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ELEMENTS OF PHYSICAL 
 GEOGRAPHY 
 
Grand Canyon of the North Platte River, Central Wyoming. (U. G. Cornell.) 
 
Elements of Physical 
 Geography 
 
 BY 
 
 THOMAS CRAMER HOPKINS, Ph. D 
 
 Professor of Geology in Syracuse University 
 
 ov ttoXA dAAa 7ro\v 
 
 BENJ. H. SANBORN & CO. 
 
 BOSTON NEW YORK CHICAGO 
 
LIBRARY of CONGRESS 
 Two Copies Mecm* 
 
 JUN 1 1908 
 
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 Copyright, igo8 
 By THOMAS CRAMER HOPKINS 
 
 THE MASON-HENRY PRESS 
 8YRACUSE, NEW YORK 
 
PREFACE i 
 
 There are good text-books on physical geography, but 
 there are many teachers and school departments not satis- 
 fied with any of them. The author has endeavored to meet 
 the requirements of these teachers as far as such needs could 
 be ascertained. With a subject as broad as physical geog- 
 raphy there will always be lack of uniformity in the man- 
 ner of presentation, as well as in the subject matter. The 
 subject is one which is undergoing many changes, and it is 
 possible that both the teachers and the subject may be 
 ahead of present text-books in many particulars. 
 
 This book is not an experiment. To accommodate the 
 many students who were going out. to teach in the schools 
 of the State, the author, several years ago, attempted to 
 bring his courses in physical geography in Syracuse Uni- 
 versity into harmony with the requirements of the Educa- 
 tional Department of the State. It was then that he 
 realized the force of the complaints of many teachers that 
 none of the text-books met these requirements. After try- 
 ing two of the leading text-books, he abandoned both and 
 prepared a text which has been used successfully, in manu- 
 script form, for two years in his own classes. Before 
 putting it in book form he studied the conditions in the 
 public schools of New York and in other states and has 
 attempted to prepare a book to meet the needs of teachers 
 and the Educational Departments in this country, not with 
 the expectation of pleasing all, but with the confident hope 
 of meeting the needs of many of those who are dissatisfied 
 with the present books. 
 
 It is not important that any class should pursue the 
 
vi PREFACE 
 
 subject in the order in which it is presented in this text. 
 The author's custom is to begin with Chapter II, because 
 his classes commence in September. This season is favora-. 
 ble for field work, which has to do more with the contents 
 of Chapters II, III and IV than with Chapter I. If the 
 work should begin in midwinter, or there should be no field 
 work, then the order given might well be followed. It is 
 expected, however, that each teacher will follow his own 
 plan, — the subject matter is divided into chapters for that 
 purpose. Each teacher will naturally expand that part of 
 the subject best illustrated by the geographic conditions in 
 the proximity of the school. Those in the glaciated area, 
 by use of the references can devote more time to the study 
 of glacial phenomena. Those on the shore of the ocean, or 
 a large lake, can give more time to shore features. Those 
 in the interior can dwell more on the work of streams and 
 ground water. Intensify the portion which the pupil can 
 best study from Nature. 
 
 Every class in physical geography should have more or 
 less laboratory and field work associated with the text-book. 
 One of the functions of the text-book— not the only one, by 
 any means — is to serve as a handbook, which the pupil 
 studies as an aid in the interpretation of what he sees in 
 the laboratory. 
 
 To aid the teacher in his work, the author has prepared 
 a small laboratory manual to accompany this text. The 
 manual must, of necessity, be a book of suggestions rather 
 than directions. The work, to be successful, depends on 
 the skill and tact of the teacher in getting the pupils to 
 study and work with real things rather than words about 
 them. Yet the author believes that a good book is as much 
 needed and fully as important in the work of the laboratory 
 as in that of the class-room. Many teachers have not had 
 
PREFACE vii 
 
 the opportunity to develop a systematic course of labora- 
 tory work, consequently much time has been wasted by the 
 pupils in routine work. The laboratory manual aims to 
 help the teacher and pupil, by suggestions and questions, 
 to a knowledge of the earth features and relations. 
 
 The text and manual together aim to assist both teacher 
 and pupil into the spirit of one of the most inspiring sub- 
 jects in our schools; to bring the pupil into contact with 
 Nature in such a way that he may see and realize his own 
 position in this world of complex activities, so that by 
 observing more closely the familiar phenomena surround- 
 ing him in his daily life he may extend his observations 
 and knowledge through the less known into the unknown, 
 and thus be an intelligent part of the great world in which 
 he lives. 
 
 The author is indebted to many teachers of physical 
 geography in different states in the preparation of this 
 text. After the manuscript was written it was submitted 
 to a number of prominent teachers in high schools, acad- 
 emies and colleges for criticism, and the valuable sug- 
 gestions made by them are incorporated as far as possible. 
 Especially does he desire to express his indebtedness to the 
 following eminent teachers for valuable aid: Professor C. 
 E. Peet, Lewis Institute, Chicago; Miss Mary G. Sullivan, 
 Buffalo High School; Dr. C. H. Richardson, the author's 
 colleague in Syracuse University; Miss Jennie T. Martin, 
 City Schools, Washington, D. C. ; Professor James H. 
 Smith, Chicago High School; Dr. F. H. H. Calhoun, 
 Clemson College, S. C. ; Sarah Emerson Green, formerly 
 the author's assistant at Syracuse University; and P. F. 
 Schneider of Syracuse. The first three above named read 
 both the manuscript and the proof with painstaking care, 
 and the others gave valuable aid in reading either the 
 
viii PREFACE 
 
 proof or the manuscript. Dr. H. A. Peck, Professor of 
 Astronomy, gave many valuable suggestions on Chapter I, 
 and Morgan R. Sanford, local forecaster for the U. S. 
 Weather Bureau, did the same in Chapter X. 
 
 For the photographs illustrating the text the author is 
 deeply indebted to many friends and colleagues who are 
 credited elsewhere. Special thanks are due to the U. S. Geo- 
 logical Survey, the U. S. Fish Commission, the Maryland 
 and Vermont State Geological Surveys, and the American 
 Museum of Natural History. Where not otherwise credited 
 the photographs are by the author, except a very few 
 where the photographer is not known. The illustrations 
 and explanations of the same form a very important part 
 of the text and should be studied as carefully as the 
 words. In some instances the picture illustrates the text, 
 in others the text is an explanation of a principle best 
 learned from the picture. 
 
 T. C. H. 
 
 Syracuse University, 
 May, 1908. 
 
CONTENTS 
 
 CHAPTER PAGE 
 
 I. The Earth as a Planet L 
 
 II. Groundwater and Rivers 40 
 
 III. Lakes, Swamps and Waterfalls 100 
 
 IV. Glaciers 138 
 
 V. The Ocean 169 
 
 VI. Shore Lines 197 
 
 VII. The Land— Minerals, Rocks and Soils 235 
 
 VIII. Physiographic Agencies 274 
 
 IX. Physiographic Features 309 
 
 X. The Atmosphere 348 
 
 XI. Geography of Plants, Animals and Man .... 400 
 
 XII. Physiographic Regions of the United States 449 
 Appendix 473 
 
CHAPTER I 
 
 THE EARTH AS A PLANET 
 
 Introductory.— Physical geography literally means a 
 description of the natural features of the earth. The de- 
 velopment of the subject during recent years has led to the 
 subdivision as follows : 
 
 1. The earth as a globe or planet, its origin and rela- 
 tion to the other heavenly bodies. 
 
 2. The atmosphere or the surrounding gaseous portion. 
 
 3. The hydrosphere or the water, including the fresh 
 water and the salt water of the ocean. 
 
 4. The lithosphere or the solid land portions, the 
 causes producing the various topographic forms and the 
 effects of these on climate and life. 
 
 5. Life geography or the effect of physical environ- 
 ment upon life and its effect on the earth features. 
 
 Physical geography includes a study of these subjects with 
 reference to their influence upon man, his industries, civiliza- 
 tion and relation to his surroundings. With this aim in view 
 it leads one within the doorway of each of the natural sciences. 
 
 To the ancient philosopher's maxim, "Know thyself," the 
 modern scientist adds "in relation to Nature." This is the foun- 
 dation of modern physical geography. In gaining this knowl- 
 edge man is better able to adapt himself to his surroundings, to 
 utilize the various forces and products of Nature, to realize not 
 only his dependence upon his fellow man and the lower forms of 
 life, but his duty towards them as well, and consciously or un- 
 consciously, he must gain respect if not love for the Omnipotent 
 Power that rules over all. 
 
 Physical Geography is the science which treats of the 
 
 l 
 
2 PHYSICAL GEOGRAPHY 
 
 natural features of the earth in their relation to man and 
 the lower forms of life. 
 
 1. The Earth a Part of the Solar System.— The earth 
 is a nearly round ball consisting of a large rock mass partly 
 covered with oceanic waters, and entirely surrounded by 
 the gaseous atmosphere. The whole mass solid, liquid and 
 gaseous, rotates on its axis as it revolves in space around 
 the sun. It is but one of a number of similar bodies called 
 planets and is in no wise conspicuous among them. It is 
 neither the largest nor the smallest; neither the farthest 
 from nor the nearest to the sun. Because we live on the 
 earth, it is most important to us, but if we could look on it 
 from some distant point in the heavens we should not see 
 anything to distinguish it particularly from the other 
 planets. 
 
 2. What the Solar System Comprises.— The earth is 
 an important member of the solar system which includes 
 the sun at the center, the planets and their satellites, the 
 planetoids or asteroids, and some comets. Besides the earth 
 there are revolving around the sun seven other planets 
 which are named in order beginning with the one nearest 
 the sun, — Mercury, Venus, Earth, Mars, Jupiter, Saturn, 
 Uranus and Neptune. Four of these, Venus, Mars, Jupiter 
 and Saturn, are plainly visible at certain periods. Two of 
 them, Venus and Jupiter, are at times the brightest bodies 
 in the heavens except the sun and moon. Part of the time 
 they are morning stars ; at other times evening stars. The 
 planets may be distinguished from the true stars by their 
 steady light. The stars twinkle. Each of the planets, ex- 
 cept Mercury and Venus, has one or more satellites or 
 moons revolving around it. Saturn has besides the satel- 
 lites several concentric bright rings surrounding it. The 
 relative sizes, distances and other data concerning the 
 planets are given in Appendix I. 
 
THE EARTH AS A PLANET 3 
 
 The asteroids or planetoids, about 600 in number, are solid 
 bodies much smaller than the planets, and revolve in orbits be- 
 tween Mars and Jupiter. One of the planetoids, Eros, about 20 
 miles in diameter, discovered in 1898, has a very eccentric orbit 
 that sometimes brings it within 13% million miles of the earth. 
 The student should learn to recognize the larger planets and ob- 
 serve their movements among the stars from season to season. 
 
 ^X\V. SOLAR SYSTJ^, 
 
 Fig. 1. The solar system, showing the order of the planets, satellites, 
 asteroids, and the orbits of a few comets. 
 
 3. Relation of the Solar System to the Universe.— 
 
 The Solar System, large and complex as it appears, is but 
 
4 PHYSICAL GEOGRAPHY 
 
 one of a number of similar systems in the universe. Most 
 of the bright stars in the heavens are suns similar to ours. 
 They appear to be much smaller than our sun, but that is 
 because they are so much farther away. In reality many 
 of them are much larger. They probably have planets, 
 satellites, comets, etc., like our own system, but they are so 
 far away that these bodies, if they exist, are not visible 
 from the earth. It is not known how many of these sys- 
 tems there are, nor how far out in space they extend, but 
 certainly a great distance beyond our comprehension. It 
 is estimated that with a large telescope one can see between 
 100 and 200 millions of stars, a large per cent of which lie 
 in the Milky Way. With few exceptions all of these stars 
 are so far away that it takes the light from them travelling 
 at the rate of 186,000 miles a second many years to reach 
 the earth. The moon is about 240,000 miles away or about 
 ten times the distance around the earth ; the sun is nearly 
 400 times farther than the moon ; and the nearest fixed 
 star or neighboring sun system is several thousand times 
 farther than the sun. The light of the sun takes about 
 8 minutes to reach the earth. The light of the nearest star 
 takes 3% years to cross the space separating it from the 
 earth. Truly the earth is a very small part of the solar 
 system and an exceedingly minute portion of the universe. 
 4. The Moon. — The earth has one satellite, the moon, 
 which revolves around it once a month (27.32 days) and 
 accompanies it through space in its journey around the sun. 
 The moon is 2,163 miles in diameter and at an average 
 distance of 238,840 miles from the earth, but it varies from 
 221,600 to 252,970 miles. It is because of its nearness to 
 the earth that it is held in its orbit around the earth in- 
 stead of pursuing an independent course around the sun. 
 (The synodic month or the time from full moon to full 
 moon is 29.53 days, but the sidereal month is 27.32 days.) 
 
THE EARTH AS A PLANET 5 
 
 5. The Phases of the Moon.— The moon emits no light of its 
 own. All the light that comes from it to the earth is reflected 
 sunlight. When the moon is in that part of its orbit nearest the 
 sun, it is nearly between the earth and the sun, and we see but 
 a mere fringe of illumination; it is then the new moon. The 
 sunlight reflected from the earth faintly illuminates its dark side 
 giving what is called the earth shine. When it has completed a 
 fourth of its circuit after new moon, it is at right angles to a 
 line connecting the sun and the earth, and we see one-half of the 
 illuminated face, that is, a fourth of the whole surface, and the 
 phase is called the first quarter. When it has completed half a 
 circuit and is on the opposite side of the earth from the sun, it 
 
 Fig. 2. The phases of the moon. 
 
 is full moon. At the third quarter the moon has completed three- 
 fourths of its circuit and one-fourth of the whole surface is again 
 reflecting light to the earth. The line separating the illuminated 
 portion from the dark portion is called the terminator. Draw 
 from observation a figure of the moon showing the light and dark 
 portion every second night from one new moon to the next; 
 arrange them in order around an ellipse and compare them. 
 
 6. The Sun. — The sun is the center of the solar sys- 
 tem. All the planets of the system revolve about it and 
 receive heat and light from it. It is much larger than all 
 
6 
 
 PHYSICAL GEOGRAPHY 
 
 the planets combined, having a diameter of 866,000 miles, 
 which would make it a million times the bulk of the earth ; 
 but since its density is less, it has only 332,000 times the 
 mass of the earth. Imagine the earth at the center of the 
 sun and the moon revolving around it in an orbit the same 
 size as the present one ; the moon would then be about half 
 way from the center to the circumference of the sun. 
 7. The Sun's Energy.— Nearly all the heat, light, and 
 other forms of energy on the surface of the earth come 
 directly or indirectly from the sun. The radiant energy 
 
 from the sun, known as 
 insolation, is thought to 
 pass from the sun to the 
 earth unaffected by in- 
 tervening space until it 
 reaches the earth where 
 part of it, the part that 
 we recognize, is percep- 
 tible as heat and light. 
 The part of the sun's 
 insolation received by 
 the earth is an exceed- 
 ingly small part of the 
 whole, and when one 
 realizes that nearly all 
 forms of heat and light come from the sun, the total 
 quantity radiated into space is something beyond compre- 
 hension. All the energy used by man in heating and light- 
 ing, all that is used in running machinery everywhere, ^11 
 that is used in lifting the waters of the sea to the clouds to 
 fall as rain, all that wonderful vital energy manifested in 
 animals and plants,— all of these and probably other forms 
 of energy as yet unrecognized are flashed like wireless tele- 
 grams across the vast space that separates us from the sun. 
 
 Fig. 3. Showing the relative size of the 
 sun and the moon's orbit. What is 
 the scale of the diagram? 
 
THE EARTH AS A PLANET 7 
 
 8. Eclipses.— Since the sun is the source of the light 
 received by the earth and the moon, when either of these 
 
 Annular Eclipse 
 
 Fig. 4. Solar and lunar eclipses. 
 
 latter bodies comes between the other and the sun, the 
 light of the sun will be cut off. The shadow thrown by 
 
8 PHYSICAL GEOGRAPHY 
 
 the intervening body on the other is known as an eclipse. 
 The shadow of the moon on the earth produces an eclipse 
 of the sun, and the shadow of the earth on the moon causes 
 an eclipse of the moon. If the moon passes entirely into 
 the earth's shadow, there is a total eclipse of the moon, if 
 only part of it passes into the shadow, a partial eclipse is 
 the result. There may be three kinds of solar eclipses: (1) 
 a total eclipse when the moon passes centrally over the disc 
 of the sun and so near the earth that the shadow reaches 
 the earth; (2) an annular eclipse, produced when the moon 
 passes centrally over the disc of the sun but is so far from 
 the earth that the end of the shadow does not reach the 
 earth ; then the moon appears as a black spot in the center 
 of the sun surrounded by a ring of light which gives the 
 name annular or ring eclipse; (3) a partial eclipse of the 
 sun produced when the moon passes a little to one side of 
 the line joining the earth and the center of the sun. 
 
 If the moon revolved about the earth in. the plane of the 
 earth's orbit, there would be a total eclipse of the moon and sun 
 once each month, but since the plane of the moon's orbit is in- 
 clined at an angle of five degrees to that of the earth's 
 orbit, there is an eclipse only when the moon passes one of the 
 nodes, that is, the points of intersection of the two orbits, at or 
 near new moon or full moon. There may be an eclipse of the sun 
 when there is none of the moon, and there must be at least two 
 solar eclipses each year. Consult the almanac for several years 
 and see how many eclipses of each kind there have been. 
 
 In 1907 there were four eclipses, two of the sun, one total 
 and one annular, and two of the moon. 
 
 9. Comets. — Comets belong in part to the solar sys- 
 tem. Several hundred of these bodies have been seen from 
 the earth at .different times. Some of them travel in ellip- 
 tical orbits which extend millions of miles out into space 
 beyond the outermost planet in our system, hence the period 
 of revolution is one of many years. Many comets travel in 
 
THE EARTH AS A PLANET 9 
 
 a parabola or a hyperbola and become visible once as they 
 pass around the sun and away again, never to return. 
 Whence they come and whither they go is not known. 
 Prom fig. 5 it can be seen that parabolas and hyperbolas 
 are curved lines, the ends of which never meet. 
 
 The comets differ in size and shape as widely as they do 
 in their orbits. They are characterized by a nucleus or 
 denser portion surrounded by a nebulous mass called the 
 coma which streams out from the nucleus and forms the 
 tail. The tail is single or double and of widely diverse 
 
 Fig. 5. Ellipse, parabola and hyperbola. The last two are diverging curves 
 which never meet. 
 
 shapes and differs in length from that of the diameter of 
 the nucleus to a length of 100,000,000 miles or more. As 
 a comet approaches the sun, the tail streams out behind it, 
 as it passes perihelion (the nearest point to the sun), the 
 tail streams out ahead of it, that is, the tail keeps on the 
 opposite side of the nucleus from the sun. Celestial pho- 
 tography has shown recently that the tails of several com- 
 ets have been suddenly broken into two or more parts. 
 
 10. Historical Comets.— The comet of 1680 is an important 
 one because it was the first whose orbit was determined by the 
 
10 PHYSICAL GEOGRAPHY 
 
 principles of gravitation. The computation was made by Sir 
 Isaac Newton who found that it passed within 140,000 miles of 
 the sun travelling at the rate of 1,332,000 miles an hour. It had 
 a tail 100,000,000 miles long. 
 
 Halley's comet (1682) is so called because Halley, a friend of 
 Newton, computed its orbit and thus identified it with previous 
 comets that had appeared at intervals of 75 years. He predicted 
 that it would make its next appearance March 13, 1759. It passed 
 perihelion within a month of that time. It appeared in 1835 and 
 is due again in 1910. Watch for it. 
 
 Biela's comet (1826) was observed in the latter part of Decem- 
 ber, 1846, to elongate and divide into two parts which travelled 
 in parallel orbits 160,000 miles apart. When they next appeared 
 in 1852 the two portions were 1,500,000 miles apart. They have 
 not been seen since. 
 
 The Comet of 1882 was the most conspicuous one in recent 
 years. It approached the sun in perihelion close enough to pass 
 through part of its gaseous envelope. Daniel's comet attracted 
 attention in the summer of 1907. 
 
 11. Meteors and Shooting Stars.— Meteors and shoot- 
 ing stars are luminous bodies which are frequently observed 
 in our upper atmosphere and are sometimes seen to strike 
 the earth. The luminosity of these bodies is thought to be 
 due to friction against the atmosphere and that before 
 entering the atmosphere they are cold and non-luminous. 
 Many of them are dissipated in the upper atmosphere, but 
 probably the fragments in the form of invisible dust reach 
 the earth in the course of time. Ten to twenty millions of 
 meteors strike the earth's atmosphere every day. It is 
 thought by some that the earth has been formed by the 
 aggregation of such particles, which would mean that un- 
 less the earth is losing matter in some way it is still increas- 
 ing in weight. 
 
 12. Meteorites.— Meteors which fall to the earth are 
 called meteorites. They \jary in size from very minute 
 fragments to bodies of many tons in weight. The great 
 
THE EARTH AS A PLANET 11 
 
 Tent meteorite in New York City which Peary brought 
 from Cape York, Greenland, weighs 36.5 tons. The 
 Bacubirito meteorite in Mexico weighs about 27.5 tons. 
 The Willamette meteorite, shown in fig. 6, weighs 15.6 tons. 
 Some are composed of stone, some of metals and some of 
 both. About four out of every hundred are nearly pure 
 iron with a little nickel. The source of meteors and 
 meteorites is not definitely known. 
 
 Fig. 6. Willamette meteorite, the third largest known, found 
 near Oregon City, Oregon. Length 10 ft., height 6 ft. 6 in., 
 weight 15.6 tons. (American Museum of Natural History.) 
 
 THE ORIGIN OF THE EARTH 
 
 All material things so far as we know have a beginning, 
 a period of growth, decline, and death. This is not true 
 of matter itself but of the forms which it takes. The fact 
 is commonly recognized in regard to plants and animals 
 but is probably no less true of many inanimate objects, ex- 
 cept that the changes go on so much more slowly that they 
 are frequently not recognized. It is now known that the 
 
12 PHYSICAL GEOGRAPHY 
 
 hills are not "everlasting." They may be "rock-ribbed" 
 but they are not as "ancient as the sun." The mountains 
 have a beginning, and a period of growth, after which they 
 begin to dwindle and gradually disappear. So it is with 
 the earth, the sun, and the solar system; they did not al- 
 ways exist as such. When and how were they formed ! 
 
