obsidian (vitreous). 
 
 3. Tachylite (scoriaceous). 
 
 4. Olivine-rock (volcanic bomb). 
 
 5. Halleflinta (fluidal). 
 
 6. " Bastkohl " (fibrous). 
 
 PLATE V. 
 
 1. Limestone (oolitic). 
 
 2. Quartz-conglomerate (pudding-stone). 
 
 3. Brecciola. 
 
 4. Rolled sand (river). 
 
 5. Sharp sand (glacial rock-meal). 
 
 6. Till (crushed slate with angular debris and rolled sand, gravel, etc.), 
 
 PLATE VI. 
 
 1. Clay-slate (slaty cleavage from pressure). 
 
 2. Calcareous mica-schist (flat- parallel). 
 
 3. Calcareous mica-schist (lenticular-parallel). 
 
 4. Hornblende-schist (irregular). 
 
 5. Gneiss (foliation). 
 
 6. Gneiss (segregation in strings). 
 
PLATE L 
 
PLATE IL 
 
PLATE 111. 
 
 
PLATE IV. 
 
PLATE V. 
 
 m 
 
PLATE VI, 
 
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 13 
 
MECHANICS AND MACHINERY. 
 
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 14 
 
METALLURGY. 
 
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 Totten's Important Question in Metrology 8vo, 2 50 
 
 The World's Columbian Exposition of 1893 4to, 1 00 
 
 Worcester and Atkinson. Small Hospitals, Establishment and 
 Maintenance, and Suggestions for Hospital Architecture, 
 
 with Plans for a Small Hospital 12mo, 1 25 
 
 HEBREW AND CHALDEE TEXT-BOOKS. 
 
 Green's Grammar of the Hebrew Language 8vo, 3 00 
 
 " Elementary Hebrew Grammar 12mo, 1 25 
 
 Hebrew Chrestomathy 8vo, 200 
 
 Gesenius's Hebrew and Chaldee Lexicon to the Old Testament 
 
 Scriptures. (Tregelles.) Small 4to, half morocco. 5 00 
 
 Letteris's Hebrew Bible . . 8vo, 2 25> 
 
 16 
 
225 
 
 
 
 UNIVERSITY OF CALIFORNIA LIBRARY 
 
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