 13. The Nebular Hypothesis.— Of the many attempts 
 to explain the origin of the solar system none has met with 
 more favor than that known as the nebular hypothesis, 
 which assumes that at one time all the material in the solar 
 system existed in the form of a rotating mass of nebulous 
 gas that occupied all the space from the center of the 
 present sun out to and beyond the limits of the orbit of the 
 outermost planet — Neptune. Under the universal law of 
 gravitation, by which every particle of matter in the uni- 
 verse attracts every other particle, these gas particles were 
 attracted towards a common center. In the course of time 
 a portion of the mass was separated in the form of a ring, 
 or, as some say, as an irregular mass, which in time, by its 
 rotation on its own axis, formed a spheroidal body revolv- 
 ing around the central mass. This was the planet Neptune, 
 which continued to revolve around the central mass from 
 which in turn the other planets and their satellites were 
 separated, the earth being the sixth one and Mercury the 
 last one. The residual central mass is the sun, which, ac- 
 cording to the hypothesis, is still contracting. The plan- 
 etary masses probably separated from the parent mass 
 while still in the gaseous condition, but contiaued to con- 
 tract until they became liquid and on further cooling, solid, 
 at least on the surface. 
 
 This hypothesis, with sundry modifications, has been widely 
 accepted because it seemed to account for so many things about 
 the system. Recently many objections to this explanation have 
 
THE EARTH AS A PLANET 13 
 
 been raised, while another explanation has been growing in favor 
 with some people because it appears to be free from some of the 
 difficulties in the nebular hypothesis. 
 
 14. The Planetesimal Hypothesis.*— The planetesimal 
 hypothesis, although it starts with a nebulous mass, differs 
 radically from the nebular hypothesis in a number of 
 particulars. Unlike the first, however, the nebula is not 
 necessarily a gas nor is it highly heated and hence it need 
 
 Fig. 7. A spiral nebula in Ursa Major. (Ritchey, Yerkes Observatory) 
 
 not pass through a liquid state. The hypothesis starts with 
 a spiral nebula, which is one of the most common forms in 
 the sky at present. The knots or denser portions in the 
 nebula are the nuclei of the future planets and satellites, 
 
 * Formulated by Professors Chamberlin and Moulton of the University 
 of Chicago. 
 
14 
 
 PHYSICAL GEOGRAPHY 
 
 and the nebulous haze surrounding the nuclei consists of 
 finely divided matter mostly solid, possibly some liquid and 
 gaseous, which is later gathered in by gravitation, and added 
 to the nuclei to form the planets. All of the material, first 
 in the nebula and later in the planets and satellites, moves 
 about the central mass in elliptical orbits. It all has a 
 double motion, first around the central axis of its own 
 nucleus or planet, and second around the central sun. 
 
 Pig. 8. The great nebula in Andromeda. (Ritchey, Terkes Observatory.) 
 
 The hypothesis supposes a relatively slow growth of the 
 earth, as of the other planets, with increasing temperature 
 in the central portions due to gravity. That is, a large 
 body will have greater pressure by gravity at the center 
 than a small one and, hence, will have greater heat induced 
 
THE EARTH AS A PLANET 15 
 
 by the pressure. In a body as large as the earth, the gravi- 
 tative attraction of all the particles towards the center pro- 
 duces an enormous pressure on the central portions, a pres- 
 sure sufficient to produce heat and raise the temperature 
 of the interior. 
 
 For a long time after the earth niiclues began to grow 
 it was too small to have an atmosphere or even a hydro- 
 sphere, both of which formed gradually as soon as the 
 planet was large enough to hold them by the force of 
 gravity. They would be increased by the parts expelled 
 from the interior by gravity pressure, as well as the parts 
 that would be drawn to the surface of the mass from the 
 surrounding nebula. Hence, the accretion of the planet- 
 esimal matter of the outer half or more of the earth would 
 be through an atmosphere and subject to the action of 
 moisture. This hypothesis likewise makes possible a much 
 longer period of time in which life was possible on the 
 earth, or in which the conditions" favored the existence of 
 life in the initial stages, than does the nebular hypothesis. 
 
 The principal points of difference between the two hypotheses 
 are, that according to the first, the earth passes from a highly 
 heated gaseous condition through a hot molten state to the pres- 
 ent solid condition, while according to the second, the earth was 
 never entirely gaseous, never necessarily molten and possibly 
 never much hotter than at present. By the first, the earth was 
 once larger than at present and included the moon which was 
 later separated from it; by the second, the earth was never larger, 
 probably not so large in the past as at the present. By the first, 
 the outer planet, Neptune, is the oldest and the inner one, Mer- 
 cury the youngest; by the second, the planets and their satellites 
 are all of about the same age, that is, they were all in process of 
 formation at the same time. According to the planetesimal 
 hypothesis the moon is devoid of water and an atmosphere be- 
 cause it is too small to hold them on the surface by gravity, and 
 not because it is so old that it has lost them as sometimes 
 claimed in the nebular hypothesis. 
 
16 PHYSICAL GEOGRAPHY 
 
 15. The Shape of the Earth.— The earth is the shape 
 of a ball that is flattened at the poles and bulged at the 
 equator, so that the equatorial diameter is nearly 27 miles 
 longer than the polar diameter. It approaches an oblate 
 spheroid more nearly than any other mathematical figure. 
 
 Evidence that the earth has a curved and not a flat sur- 
 face: (1) Its shadow on the moon is always a curved one. 
 Could this be true of a flat surface? (2) New stars ap- 
 pear in front of the observer and old ones disappear behind 
 him as he travels toward the north or south. How would 
 
 Fig. 9. Expansion of horizon with elevation indicates curvature of the earth. 
 
 it be on a flat surface? (3) The horizon expands rapidly 
 as the observer ascends to higher altitudes. Wo,uld this be 
 true on a flat surface? (4) At sea the slender toprigging 
 of a vessel is visible farther than the larger but lower hull. 
 Why? (5) There is a marked difference in time with a 
 change of longitude ; thus the sun rises more than three 
 hours later in San Francisco than it does in Philadelphia, 
 and nearly nine hours later than it does at London. Tlow 
 would it be if the earth were flat ? ( 6 ) The earth has been 
 circumnavigated many times. (7) The flattening at the 
 poles is indicated by the increased weight of a body in high 
 latitudes over that of the same body at the equator, and by 
 
THE EARTH AS A PLANET 17 
 
 the greater length of a degree of latitude near the poles. 
 (See sec. 28 and fig. 16). 
 
 16. Cause of the Shape of the Earth.— Nearly 200 
 years ago it was shown that an oblate spheroid is one of 
 the figures of equilibrium for a rotating body, and the de- 
 gree of oblateness or flattening is due to the rate of rota- 
 tion. More recently it has been shown that the oblateness 
 of the earth corresponds to the requirements of a rotating 
 fluid mass of the size and rate of rotation of the earth. 
 This was cited as evidence that the earth was fluid at one 
 time in its history before reaching its present solid form. 
 But there are good reasons for thinking that a solid earth 
 would take the same shape after a long period of time, due 
 to the shifting of materials on the surface, or according to 
 the planetesimal hypothesis there would be more material 
 accumulate at the equator than at the poles. 
 
 Gravitation shapes the material into a sphere. Rotation 
 causes the flattening of the sphere into the oblate spheroid. It 
 is gravitation that holds bodies on the earth, and the force in- 
 creases with the mass of the planet. If the earth were the size 
 of the moon, bodies would have much less weight on its surface. 
 Gases would be so light that they would fly off into space and 
 there would be no atmosphere, hence no water, and no life. If 
 the earth were as large as Jupiter, bodies on the surface would 
 be correspondingly heavier. 
 
 17. Size of the Earth.— The diameter of the earth 
 through the poles is 7,899.6 miles; through the equator 
 7,926.6 miles. Compute the circumference, the area, the 
 volume and the weight of the earth in tons from the follow- 
 ing data : 
 
 1. The circumference equais the diameter multiplied 
 by 3.14159. 
 
 2. The area equals the product of the diameter by the 
 
 circumference of a great circle. 
 2 
 
18 
 
 PHYSICAL GEOGRAPHY 
 
 3. The volume equals the area of the surface multi- 
 plied by one-third of the radius. 
 
 4. The mass equals the volume multiplied by the den- 
 sity. The mean density of the earth is 5.6. A cubic foot 
 of water weighs 62.5 lbs. 
 
 18. Problem of Eratosthenes.— The diameter of the earth 
 was not the dimension first determined, as there is no way of 
 measuring it directly. The part that was actually measured was 
 an arc of the circumference. This problem was first solved by 
 Eratosthenes two centuries before the Christian era, He deter- 
 
 -Fig. 10. Illustrating the problem of Eratosthenes. The sun's rays, vertical 
 at A, are inclined 7° 12' to the vertical sz' at s, which is the angle at 
 the center of the earth, C, measured by the arc AS. Fifty times this arc 
 equals the circumference of the circle or the distance around the earth. 
 
 mined that Syene in Egypt was close to the same meridian, 
 hence to the same great circle as Alexandria. He had observed 
 that at noon on the longest day in midsummer the sun's rays 
 shone on the bottom of a deep well at Syene in Egypt. "What 
 inference could he draw from this? He measured the angular 
 distance of the sun from the zenith at Alexandria on the same 
 day at noon and found it equaled 7 degrees and 12 minutes, or 
 exactly one-fiftieth of a circle, which is the same as the angle at 
 
THE EARTH AS A PLANET 19 
 
 the center of the earth formed by the radii from these cities. 
 Prove this. The distance between the two cities had been 
 measured and found to be 5,000 stadia, hence by multiplying this 
 distance by fifty he obtained the total distance around the earth 
 as 250,000 stadia. Unfortunately we have no means of knowing 
 at the present time the length of a stadium in any of our units 
 of measurement, so that we have no certain means of comparing 
 the accuracy of the result obtained by Eratosthenes with those 
 obtained by similar means in more receDt times. 
 
 19. Structure of the Earth.— The earth is frequently 
 divided for convenience of study into three parts or spheres : 
 (1) The outer gaseous envelope, the atmosphere; (2) the 
 liquid envelope, the water or hydrosphere which nearly 
 surrounds (3) the solid rocky part, the lithosphere, the 
 inner portion of which is sometimes called the centrosphere. 
 A fourth is sometimes added called the biosphere, or life 
 sphere. These are not true mathematical spheres, nor are 
 they very sharply separated at times. Both the hydro- 
 sphere and the atmosphere penetrate the lithosphere and 
 large quantities of the atmosphere are dissolved in the 
 hydrosphere as well as large quantities of water as invis- 
 ible vapor in the atmosphere. The life sphere is confined 
 chiefly to the water and the contact of the atmosphere 
 with the lithosphere. It is scattered through the water 
 sphere to a greater depth, probably, than in either the gas- 
 eous or the rock portions, yet the greater portion of it lies 
 close to the lower portions of the atmosphere. The air, 
 water and land portions of the earth, which form the 
 greater part of the subject of physical geography or 
 physiography, are discussed in the following chapters. 
 
 20. Motions of the Earth.— The earth has (1) a daily 
 rotation on its axis, and (2) a yearly revolution around 
 the sun. Besides these, it has (3) an onward motion 
 through space in company with the other parts of the solar 
 system, but this is not so apparent as the other two and is 
 
20 PHYSICAL GEOGRAPHY 
 
 not marked by such pronounced effects. There are a 
 number of other minor motions of interest to the astron- 
 omer. 
 
 21. Rotation.— The rotation of the earth on its axis 
 causes the sun and the stars to appear to revolve about the 
 earth, the sun appearing to rise in the east and set in the 
 west, producing the successive changes of day and night 
 and thus giving the measure of time, the day. The rota- 
 tion of the earth is one of the factors along with others in 
 producing the tides, the belts of planetary winds and 
 calms ; and it affects the direction of the ocean currents. 
 The rotation also produces the bulging at the equator and 
 the flattening at the poles. It causes a deflection of fall- 
 ing bodies. A ball dropped from the top of a tower would 
 be deflected to the east of the base of the tower, instead of 
 falling directly vertical. The deviation is greatest at the 
 equator and zero at the poles. Why? In the latitude of 
 New York it is about 1 inch for a fall of 500 feet. 
 
 22. Foucault's Pendulum.— In the middle of the last century 
 Foucault demonstrated the rotation of the earth by means of a 
 pendulum consisting of a heavy weight suspended on a long, 
 slender cord which is started to swing due north and south 
 across a plane surface covered with fine sand. Attached to the 
 bottom of the pendulum is a sharp point which traces a mark in 
 the sand as it swings. If the earth were still, the pendulum 
 would continue to swing on this line but the rotation causes this 
 plane under the pendulum to rotate to an extent varying with 
 the latitude, from zero at the equator to a complete revolution at 
 the poles. This pendulum is still in use at the Pantheon in Paris 
 where visitors may see the rotation taking place as Foucault did 
 in 1851. 
 
 23. Directions.— The terms north, south, east and 
 west are used to signify directions on the surface of the 
 earth and also in space. North with reference to the 
 earth really means the direction of the north pole, one end 
 
THE EARTH AS A PLANET 21 
 
 of the axis of the earth, and would be a curved line cor- 
 responding to the meridian at the point where the direc- 
 tion is taken. What we really think of, however, is the 
 line on the plane of the horizon which marks its intersec- 
 tion with the plane of the meridian. North in the heavens 
 refers to the direction of the axis of the earth prolonged 
 to infinity passing nearly through the north star. At a 
 point on the equator this direction would be identical with 
 north on the earth, but as one approaches the north pole 
 the two lines diverge until near the pole they are at nearly 
 right angles to each other. Represent this by a diagram 
 for (1) your latitude, (2) the equator and (3) the north 
 pole. 
 
 At the north pole all directions on the horizon are south 
 and the line to the north star is perpendicular to the hor- 
 izon. At all other points on the earth, south is the oppo- 
 site direction from north until one arrives at the south 
 pole where there is no south but all directions are north. 
 
 East refers to the direction on the horizon at right 
 angles to the north and south line but which if followed 
 proves to be a curved line. West is the opposite of east. 
 The equator and the parallels of latitude are east and 
 west lines yet they are circles on the globe. The terms 
 east and west are used for directions of rotation and revo- 
 lution-, thus the earth rotates toward the east because any 
 one point on the earth at any instant is moving east in the 
 plane of the horizon. 
 
 The plane of the horizon is the plane perpendicular to 
 the plumb line. The point where the extension of the 
 plumb line pierces the heavens is called the zenith and the 
 direction is up. The point opposite the zenith is the 
 nadir and the direction is down. 
 
 24. Revolution. — The revolution of the earth around 
 the sun causes the latter to appear to shift its position in 
 
22 
 
 PHYSICAL GEOGRAPHY 
 
 the heavens from day to day. In connection with the in- 
 clination of the earth's axis the revolution also causes the 
 change of seasons. The earth travels around the sun in 
 an elliptical orbit with the sun at one focus of the ellipse. 
 At the nearest point (perihelion) it is about 91,500,000 
 miles distant; at the most remote point (aphelion) it is 
 about 94,500,000 miles away. The inclination of the 
 
 Fig. 11. The seasons. The sun is about three million miles nearer the earth 
 in January than it is in July. Notice the variation in light and darkness 
 through the different seasons. 
 
 earth's axis to that of the axis of the ecliptic or the earth's 
 path around the sun is 23 degrees 27 minutes, which means 
 that the plane of the earth 's equator is inclined at the same 
 angle to that of the plane of the ecliptic. This inclination 
 remains fixed (or nearly so) with reference to space and 
 distant stars in the heavens, so that the axis of the earth 
 
THE EARTH AS A PLANET 23 
 
 with slight variations always points to the same star in the 
 heavens, but it causes the earth to assume quite different 
 positions with reference to the sun, as shown in fig. 11. 
 
 25. The Seasons.— On December 21st the northern 
 hemisphere reaches its maximum inclination from the sun, 
 the vertical rays of the sun are on the Tropic of Capri- 
 corn, their southern limit, and it is then the winter solstice 
 (Sun stands). The area around -the north pole is in dark- 
 ness, and it is winter in the northern hemisphere, while the 
 area around the south pole is in continual sunshine and it 
 is summer in the southern hemisphere. The opposite con- 
 dition prevails on June 21st, the summer solstice, when the 
 northern hemisphere is inclined toward the sun and the 
 rays are vertical on the Tropic of Cancer. It is then 
 summer in the northern hemisphere and winter in the 
 southern. On March 21st and September 23rd the axis 
 of the earth is perpendicular to the line joining the center 
 of the earth and the center of the sun and the sunshine 
 extends from pole to pole when the days and nights are 
 equal (the equinoxes). Name the corresponding seasons. 
 
 By consulting fig. 11 it may be seen that the winter in 
 the northern hemisphere does not come when the earth is 
 farthest from the sun, but when it is near perihelion, and 
 the summer season when it is near aphelion, showing that 
 the few degrees difference in the angle at which the sun's 
 rays strike the earth have a greater influence on the tem- 
 perature than the three millions of miles difference in 
 distance. The heat of summer and the cold of winter are 
 increased by reason of long days and short nights in the 
 summer and long nights and short days in the winter. 
 
 It is thought that the space between the sun and the 
 earth is exceedingly cold; and that the sun's rays or inso- 
 lation are changed to heat only after entering the earth's 
 
24 
 
 PHYSICAL GEOGRAPHY 
 
 atmosphere, and very little there until they strike the 
 solid earth. 
 
 If the axis of the earth were perpendicular to the plane of 
 the ecliptic what would be the effect on the seasons? What 
 would be the effect on the winter and summer in New York State 
 if the axis were inclined twice as much as at present? The axes 
 of some of the other planets are inclined much more than that 
 of the earth. (See Appendix I.) 
 
 26. Localization of Places,— Latitude and Longitude. 
 
 — In Altoona, Pa., all the roadways running north and 
 
 south are called avenues 
 and those running east and 
 west are called streets, and 
 both are numbered con- 
 secutively. Now if the 
 place where the numbering 
 begins is known, one only 
 needs to know the number 
 of the street and avenue 
 to locate any place in the 
 city with reference to any 
 other point. (Study fig. 
 12). 
 
 The plan in the above 
 city is a modification of 
 that used in locating places 
 on the globe or on maps 
 representing a part of the surface of the globe. Lines on the 
 globe represent imaginary ones on the earth and those run- 
 ning north and south from pole to pole are called meridians 
 of longitude while those running east and west around the 
 earth are called parallels of latitude, except the one mid- 
 way between the poles which is called the equator. Since 
 each one of these lines is a circle around the earth it con- 
 
 
 .£ 
 
 
 fith 
 
 St 
 
 
 
 
 
 
 
 
 •1th 
 
 St 
 
 • a 
 
 
 
 
 
 
 
 3rd 
 
 St 
 
 
 
 
 
 
 
 
 2nd 
 
 St 
 
 
 
 
 
 
 
 
 I Si 
 
 5>t 
 
 
 
 b 
 
 
 
 
 
 JMai 
 
 i s 
 
 
 
 
 
 
 
 
 O 
 
 t» 
 
 
 
 
 £ 
 
 2? 
 
 
 
 
 si 
 
 
 > 
 
 < 
 
 < 
 
 > 
 
 > 
 < 
 
 
 
 
 > 
 
 
 
 
 * 
 
 it — 
 
 
 
 
 n> 
 
 
 
 
 
 
 Fig. 12. City streets on N-S and 
 E-W lines, a is at 4th street and 
 2nd avenue N. E. or, from the 
 center of the city, a is 2 blocks 
 east and 4 north. Locate b, d, 
 and g in the same way. 
 
THE EAKTH AS A PLANET 
 
 25 
 
 tains 360 degrees and may conveniently be divided into 
 360 parts, each representing one degree. Where more 
 lines are desired each degree may be divided into 60 parts 
 called minutes and each of these again divided into 60 
 parts called seconds and each of these into as many frac- 
 tions as desired. Not all of these lines are drawn on the 
 globe; in fact only a few of them are represented, but it 
 is understood that the space between any two may be sub- 
 divided as indicated. It is only necessary to understand 
 the method of numbering the lines and the starting point 
 to know the location of any point on the earth, when its 
 
 latitude and longitude 
 are known. Latitude is 
 measured north and 
 south from the equator 
 to the poles. Since the 
 poles are 90 degrees 
 from the equator there 
 can be only 90 degrees 
 north latitude and the 
 same number in south 
 latitude. 
 
 27. Determination of the Latitude.— At sea the latitude is 
 generally determined by finding the altitude of the sun by means 
 of an instrument called the sextant. There are several different 
 ways in which it can be determined on the land without the use 
 of a sextant or any other expensive instrument. The north star 
 is very nearly vertical over the north pole, hence its altitude 
 over that point is 90 degrees. At the equator the north star 
 would appear on the horizon, that is, its altitude would be zero. 
 Hence the altitude of the north star above the horizon gives the 
 latitude of any place in the northern hemisphere, subject to a 
 slight correction. For methods of finding the altitude of the 
 star, see laboratory exercises. 
 
 At the times of the equinoxes, March 21st and September 
 23rd, the sun is on the equator, where a person at noon on the 
 
 
 
 
 
 
 g 
 
 
 z 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 u 
 
 
 
 
 
 
 
 20° 
 
 
 
 
 
 
 
 r 
 
 3 
 
 
 
 
 
 b 
 
 
 
 
 
 
 
 
 
 
 ™ 
 
 Eni 
 
 
 
 
 
 
 
 
 
 
 e 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 1 
 
 
 >,ff 
 
 
 
 A 
 
 "J 
 
 fe. 
 
 )' y 
 
 >' 
 
 ST 
 
 ?u'i? 
 
 ?'u? 
 
 p*f 
 
 ff, 
 
 
 
 3n' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Fig. 13. Latitude and longitude. Lo- 
 cate points a, b, c, d, e, f, and g the 
 same as in fig. 12 using degrees of 
 latitude in place of streets and degrees 
 of longitude in place of avenues. 
 
26 
 
 PHYSICAL GEOGRAPHY 
 
 dates mentioned would see the sun directly overhead or at an 
 altitude of 90 degrees, and a person at the north pole at the same 
 time would see the sun on the horizon. Hence on the dates 
 mentioned the altitude of the sun at midday, when subtracted 
 from 90 degrees, would give the latitude of the place. On any 
 other day in the year, the same method may be followed by the 
 subsequent addition or subtraction of the sun's angular distance 
 
 Souihfote Meridians ofLanf'Au/e 
 
 Fig. 14. Parallels and meridians. In the upper figure the lines do not 
 meet at the center of the earth because the meridians are not circles; 
 the angles are measured by the arc on the surface. 
 
 from the equator. This can be obtained for any day in the year 
 by consulting a nautical almanac. In this method care must be 
 taken to get the altitude of the sun when it is on the meridian or 
 the true north and south line, which may be determined by means 
 of a magnetic needle or compass and the correction made for the 
 local magnetic variation; or at night by noting and marking 
 
THE EARTH AS A PLANET 
 
 27 
 
 carefully the direction of the north star; or by noting the direc- 
 tion of the sun's shortest shadow cast by any vertical post. (See 
 laboratory exercises.) 
 
 Fig. 15. Determination of latitude from the north star; hh, hh' etc. plane 
 of horizon. At the equator E the star is in the horizon, elevation and 
 latitude zero. At 40 N. latitude elevation of N. star is 40°. Elevation 
 of the star at any point equals latitude of the place. 
 
 28. Length of a Degree 
 
 were a perfect sphere the 
 degrees of latitude would be 
 of the same length in all 
 places, but since it is bulged 
 at the equator and flattened 
 at the poles, the degree is a 
 little longer at the poles, 
 being 69.407 miles, while on 
 the equator it is 68.704 miles. 
 (Fig. 16). 
 
 29. Longitude. — Since 
 longitude is measured east 
 and west around the earth it 
 is necessary to select a begin- 
 ning point which is called the 
 prime meridian. Any merid- 
 
 of Latitude.— If the earth 
 
 Fig. 16. Degrees of latitude are 
 longer at the poles than at the 
 equator because they are meas- 
 ured by the arc of the curve and 
 the flattening at the poles makes 
 the arc approach that of a larger 
 circle than at the equator. The 
 differences are exaggerated for 
 clearness. 
 
28 PHYSICAL GEOGRAPHY 
 
 ian might be selected, but the one commonly used by the 
 English speaking nations is the one which passes through 
 the Royal Observatory at Greenwich, England, and is called 
 the meridian of Greenwich. Prom this point the longi- 
 tude is counted 180 degrees east and the same number 
 west, the two meeting on the 180th meridian. Why are 
 there only 90 degrees of latitude and 180 degrees of longi- 
 tude? Why couldn't the longitude be counted all the way 
 around in one direction, 360 degrees either east or west? 
 
 Degrees of longitude are longest on the equator (69.652 
 miles) and grow shorter both north and south from the equator 
 to zero at the poles. A degree at 40 degrees latitude equals 
 53.431 miles and at 60 degrees latitude it is only 34.914 miles. 
 
 30. Determination of Longitude.— Longitude is determined 
 by finding the difference in time between the place in question 
 and the meridian of Greenwich or some point whose longitude is 
 known. Since the earth rotates on its axis once in 24 hours, in 
 one hour a point on the surface must go l-24th of 360 degrees 
 or 15 degrees, or one degree in four minutes. Hence the differ- 
 ence in time expressed in hours multiplied by 15 will give the 
 difference in longitude expressed in degrees. For example, a 
 place two hours west of Greenwich is in 2x15 or 30 degrees west 
 longitude. Longitude is commonly determined by a chronometer 
 or by telegraph. Thus if one has a chronometer, which records 
 Greenwich time, it is only necessary to determine carefully the 
 time by this chronometer when the sun crosses the meridian at 
 the point to be determined and multiply the difference between 
 this time and 12 o'clock by 15 to have the longitude of the place. 
 By the other method if a person in Buffalo should telegraph to 
 St. Louis the exact time when the sun is on the meridian at 
 Buffalo and the person in St. Louis should substract this from 
 the time when the sun is on his meridian and multiply the res- 
 suit by 15, (if in hours, or divide by 4 if in minutes) he would 
 have the difference in longitude between the two places. For 
 accuracy an addition or subtraction must be made for the equa- 
 tion of time (Sec. 33) obtained from the Nautical Almanac. 
 
THE EARTH AS A PLANET 29 
 
 TIME 
 
 31. The Julian Calendar.— The chronology of ancient 
 history is very confusing and uncertain owing to the lack 
 of any definite system for recording time. Julius Cassar, 
 in the year 46 B. C, reformed the Roman Calendar into 
 the Julian Calendar by making every fourth year contain 
 366 days and the three intervening 365 days each. He 
 also changed the beginning of the year from the first of 
 March to the first of January and gave his own name to 
 the month of July while August was later named in honor 
 of his successor, Augustus.* 
 
 32. Gregorian Calendar.— The average length of the 
 year in the Julian calendar was 365.25 days, which is 
 about 11 minutes too long, a difference which became 
 manifest after several centuries. It was to correct this 
 that Pope Gregory XIII, in 1582, made another change in 
 which 10 days were dropped from the calendar, the day 
 after March 11th being called March 21st. He modified 
 the part in reference to the leap years so that the even 
 centuries are leap years only when divisible by 400 ; thus 
 the year 1900 according to the Julian calendar would be 
 a leap year and have 366 days, but according to the Gre- 
 gorian calendar it would have 365 days. The Gregorian 
 calendar was at once adopted in the countries whose 
 church adhered to Rome, but it was not adopted in the 
 United States and England until 1752, and it has not yet 
 been adopted in Russia and Greece. Hence in the his- 
 tories we frequently find the letters O. S., old style, refer- 
 ring to the Julian calendar and N. S., new style, for the 
 Gregorian calendar. 
 
 * Augustus did not want his predecessor's month, July, to be longer than 
 his own month, so he took a day from February and added it to August. 
 
30 PHYSICAL GEOGRAPHY 
 
 33. The Day.— The sidereal day is the length of time 
 it takes the earth to make a complete rotation with refer- 
 ence to a star, that is, until the star is again on the same 
 meridian. 
 
 The solar day is the time of rotation with reference to 
 the sun. Suppose the sun and a star on the meridian at 
 the same time ; during the interval until the star is again 
 on the meridian, the sun will lack 3 min. 56.55 sec. of being 
 there owing to the forward movement of the earth in its 
 orbit. Hence the solar day is that much longer than the 
 sidereal day. 
 
 But solar days are not all the same length owing to the 
 fact that the earth moves more rapidly in some portions of 
 its orbit than in others. Since it is not possible to con- 
 struct a clock that will follow all the variations of the sun 
 from day to day, the length of our day is based not on the 
 real sun but on a mean sun, moving through the heavens 
 at the average rate of the true sun. This is called mean 
 solar time, which is the time measured by our clocks. The 
 difference between true solar time and mean solar time is 
 known as the "equation of time," and may be found in 
 the almanac frequently marked "sun fast" or "sun slow." 
 It should be noted that even the mean solar day is actually 
 determined by computation from the sidereal day. 
 
 The civil day begins and ends at midnight rather than at noon 
 as a matter of convenience. For the same reason the astronomical 
 day begins at noon. It is also a matter of convenience to have a 
 fixed place where the day changes or one day leaves off and an- 
 other begins. 
 
 The conventional day. It is always apparent noon on the 
 meridian under the sun in its apparent passage around the earth. 
 In imagination if we should follow the sun from noon on Monday 
 around the earth until we returned to the starting point after 
 24 hours, it would have been noon all the time and the question 
 arises, "Where did we pass from Monday to Tuesday?" This 
 place for the change of date was at one time fixed at the 180th 
 
THE EARTH AS A PLANET 31 
 
 meridian east or west from Greenwich, that is, on the opposite 
 side of the earth from the prime meridian, so that vessels crossing 
 this line would add or subtract a day, depending upon which 
 way they were going. It was found that the 180th meridian ex- 
 tended through groups of islands belonging to the same nation, 
 so that it was found advisable to shift it enough to have it come 
 between nations and yet vary as little as possible from its first 
 position. It is now called the international or intercalary date line 
 and is shown on fig. 18. The day which changes here is known 
 as the conventional day. 
 
 The lunar day is the interval between successive passages of 
 the moon across the meridian and is nearly an hour longer than 
 the solar day. 
 
 In both the sidereal day and the astronomical day, the hours 
 are numbered from 1 to 24, thus avoiding the repetition of A. M. 
 and P. M. This method of numbering the hours is used on the 
 railways in Canada and Spain. Why is it not used in the United 
 States? 
 
 34. Standard Time.— If every point on the earth 
 kept its time by the sun accurately, it would lead to a 
 constant change of time as one travelled east or west. 
 This was found to be so confusing on the railroads that 
 some years ago a standard time was adopted, in which in- 
 stead of changing the time every minute or second, or at 
 every town, it is changed only once an hour and on the 
 even hours from Greenwich. Thus in the eastern United 
 States the time is based on that of the 75th meridian or 
 the one passing through Philadelphia. Further west it is 
 based on the 90th or St. Louis meridian, the 105th or Den- 
 ver meridian, and the 120th or the one passing on the 
 boundary between California and Nevada. The time, 
 however, does not change on these meridians, as by so 
 doing it would give the place immediately west of the line 
 time nearly an hour different from sun time; so, to make 
 the difference from sun time as little as possible, it is 
 aimed to make the change of time midway between these 
 
32 
 
 PHYSICAL GEOGRAPHY 
 
 standard meridians, but on the railways it is most con- 
 venient to make the change at the end of a division which 
 is generally marked by some large or important city. (See 
 %. 17). 
 
 The different names given to these time belts from 
 east to west are Eastern, Central, Mountain and Pacific 
 time and they are respectively 5, 6, 7, and 8 hours slower 
 than Greenwich time. The accurate standard time is sent 
 regularly at twelve o'clock each day from the naval ob- 
 
 FiG. 17. Standard time belts in the United States. These 
 belts continue at intervals of 15° longitude, making 24 in 
 the circumference of the earth. Since they count both 
 ways from Greenwich, they meet on the International Date 
 line. (Fig.' 18.) 
 
 servatory at Washington to all the important telegraph 
 offices in the United States. Standard time is used on the 
 railways in most of the European countries. 
 
 35. Magnetism.— Magnets are bodies which have the 
 power of attracting iron and being in turn attracted by 
 iron and in a much less degree the metals manganese, co- 
 balt and nickel. Magnets are natural and artificial. The 
 natural magnet is the mineral lodestone, or magnetite. A 
 
THE EARTH AS A PLANET 33 
 
 piece of hardened steel may be made into a permanent mag- 
 net by rubbing it on a piece of lodestone or better, by plac- 
 ing it inside of a coil and subjecting it to a strong electric 
 current. If the piece of magnetized steel or piece of lode- 
 stone be now freely suspended on a pivot, it will form a 
 magnetic needle, which, properly mounted, forms the 
 mariners' compass. In the absence of a pivot it may be 
 floated on a cork in a vessel of water. 
 
 36. The Earth a Magnet.— If two compass needles are 
 brought near each other, it will be seen that the north end of one 
 repels the north end of the other, but attracts the south end. 
 From this and other observations it is thought that the earth it- 
 self is a great magnet and that the poles of the great earth mag- 
 net are near, but not at the north and south poles of the earth. 
 The north magnetic pole lies in the region north of Hudson Bay 
 and west of Baffin Bay. Recent studies seem to show that it is 
 not a fixed point but an area of considerable size. The north end 
 of the compass needle points toward this magnetic pole, not the 
 true north pole; hence in northern Greenland, the compass 
 needle points south of west instead of north. In only a few 
 places does the magnetic needle point to the true north and 
 these points are connected by lines known as agonic lines. At 
 all other points the needle varies from a true north direction, 
 which variation is known as the magnetic variation or declination. 
 Points having the same declination are connected by a line 
 called an isogonic line. Note the position of the agonic and iso- 
 gonic lines on fig. 18. 
 
 Midway between the magnetic poles is the magnetic equator, 
 where a needle suspended freely lies horizontal. As the needle is 
 taken north from the magnetic equator the north end dips below 
 the horizontal until a point directly over the magnetic pole is 
 reached, where it stands vertical. A needle so suspended as to 
 swing freely in a vertical plane is called a dipping or dip needle, 
 and lines connecting points where the angle of dip is the same 
 are isoclinal lines (see map on fig. 18). The isoclinals appear to 
 be very nearly parallel with the isotherms, which would indi- 
 cate some possible relation between the earth's magnetism and 
 the heat on the surface. It is thought that in some way the ro- 
 tation of the earth is a cause or the cause of its magnetism. 
 
34 
 
 PHYSICAL GEOGRAPHY 
 
 _ En 
 
 .£ S ■** 
 
 "S « *° 
 
 Q d 
 
 1 9 • 
 
 05 .2 »d 
 
 « a 
 % - § 
 
 00 C3 
 
 ^ a 
 
THE EARTH AS A PLANET 35 
 
 MAPS AND MAP PROJECTION 
 
 The representation* of the different geographic features 
 of the earth's surface on paper has been tried in a great 
 many different ways in order to gain accuracy, combined 
 with ease and rapidity of construction and economy of 
 duplication. 
 
 37. Globe. — The ordinary globe shows all features 
 in their true horizontal relations better than any other 
 method, but it is too expensive and too inconvenient for 
 most purposes. A globe on which the mountains and 
 plateaus are shown in relief and the ocean basins shown 
 by depression is more realistic and likewise more expen- 
 sive. 
 
 38. Model. — Next to the globe, a model or relief map 
 constructed of plaster, clay or papier-mache is one of the 
 best ways of showing the surface features. A model may 
 be made of the entire globe but more commonly it is used 
 for small portions that can thus be shown on a larger scale. 
 The advantage of the model is that it shows vertical as 
 well as horizontal relations, but the objections are the ex- 
 pense of construction and duplication and the inconvenience 
 in carrying about or storing for reference. 
 
 39. Maps. — Maps in which the features are shown 
 on the surface of thin paper are the cheapest to make, 
 much more convenient to handle and store away, and much 
 less expensive than either globe or model. Hence there 
 are hundreds of times as many maps in use as models or 
 globes. 
 
 40. Projections. — Since the earth is spherical in form 
 the attempt to represent its surface on a flat paper is at- 
 tended with more or less distortion. A curved area spread 
 out flat necessitates crumpling in some places and stretch- 
 ing in others. To overcome this difficulty various methods 
 
36 PHYSICAL GEOGRAPHY 
 
 have been devised for projecting the lines of the curved 
 surface upon a flat one. Some of the various methods em- 
 ployed are described in Appendix II. 
 
 41. Scale of the Map.— The scale means the ratio of the 
 distances between points on the map and the corresponding 
 points on the earth. It may be given in units such as, 1 inch 
 equals one mile or by fractions 1-63360 or 1:63360, which means 
 that one inch on the map corresponds to one mile on the earth. 
 The scale used in the construction of a map depends on the size 
 of the area to be mapped, the purpose for which the map is 
 wanted and the money available for its construction. An in- 
 crease in the scale would mean an increase in the cost of con- 
 struction. Many of the contour map sheets published by the 
 United States Geological Survey are on a scale of 1:62500, but 
 some have a scale of 1:125000 and some 1:250000 while others 
 have a smaller scale. Maps of the whole United States have a 
 much smaller scale, some being 1:2,500,000, some 1:7,000,000 and 
 still others 1:14,000,000. The scale should always be marked on 
 a map either by ratios or graduated lines or in both ways, ex- 
 cept on small scale maps of large areas where the latitude and 
 longitude lines indicate the scale. 
 
 42. Contour Maps.— Elevations and depressions on 
 the surface of the earth may be represented on the maps 
 in several different ways. (1) By relief maps or models. 
 On the flat surface relief may be shown by (2) shading, 
 (3) hachures or broken lines and (4) contour lines. 
 
 The model or relief map shows to the eye the features 
 of relief better than any plan yet devised to show the same 
 on a map. Of the different methods in use of representing 
 relief on a flat surface, shown in fig. 19, the contour map 
 is superior for many purposes. The hachures and the 
 shading show hills and valleys but they do not show the 
 height of the hills or the depth of the valleys. The con- 
 tour map shows not only the relative but the actual ele- 
 vation of any and every point on the area. 
 
 The map is constructed by drawing lines connecting 
 
THE EARTH AS A PLANET 
 
 37 
 
 Fig. 19. Representation of an area (1) by shading, (2) by 
 contour lines, and (3) by haehures. The method by con- 
 tours is the only one that gives actual elevations. 
 
38 PHYSICAL GEOGRAPHY 
 
 all points that have the same elevation above sea level. 
 (Any known point may be taken as a base, but sea level 
 is generally taken for convenience). The number of con- 
 tour lines drawn on the map varies with the regularity of 
 the slopes, the scale of the map, the heights of the hills, 
 and the amount of detail desired in the map. The vertical 
 distance between the lines known as the contour interval 
 is sometimes 2, 5, or 10 feet on a large scale map of a 
 small area with high hills. In a mountain district the in- 
 terval is 50, 100, 500, or 1000 feet. (State the reasons 
 why an interval of 5 feet is used on the Donaldsonville, 
 La., topographic sheet,' and 100 feet on the Charleston, 
 W. Va., sheet). 
 
 In the U. S. Geological Survey maps the contour lines 
 are printed in brown to avoid confusion with streams, 
 roads, and other lines. 
 
 The first contour line (which is generally not in brown) 
 on any continent or island area is the one marking the 
 separation between the land and the sea, that is, the line 
 marking the contour of the land. The second line would 
 mark the contour of the land if the water should rise 10 
 feet (or the space of the contour interval) and so on. If 
 one considers the contour lines as marking the water level 
 at successive stages, the significance of the name becomes 
 apparent. A contour line never ends except at the mar- 
 gin of the map. On a map of an island or of an entire 
 continent all contour lines are continuous. 
 
 43. The United States Topographic Atlas.— The United States 
 Geological Survey contour map sheets in the topographic atlas of 
 the United States will in time cover the entire area of the 
 country on a scale of approximately one, two or four miles to the 
 inch. This is one of the most useful maps published in this 
 country and, because of its comparative accuracy, great detail, 
 and small cost, its economic and scientific features should be 
 known by all. It shows not only such topographic features as 
 
THE EARTH AS A PLANET 39 
 
 rivers, lakes, roads, railroads, villages, often separate houses, 
 ferries, bridges, mines, quarries, etc., but by contour lines the 
 absolute and relative elevation of any and all points on the area. 
 
 The atlas sheets are valuable aids in the study of geography 
 and geology. Some of the points which the student can frequent- 
 ly interpret from the contour map are: (1) The elevation of any 
 and all points above sea level and hence of any point relative to 
 any other. From one of these maps covering your home dis- 
 trict it should be possible for you to tell how many feet your 
 house is above or below the school house. Try it. (2) The 
 steepness of the hillsides. (3) The location of the cliffs. (4) 
 The extent of the drainage basins. (5) The topographic age or 
 place in the cycle of erosion, whether young, mature or old. 
 (6) The kind and structure of the rocks, whether igneous or 
 stratified, whether folded, crumpled or not. (On some areas this 
 cannot be determined from the map.) (7) Whether river piracy 
 has taken place or is taking place. (8) Frequently the char- 
 acter of the climate can be inferred along with the probable in- 
 dustries carried on in the region, and the density of the popula- 
 tion. 
 
 They are serviceable and interesting to travellers. One 
 learns in time to select the best roads from the study of the 
 map, or in a region where roads are absent, to choose the best 
 route for travel from place to place. 
 
 The contour maps are of great service in laying out the 
 routes for roadways, railways, electric lines, aqueducts, pipe lines 
 and irrigating ditches. 
 
 For these and other reasons contour maps should be thor- 
 oughly studied so that the student can properly interpret them. 
 
 REFERENCES 
 
 1. Elements of Astronomy, F. R. Moulton, The Macmillan Co. 
 
 2. Elements of Descriptive Astronomy, Howe, published by 
 Silver, Burdett & Co. 
 
 3. Manual of Astronomy, Young, Ginn & Co. 
 
 4. New Astronomy, Todd, American Book Co., New York. 
 
 5. Maps and Map Reading, Ravenstein, International Geog- 
 raphy, D. Appleton & Co. 
 
 6. Text Book on Geology, Chamberlin and Salisbury, Henry 
 Holt & Co., Vol. 2, Chap. 1. 
 
CHAPTER II 
 GROUNDWATER AND RIVERS 
 
 44. Rainfall. — Where do the raindrops come from 
 and where do they go? A vessel of water exposed to the 
 air on a dry day is soon emptied. The water evaporates, 
 that is, it passes into the air as invisible vapor. Evapora- 
 tion is taking place over all the oceans, lakes, rivers, and 
 moist land areas, sometimes rapidly, sometimes slowly. 
 This is the source of supply for the rain. Lowering the 
 temperature and pressure of the air causes the invisible 
 moisture to form clouds and thus become visible ; on 
 further decrease of temperature and pressure, the water 
 condenses and falls to the earth as rain or snow. Part of 
 the precipitation is again evaporated from the surface and 
 goes back into the air to be again precipitated elsewhere ; 
 part of it flows off on the surface directly into the streams 
 and thence back to the ocean; part of it sinks into the 
 earth and becomes groundwater. Some that falls as snow 
 in cold climates forms streams of ice called glaciers that 
 move slowly downward towards the sea, in some places 
 even flowing into the sea. (See Chap. IV). 
 
 The proportion of the total rainfall that is evaporated direct- 
 ly back into the air is variable, depending upon such factors as 
 the temperature of the atmosphere, the rate of the rainfall, the 
 nature and condition of the surface, and especially the humidity 
 or degree of saturation of the atmosphere. In a slow, drizzling 
 rain a much larger portion will sink into the earth than in a 
 dashing rain, which on a steep slope runs directly into the 
 stream channels and on a flat surface stands in pools until it is 
 partly evaporated into the air. 
 
 40 
 
GROUNDWATER AND RIVERS 41 
 
 Much of the rain that falls on sand or a broken rock surface 
 sinks into the earth through the pores, while a large part of that 
 which falls on a hard rock or baked clay surface runs off into 
 streams or stands in pools on the surface. 
 
 45. Groundwater.— The portion of the rainfall that 
 sinks into the earth is called groundwater or underground 
 water. It penetrates all rocks to a great depth, passing 
 through the cracks, crevices and the pores of the rock. It 
 moves down by force of gravity, capillarity, and pressure. 
 
 A part of the groundwater finds its way to the surface 
 again, some of it quickly, some of it after a long period of 
 time and some of it remains below the surface indefinitely. 
 
 Depth of groundwater. The lower limit of the ground- 
 water occurs at depths of five or six miles below the sur- 
 face, where the pressure from the overlying material is so 
 great that even the finest pores are closed and the rock 
 becomes too dense for the water to find its way through it. 
 
 The water table. The successive rainfalls through the 
 ages past have filled the rocks with water from the lowest 
 limit up to a place where there is a balance between the 
 annual supply from the rains and the loss through escape 
 to the surface. This upper limit of the zone of saturated 
 rocks is known as the water table, the level of permanent 
 groundwater or the permanent water plane. It serves to 
 mark the upper boundary of the water zone or the zone of 
 permanent groundwater, or the zone of saturation. 
 
 In some places the water table is at the surface, in some 
 places a few inches or a few feet below the surface, while 
 in others it is several hundred feet below the surface. 
 
 The depth of the water table depends upon the surface 
 features, the climate and the rocks. It lies nearer the 
 surface in the valleys and plains than it does in the 
 mountains and plateaus. One reason why the former are 
 more productive than the latter is that in the one in many 
 
42 PHYSICAL GEOGRAPHY 
 
 places the water table is near enough to the surface to fur- 
 nish moisture to the plant roots in dry seasons, whereas in 
 the other during a prolonged rainless season the water 
 near the surface is evaporated and the water table sinking 
 too deep to be touched by the roots, the vegetation withers 
 and dies. 
 
 The level below which the moving water does not sink in dry- 
 weather is the -permanent water table. In wet seasons this level 
 rises towards, sometimes to the surface, to sink again during 
 the dry season. This fluctuating upper surface of the water 
 zone that varies with the seasons is known as the temporary 
 water table. 
 
 Aquifer. "While the rocks below the water table are satur- 
 ated, some of the layers are so fine grained and dense that the 
 water can move through them only with extreme slowness, while 
 other layers are coarse grained and permit free movement of 
 the water. The latter are called aquifers (aqua, water; fero, to 
 bear) and are very important economically since they are the 
 beds which supply the wells and springs. (See figs. 32 to 35). 
 
 46. Destructive Action of Groundwater.— While per- 
 colating through the rocks the groundwater has in some 
 places a destructive, in some places a constructive effect on 
 the rocks through which it is passing. It comes in con- 
 tact with some minerals that are soluble and takes them in 
 solution, and this solution acts as a solvent for others. The 
 material dissolved is carried away by the streams to the 
 ocean, leaving cavities in the rock from which the material 
 was carried. 
 
 47. Caves. — Carbon dioxide, derived partly from the 
 air and partly from the soil, dissolves limestone when it 
 is brought in contact with this rock by the percolating 
 groundwater which likewise acts as the agent to carry 
 away the material after it is dissolved. In this way such 
 caves as Mammoth Cave in Kentucky, Luray in Virginia, 
 Wyandotte and Marengo in Indiana and Howe's Cave in 
 
GROUNDWATER AND RIVERS 43 
 
 New York are formed. (See figs. 20, 21, 27a, 28 and 29.) 
 The above are some of the best known eaves in the 
 United States, but there are hundreds of similar ones not 
 so widely known. Nearly every bed of limestone has num- 
 erous caverns large or small. In the upland areas of cen- 
 tral Kentucky it is estimated that there are not less than 
 
 Fig. 20. Vertical section of limestone showing caves and sink 
 holes. Notice the vertical cliff and talus slope at the left. 
 
 10,000 miles of limestone caverns. Limestone caves vary 
 in length from a few feet to many miles, in depth below 
 the surface from, a few feet to several hundred feet. 
 
 48. Life in Caves. — As might well be imagined caves 
 frequently form retreats or hiding places for different 
 animals, the most common being the bats, which fly abroad 
 in summer nights but spend the days and the winter season 
 in the caves where they sometimes cluster in great masses 
 hanging from the roof of the cavern. Beetles, lizards, 
 mice, wolves, bears, and foxes are some of the other animals 
 that find a home in the caves. Blind fish are sometimes 
 found in them. 
 
 Savage man in ages past found shelter there. Relics of his 
 handiwork, his implements and his carving on the walls, have 
 been found in different caves often associated with bones, and 
 pictures made by him of now extinct animals and even the bones 
 of primeval man himself have been found. 
 
 Corrading Action of Cave Streams.— Besides the dis- 
 solving action of the groundwaters on the rocks there is in 
 
44 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 21 Map of portion of the explored galleries in Mammoth Cave, Ken- 
 tucky. Some of the galleries are much higher than others. There 
 is a descent of many feet at the entrance, and one crosses several 
 lofty hills in traversing the different chambers. The shaded portions 
 contain water. This cave has been explored through nearly 200 miles 
 of galleries. Scale about 1 V4 miles to one inch. 
 
GROUNDWATER AND RIVERS 45 
 
 places a corrading or wearing action on the bottoms and 
 sides of caves similar to the work of surface streams. In 
 some places several caves occur one above the other. The 
 upper ones are dry while the lowest one frequently has 
 a stream in part of the cave. Most of the eorrading 
 work done in the cave is not done by the permanent stream 
 but by the temporary streams that pour in through open- 
 ings in the roof during the rainy seasons. 
 
 Pig. 22. "The Bottomless Pit." A limestone sink near Flagstaff, 
 Arizona. The sink is 100 feet in diameter. The stream that 
 disappears here is not known to reappear at the surface. In a 
 wet season the water fills the pit, overflows and forms a lake. 
 The flat in the picture is the slit-covered lake bed as it appears 
 during low water. (Hackett.) 
 
 Lost River in Indiana flows through limestone caverns for 
 about 10 miles of its course, but in flood season when there is 
 more water than can find escape through the underground chan- 
 nel the surplus flows in the surface channel until the flood sub- 
 sides when it disappears into the cave. Presumably there is 
 considerable corrasion in such a cave. 
 
 49. Sink Holes. — In nearly every limestone region 
 where there are caves there are numerous basin-like or 
 
46 
 
 PHYSICAL GEOGRAPHY 
 
 funnel-shaped depressions, called sink holes or swallow- 
 holes. These are often shaped like a funnel, the large 
 opening serving to catch the rainfall and to lead it into the 
 narrow opening at the bottom, corresponding to the stem 
 of the funnel. Through the sink hole the surface water 
 drains into larger caverns. (See figs. 20 and 22.) 
 
 A limestone surface much diversified by the action of 
 the groundwater dissolving the rock along cracks and joint- 
 planes, thus leaving many deep irregular fissures, is called 
 
 !Fig. 23. Surface of limestone outcrop at Syracuse Caves. The 
 openings were formed by the ground-water dissolving the 
 rock along the cracks and joint places. Some of the 
 cavities extend to a depth of more than 100 feet. 
 
 by the Germans the Karsten. There is no English word 
 for this phenomenon although it occurs in many places in 
 New York and elsewhere in the United States. (See fig. 23.) 
 50. Natural Bridges.— Natural bridges are formed 
 sometimes by the breaking down of part of the roof over 
 one of these subterranean streams. The portion of the 
 roof that remains spanning the now open chasm is called 
 
GROUNDWATER AND RIVERS 
 
 47 
 
 a natural bridge. Natural bridges are sometimes formed 
 in other ways. (See figs. 24, 25, 146 and 148.) 
 
 51. Constructive Action of Groundwater.— Some of 
 the mineral material taken in solution by the groundwater 
 
 Fig. 24. Natural Bridge, Va. The remnant of the roof of a 
 cave formed under a waterfall. (U. S. Geol. Survey.) 
 
 is carried in solution to the ocean while part of it is de- 
 posited again, sometimes on the surface where the ground- 
 water emerges, and sometimes underneath the surface. In 
 
48 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 25. The Caroline Bridge, Utah. The longest natural bridge in the 
 world. Length 350 feet, width 60 feet, thickness 60 feet. Copy of 
 painting made from photographs, sketches, and the measurements. 
 The rock is light colored sandstone. (Courtesy of E. F. Holmes.) 
 
 Fig. 26. Small calcite veins in limestone, formed by ground- 
 water carrying carbonate of lime in solution and depositing 
 it in cracks in the limestone. (U. S. Geol. Survey.) 
 
GROUNDWATER AND RIVERS 
 
 49 
 
 percolating through the rocks, the water and the carbonic 
 acid gas in the water are under pressure when they take 
 up more carbonate of lime than they can hold in solution 
 under less pressure ; hence, when the water reaches a large 
 cavity or the surface, where the pressure is lowered, some 
 of the acid gas escapes into the air, some of the water is 
 evaporated and part of the mineral matter is deposited. 
 
 52. Veins.— When the mineral matter carried in solution is 
 deposited in cracks or fissures in the rocks, it forms veins, in 
 
 Fig. 27. Gold-silver vein near Ouray, Colorado. The vein 
 is composed of quartz containing gold and silver. It 
 is about 20 feet wide and thousands of feet in depth. 
 It fills a deep fissure in the dark colored volcanic 
 rock which shows on each side of the white quartz. 
 Such veins are called fissure veins. 
 
 which are formed compounds or ores of different metals such as 
 gold, silver, lead, zinc, copper, etc. Mingled with the ores are 
 variable quantities of other minerals known as gangue or vein- 
 stuff consisting of calcite, fluorite, barite, quartz, and other min- 
 erals, all of which are carried by the groundwaters into fissures 
 and there deposited to form the vein. Man is largely dependent 
 4 
 
50 
 
 PHYSICAL GEOGRAPHY 
 
 upon these veins for the supply of metals needed in the different 
 industries, because in the original condition of the rocks the 
 metals are so scattered and diffused that they cannot be profit- 
 ably extracted until they are segregated as ores in the veins oy 
 the action of the groundwater. 
 
 FlG 27a. Stalactites, stalagmites and columns in Marengo 
 Cave, Ind. (Hessler and Smith.) 
 
 53. Cave Deposits. — The water that very slowly drips 
 from the roof of a limestone cave is partly evaporated and 
 at the same time permits the escape of part of the carbon 
 dioxide, which causes part of the lime carbonate to be pre- 
 cipitated in the form of an icicle-like deposit called a 
 stalactite. A corresponding projection built up on the 
 floor of the cave is called a stalagmite. How can you 
 prove that these are carbonate of lime? Many of the 
 
GROUNDWATER AND RIVERS 
 
 51 
 
 stalactites have a small hole running lengthwise through 
 the middle. How do you account for it? 
 
 If the stalactite and the stalagmite grow together 
 forming a continous deposit from the roof to the floor it 
 is called a column or 
 pillar. A growth 
 along the wall of the 
 cave extending from 
 the floor to the roof 
 is called a pilaster. 
 In some places this 
 deposition goes on 
 until the cave that 
 was originally formed 
 by the groundwater 
 is completely filled by 
 it. The more mas- 
 sive and compact de- 
 posits formed in the 
 cave are quarried and 
 used as onyx marble 
 or Mexican onyx. ( See 
 figs. 27a, 28 and 29.) 
 
 54. Spring" Deposits.— The calcite or carbonate of 
 lime is frequently deposited around springs, which are 
 streams of groundwater appearing at the surface. The 
 deposit of the spring is formed similarly to that in the 
 cave, namely, by the escape of the carbonic acid gas and 
 evaporation of some of the water, causing part of the 
 dissolved lime to be deposited. It is frequently deposited 
 on the surface of moss, leaves, or twigs because a large 
 area is there exposed to evaporation. Such porous de- 
 posits are called calcareous tufa. The more massive de- 
 posits formed by springs and streams are called traver- 
 
 
 
 
 -5 
 
 
 
 |4j 
 
 '•■' 
 
 .■■' 
 
 
 
 
 
 
 
 ■ i./ 
 
 ■ r 
 
 f \M 
 
 
 i 
 
 
 ■ t 
 
 
 TSp.1 
 
 Fig. 28. "Tower of Babel," Marengo Cave, 
 Indiana. Small stalactites on the roof. 
 Stalagmites on the floor. A column ex- 
 tending from roof to floor. (W. S. 
 Blatchley. ) 
 
52 
 
 PHYSICAL GEOGRAPHY ' 
 
 tine, a name which is sometimes used for all the deposits 
 of carbonate of lime from solution. The Coliseum and 
 St. Peters and many other large buildings at Rome are 
 constructed of travertine, quarried from an extensive de- 
 posit formed by the springs at Bagni near Rome. (See figs. 
 30 and 176). 
 
 Other materials than lime may he brought to the surface by 
 the springs and deposited, such as iron oxide, sulphur, and silica. 
 The silica-depositing springs are generally hot' springs. 
 
 55. Induration.— 
 
 Mineral matter, such 
 as silica, and the car- 
 bonates of lime and 
 iron carried in solu- 
 tion by the ground- 
 waters, is sometimes 
 deposited in the open 
 spaces between the 
 grains in a bed of 
 sand or gravel, ce- 
 menting the particles 
 together and thus 
 changing it into a 
 bed of sandstone or 
 conglomerate. This is 
 one of the principal 
 ways in which beds 
 of sediment are in- 
 durated or changed to solid rock. Frequently the water 
 is brought to the surface by capillarity, where it evaporates, 
 precipitating the mineral matter in the pores. The fact 
 that many sandstones are harder on the surface of the out- 
 crop than in the interior of the bed is accounted for in 
 this way. 
 
 FlG. 29. "Pillar of the Constitution" in 
 Wyandotte Cave, Indiana. A huge 
 column of calcite, surrounded by small 
 stalactites on the roof. (W. S. 
 Blatchley.) 
 
GROUNDWATER AND RIVERS 
 
 53 
 
 In many places in the northern United States, portions of the 
 glacial sand and gravel deposits are cemented by calcite de- 
 posited from solution in the groundwater. The student may 
 readily test this by placing a piece of the material in some dilute 
 acid and noting the rapid effervescence, followed by the crumbling 
 of the piece into separate grains or pebbles. It is this small per 
 cent of lime that makes the glacial gravels better road-making 
 material than the gravels from the creek beds. 
 
 
 
 
 ill *» <; 
 
 ■<, > 
 
 ----- : - 7 ;■" 
 
 > "3 
 
 
 
 fkjgt iff 
 
 
 
 
 
 
 ...,.-: 7 ; 
 
 jiS ? .:• ~ 
 
 
 'FlG. 30. Travertine, carbonate of lime deposited by hot springs, 
 Yellowstone National Park. (Detroit Pub. Co.) 
 
 56. Reappearance of Groundwater at the Surface.-— 
 
 What becomes of all the groundwater that sinks into the 
 earth? Part of it is brought up by capillary attraction 
 and evaporated from the surface in dry weather. Part 
 of it is brought up through the roots and stems of plants 
 and evaporated from the leaves. Part of it reaches the 
 surface through artificial openings such as wells, artesian 
 wells, mines, tunnels, and borings. Part of it combines 
 chemically with minerals beneath the surface and is, tem- 
 porarily, at least, locked up as water of crystallization. 
 The water of crystallization is abundant in much of the 
 loose surface rock, in clay and brown iron ore. It 
 may be detected by taking a handful of clay soil, drying 
 
54 PHYSICAL GEOGRAPHY 
 
 it thoroughly and putting part of it in a test tube. Heat 
 it over a gas lamp, when the water of crystallization will 
 be separated and condensed as drops on the side of the 
 tube. The amount of water may be determined by weigh- 
 ing the sample before heating and after heating. The 
 experiment is better performed with gypsum or limonite. 
 Part of the groundwater penetrates the rocks to great depths 
 and may not get back to the surface for many centuries; pos- 
 sibly a small part of it may never return. A considerable and very 
 important part of the groundwater is returned to the surface 
 through springs and seepage, including hot springs and geysers. 
 
 57. Wells are openings dug or bore^ from the sur- 
 face down to a short distance below the groundwater table 
 for the purpose of obtaining water; in th| ordinary well 
 the water stands as high and no higher ,^han the water 
 table. In fact, the best way to locate the w&ter table in any 
 
 Fig. SI. Variation of the water table with the seasons. 
 
 a, temporary water table, April. Water in all the wells. 
 
 b, temporary water table, June. W is dry. c, permanent 
 water table, September. W' and W are dry. v', Young 
 valley with temporary stream in wet season only. v 2 Larger 
 valley contains stream until the temporary water table 
 sinks below b. V3 Mature valley, contains a permanent 
 stream. 
 
 region is by the level of the water in the wells when they 
 are first opened. Sometimes excessive use of the water 
 from a few large wells or many small ones may cause a 
 lowering of the water table that is often of serious im- 
 portance. 
 
 Every well opening sunk below the water table will 
 not prove productive because in some places the rocks 
 
GROUNDWATER AND RIVERS 
 
 55 
 
 are so dense that very little water can find its way through 
 into the well. In porous rocks the wells are fed by water 
 which seeps through the pores into the well opening and 
 any well sunk into an aquifer or porous layer below the 
 level of the water table will be productive. In the denser 
 rocks the wells are fed by tiny underground streams. The 
 well that strikes one or more of the little streamlets may 
 have a bountiful supply of water while another close by 
 that has missed the streamlets (or so-called veins of water) 
 may be barren. 
 
 The reason that some wells go dry in times of drought 
 is that the water table sinks below the bottom of the well. 
 Sometimes the reverse is true when the water table rises 
 near or even to the surface and the well is filled to over- 
 flowing. (See fig. 31.) 
 
 58. The artesian well differs from the common well 
 in that it occurs only in inclined strata down the slope of 
 
 Pig. 32. Artesian wells W, W, W, in which the water supply- 
 comes from the different aquifers A, A', A". 
 
 which the groundwater moves and enters the well under 
 pressure which causes it to rise in the well above the 
 
 water plane. The water 
 may even flow out of the 
 mouth of the well which it 
 does frequently with con- 
 siderable force. 
 Hl^s^ The name arte- 
 sian is derived 
 
 Pig. 33. A more favorable condition for artesian fv>riryi Artois a 
 wells than that shown in B, because the strata . ' . 
 
 are not so highly inclined. province in 
 
56 PHYSICAL GEOGRAPHY 
 
 Prance where the first well of this kind was bored. It was 
 a very strong flowing well and for a long time only flowing 
 ones were called artesian, but now the name is used for all 
 deep wells where the water enters under pressure and rises 
 considerably above the point of entrance and above the 
 water plane. (See figs. 32 and 33.) 
 
 The necessary conditions for an artesian well are (1) 
 a layer of porous rock, the aquifer, through which the 
 water can percolate freely; (2) the strata inclined to the 
 horizontal ; ( 3 ) the porous layer outcropping in a region 
 of considerable rainfall, and (4) the aquifer overlain by 
 a layer of rock less pervious; (5) all the strata dipping 
 into the groundwater zone. It is immaterial what kind 
 of rock is below the aquifer ; if impervious it will hold 
 the water above it ; if porous it will fill with water and in 
 that way become impervious. (6) There should be no 
 natural escape for the. water between the outcrop and 
 the well; (7) nor any obstruction to prevent the water 
 reaching the well. (Study the diagrams, figs. 32, 34 and 
 35.) 
 
 The most favorable condition for an Artesian well is a gentle 
 inclination of the strata as in fig. 34 and not highly inclined, as 
 
 Fig. 34. Section from the Black Hills across portion of the 
 Great Plains. The Dakota sandstone is the aquifer which 
 receives the rainfall on its upturned edges in the Black 
 Hills and carries it as groundwater hundreds of miles out 
 under the dry plains where it is obtained by artesian 
 borings. (After Darton). See Fig. 33. 
 
 in Fig. 33 B because in the latter case the well must be near the 
 outcrop in order to reach the aquifer or water-bearing layer, 
 
GROUNDWATER AND RIVERS 
 
 57 
 
 while in the first case the well may be many miles distant, even 
 in a semi-arid or desert region, and yet get the water from the 
 rain belt far away. Thus there are artesian wells on the desert 
 of Sahara fed by the rainfall on the bordering mountains. The 
 
 FlG. 35. Flowing artesian well at Woonsocket, South Dakota. It 
 throws a 3-inch stream to the height of 97 feet. This well is 
 about 200 miles from the Black Hills. (N. H. Darton, Nat. Geog. 
 Mag. Aug. 1905.) 
 
58 PHYSICAL GEOGRAPHY 
 
 rain that falls on the sharp crested foothills of the Rocky Moun- 
 tains and the Black Hills is carried in a hed of sandstone out 
 under the great Western Plains for many miles where it is ob- 
 tained from artesian wells, in some places even in sufficient 
 quantities for irrigation purposes. The gently inclined beds of 
 clay and sand on the coastal plain of Long Island and New Jersey 
 favor productive artesian wells, which might even be sunk out 
 in the ocean and furnish a bountiful supply of fresh water. Draw 
 a diagram to illustrate this. (See figs. 35 and 33.) 
 
 59. Spring's. — Much of the groundwater returns to 
 the surface in the form of springs, which are streams of 
 groundwater emerging at the surface, and varying in size 
 from tiny trickles to great rivers. Silver Spring in 
 Florida and Mammoth Spring in Arkansas are each large 
 enough to float a small steamboat. 
 
 Sometimes the groundwater descends only a few feet 
 below the surface until it finds its way back to the sur- 
 face through a spring. Sometimes it descends thousands 
 of feet before it is returned. 
 
 60. Temperature of Springs.— The temporary springs fe& 
 from water near the surface vary in temperature during the year, 
 becoming warmer in summer and cooler in winter. The perma- 
 nent springs, however, are fed by water from below the per- 
 manent water table which is generally below the zone of variable 
 temperature, and the water has a uniform temperature through- 
 out the year, generally about 55 degrees P. (Compare the tem- 
 perature of the water in some of the springs in your neighbor- 
 hood in the summer and in the winter months. Why does the 
 water seem colder in the summer and warmer in the winter?) 
 Some springs in a rocky region have a temperature considerably 
 below 55 degrees because part of the water comes from melting 
 ice whicn accumulates in the talus slopes during the winter and 
 melts slowly during the summer. Sometimes the ice forms in 
 limestone caves. There are several of these caves in the lime- 
 stone near Syracuse, N. Y. 
 
 61. Hillside Springs.— The very large springs gen- 
 erally occur in the bottom of the valley. Why? But a 
 
GROUNDWATER AND RIVERS 
 
 59 
 
 great many small and medium sized springs emerge at 
 different elevations on the hillsides, frequently a number 
 of them at the same level. These are known as hillside 
 
 FlG. 36. Hillside Springs on an area of five square miles at 
 Eureka Springs, Arkansas. The shaded portion repre- 
 sents a porous chert rock which forms hills 200 to 400 
 feet above the underlying limestone. The latter forms the 
 base of the hills 20 to 150 feet above the bottom of the 
 valleys. The springs emerge on a thin bed of shale which 
 separates the two rocks. 
 
 springs and are caused by the groundwater in its descent 
 from the surface meeting a bed of clay, shale, or other 
 
60 
 
 PHYSICAL GEOGEAPHY 
 
 dense rock and following along the top of this layer until 
 it emerges on the surface. (Figs. 36 and 37.) 
 
 PiG. 37. Vertical section through Eureka Spring, Ark. Com- 
 pare with Fig. 36. The groundwater percolates through 
 the upper layer B faster than it can penetrate the shale 
 layer. It moves along the top of the shale until it emerges 
 at the surface forming springs at s, s, s, s. 
 
 Seepage. — Ground water generally collects into little 
 streams on the top of the impervious layer and the emerg- 
 ence of such a stream at the surface forms a spring. Some- 
 times, however, the water flows in a sheet along the entire 
 surface of the dense layer and then instead of flowing out 
 in streams, it seeps or trickles out along the line of outcrop 
 of the layer in sufficient quantities to keep the surface wet, 
 frequently forming a swamp or bog on the hillside. This 
 is called a seepage spring. 
 
 Fissure Springs.— Fissure springs consist of those in 
 which the water in its underground passage, enters a 
 fissure or crack leading to the surface through which the 
 water emerges under hydrostatic pressure, as in an arte- 
 sian well. 
 
 62. Mineral Springs.— All spring water contains some 
 mineral matter in solution but certain ones known as min- 
 eral springs are characterized by an excessive amount of 
 some common mineral matter, as carbonate of lime, car- 
 bonate of iron, or hydrogen sulphide, or by the presence 
 of some rare compounds like those of lithium. The most 
 common mineral springs are the lime, sulphur, iron 
 
GROUNDWATER AND RIVERS 61 
 
 (chalybeate), magnesia, carbonic acid, potash, soda, lithia, 
 silica springs. Some of the mineral springs are hot and 
 others are cold. 
 
 Some have a wide reputation for the curative proper- 
 ties of the water, for the benefit of which people travel 
 long distances. In some places the waters are bottled 
 and shipped to distant points. What mineral springs can 
 you name in New York State? Your own State? Make 
 a list of the places and the kind of springs. The springs 
 shown in fig. 36 are widely known mineral springs. 
 
 63. Hot springs are those in which the water has a high 
 temperature, sometimes at or near the boiling point. Such 
 springs occur in the region of active or extinct volcanoes, where 
 the rocks have not yet cooled from the former highly heated con- 
 dition. The circulating groundwaters coming in contact with 
 these heated rocks below the surface are warmed and emerge 
 in the spring as hot water. 
 
 In some places where hot springs are remote from any vol- 
 canic rocks, they may be caused (1) by intrusive molten rocks 
 which have not reached the surface; or (2) by heat produced 
 by friction in the bending and fracturing of the rocks in the fold- 
 ing of mountains; or (3) by chemical action going on in the 
 rocks through which the water is passing. Hot springs are found 
 in mountainous countries, in Arkansas, Virginia, South Dakota, 
 and many of the Rocky Mountain and Pacific States. 
 
 64. Geysers. — Geysers are boiling springs that erupt 
 intermittently. The water is thrown out periodically, 
 sometimes to a height of several hundred feet. The 
 eruptions take place in some geysers at quite regular in- 
 tervals, while in others the intervals are very irregular, 
 sometimes several hours or several days. 
 
 The water in all geysers contains alkali (soda or potash) 
 in solution, which in turn dissolves silica in the deeper 
 portions of the circulation. When the heated silica-bear- 
 ing waters approach the surface the decrease in pressure 
 and loss of temperature causes some of the silica to be 
 
62 
 
 PHYSICAL GEOGRAPHY 
 
 deposited along the sides of the opening, making a smooth 
 but crooked and irregular tube through which the water 
 finds its way to the surface. 
 
 The eruption of the geyser is caused by the high temperature 
 in the deeper portions of the tube which causes the water to be 
 heated above the boiling point. A portion of it finally changes 
 to steam, the expansion of which lifts the plug of colder water 
 in the upper part of the tube, causing it to overflow and thus re- 
 lease the pressure on the water towards the bottom. This re- 
 
 Fig. 38. Old Faithful geyser in Yellowstone National Park. The 
 white mound is composed of silica deposited from the waters 
 of the geyser. (U. G. Cornell.) 
 
 lease of pressure permits a large volume of steam to form sud- 
 denly, and forcibly expel all the water from the tube. The 
 water partially cooled in the air runs back, fills up the tube and 
 stands until the bottom is again heated above the critical point, 
 that is, the point where the water will change to steam under the 
 existing pressure, when another eruption takes place. The crit- 
 
GROUNDWATER AND RIVERS 63 
 
 ical point where water changes to steam at sea level on the sur- 
 face of the earth is 212 degrees F., but deep beneath the surface 
 under the increased pressure it may reach a temperature of 250 
 degrees or more before it forms steam. Another possible explan- 
 ation for some of the geysers is that steam accumulates in an 
 underground cavity until it has sufficient force to overcome the 
 resistance of the column of water when it violently expels the 
 water from the opening. 
 
 The constant loss of heat from the eruptions of hot water 
 causes a decrease in the activity of the geyser which in time be- 
 comes a hot spring and finally a cold spring. In the Yellowstone 
 Park there are about 3,000 openings, some of which are geysers 
 but the majority of them are now springs, some hot and others 
 cold. A decrease in the activity of some of the geysers has 
 been noted in the past few decades. Even "Old Faithful" that 
 formerly erupted regularly every hour is now becoming irregular 
 with sometimes an interval of an hour and a half between erup- 
 tions. The decrease in activity of some of the geysers is balanced 
 in part at least by increased activity in others. 
 
 At present there are four geyser localities known in the 
 world: one in the Yellowstone National Park in Wyoming, one 
 in Iceland, one in New Zealand, and one in South America near 
 the headwaters of the Amazon. 
 
 RIVERS 
 
 Part of the rain that falls does not sink into the 
 ground at all but runs directly into depressions and 
 through these to the sea. It mingles on the way with the 
 water from springs, seepage, and the melting snows, 
 which all together form the brooks, creeks, and rivers 
 which fill the lake basins, and, running into the sea, re- 
 place the loss that results from evaporation. The moisture 
 evaporated from the ocean is carried as vapor through the 
 air, falls as rain or snow upon the land, and is carried 
 back to the ocean through the rivers. In this great cir- 
 culating system, the rivers are of special interest to the 
 geographer, because they have more to do with modify- 
 ing the surface of the earth, and in sculpturing the beau- 
 
64 PHYSICAL GEOGRAPHY 
 
 tifui and varied features of the landscape than any of the 
 other parts of the system. 
 
 65. Origin of the River Valley.— River valleys may 
 begin and grow in one or both of two ways: (1) The rain 
 that falls on the border of a new land mass forms gullies, 
 some of which deepen and lengthen and widen until they 
 form river valleys. (2) The rain that falls on a new 
 land area runs into existing depressions until they are 
 filled, each overflowing into the next lower one, and from 
 the lowest into the sea. The depressions when first filled 
 with water are lakes, which in time are filled up with 
 sediment. The streams cut gorges and valleys between 
 the lake basins and finally through the filled basins until 
 there is a continuous channel for the river from the inner- 
 most rainfall to the sea. Probably in all river systems 
 there is a combination of these two methods. Since the 
 first method is the simplest it will be described, and the 
 reader can apply the same principles to the second. 
 
 66. Gullies. — The rain on the hillside washes away 
 the softer material first and forms a little depression or 
 gully. The depression gathers more water and so con- 
 tinues to wear faster than the land on either side. After 
 the gully is once started, the frost and wind and the other 
 weathering agents (what are the others?) assist the rain 
 in loosening and moving away the material at the sides 
 and at the head of the gully. Refer to sections 71, 212 and 
 213 for description of weathering and disintegration of 
 rocks. 
 
 The material so loosened is carried by the rain, assisted 
 by gravity, to the bottom of the gully where it is swept 
 along first by the temporary stream, and later by the per- 
 manent stream, and, as it grinds against the sides and 
 bottom of the channel, it corrades or wears away frag- 
 ments of the rock and thus lowers the bottom of "the gully. 
 
GROUNDWATER AND RIVERS 
 
 65 
 
 FlG. 39. Gullies and valleys in youth in soft material in an 
 arid region. Compare with Fig. 64. Though the annual 
 rainfall is light it is concentrated in heavy showers. Bates' 
 Hole, Wyoming. (U. G. Cornell.) 
 
 FlG. 40. Telephoto view of gullies in the Bad Lands, South 
 Dakota. Gullies in a dry climate. Compare with Pigs. 39 
 and 42. 
 
66 PHYSICAL GEOGRAPHY 
 
 As this process goes on, the bottom of the gully is finally 
 cut below the water table into the zone of perpetual 
 groundwater and then, and not till then, does the valley 
 gain a permanent stream. The erosion then goes on con- 
 
 
 
 \ 'v ■ :. 
 
 
 
 
 ".-_.. . ...'«*" ,:"" 
 
 
 
 *** 
 
 ™"" "*' - . : : ;; 
 
 
 
 ^> ^ 
 
 
 .... . -****♦ 
 
 
 
 L. v- • '"^'•'■^•fc. 
 
 j. — ' i J5> ' 
 
 
 y jj. • " ^B 
 
 ST^^^t, , . i j*jr 
 
 
 
 : f . JBK? 
 
 ||B!r ' '"^JiW ir 
 
 ^0m 
 
 K 
 
 
 
 
 ' ^M 
 
 
 
 
 FiG. 41. Toad Stool Park, Adelia, Nebraska. Copyright 1898 by E. H. 
 Barbour. Not every gully becomes a river valley. Observe the 
 great number of gullies in proportion to the stream valleys in the 
 hills in the background. 
 
 tinuously throughout the year, and is supported by the 
 springs and seepage that emerge at the sides of the valley 
 and keep up the water supply during the dry season. 
 
 The head of the gully or valley may extend back into 
 the land area until it reaches a permanent divide where 
 the streams flow in another direction. As the valley 
 lengthens, tributaries develop along the side similar to 
 the original gully, and tributaries to these in turn until 
 the area is covered with a great system consisting of the 
 main stream with all its tributaries. 
 
GROUNDWATER AND RIVERS 67 
 
 Fig. 42. Gullies in hard volcanic rock on the side of Mt. Potosi, Ouray Co., 
 Col. Compare with Figs. 39 and 64. The rocks shown in this view are 
 all hard volcanic lavas. 
 
 It must not be inferred that every gully becomes a 
 river valley. . To one such there are thousands that are never 
 anything but gullies, and possibly not large ones at that. 
 
 67. Definition. — A river is a stream of water together 
 with the rock waste which it carries. It has its source in 
 the springs, seepage, rainfall, and snowfall in and around 
 the upper end of its valley. Not infrequently a lake is 
 the source of a river, but generally it is only part of a 
 river, in a wider and expanded portion of the valley; and 
 the stream or streams that flow into the lake are but the 
 headwaters of the river that flows out of it. Some rivers 
 have their sources in melting glaciers. Small streams are 
 commonly called creeks, brooks or rivulets but the distinc- 
 tion is seldom made in geography because it is merely one 
 
68 
 
 PHYSICAL GEOGRAPHY 
 
 of size and what is called a creek in one locality may be 
 larger than one called a river elsewhere. 
 
 The land over which the stream flows is the bed and that im- 
 mediately bordering the stream confining it to the bed forms the 
 banks. The mouth of the river is the place where it flows into 
 the sea, a lake, or another river. A river basin is all the land 
 drained by the river and its tributaries. A river system includes 
 the main river and all its tributaries. A divide is the parting be- 
 tween the surface waters of two valleys or basins. It may be a 
 sharp ridge in mature topography, or a broad flat or plateau in 
 young topography, or it may rarely be a body of water. The 
 divide between the Amazon and Orinoco rivers is so low in one 
 place that it is possible to cross it in a boat; in fact, it shifts 
 back and forth over a considerable length of water depending on 
 the local rainfall and the height of the water in the two rivers. 
 (Trace out and describe the divides on the Charleston and Ottawa 
 or Fargo sheets of the Topographic Atlas. The first is an ex- 
 ample of mature topography and the other two of youthful topog- 
 raphy. See Sec. 85) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 LAK 
 
 E TEA 
 
 ROF1 
 
 HE CU 
 
 OUDS 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 £ 
 
 
 
 
 
 
 CI 
 
 
 
 
 
 
 
 cc 
 o 
 
 i 
 
 
 
 
 
 
 1 
 
 cc 
 
 
 
 
 
 
 
 
 • 2 
 
 o 
 
 
 
 z 
 
 
 u. 
 
 2 
 
 Hi 
 
 tjsoa 
 
 ft 
 
 o 
 
 en . — 
 
 
 
 
 
 
 
 
 _J 
 
 
 
 Fig. 43. Profile of the Hudson-Mohawk River. Observe the 
 contrast between the upper and lower Hudson and between 
 the upper Hudson and Mohawk. Vertical scale 2000 feet 
 to one inch. Horizontal scale 100 miles to one inch. — 
 (U. S. Geol. Survey.) 
 
GROUNDWATER AND RIVERS 69 
 
 68. Profile of a River. — The slope of a river channel or the 
 angle of the inclination to the horizontal is one of the chief 
 factors in determining the velocity of a river; the steeper the 
 slope the more rapid the current. A line representing the slope 
 of a river channel from the headwaters to the mouth of a river 
 is called the .pro-file. In general the slope is steeper near the 
 headwaters of the river and decreases towards the mouth. Com- 
 pare the profiles of some of the principal rivers of the United 
 States and draw the profile of a river from furnished data. (See 
 Bulletin 44 of the Water Supply and Irrigation Papers published 
 by the U. S. Geological Survey.) 
 
 W?" 
 
 
 
 
 s 
 
 
 
 
 
 
 
 1 SH|j \ 
 
 - - L ■ 
 
 # 
 
 
 1 1 B 
 
 Fig. 44. East branch of Limestone Creek, Manlius, N. Y., show- 
 ing reach or pool in foreground and rapids in the back- 
 ground. Very little, almost no erosion is going on at the 
 reach. On the rapids the rocks are being ground to pieces 
 and the finer portions carried to a lower level. 
 
 69. Reaches and Rapids. — A river is rarely if ever 
 of uniform slope from the mouth to the head, but gener- 
 ally consists of a series of alternating pools or stretches of 
 quiet water called reaches separated from each other by 
 ripples or rapids where the current flows swiftly. Por- 
 tions of the pools are generally being filled with sand and 
 mud, and the rapids are cutting the channel deeper and 
 
70 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 45. West branch of Limestone Creek, 
 Manlius, N. Y., showing rapids in the fore- 
 ground. At this point the stream, owing 
 to its curvature, is cutting sideways and 
 widening its valley at the reach. Notice 
 the undercutting of the bank on the right. 
 
 Fig. 46. Potomac River, Barnum, Md., showing rapids at low 
 water and the tools which the stream uses in degrading its 
 channel. Most of the work done by the stream is accom- 
 plished during the high water stage. (Maryland Geological 
 Survey. ) 
 
GROUNDWATER AND RIVERS 71 
 
 slowly receding towards the headwaters. In the pools or 
 flats the river is aggrading its channel, that is, depositing 
 sediment and raising its bed ; on the rapids the stream is 
 degrading its channel, that is, cutting it deeper. Some 
 portions of the river course are neither aggrading nor 
 degrading but are graded. As a stream advances in age 
 the graded portions tend to increase in length and when 
 they are all connected and all rapids have disappeared, 
 the stream is completely graded and has reached base 
 level. (Study figs. 44, 45 and 46.) 
 
 Fig. 47. Streams flowing into a lake form deltas 
 and deposit sediment until the lake basin is 
 filled to the level of the outlet. Compare with 
 Fig. 48. 
 
 70. Base Level. — The base level is reached by a river 
 when the rapids disappear and as a stream of clear water 
 it flows with a slow motion, neither eroding nor deposit- 
 ing material, over a plain having a gentle, uniform incli- 
 nation from the headwaters to the mouth. It is the low- 
 
72 
 
 PHYSICAL GEOGRAPHY 
 
 est level to which the river mechanically erodes the land 
 over which it is flowing. (Some writers define the term 
 base level as the level of the sea or other body of water 
 into which the river flows. For a discussion of the mean- 
 ing of the term see Davis, Journal of Geology, Vol. x, p. 
 77.) 
 
 71. Work of Rivers. — The work of a river consists in dis- 
 secting the upland areas and carrying the material along with 
 the excess rainfall to the lowlands and finally to the sea. In this 
 
 3TiG. 48. After the lake is filled, the stream from 
 the outlet is supplied with sediment, degrades 
 its channel, and then picks up and carries 
 onward the sediment formerly deposited in the 
 lake basin. Compare with FiG. 47. 
 
 work it is assisted by the weathering agents, such as wind, frost, 
 heat of the sun, gravity, chemical action, and animal and plant 
 life, which cause the rocks to disintegrate and crumble into 
 fragments. The rain washes the loose materials into the stream 
 channels, and the current carries them toward the sea. The 
 journey is not a continuous one, because the material is dropped 
 and picked up again many times between the mountain and the 
 
GROUNDWATER AND RIVERS 73 
 
 sea. Thus, when a river flows into a pond or lake, nearly all the 
 sediment is deposited until the lake is completely filled, after 
 which the river, under new conditions, picks up the materials and 
 carries them on to a lower level. Most of the transportation is 
 done during flood season, but the disintegration goes on contin- 
 uously throughout the year. (See figs. 47 and 48.) 
 
 72. Corrasion. — The material carried by the stream, 
 the sand, mud, and gravel, corrades or grinds away the 
 rocks in the channel. The sand and pebbles are the tools 
 
 Fig. 49. Pot hole formed in rock by the grinding action of the 
 pebbles and sand in the eddying waters on the rapids. (U. S. 
 Geol. Survey.) 
 
 that do the grinding, while the water acts as a carrier. 
 In the rapids, eddies are formed and pebbles are caught 
 and swirled around in the waters until a circular depres- 
 sion or pot-hole is formed which may be from a few inches 
 to many feet in depth and diameter. Pot-holes are also 
 formed underneath glaciers where a surface stream de- 
 scends through a crevasse or moulin. (See Sec. 126, fig. 
 116). Deep, narrow gorges like Ausable Chasm and Wat- 
 
74 PHYSICAL GEOGRAPHY 
 
 kins Glen indicate rapid corrasion or down-cutting by the 
 stream. 
 
 73. Transportation. — Rivers transport materials in 
 several different ways: (1) Floating on the surface. 
 Great quantities of vegetable material are carried in this 
 way and at times limited quantities of earthy material. 
 Where the water rises gradually over a dry sand deposit, 
 little cakes and patches of the dry sand are floated away 
 on top often a long distance before they are disturbed 
 and sink. Place a sewing needle gently on the surface of 
 a cup of water and it will float in the same way. When 
 the river undercuts its banks and a part of the forest or 
 vegetable covering slides into it, the earthy material 
 clinging to the roots is carried away with the floating 
 trees and grass. In cold climates the blocks of ice borne 
 away on the spring floods frequently carry fragments of 
 rock and earth long distances down the stream before the 
 ice melts and drops them in the channel. (2) Great 
 quantities of mud and fine sand are carried along sus- 
 pended in the water borne up by the many upward whirls 
 in the current. (3) Boulders, pebbles, and sand are 
 rolled and pushed along the bottom, and hence are being 
 continually worn rounder, smoother and smaller. The 
 larger boulders are moved in the more rapid portions of 
 the stream as in the mountain torrents, while through 
 the flood plain in the lower portion of the river, the 
 burden is mostly sand and mud. It is surprising how 
 great a quantity of sand is being moved along the bottom 
 of the lower courses of a great river like the Mississippi 
 or the Missouri. (4) Besides the above there is the in- 
 visible load which the river carries in solution, consist- 
 ing of compounds of lime, iron, magnesia, soda, potash 
 and minute quantities of other materials dissolved from 
 the rocks. This part of the work goes on all the year, 
 
GKOUND WATER AND RIVERS 75 
 
 even during the low water stage in the dry season when 
 the waters are free from sediment. 
 
 74. Transporting 1 Power of Streams.— The carrying 
 power of streams varies greatly with the velocity of the 
 water, the velocity being frequently a factor of the vol- 
 ume. In the Johnstown, Pa., flood the great volume of 
 water from the broken reservoir moved down the same 
 slope as that over which the Conemaugh river flows at all 
 times. Yet the force of the flood, due to the increased 
 volume of water, was sufficient to twist railroad irons, move 
 freight cars, and even railway locomotives, and cause enor- 
 mous destruction of property. The increase in the carry- 
 ing power is in a much greater ratio than the increase in 
 velocity, hence the great destruction wrought by streams in 
 flood time. The carrying power increases as the sixth 
 power of the velocity. That is, if the velocity is increased 
 10 times the carrying power is raised 1,000,000 times. 
 
 The transporting power of streams having different velocities 
 is shown by the following: 
 
 3 inches per second will just move fine clay. 
 6 inches per second will move fine sand. 
 
 12 inches per second will move fine gravel. 
 
 24 inches per second will move pebbles an inch in diameter. 
 
 36 inches per second will move pebbles as large as an egg. 
 
 10 miles per hour will move masses of iy 2 tons. 
 
 20 miles per hour will move masses of 100 tons. 
 
 The load carried by a stream is often a small fraction of the 
 carrying capacity of the stream. If the water is flowing over 
 hard rock it may be unable to pick up any load. It is not always 
 the rapid current that is carrying the greatest load; although it 
 has the capacity it may not have the load to carry. 
 
 75. How the Energy of the Stream is Expended.— 
 
 Part of the potential energy of the stream is used up in 
 transporting its load, and part in corrading its channel. 
 If the stream is full loaded, that is, has all the material it 
 
76 
 
 PHYSICAL GEOGKAPHY 
 
 FlG. 50. An underloaded stream which is corrading its channel 
 in granite. View in the canyon of the North Platte River. 
 (U. G. Cornell.) 
 
 " "" 
 
 
 
 
 'm 
 
 !«fO^ 
 
 
 '•'.•• •' * fefe 1 -''^' v' : - 
 
 i# fffl 
 
 "*"""' >/m -' ." 
 
 
 ^^ , 
 
 ' 
 
 
 ~z~~?i***p*? r T~>~'' 
 
 1^ 
 
 a, _«,. . - • ._ .^Zf"~ 1 
 
 ^ssHw»"" '—„ "■" ' -t«^S|E^H 
 
 
 
 
 : ; -dB? 
 
 'Sfci ' 
 
 
 
 *3$E£$ 
 
 FlG. 51. An overloaded stream, Uncompaghre Creek, Ouray, 
 Col. Above this point the stream flows through narrow 
 canyons, similar to that in Fig. 50, carrying much sediment 
 which is deposited in this broader part of the valley below 
 the canyons. Along with the bowlders, gravel and sand 
 there is considerable driftwood deposited. 
 
GROUNDWATER AND RIVERS 
 
 77 
 
 can carry, it will not do any eroding. If it is overloaded 
 it will deposit part of the load; if it is underloaded, the 
 excess energy will be expended in deepening and widening 
 
 Fig. 52. An overloaded stream, Uncompaghre Creek above Sneffels, Col. 
 The same stream as in FiG. 51 but nine miles nearer the source. 
 Note the narrower valley, the steeper slope in the channel and the 
 coarser material deposited in the channel. The white spot near the 
 middle of the picture is a cataract. 
 
 the channel by corrasion. The Missouri river is over- 
 loaded across the plains and underloaded on most of its 
 course through the Rocky Mountains. Hence it is deep- 
 ening its channel through the mountains and building it 
 up across the plains. ( Explain the different ways in which 
 a stream may become overloaded. See figs. 51, 52 and 53). 
 76. Deposits Made by the River.— Probably the lar- 
 gest deposits made by the river are those made on the 
 flood plain and in the delta, but before the sand and mud 
 
78 
 
 PHYSICAL GEOGRAPHY 
 
 reach either of these stopping places they may have been 
 dropped and picked up many times and had many rough 
 tumbles and a varied experience in the upper courses of 
 the streams. 
 
 Fig. 53. An overloaded stream, Taughannock Creek, N. Y. 
 The mass of material in the channel has been swept by 
 the stream in flood season from the narrow gorge in the 
 hills in the background. (E. R. Smith.) 
 
 The bulk of the material moved by a river is carried in flood 
 time because of the increased volume and velocity of the water, 
 but it is frequently moved only a short distance, to be dropped 
 until moved again by a subsequent flood. Sometimes a stream 
 may be so overloaded that it will deposit part of the load and 
 pick it up again, when it has no load, even at low water. 
 
 77. Flood Plains.— All streams as they approach old 
 age develop more or less extensive plains bordering the 
 channel, — plains so low that they are covered with water 
 during flood season in the river, hence the name flood 
 plain. The water covering the flood plain is the overflow 
 from the channel and has lost much of its former velocity, 
 because, first the water is shallower than in the channel, 
 and, second, the vegetation acts as a check on the velocity. 
 
GROUNDWATER AND RIVERS 79 
 
 Hence much of the sediment— the sand and mud— is de- 
 posited, forming the rich alluvial soil that makes the flood 
 plains such rich farming regions. 
 
 Fig. 54. Flood plain of stream flowing into Chesapeake Bay, 
 Calvert Co., Md. Rivers generally have a meandering 
 course on a flood plain. (Maryland Geological Survey.) 
 
 The flood plains are very large, covering many thou- 
 sands of square miles on the lower courses of old and large 
 rivers like the Mississippi and the Nile. In general the 
 flood plain narrows in ascending the river. Frequently 
 in the middle and upper courses of the streams there is a 
 narrow flood plain on one side of the stream while the 
 other flows against the bordering cliff. 
 
 Why are there no large flood plains on the Hudson and the 
 Niagara rivers? Do you know of any large flood plains on any of 
 the rivers in New York? (See figs. 54, 55, and 57 and map of 
 the lower Mississippi River.) 
 
 78. Meanders. — When a river has graded a portion 
 of its course and formed a flood plain, it ceases to corrade 
 the bottom of its channel at that place but may continue 
 to cut at the sides or banks. Where the current is de- 
 flected to one side it cuts away the bank at that point, pro- 
 
80 PHYSICAL GEOGRAPHY 
 
 during a curve which deflects the current across to the 
 opposite bank below, where another curve is formed. In 
 
 PlG. 55. Meandering stream — Coal Creek on the Laramie plains, 
 Wyoming. This stream is utilized to transport the logs from the 
 forests in the adjoining mountains to the mills far out on the plains. 
 U. G. Cornell.) 
 
 Fig. 56. Meanders, M, M', M", R, R, R, former course of the 
 river. C beginning of a cut-off. D is a cut-off. The ends 
 of the lagoon LL are being filled with sand and mud at a, a. 
 
 both places the bank is worn away and the stream in time 
 becomes quite crooked or meandering. While the stream 
 is cutting the outside of the meander curve, sand and 
 
GROUNDWATER AND RIVERS 
 
 81 
 
 gravel are being deposited on the inside of the curve 
 (why? study the diagrams) and the whole channel is 
 gradually shifted into or even across its flood plain. The 
 
 Fig. 57. Map of portion of the Mississippi River, showing 
 meanders and cut-offs. The lakes are ox-how lakes and 
 portions of the abandoned channel. Note the sand de- 
 posits a, a, a, on the inner bank at many of the curves. — 
 (After the Miss. River Com.) 
 
 meander curve once started continues to increase its cur- 
 vature until the stream cuts across the neck between two 
 approaching curves and thus straightens that portion of 
 the channel. The cut-off is gradually silted up at the 
 ends, forming first a lagoon and later an ox-bow lake. 
 These ox-bow cut-offs, so common on the flood plains of 
 6 
 
82 PHYSICAL GEOGRAPHY 
 
 large rivers, may frequently be observed on small brooks 
 where they are following a winding course through a 
 meadow. Study the Mississippi River maps and figs. 55, 
 56 and 57. 
 
 When the meander curve reaches the outer limit of the flood- 
 plain of the river, it begins to undercut the river bluff and thus 
 widen the valley. Study meander curves on nearby streams; 
 where possible observe them at intervals of a few months or 
 years. Suggestion to the teacher — take photographs each year 
 for comparison. (See fig. 45.) 
 
 79. The natural levee is formed on the flood plain 
 on the immediate bank of the stream. In flood season the 
 river overflows its banks and spreads out in a thin sheet 
 of water, moving slowly down the valley over the level 
 area, but the water in the channel moves much more 
 rapidly than that on the flood plain because it is much 
 deeper. At the contact of the swiftly moving water of 
 the channel and the slower moving water of the flood 
 plain, there is a deposition of sand and mud due to the 
 check in the velocity. The increase in size of this em- 
 bankment is aided by the dense growth of willows, alders, 
 and other bushes along the bank which catch the drift and 
 add it to the bank as well as aid in checking the current 
 and adding to the deposit of the sediment. 
 
 80. Artificial Levees.— Man attempts to improve on nature's 
 methods by adding material to the top of the natural levees, pro- 
 ducing artificial ones in the endeavor to keep the river in its 
 channel and prevent it from overflowing the flood plain. As the 
 levee is built up, the river deposits material on the bottom of the 
 channel, making it necessary to keep adding to the top of the 
 levee until it is sometimes built up many feet above the border- 
 ing area, so that steamboats in the river are sometimes above 
 the level of the neighboring farms. A break in such a levee 
 (called a crevasse) often proves to be very destructive to the 
 bordering flood plain. Sometimes the river even leaves the exist- 
 ing channel permanently and forms a new channel elsewhere to 
 
GROUNDWATER AND RIVERS 
 
 83 
 
 repeat the process, and in this way by a repetition of such changes- 
 finally raise the level of the entire plain. 
 
 Fig. 57a. Strengthening a levee on the Mississippi River at Lagrange, Miss., 
 during the flood season. (National Geog, Mag., Oct., 1907.) 
 
 81. River Swamp.— The river swamp generally oc- 
 cupies the outer borders of the flood plain next to the 
 river bluffs, because the building up of the natural levee 
 along the banks of the channel causes the plain to slope 
 from the channel towards the bluff and hence causes a 
 
 Fig. 53. Cross section of a river valley — showing the flood 
 plain, river swamp, natural levee (the small elevation 
 on each side of the river channel), the position of the 
 water table (WP). Liable to be springs or seepage and 
 hillside bogs at S S. 
 
 part of the rainfall on the flood plain to drain away from 
 the stream instead of toward it. Likewise the water 
 
84 PHYSICAL GEOGRAPHY 
 
 from the bluffs, unable to find its way across the natural 
 levee, accumulates in the depressions along the base of 
 the bluff and aids in forming the river swamp. 
 
 82. Levee Lakes.— The upbuilding of the flood plain along 
 the channel banks sometimes forms a dam across the mouth of 
 a tributary, and thus produces a lake on the tributary, while in 
 other places, instead of forming a lake the tributary flows for 
 many miles parallel with the main stream between the levee and 
 the bluffs until it finds a place where it can penetrate the levee 
 bank into the main stream. The above points should be studied 
 on detailed maps of flood plains such as the Donaldsonville and 
 Point a la Hache, La., contour sheets of the topographic atlas 
 and the sheets of the Mississippi River Survey, and the streams 
 near the schoolhouse; (See fig. 221.) 
 
 83. Deltas. — A river flowing into a body of still water 
 as a lake or the ocean, where there are no strong tides, 
 deposits all of its load of sediment, building up an accu- 
 mulation called a delta. There is generally no sharp line 
 of separation between the delta and the flood plain; the 
 latter has been built up on the land and the former has 
 been formed in the sea or lake. The river divides on the 
 delta and finds its way into the sea by several, sometimes 
 by a great many channels called distributaries. The head 
 of the delta is frequently located where the first distribu- 
 tary leaves the main channel. 
 
 Fig. 59. Cross section of a delta showing position 
 of the beds. A, top-set beds. B, fore-set beds. 
 C, bottom-set beds. S, sea level. 
 
 Deltas, like flood plains, have a fertile soil and fre- 
 quently support a dense population. Both are fertile 
 because they are composed of the rich surface soil from 
 other parts of the basin. It contains much humus 
 and is frequently renewed. 
 
GROUNDWATER AND EIVERS 
 
 85 
 
 The structure of the delta as shown by the diagram 
 is characteristic. The middle portion consists of mingled 
 sand and mud beds formed at the end of the delta where 
 the river current first meets the still water. 
 
 At this point a larger part of the load is dropped than 
 at any other and the material comes to rest in inclined 
 layers, the fore-set beds, dipping towards the open water. 
 
 Fig. 60. Walnut canyon, near Flagstaff, Ariz., showing delta 
 structure in the sandstone of the canyon walls. Commonly 
 known as cross bedding or false bedding. (A. E. Hackett.) 
 
 But some of the fine materials is carried out into deeper 
 water forming the mud layers that sometimes reach con- 
 siderable thickness and great extent, the bottom-set beds, 
 which form the submarine delta. 
 
 The delta of the Indus River has built up the submarine por- 
 tion nearly to the sea level over such an extensive area of now 
 shallow sea that in places large vessels cannot even get within 
 sight of the shore. 
 
 Over the top of the inclined beds is a deposit of horizontal 
 beds, the top-set beds, made by the river in flood time and not 
 essentially different from the flood-plain deposits. All these 
 
86 
 
 PHYSICAL GEOGRAPHY 
 
 structural features may be observed in the mud deposit formed 
 in the pool on the roadside by a summer shower. 
 
 84. Alluvial Fan.— An alluvial fan is somewhat like 
 a delta. It is formed at the point where a mountain tor- 
 rent or stream with a steep slope carrying a great deal of 
 
 Fig. 61. An alluvial fan at Ouray, Col. The fragmental ma- 
 terial on which the trees are growing was swept out of the 
 narrow canyon faintly visible near the right of the view. 
 
 sediment flows out on a valley floor or flood plain of a 
 larger stream, or on a plain of any kind. The velocity of 
 the swift current is checked suddenly and the load nearly 
 all deposited at the border of the plain, building up a 
 fan-shaped mass over which the stream flows in shifting 
 channels in wet weather. In dry weather the water fre- 
 quently disappears from the surface entirely, flowing 
 through the mass as groundwater. It differs from a delta 
 in being built up on the land instead of in the water, hence 
 the material is not well stratified, but consists of a jumbled 
 mass of coarse and fine deposit almost devoid of any 
 stratification. The delta of a large stream rarely con- 
 tains material coarser than sand or very small pebbles 
 
GROUNDWATER AND RIVERS 
 
 87 
 
 but the alluvial fan sometimes contains boulders mingled 
 with pebbles, sand and mud. If the stream forming the 
 fan is small and descends a very steep slope the deposit 
 will have a steep surface and resembles the section of a 
 
 Fig. 62. Talus cones in the Rocky Mts., Col. The rock 
 fragments loosened by the frost and other weathering 
 agencies roll down slight depressions on the moun- 
 tain side and accumulate in conical mounds at the 
 base. 
 
 cone, when it is called an alluvial cone. Talus cones are 
 similarly formed by gravity and rainwash at the base of 
 steep mountain or hill slopes. (Compare figs. 61 and 62.) 
 
 85. Life History of a River— The Cycle of Erosion.— 
 The successive changes which a stream undergoes from 
 the time it starts on an upland area until the upland has 
 been reduced to a lowland constitutes the life history of 
 the stream. It has a beginning, a period of development, 
 decline and disappearance. It is customary to distinguish 
 at least three different stages in the cycle as youth, matur- 
 ity and old age. 
 
 Youth is the period of rapid growth in the beginning 
 of the cycle. Some of the characteristic features of this 
 
88 PHYSICAL GEOGRAPHY 
 
 stage are narrow V-shaped valleys, cataracts and rapids, 
 lakes and swamps on the upland and inter-stream areas, 
 few tributaries, and broad stretches of undrained or poor- 
 
 
 
 m 
 
 I i/Jfc 
 
 ji 
 
 
 
 . ' «V ' : J 
 
 
 
 
 
 
 
 
 m Br 1 *nl 
 
 
 
 ppyp 
 
 "if 
 
 pi i » m (■'iftv 
 
 
 ^'^w-- ■E^^^9 4 
 
 
 
 Fig. 63. In the canyon of the North Platte River. Stream 
 in youth in hard rock on an arid plateau area. (U. Gr. 
 Cornell.) 
 
 ly drained country bordering the valley. The conditions, 
 of course, are different on a stream developing on a plain 
 from the one on the plateau or mountain, yet the youthful 
 stage of each can be recognized from its advanced or ma- 
 ture stage by some or all of the above features. Fox 
 
GROUNDWATER AND RIVERS 
 
 89 
 
 Fig. 64. Valley in youth in soft material formed by rain wash in a 
 humid region, Calvert Co., Md. Compare with FiGS. 63, 39, 40, 
 and 42. (Maryland Geological Survey.) 
 
 River on the Ottawa, 111., topographic atlas sheet is a type 
 of topographic youth. (See figs. 63 and 64.) 
 
 Maturity of the streams is characterized by the ab- 
 sence of lakes and swamps, which have been filled or 
 drained, the absence of cataracts, decrease in the num- 
 ber of rapids, increase in the number of tributaries, and 
 complete dissection of the inter-stream areas. The di- 
 vides are sharp ridges. There is some shifting of the 
 divides. The sides of the valley are steep, with many 
 cliffs and talus slopes; small flood plains have developed 
 in places, the river is beginning to meander ; the cross 
 sections of the valley are changing from a V-shape to a 
 U-shape. In the mature stage the erosion is at the maxi- 
 mum, and there is the greatest percentage of steep hill- 
 sides over the area. A large per cent of the rainfall is 
 conducted rapidly into the stream channels resulting in 
 
90 PHYSICAL GEOGRAPHY 
 
 destructive floods in the wet season. The tributaries of 
 the Ohio River in West Virginia are good examples. In 
 the mature stage the upland plains have almost or entire- 
 ly disappeared, that is, they have been dissected by the 
 stream and its tributaries into hills and valleys, the tops 
 of the hills being the remnants of the former upland 
 plains or plateaus. 
 
 Fig. 65. Pine Creek, Pa. A revived stream approaching 
 maturity in the Alleghany plateau. 
 
 In old age the narrow, sharp divides of the mature 
 stage are cut down into low rounding hills with gentle 
 slopes; the talus slopes extend to the top of the hills, the 
 cliffs have disappeared ; flood plains increase in size with 
 corresponding increase in the meanders of the river, and 
 formation of ox-bow lakes. Deltas increase in size and 
 natural levees and river swamps become prominent. 
 (Study the diagrams showing changes in profile and in 
 cross section, also the contour maps cited, and the streams 
 seen in your field trips). In extreme old age the hills and 
 
GROUNDWATER AND RIVERS 91 
 
 uplands are nearly all worn down to the level of the val- 
 leys, when the whole area is called a peneplain, (Sec. 216) 
 the final stage of erosion being that of base level. (Sec. 70.) 
 In old age the upland plains have disappeared and low- 
 land plains have formed and are increasing in size. 
 Lakes and swamps are forming on the flood plains, but 
 have all disappeared from the upland. 
 
 Fig. 66. Cross sections of a valley in 
 youth AA, maturity B, and old age D. 
 M is a monadnock. (See Section 216.) 
 
 86. Accidents or Interruptions to the Cycle.— The 
 
 cycle of erosion on a hard rock area is so long that there 
 is generally an interruption of some sort before any river 
 completes the whole cycle. The principal interruptions 
 to the cycle are an elevation or depression of the whole 
 or part of the area drained by the river. There is abun- 
 dant evidence that many land areas have been elevated and 
 depressed several times during their history. In a great 
 many places at the present time, the land is slowly rising 
 and in other places sinking. (Sec. 217.) 
 
 The depression of the lower portion of a river basin 
 carries part of it below the level of the sea which extends 
 up the valley as a bay, such as Delaware or Chesapeake 
 Bay, or an estuary such as the Hudson River below Troy. 
 The river is dismembered of its tributaries on the drowned 
 portion. Thus the Potomac, Rappahannock, York, and 
 James rivers that now flow into Chesapeake Bay were 
 tributaries of the Susquehanna River before it was 
 drowned. Study contour sheets for examples of dismem- 
 bered rivers. 
 
92 PHYSICAL GEOGRAPHY 
 
 If only the middle or upper portions of a river basin 
 are depressed, or depressed more than the lower portion, 
 the river will permanently overflow its flood plain, and 
 swamps or lakes will be formed. 
 
 87. Revived Rivers.— By the elevation of a river 
 basin the stream and its tributaries are revived or rejuv- 
 enated and enter upon a new cycle. The velocity of the 
 current is quickened, and it begins to degrade and lower 
 its channel as it did in the beginning. Where the river 
 had reached old age and was meandering on its flood 
 plain before the elevation it will cut its way down in the 
 channel it occupied and intrench itself in the same wind- 
 ing course that it had on the flood plain. See Canado- 
 guinett Creek on the Harrisburg, Pa., topographic sheet. 
 
 88. Superimposed Rivers.— If the elevation continues 
 far enough, it causes the river to cut through the old flood 
 plain deposits and to be superimposed on the hard rocks 
 underneath. If the elevation proceeds slowly or by 
 stages the river will begin to widen its new trench and 
 develop a new flood plain at the lower level, into which 
 the river may again cut by subsequent elevation. 
 
 89. Terraces. — The remains of the flood plains left along the 
 sides of the valley of a revived river form terraces, and the high- 
 est ones are the oldest. Similar, but much smaller terraces may 
 
 Fig. 67. Alluvial terraces formed by the uplift 
 of an area and consequent downcutting by 
 the stream. Terraces t t remnants of an 
 early flood plain, t' t' of a later flood 
 plain. F is the present plain. 
 
 be formed by the ordinary down-cutting of the river in its first 
 cycle. Terraces of this kind composed of sand, gravel, and silt, 
 are called alluvial terraces and differ from the rock terraces 
 
GROUNDWATER AND RIVERS 
 
 93 
 
 which are caused by the harder and more resistant rocks pro- 
 jecting as ledges or terraces along the sides of the valley. (See 
 diagrams.) 
 
 Fig. 68. Rock terraces, t t, formed by harder layers 
 of rock projecting on the hillside. R, river, N, 
 natural levee. 2, 3, 4, former positions of the 
 river channel. The stream is now aggrading 
 its valley and building up its flood plain. 
 
 90. Reversed Drainage.— The lower or middle por- 
 tion of a river basin may be elevated more rapidly than 
 the upper portion. If it is elevated more rapidly than 
 the river abrades its channel, it will form a dam across 
 the valley and a swamp, marsh, or lake will be formed 
 
 Fig. 69. Rock terraces in the Alleghany plateau. The coal and under- 
 lying clay beds disintegrate more rapidly than the intervening sand- 
 stone beds which form projecting ledges or terraces. Springs emerge 
 at the outcrop of the coal and form hillside bogs. 
 
 above the dam, similar to that when the upper portion of 
 the valley subsides faster than the lower portion. If the 
 elevation continues the water may find an outlet over the 
 divide at the headwaters, cut a deep channel, and thus re- 
 verse the drainage of a large part of the river basin. The 
 
94 PHYSICAL GEOGRAPHY 
 
 drainage is sometimes reversed by river piracy in the 
 shifting of divides. (See see. 93.) Some of the tributaries 
 of the Ohio and Allegheny Rivers in Western Pennsylvania 
 formerly flowed northward into what is now the Lake Erie 
 basin. They were reversed by the glacier which came from 
 the north. 
 
 91. Antecedent River.— If the elevation of a land area takes 
 place no faster than the river abrades its channel, then the 
 stream will saw its way down through the rising land, which may 
 be a plain, a plateau, a mountain range, or even a mountain sys- 
 tem, raised thus across the stream without diverting it from its 
 original course. Such a stream is called an antecedent river as 
 it was there before the elevation occurred. The Colorado River, 
 where it flows through the Grand Canyon is an example. What 
 other examples can you find? 
 
 The elevation of a coast indented with bays and estuaries will 
 produce engrafted rivers; that is, the rivers that previously flowed 
 directly into the arm of the sea will become engrafted on one 
 main stream flowing across the newly uplifted land. 
 
 The coming of a continental glacier, such as once covered New 
 York State and a large part of North America, would for the 
 time being destroy all the rivers in the area covered, and after 
 melting of the ice many of the rivers would begin to form new 
 valleys and a somewhat complicated system of drainage would 
 result. (Explained further in Chapters III and IV.) 
 
 92. Water Gaps and Wind Gaps.— If a number of 
 streams flow across the outcropping edges of hard and soft 
 layers as shown in fig. 70, tributaries will develop on the 
 soft layers at right angles to the main stream. These are 
 called subsequent streams. It often happens that one of 
 the main streams (as in fig. 71) deepens its channel faster 
 than its neighbors. Its tributaries will then cut deeper 
 and longer which in turn aids in deepening the main 
 stream channel (how?) until in time its tributary (a) 
 cuts back until it gains in succession the head waters of 
 2, 3, 4, and 5. Another tributary (b) might in a similar 
 way decapitate "he captured branches of a as shown in 
 
GROUNDWATER AND RIVERS 
 
 95 
 
 fig. 71. The points where the stream cuts through the 
 hard layers which now form ridges as at W. "W. are called 
 water gaps. The low depressions or notches in the ridges 
 at PPP where streams formerly flowed are now called 
 wind gaps and are utilized for highways in crossing the 
 ridges. (Study the Harrisburg, Pa. or the Harper's Ferry, 
 Va., topographic sheets for good examples of water gaps 
 and wind gaps.) 
 
 Fig. 70. An early stage in river piracy. AA and 
 BB outcropping edges of hard rocks. 
 
 93. Migration of Divides.— The shifting of the waters 
 from one valley to another as described in the preceding 
 paragraph causes a corresponding shift in the divides be- 
 tween the valleys. This process of stream capture is 
 known as river piracy. The shifting or migration of the 
 divides goes on through youth and maturity until the 
 divides become pretty well established in old age. Trace 
 out on figs. 70 and 71 the divides before and after the shift- 
 ing of the streams. 
 
96 
 
 PHYSICAL GEOGRAPHY 
 
 Examples of river piracy. Many examples of piracy and shift- 
 ing divides may be traced out on the topographic contour maps 
 with a little care. In New York good examples may be found on 
 the Kaaterskill and Plaaterskill topographic sheets. 
 
 In Pennsylvania the North Branch of the Susquehanna used 
 to flow into the Delaware River through the Schuylkill valley by 
 way of Wilkes-Barre, but a tributary of the West Branch of the 
 
 Fig. 71. A later stage of river piracy than that 
 illustrated in Fig. 70. Stream No. 1 has 
 deepened its channel faster than 2, 3, 4, and 
 5. Hence its tributaries have captured the 
 upper portions of the other streams leaving 
 wind gaps at P, P, P, P, and forming water 
 gaps at W, "W. Stream 1 is the pirate, streams 
 2-6 have been beheaded. 
 
 Susquehanna from Northumberland cut back into the softer 
 shales faster than the old Susquehanna-Schuylkill could cut 
 down the hard conglomerate over which it was flowing, so that 
 the Schuylkill was decapitated at Wilkes-Barre and the upper 
 portion drained into the Susquehanna. This change should be 
 traced out on the geological map of Pennsylvania if one is at 
 hand. 
 
GROUNDWATER AND RIVERS 
 
 97 
 
 Study fig. 72 and see how the Shenandoah River captured the 
 headwaters of Beaverdam Creek and left a wind gap at Snicker's 
 Gap in the Blue Ridge. 
 
 
 
 Tver 
 
 
 
 
 
 '/i 
 
 
 X~J 
 
 v\£ 
 
 
 — ^ 
 
 «|^ 
 
 
 /$ 
 
 A 
 
 
 
 5) •$? 
 1/ 0* 
 
 
 //e/pe/v ft r '7/?./fait ' 
 
 
 
 r dm 
 
 Snickers Gap 
 
 
 J*%L 
 
 
 ~" ^fe 
 
 •>"" 
 
 "N \ CfceA 
 
 %£\£y 
 
 fl 
 
 Fig. 72. River Piracy. — B, present condition. A, probable condition ages 
 ago. In A, Snicker's gap is a water gap through which Beaverdam 
 Creek is flowing. In B the gap is a wind gap caused by the more rapid 
 downcutting of the Shenandoah River enabling it to capture the headwaters 
 of the other stream. Shenandoah River is the pirate, Beaverdam Creek 
 has been beheaded. (After Willis.) 
 
 94. Streams in Arid Climates.— There are some forms 
 of erosive action that are characteristic of dry or arid 
 climates. In desert regions the little rain that falls 
 descends in heavy thunder showers, separated often by 
 long intervals, sometimes several months, sometimes sev- 
 eral years. The long intervals of dry weather cause the 
 death of all vegetation and the heavy rains, falling on 
 the bare soil, flow rapidly into and along the channel 
 ways, called wadies in the Sahara desert, there cutting 
 deep trenches with steep, frequently perpendicular sides. 
 
 7 
 
98 
 
 PHYSICAL GEOGRAPHY 
 
 The wady is frequently used as a highway by the trav- 
 eller of the desert because he there finds some shade and 
 protection from the hot scorching winds of the desert, and 
 further any spring or water hole in the region is likely 
 
 Fig. 72a. Arroyo, near Kingman, Arizona. A watercourse in an arid region 
 subject to great floods from occasional cloud bursts, but dry most of the 
 time. (D. T. McDougal.) 
 
 to be there. It is because these wadies are so frequented 
 by travellers that sometimes persons are drowned in them 
 by the down-rushing flood following one of the sudden 
 storms. Similar deep gullies cut by the heavy rainfalls 
 in the arid regions of the southwest United States are 
 called arroyos. (See fig. 72a.) 
 
 95. Playas.— In interior basins, that is, areas in which the 
 rivers have no outlet to the sea, there are in places broad shal- 
 low depressions, probably formed by the wind, that are covered 
 with water after a heavy rain, but from which the water is 
 
GROUNDWATER AND RIVERS 99 
 
 evaporated during the long, dry seasons. Such areas are called 
 playas, a Spanish word meaning shore or strand. A playa of this 
 kind occurs in Black Rock desert in Nevada, covering nearly a 
 thousand square miles, which in the wet season is covered with 
 water a few inches deep carried in by the Quinn River which flows 
 into it. When the water is agitated, by high winds it becomes 
 a lake of mud. During the summer season the water evaporates 
 and the area is covered with a barren clay flat. Deeper depres- 
 sions may form salt lakes. (See Chapter III.) 
 
 REFERENCES 
 
 Groundwater: 
 
 Fuller, Underground waters of the U. S., Water Supply and 
 Irrig. Papers No. 114 of the U. S. Geol. Survey. Many 
 of the other bulletins in the same series contain ex- 
 cellent articles on this subject and that of rivers. 
 Nos. 44 and 67 are especially valuable. 
 
 Schlichter, Crosby, et al, Underground Resources of Long 
 Island, Professional Paper No. 44 U. S. Geol. Survey. 
 
 Observations and Experiments on the Fluctuations in Level 
 and the Rate of Movement of Groundwater, Bull. 
 No. 5 Weather Bureau, U. S. Dept. of Agr. 
 
 Hovey, Celebrated American Caverns, Robert Clarke Co. 
 Rivers: 
 
 Russell, Rivers of North America, G. P. Putnam Sons, 1898. 
 
 Davis, Rivers and Valleys of Pennsylvania, National Geog. 
 Magazine, Vol. I, 1889. 
 
 McGee, The Flood Plains of Rivers, Forum, April, 1891. 
 
 Gannett, Profiles of Rivers, U. S. Water Supply and Irriga- 
 tion Papers, No. 44. 
 
 Gannett, The Flood of April, 1897 in the Lower Miss., Scot. 
 Geog. Mag., Vol. 13, 1897. 
 
 Powell, Exploration of the Colorado River, Washington, 1875. 
 
 Penck, Valleys and Lakes of the Alps, 8th Int. Cong. Geog- 
 raphy. 
 
 Tarr, Watkins Glen and other Gorges of the Finger Lake 
 Region, Pop. Sci. Monthly, May, 1906, Vol. 68, p. 387. 
 
 MacDougal, The Delta of the Rio Colorado, Bull, Am. Geog. 
 Soc, Jan., '06. 
 
 Cole, Delta of the St. Clair River, Mich. Geol. Surv., Vol. IX, 
 Pt. I. 
 
CHATTER III 
 LAKES 
 
 If one should take the delightful water trip from 
 Duluth, at the head of Lake Superior, to Montreal, he 
 would travel on four of the greatest lakes in the world 
 and on five different rivers, yet all the way he would fol- 
 low the natural course of the water flowing from Duluth 
 to the sea. He would actually travel over a part of one 
 great river, but the lakes are so large as to obscure the 
 importance of the comparatively small rivers flowing from 
 lake to lake. The connecting rivers St. Mary's, St. 
 Clair, Detroit and Niagara have been given separate names 
 and commonly considered separate rivers. 
 
 A lake is a body of comparatively still water, nearly 
 surrounded by land. In some localities the smaller. bodies 
 of water are called ponds. In most of the lakes the water 
 is fresh, in some it is salt, and in others alkaline. 
 
 96. Relation to Rivers.— Sometimes a lake is the head of a 
 river; more frequently it is a part of a river, occupying an ex- 
 panded portion of the valley. Generally it is so much larger, 
 wider and deeper than the river that the relation of the two is 
 not rcognized. Nearly all lakes have one or more streams flow- 
 ing into them and one (rarely two) flowing out. In most lakes 
 there is no perceptible current or flow of water as in the river. 
 
 While in a moist climate a lake may be the head of a river, 
 in an arid climate it may be the terminus of a # river. In the 
 latter case the lake will be salt or alkaline. 
 
 97. Origin of Lake Basins.— Lakes are formed in 
 many different ways: (1) Any depression (basin-like) 
 which extends below the water table on a new land area in 
 
 100 
 
LAKES 
 
 101 
 
 a moist climate will soon fill with water and form a lake. 
 Such depressions may be due to inequalities on the sea 
 bottom before the uplift, or made during the uplift, or 
 may be made subsequently by the action of the wind, such 
 as the playas already mentioned. (2) Lakes are formed 
 
 £ ; <-,«• *jL, :* Ls ; 
 
 
 
 '"' - L' 
 
 Tig. 73. Delta of the Trinity River in Galveston Bay, Texas. The delta will 
 in time extend across the bay and Turtle Bay will then be a lake and 
 later a swamp. Compare with Salton Sink in Fig. 79 where the delta 
 has cut off the end of the gulf. 
 
 by rivers on the flood-plain (a) by cutting off meanders, 
 the ox-bow lakes; or (b) by building up a natural levee 
 across the mouth of a tributary, as on the lower Ked 
 Kiver; or (c) by a tributary building an alluvial fan 
 across the main stream. (3) A river may build a delta 
 across a gulf or bay, thus forming a lake. (Figs. 73 and 79. ) 
 (4) Lakes may be formed by the warping or twisting 
 of the earth's crust (diastrophic lakes). Any bending of 
 
102 PHYSICAL GEOGRAPHY 
 
 the crust that produces a basin-like depression will result 
 in a lake in a moist climate. Lake Superior was formed 
 in part at least in this way. 
 
 The elevation of a portion of a stream valley would 
 cause a lake in the valley above the elevation, providing 
 the stream did not cut down its channel as fast as the 
 elevation took place. 
 
 (5) Lakes are formed by glaciers in several ways : (gla- 
 
 FiG. 74. View from St. Regis Mt. in the Adirondack Mountains, showing 
 numerous lakes of glacial origin. There is great irregularity in size 
 and shape. Some are due to depressions in the glacial moraine deposit, 
 others to depressions worn in the rock. (S. R. Stoddard.) 
 
 ciers are described in chapter IV) (a). The moraine forms 
 dams across a valley, especially on streams flowing 
 towards the glacier. Such are the Finger Lakes in cen- 
 tral New York, (b) The ice erodes depressions in the 
 rock which fill with water and form lakes after the re- 
 treat of the ice. (c) In a heavy moraine deposit there 
 will be many kettle-like depressions which form lakes, 
 (d) Where the water from the melting glacier flowed 
 over the edge of a cliff it scooped out a basin at the 
 foot similar to that at the bottom of Niagara Falls. Sev- 
 
LAKES 
 
 103 
 
 eral small lakes of this kind occur in the vicinity of Syra- 
 cuse, New York. (See chapter IV). 
 
 1 22' 15'. 
 
 122* 
 
 Pig. 75. Contour map of Crater Lake, Oregon. The numbers on the lake 
 represent depth of water in feet. Numbers on the contour lines in- 
 dicate feet above sea level. Maximum depth of water 1975. A caldera 
 lake, due to sinking of the center of a volcanic mountain. (U. S. Geol. 
 Survey.) 
 
 (6) Volcanoes may form lakes by streams of lava 
 flowing across a valley and thus forming a rock dam; or 
 
 FiG. 76. Cross section through Crater Lake. Section through the island 
 shown on Fig. 75. (U. S. Geol. Survey.) 
 
104 
 
 PHYSICAL GEOGRAPHY 
 
 by the subsidence of the bottom of the crater forming a 
 caldera or crater lake. (See Crater Lake sheet in the 
 U. S. Topographic Atlas, No. 2). 
 
 (7) Earthquakes sometimes cause the subsidence of 
 considerable areas which fill with water and form lakes. 
 Several such lakes were formed near the mouth of the 
 Ohio River in southeastern Missouri in 1811. Near the 
 
 Fig. 77. Reelsfoot Lake, Term., formed by subsidence of the area during 
 the earthquake of 1811. Stumps are the remains of the forest which was 
 submerged at that time. (M. L. Fuller.) 
 
 village of Lone Pine in Owen Valley, California, a lake 
 was formed by an earthquake shock in 1872. Pig. 77 shows 
 a lake formed by the Mississippi Valley earthquake in 1811. 
 (See Sec. 239.) 
 
 (8) Landslides and avalanches sometimes form dams 
 across valleys, causing lakes. In 1893 a landslide esti- 
 mated to contain about 800,000,000 tons of rock fell across 
 
LAKES 105 
 
 one of the tributaries of the Ganges River, and built a dam 
 nearly a thousand feet deep, which caused the water to 
 back up the valley about four miles, and form a lake of 
 that length. 
 
 (9) Small lakes are sometimes produced by beavers 
 building dams across the stream. Many of the "Beaver 
 Meadows" through the northern United States are the 
 
 Fig. 78. Beaver Dam seen from below. The beavers build the obstruction in 
 a stream channel which produces a lake. (U. S. Biological Survey.) 
 
 remnants of beaver dams now partly or wholly filled by 
 vegetation. (Fig. 78.) Sometimes growing vegetation be- 
 comes sufficiently dense to obstruct the stream channel and 
 produce a lake. 
 
 (10) Small lakes are sometimes formed by the chemical 
 action of the groundwater dissolving and carrying away 
 
106 
 
 PHYSICAL GEOGRAPHY 
 
 large quantities of rock material, leaving depressions that 
 fill with water and form lakes. In limestone regions such 
 depressions frequently have an opening at the bottom into 
 a cave and are called sink-holes. "When the hole at the 
 bottom of the depression becomes stopped so that the 
 water does not get through, the depression fills with 
 water, forming a small lake. In the limestone regions of 
 Kentucky and Indiana, where surface water is scarce, the 
 farmers frequently stop the opening in the bottom of the 
 sinks with clay in order to hold the water for the stock. 
 (See fig. 22, Sec. 49.) 
 
 Fig. 78a. Natural rock dam on Pucaswa River, Ontario. View looking 
 up stream. The massive rocks in the channel form part of a dyke of 
 harder material than the rocks on either side. Erosion of the softer 
 material has formed a pool or lake above the dyke and a shallow 
 channel below. 
 
 (11) Lakes or ponds of limited extent are sometimes 
 formed along stream courses where the stream crosses the 
 
LAKES 
 
 107 
 
 Fig. 79. Relief map Salton sink before it was flooded. The gulf of California 
 at one time extended northwest beyond Indio. The distributary channels 
 indicate the delta deposit. A large part of the low area north of the 
 delta is now (1907) covered with water. The S. P. R. R. was moved 
 northeast to the higher land. Compare with Pig. 73, which shows an 
 earlier stage of a similar phenomenon on a smaller scale. 
 
108 
 
 PHYSICAL GEOGRAPHY 
 
 outcropping edge of a layer of hard rock that is both over- 
 lain and underlain by softer layers. The action of the 
 weather and water wears away the softer rock faster than 
 the harder which then forms an obstruction or natural 
 dam across the stream. (Fig. 78a). 
 
 98. Some Examples of the Different Classes of Lakes: — 
 (1) Great Salt Lake and many of the other lakes in the Great 
 Basin area are remnants of lakes of the first class. Black Rock 
 desert on the Quin River in Nevada is a good example of the 
 playa, which is a lake only in the wet season, and a mud-covered 
 plain the remainder of the year. 
 
 Fig. 80. Beach of Salton Sea. Ancient beach at right. Present (1907) 
 beach at left. Intermediate stage in the center. The beach at the right 
 is 22 feet above sea level. (D. T. McDougal.) 
 
 (2) Good examples of the second class occur on the flood- 
 plains of the lower Mississippi River. Study the maps of the 
 Mississippi River Commission. (See fig. 57). 
 
 (3) Salton Sink in Southern California was at one time part 
 of the Gulf of California. The Colorado River flowed into this 
 gulf at Yuma and depositing the great mass of material eroded 
 from the canyons, it built out the enormous delta which in time 
 extended entirely across the gulf, thus cutting off the northern 
 
LAKES 
 
 109 
 
 end and forming a great salt lake. The river established a chan- 
 nel on the south side of the delta, flowing into the open gulf, but 
 sometimes during high floods part of the water would overflow 
 into the sink on the north side. (Figs. 79, 80 and 81). 
 
 The rainfall was so light on this area and the air so dry and 
 warm that evaporation took place rapidly; the lake dried up and 
 the lake bottom, formerly the gulf bottom, became a dry plain in 
 part covered with salt and lying, at the lowest point, 287 feet 
 below the sea level. 
 
 The soil covering this low plain is very productive where 
 there is sufficient water, so a few years ago an irrigating ditch 
 was dug from the river across the delta plain and the country 
 laid out in farms. 
 
 Everything prospered at first, but during a high flood the 
 river became unmanageable like an untamed horse that has sud- 
 
 Fig. 81. New River at Calexico, February, 1907. Some of the houses 
 of Mexical visible on the bluff at the left, the remainder of the town 
 was swept away by the river. (D. T. McDougal.) 
 
 denly discovered its power. The water flowing through the ditch 
 was given a much lower base than the main river, hence it be- 
 came at once a revived river and began to cut down and degrade 
 
110 
 
 PHYSICAL GEOGRAPHY 
 
 its channel. This cutting began during a flood when the open- 
 ing became so large that the engineers were unable to check it, 
 and nearly all the water of the river continued to flow through 
 the irrigating channel. 
 
 Since this inflow of waters threatened to flood all the de- 
 pressed area, the railway company whose road was being des- 
 troyed, joined forces with the irrigation company and at an 
 enormous expense completed a dam across the ditch at the river, 
 
 Fig. 82. Lakes Thun and Brienz were formerly one which was severed at 
 Interlaken by mass of sediment carried in by the two streams shown on 
 the sketch. Interlaken is built on the dividing delta. 
 
 but in a short time the river cut a new channel around the dam 
 and again (January, 1907) poured its flood of waters into the 
 sink. Another dam was completed and the river again turned 
 into its former channel. 
 
 A great cataract, nearly a mile wide and 90 to 100 feet high, 
 was formed on the lower course of the irrigating river and be- 
 fore the break was closed was cutting its way back at the rate 
 of one-third of a mile per day. 
 
 This is one of the most difficult and serious problems that 
 has ever confronted irrigating engineers. If they do not suc- 
 ceed in keeping the river in its old channel, what will be the re- 
 sult in the Salton basin? Suppose they find no means of stopping 
 the receding waterfall, what will be the result when it reaches 
 the great Laguna dam above Yuma? This dam was constructed 
 
LAKES 
 
 111 
 
 across the Colorado River at a cost of a million dollars, for pur- 
 poses of irrigation. With no interference from man, what would 
 finally become of the cataract? Why should this cataract recede 
 so much faster than Niagara Falls? 
 
 The Alpine lakes, Thun and Brienz, in Switzerland, were at 
 one time united in a single lake. Two streams flowing in from 
 opposite sides formed deltas which extended into the lake until 
 they met in the middle and thus cut the lake in two. The town 
 of Interlaken (meaning, between the lakes) is built on the 
 dividing delta. (Fig. 82.) 
 
 99. The Great Laurentian Lakes.— Upon the north- 
 ern boundary of the United States is a chain of the lar- 
 gest fresh-water lakes in the world. They formed a use- 
 ful and important highway to the Indian and the pioneer, 
 and are now serving in the same way for a great and in- 
 creasing inland commerce. The agricultural products 
 and mineral wealth of the great west find their way in 
 large quantities over these lakes to the eastern markets, 
 while products of the eastern coal fields and the great 
 factories pass westward in return. The dimensions of the 
 Great Lakes are shown in the following tabulation : 
 
 The Great Laurentian Lakes 
 
 
 Lake 
 
 Lake 
 
 Lake 
 
 Lake 
 
 Lake 
 
 
 Ontario 
 
 Erie 
 
 Huron 
 
 Michigan 
 
 Superior 
 
 Area in square miles 
 
 7,240 
 
 9,960 
 
 17,400 
 
 20,200 
 
 31,200 
 
 Length of shore line 
 
 800 
 
 590 
 
 735 
 
 875 
 
 1,300 
 
 Maximum depth 
 
 738 
 
 210 
 
 730 
 
 870 
 
 1,008 
 
 Average depth 
 
 300 
 
 70 
 
 210 
 
 335 
 
 478 
 
 Depth below sea level 
 
 491 
 
 
 149 
 
 289 
 
 406 
 
 Elevation of surface 
 
 
 
 
 
 
 above sea level 
 
 247 
 
 573 
 
 581 
 
 581 
 
 602 
 
 100. Salt lakes are formed in an interior basin which 
 has a moderate rainfall, sufficient at least to cause some 
 of the water flowing from the surrounding highlands to 
 
112 
 
 PHYSICAL GEOGRAPHY 
 
 extend as far as the lowest depression in the basin. The 
 area of snch a lake fluctuates with the seasons and the 
 climate, rising in the wet season and sinking in the dry 
 season. If the climate becomes more arid, the lake will 
 
 soo 
 
 /000 
 
 mo 
 
 Fig. 83. Diagram showing comparative depth of the Great Lakes. 
 
 decrease in size and may even disappear, leaving a deposit 
 of salt. If the climate becomes more moist, the lake will 
 increase in size until it fills the basin and overflows, when 
 the salt will be carried out and the lake become fresh. 
 
 Great Salt Lake in Utah is growing smaller and salt is being 
 deposited around the borders at present, but at one time it 
 covered a larger area in the Great Interior Basin and overflowed 
 to the north. 
 
 In early geological times there was a dry climate in central 
 New York, probably as dry as that in Utah to-day, as shown by 
 the great beds of rock salt which were formed at that time. 
 
 There are fresh water lakes in the Great Interior Basin of 
 the United States and other dry regions, but they have an out- 
 let. Salt lakes are those which have no outlet, that is, they are 
 the last basin into which the water flows and from which it 
 escapes only by evaporation. The ocean is the greatest body of 
 salt water and it is the basin into which most of the great rivers 
 of the world empty. 
 
 Salinas are salt plains, sometimes marshes, sometimes 
 dry plains, that were probably salt lakes but which have 
 dried out from change of climate or other cause. Some 
 of them are marshes at one season of the year and dry 
 salt plains at other seasons. 
 
LAKES 113 
 
 Alkaline lakes are formed similarly to salt lakes when 
 the inflowing streams carry more alkalies than salt in so- 
 lution. (See fig. 84.) 
 
 Fig. 84. An alkali lake on the Laramie plain 18 miles west of Laramie. 
 This lake has no outlet. The temporary streams flowing into the 
 lake after heavy rains carry some alkali which accumulates from 
 year to year as the water escapes by evaporation. (U. G. Cornell) 
 
 101. Fluctuations of Lake Levels.— The level of some 
 lakes varies greatly from time to time due to one or more 
 of several causes. (1) One of the most common and 
 noticeable changes in level is due to the change in season 
 from wet to dry. During the wet season the water level 
 in the lake rises from a few inches to many feet in differ- 
 ent lakes. During the dry season the level sinks a cor- 
 responding distance due to the greater evaporation, and 
 in arid districts the water may even evaporate entirely 
 from lakes that are of considerable size in a wet season. 
 
 (2) Prevailing winds sometimes produce a marked 
 effect. With a strong west wind continuing for several 
 days, the water has been known to rise as much as fifteen 
 feet at the east end of Lake Erie, with a somewhat cor- 
 responding depression at the west end. 
 
 8 
 
114 PHYSICAL GEOGRAPHY 
 
 (3) Difference in atmospheric pressure may cause a 
 temporary subsidence of the surface at one place, and ele- 
 vation at another. Thus a marked high pressure area at 
 the west end of Lake Erie might cause a sinking of the lake 
 surface there and a rise of the surface at the east end. This 
 rising and sinking of the surface is called a seiche. During 
 a seiche the water rises or sinks from a few inches to a few 
 feet. (See sees 289 and 296.) 
 
 102. How Lakes Disappear. — As already stated lakes 
 on the upland are signs of youthful topography. They 
 are short-lived in comparison with rivers, plains, moun- 
 tains and other natural features. Lakes may disappear 
 in different ways: (1) If the stream that drains the lake 
 cuts its channel deep enough it will drain the water from 
 the lake basin. The bottom of Lake Erie is at about the 
 same level as the bottom of Niagara Falls; should the 
 falls recede as far as Buffalo, Lake Erie would be drained 
 and there would be a river flowing across what is now the 
 lake bed. 
 
 (2) The streams flowing into lakes carry sediment 
 which is deposited in deltas and distributed over the lake 
 bottom until the basin is filled and the lake disappears. 
 This is one of the most active agencies in destroying lakes. 
 
 Deltas should be studied in the vicinity of the school. Where 
 permanent lakes are absent, deltas may be studied in pools formed 
 by rains. (See fig. 82.) 
 
 (3) Many lakes are slowly being destroyed by animal 
 and vegetable matter which accumulates in sufficient quan- 
 tities to fill the basin. Small molluscs, commonly known 
 as periwinkles, grow in great numbers in some of the small 
 lakes and as they die their shells accumulate on the lake 
 bed forming bodies of shell marl which occur in some 
 places fifty feet or more in depth. Marl is frequently 
 composed partly of plant remains. Vegetation grows 
 
LAKES 115 
 
 on the bottom of lakes and around the margin. In the 
 small lakes in cold climates a plant known as the sphag- 
 num or peat plant grows in great luxuriance even on top 
 of the water; the remains of this vegetation accumulates 
 on the lake bed as peat, or muck until it finally fills the 
 lake basin. Frequently the filling of the basin is due to 
 
 FlG. 85. Upper Ausable lake in the Adirondack Mountains. The lake 
 is being filled by vegetable matter. The shrubby growth at the sides 
 is on the part completely filled. The shrub area is extending towards 
 the center of the lake. The bordering forests are crowding upon the 
 shrub area. Notice the zonal arrangement of the vegetable growth. 
 Part of the bordering flat is a quaking bog. (S. R. Stoddard.) 
 
 the combined action of these two agencies. Many of the 
 peat and muck areas (vegetable) are underlain by marl 
 (animal) deposits. Hundreds of small lakes in New 
 York and elsewhere have been destroyed in this way. (Fig. 
 85.) 
 
 (4) Lakes may be destroyed by volcanic action in one 
 
116 
 
 PHYSICAL GEOGRAPHY 
 
 of two ways: (a) by material ejected from a volcano fill- 
 ing the basin; or (b) as in the case of the lake on Mount 
 Pelee, Martinique, the eruption takes place underneath 
 the lake and blows it out of existence. 
 
 (5) Winds also assist in filling lake basins by blowing 
 in sand and dust from the surrounding area. 
 
 UV*''* 
 
 Gilbert's map of glacial lake Iroquois 
 Fig. 86. The dotted line on the shaded area shows the present boundary 
 of Lake Ontario. The greater lake Iroquois drained through the Mohawk 
 valley because the glacier then filled the St. Lawrence valley and pre- 
 vented the water from flowing through that valley as it does at present. 
 
 103. Fossil Lakes. — Areas formerly covered by lakes that 
 have been filled or drained by some means, are classed as fos- 
 sil lakes, and they may be recognized by the following marks: 
 (1) By characteristic shore features or markings, such as cobble 
 or gravel beaches, or sand, gravel or wave-cut terraces. (Des- 
 cribed in Chapter VI on Shore Features) (2) By characteristic 
 lake-bed deposits such as peat, marl, diatomaceous earth, (see 
 sec. 105) and bog iron ore. Lake Iroquois at the close of the 
 glacial period, covered a large area south and east of Lake 
 Ontario, an area now bordered by shore features and covered 
 with lake-bed deposits.* (Fig. 86.) 
 
 * Fossil Lake Passaic in New Jersey is described in the Annual Report 
 New Jersey Geological Survey, 1893, and fossil Lake Agassiz, northwest of 
 Lake Superior, is described in a large monograph of the U. S. Geological 
 Survey. 
 
LAKES 
 
 117 
 
 Fig. 87. View in a gravel quarry on Fossil Lake, Iroquois beach near Wolf 
 Street in Syracuse. Notice the characteristic beach structure in the 
 gravel, the slope of the layers from right to left. The island shore line 
 was on the right. 
 
 104. Life in Lakes and Rivers.— All the rivers and 
 most of the lakes except the salt and alkaline lakes contain 
 many forms of animal and vegetable life. The animal 
 life is probably more prolific in the larger lakes and the 
 vegetable life more abundant in the smaller and shallower 
 lakes. As already stated many of the smaller lakes ter- 
 minate by being filled with the accumulated remains of 
 the animals and plants. 
 
 Some animals, such as eels and salmon spend part of 
 their existence in salt water and part in fresh; but with a 
 few exceptions of this kind, the life, both animal and plant, 
 in the rivers and lakes is decidedly different from that in 
 the sea. The life of the sea is more varied and locally more 
 prolific than in the lakes. 
 
 105. Diatoms. — There is one class of exceedingly small, 
 
118 
 
 PHYSICAL GEOGRAPHY 
 
 microscopic plants known as diatoms, that are found abundant- 
 ly in both the lakes and the ocean. The diatoms are composed 
 of opal, that is, silica, combined with water. So small are these 
 plants that a German scientist, Ehrenberg, has estimated that 
 there are about four billions of them in a cubic inch. Yet so 
 
 Fig. 88. Micro-drawing of diatoms from the mountains at Lompoc, Cal. 
 (W. F. Prouty.) 
 
 numerous are they that in some places they form deposits many 
 hundreds, even thousands of feet in thickness. The material 
 composed of diatoms is known as tripoli or diatomaceous earth. 
 It is so light and porous that it floats on water. It is used as a 
 polishing powder, as a filler for soaps, as an absorbent for nitro- 
 
LAKES 
 
 119 
 
 glycerine in making dynamite, and as fire-proof material in 
 buildings. A slippery brown material that covers the stones in 
 the brook in many places is composed of diatoms. The large 
 deposits of diatoms in California are in some places snow white, 
 in others colored by the impurities mingled with them. It is 
 estimated that an area of more than 10,000,000 square miles of 
 the sea bottom is covered with diatomaceous deposits. (See 
 figs 88 and 89.) 
 
 Fig. 89. View of mountains formed by a white diatom deposit at Lompoc, Cal. 
 The deposit composed entirely of diatom remains is more than 1000 feet 
 thick, and covers an area of many square miles. 
 
 106. Functions of Lakes.— Lakes have a number of 
 important functions which are directly or indirectly of 
 commercial importance to man in his varied industries. 
 (1) They serve as a regulator of floods. A river like the 
 St. Lawrence with many large lakes in its course is never 
 troubled with such destructive floods as visit the Ohio 
 
120 PHYSICAL GEOGRAPHY 
 
 River which has almost no lakes in its basin. The rain 
 that falls in the upper St. Lawrence basin flows into the 
 Great Lakes where it spreads out over thousands of 
 square miles of lake surface with almost no effect on the 
 Niagara or St. Lawrence rivers below, while the rain that 
 falls in the upper Ohio Valley, having no lakes in which 
 to spread, runs rapidly into the river channels causing 
 great floods. In flood season the Ohio River has been 
 known to rise 50 to 60 feet above low water while a rise 
 of half as many inches is rare in the St. Lawrence. (2) 
 They form a valuable water supply for cities. (3) They 
 serve as highways of navigation. The commerce on the 
 lakes on our northern boundary now reaches quite ex- 
 tensive proportions. (4) They form valuable fishing 
 grounds. (5) The larger lakes form excellent sites for 
 cities and the smaller ones for summer resorts. (6) They 
 temper the climate in their vicinity. (7) They furnish 
 a constant and steady supply of water to the rivers flow- 
 ing from them. .They serve as settling tanks for the 
 rivers. The waters flow in muddy, the mud settles and 
 the stream flows out clear. 
 
 107. Life History of Lakes.— Like other natural 
 phenomena, a lake has a period of growth, maturity, de- 
 cline, old age, and death, which may be termed its life- 
 history. This is not uniform but varies with different 
 classes of lakes. The greatest variation is between lakes 
 in dry and those in moist climates. In moist climates the 
 average life of the lake is not long in comparison with the 
 life of a river or mountain, but much longer than the life 
 of any animal or plant. 
 
 Lakes may come into existence in any one of the sev- 
 eral ways mentioned in the preceding pages. With the 
 exception of a very few lakes that have been blown up by 
 volcanic explosions, they are destroyed slowly by the com- 
 
LAKES 121 
 
 bined action of the different agencies previously described. 
 When a lake basin is filled, the lake disappears as a body 
 of water and the streams meander across the fertile plain 
 formed of lake deposits. In the course of time the stream 
 leading away from the old lake basin will lower its chan- 
 nel, because it now carries sediment which was formerly 
 deposited in the lake. This will cause the streams flowing 
 over the plain of the lake-filled basin, to quicken their 
 velocity and hence erode the soft materials, finally carry- 
 ing away all the deposits that filled the lake, thus destroy- 
 ing the last vestiges. The streams on the Fargo, North 
 Dakota, topographic sheet are flowing over a lake-filled 
 plain and are just beginning the work of carrying away 
 the sediment. (See figs. 47 and 48.) 
 
 The lake is thus seen to be an incident in the life of a 
 river which deposits in the lake bed the load of sediment 
 it is carrying from the mountains to the sea. At a later 
 period after having filled the lake basin, it again takes up 
 the sediment and carries it on to the next stopping place 
 and finally to the sea, the largest lake of all. 
 
 Many small lakes have a different history from the above, 
 because they have scarcely any sediment carried into them; in 
 fact, there are many small lakes that have no surface streams 
 flowing into them and either no stream or else a very small, 
 sluggish stream flowing out. (See fig. 90). Such lakes will be 
 filled in tinn by the remains of plants and animals that grow and 
 die in the lake. Such a lake forms first a swamp which later 
 becomes solid and forms a meadow or vly as it is called in the 
 region of the Adirondacks. There are no deltas, beaches, or 
 evidences of wave action in most of these small muck-and-marl- 
 filled lakes. 
 
 108. Lakes in Arid Regions.— In arid regions the life 
 history of the lake is somewhat different, being in general 
 longer and more complex than in a humid region. In an 
 enclosed basin-area the lowest depressions will have no 
 
122 
 
 PHYSICAL GEOGRAPHY 
 
 outlet and hence cannot be destroyed by draining. The 
 sediments and salts carried in and deposited, raise the 
 lake-bed, but this in turn raises the level of the water and 
 
 
 Fig. 90. Glacial lake near Pilot Harbor, Ontario. The end of 
 the lake at the left has been filled and is now covered with 
 swamp grass and shrubs. On the middle portion the forest 
 grows to the water's edge. The lake will in time be filled 
 with vegetable matter and form a meadow. 
 
 causes it to spread out over a greater area. But increased 
 area means increased evaporation and hence the lake in- 
 creases or diminishes as the case may be, until the evapo- 
 ration equals the inflow. The lake will be subject to many 
 vicissitudes with change of climate, until it finally ends 
 in one of two ways: (a) aridity may increase until the 
 lake dries up and disappears as such until there is another 
 change in climate; or (b) the humidity may increase un- 
 til the entire basin fills up and overflows when it ends as 
 any other lake in the humid region. Lakes may become 
 salt in a humid region by being depressed below sea level 
 where the sea water has access to the basin, when it be- 
 comes for a time an arm of the sea. 
 
LAKES 123 
 
 Following the glacial period, Lake Champlain was an arm 
 of the sea which extended up the St. Lawrence Valley and filled 
 the Champlain Valley 130 feet above the present level of the 
 lake. A later elevation of the land drained the lake to its 
 present level and the fresh water streams flowing into and 
 through it carried the salt to the sea, thus changing it to a fresh 
 water lake. 
 
 109. Swamps and Marshes.— Swamps are for the 
 most part closely associated with lakes and rivers and 
 are likewise a kind of connecting link between the water 
 and land areas. There are both fresh water and marine 
 marshes.* The fresh water swamps may be conveniently 
 divided into river, lake, and upland swamps. 
 
 The river swamps may be divided into terrace and 
 flood-plain swamps. The terrace swamps, sometimes 
 called hillside bogs, are formed by the outcrop on the hill- 
 side of a bed of clay, shale, or similar rock that causes a 
 continual seepage of the groundwater into the clay soil on 
 the surface. They are abundant in the bituminous coal 
 fields of the Appalachian plateau where they are caused 
 by the outcrop of the clay beds that underlie the coal 
 seams. The flood plain swamps are in great numbers on 
 nearly every river flood plain and delta as already de- 
 scribed. (See figs. 58 and 69.) 
 
 Lacustrine or lake swamps are of two classes : those 
 formed on the lake margin caused by a rise and overflow 
 of the lake or by the elevation to the surface of all or part 
 of the lake bottom through the accumulation of vegetable 
 or animal remains, such as the shell deposits which form 
 the marl. The second class, known as quaking hogs, is 
 caused in the final stages of lake-filling by vegetation, 
 when the floating plants on the surface join those growing 
 out from the shore, forming a continuous surface of vege- 
 
 * There is a tendency at present to use the word "swamp" for the fresh 
 water forms and "marshes" for the marine. 
 
124 
 
 PHYSICAL GEOGRAPHY 
 
 tation across the remnant of lake water underneath. The 
 climbing bog is formed by the vegetation drawing the 
 water by capillary attraction above the level of the lake, 
 
 Fig. 91. Climbing bog, L, lake. B, bog. PP, peat plant growing on float- 
 ing vegetable remains. M, muck accumulating on the bottom. C, 
 climbing bog. (After Shaler.) 
 
 extending the bog above and beyond the former lake- 
 shore. (See figs. 91 and 92.) 
 
 Upland swamps may be formed on clay soils by the 
 accumulation of plant remains which prevent the rapid 
 drying out of the moisture while the underlying clay re- 
 tards its descent as groundwater. Such swamps some- 
 times build up many feet above the level of the surround- 
 ing flat on which they are located, and at times after 
 
 Pig. 92. Bog and swamp formed by lake filling. DD, diatomaceous de- 
 posit. II, iron ore. PP, peat. S, swamp. B, quaking bog. 0, 
 climbing bog. W, remnant of lake not yet filled. (After Shaler.) 
 
 heavy rains, have been known to burst and flood the ad- 
 joining areas with a mass of black mud or muck formed 
 by the decaying vegetation. 
 
 110. Salt Marshes. — Besides the fresh water swamps 
 there are vast areas of salt marshes along the seaboard. 
 (See chapter on Shore Lines). Professor Shaler esti- 
 mated that there are at least 350,000 acres of marsh land 
 
LAKES 
 
 125 
 
 between New York City and Portland and that 200,000 
 acres of this could be reclaimed, drained, and made into 
 agricultural land that would have a value of $40,000,000. 
 
 111. Economic Features of Swamps and Marshes.— Swamps 
 and marshes are not entirely barren stretches. Among the 
 many economic products from them might be named the fol- 
 
 FlG. 93. Marl deposit in former lake bed at Warners, N. Y. 
 now being quarried for use in the manufacture of Portland 
 cement. (S. H. Ludlow.) 
 
 lowing: rich agricultural land after drainage, timber, peat, cran- 
 berries, tripoli, marl, phosphates, bog iron ore, regulation of 
 streams, game. What other economic products or features of 
 swamps can you name? Enumerate some of the undesirable 
 features of swamps. 
 
 FALLS AND RAPIDS 
 
 112. A stream flowing from a lake at one level to 
 another at a lower level, or in flowing from an upland to 
 a lowland valley will have rapids or falls at the abrupt 
 descents in the course. Lake Superior is 21 feet higher 
 
126 PHYSICAL GEOGRAPHY 
 
 than Lake Huron and the St. Mary's River which con- 
 nects the two descends this distance over the rapids at 
 the very outlet of Lake Superior. Lake Erie is 326 feet 
 above Lake Ontario and the connecting river descends 
 half of this distance suddenly at the falls in the Niagara 
 River and the other half mostly in the rapids above and 
 below the falls. 
 
 Falls or rapids may come into existence in a stream 
 where its course leads it over a cliff or steep slope, or they 
 may develop on a stream course which was at first uni- 
 form, providing there are one or more hard layers of rock 
 separated by softer layers all lying horizontal or inclined 
 up stream. Where the stream flows across the outcrop- 
 ping layers of the ledges, the underlying softer one will 
 be eroded more rapidly than the overlying harder one 
 which in time is undermined until the overhanging por- 
 tion breaks down of its own weight and thus causes the 
 falls to move slowly up stream. This process will con- 
 tinue until the grade of the stream brings the bottom of 
 the channel above the top of the soft layer, when the falls 
 will change to rapids, and the rapids recede until they 
 are graded and thus disappear. 
 
 113. Niagara Falls.— The Niagara River flows over 
 the Lake Erie plain from the lake to the falls where it 
 drops 160 feet into the gorge through which it flows un- 
 til it emerges on the Lake Ontario plain at Lewiston, 
 seven miles below. Above the falls the river flows over 
 the Niagara limestone which also forms the cap rock on 
 both sides of the gorge. Underlying the hard limestone 
 is a bed of softer shales which is more readily eroded by 
 the water than the hard limestone at the top. The water 
 plunging into the pool at the base, of the falls wears away 
 the softer shales and leaves the limestone projecting as 
 an overhanging ledge until it breaks off by its own weight, 
 
LAKES 
 
 127 
 
 causing the falls to recede the width of the fallen mass. 
 The repetition of the process has caused the falls to move 
 back, thus lengthening the gorge more than three hundred 
 feet since the first measurement was taken in 1842. (Study 
 figures 94 and 95, and the U. S. topographic map of Niagara 
 Falls.) 
 
 Fig. 94. Part of Niagara Falls and gorge. View from Goat Island. Notice 
 the shallowness of the water near the American shore. (E. R. Smith.) 
 
 The continuation of this process in the past has 
 caused the river to cut the gorge all the way, about seven 
 miles, from Lewiston to the present position, and if the 
 movement continues, the falls will eventually be carried 
 back to Lake Erie and the lake will be drained. How- 
 ever, it is probable that the falls will change to rapids 
 and new falls develop on higher beds before Lake Erie 
 is drained. 
 
 If the rate was uniform in the past, as at present, (about 
 
128 
 
 PHYSICAL GEOGRAPHY 
 
 five feet per year), how old are the falls now? How long will 
 it be until they reach Lake Erie at the same rate? (See the 
 contour map sheets of this region for distances.) Can you infer 
 from the diagrams showing the position of the rocks, whether 
 
 FlG. 95. Vertical section at Niagara Falls. The softer shales underneath 
 are worn away by the water. The overlying hard limestone breaks off 
 and is carried down the gorge. The repetition of this process causes 
 a recession of the falls and the lengthening of the gorge. (After 
 Gilbert. ) 
 
 the rate of recession has been increasing or decreasing, and 
 how it will be in the future? What difference would it make 
 if the Niagara limestone were near the surface of Lake Erie in- 
 stead of below the bed of the lake? 
 
LAKES 
 
 129 
 
 The rapids on the St. Mary's River will recede in time until 
 the surface of Lake Superior is lowered to, or near the level of 
 Lake Huron, but the recession will be very slow, because the 
 water flowing out of the lake carries little or no sediment and 
 hence no graving tools to cut away the rock over which it is 
 flowing. The rock being a hard sandstone is not soluble, so that 
 it cannot be carried away in solution. 
 
 114. Falls Formed by Frost.— At the Stone Quarry, 
 Falls, near Manlius, New York, there is a hard limestone 
 
 FiG. 96. Stone Quarry Falls at Manlius, N. Y. The falls pro- 
 ject into the gorge with a recession on each side. The dis- 
 integration by the frost on each side of the falls is more 
 rapid than the wear of the rocks by the water. 
 
 rock at the top of the falls underlain by shaly limestone 
 and shale similar to Niagara Falls, except that the lime- 
 stone is thicker in proportion to the shale. Here the water 
 does not undermine the limestone by wearing away the 
 softer shale but the shale projects out beyond the lime- 
 stone and forms a rounded prominence at the head of the 
 gorge over which the water descends by successive stages 
 9 
 
130 
 
 PHYSICAL GEOGRAPHY 
 
 from layer to layer. The middle and foot of the falls 
 project several feet beyond the top instead of the reverse 
 as at Niagara Falls. (See fig. 96.) 
 
 At the Stone Quarry Falls, the gorge is wider than 
 the falls and there is a recession at the head of the gorge 
 
 
 
 •*&?■ 
 
 •H$!« 
 
 
 m 
 
 
 
 ■ P*ll[PPI^B* ^^^^^j^^^""^ .Jf**:: f ., -**'- 
 
 FiG. 97. View in Havana Glen, N. Y., illustrating the effect of joint planes 
 on the direction of the stream and bordering cliffs. Near the middle of 
 the picture the stream makes a turn at right angles in changing from one 
 system of joint planes to another. 
 
 on each side of the projection under the falls. The ex- 
 planation is found in the relatively greater work of the 
 frost. Under the falls the rock is protected by the run- 
 ning water which does not freeze ; at the sides, which are 
 moistened by the spray, the frost splits off fragments, 
 causing the greater recession. Instead of erosion under 
 the falls there is even deposition at times of some carbon- 
 
LAKES 
 
 131 
 
132 
 
 PHYSICAL GEOGRAPHY 
 
 ate of lime from that held in solution by the water in the 
 stream. 
 
 In some places waterfalls recede by the splitting off 
 of blocks along the vertical joint planes. Joint planes are 
 natural planes of parting, generally vertical, that intersect 
 all rocks, but are especially prominent in some sedimentary 
 formations. Where the bottom of the cliff is eroded, the 
 overhanging portions break away along these planes and 
 fall in huge blocks leaving the smooth vertical walls of the 
 joint plane. These sometimes influence the direction of a 
 stream at the falls. (See fig. 97) 
 
 Fig. 99. Montour Falls near Watkins Glen, N. V. The water flows over a 
 prominence with a depression on each side formed mainly by action of the 
 frost. What causes the vertical face at the base of the falls ? 
 
 At Barnett Falls, Vermont, as shown in fig. 98 the 
 stream is being turned from its present course by the 
 natural cleavage planes in the rocks. There are many ex- 
 
LAKES 
 
 133 
 
 amples of falls of this kind in "Watkins and Havana Glens, 
 and elsewhere in the Finger Lake region of New York. 
 
 Other natural planes of parting in the rock sometimes 
 have an effect similar to that of joint planes. (See fig. 98.) 
 
 How many of the waterfalls that you have seen belong 
 to the Niagara type? Can you explain the origin of any 
 of the others that are of a different type? Montour Falls 
 near Watkins Glen belong to the Stone Quarry type. 
 (See fig. 99.) 
 
 Fig. 100. Tinker Falls near Tully, N. Y. The water falls from 
 the hard Tully limestone upon the softer Hamilton shales. The 
 deep recession back of the falls, 30 feet or more, is due to the 
 action of frost and other weathering agencies. 
 
 Falls and rapids may be formed in other ways than 
 those described above, but the ones mentioned are typical 
 of hundreds of similar examples scattered over New York 
 and other parts of the United States. 
 
 Waterfalls are more numerous in the Northern United 
 States than in the central and southern portions, because of the 
 action of the glacier that formerly covered the area. The gla- 
 cier by deepening and widening many of the larger valleys and 
 
134 
 
 PHYSICAL GEOGRAPHY 
 
 removing the talus material at the bottom of the hill slopes, 
 caused the smaller tributary streams to enter the main valleys 
 over cliffs, thus producing cataracts. These are characterized 
 as hanging valleys (see sec. 136). In some instances the trib- 
 utary valleys were filled by glacial debris causing the stream to 
 form a new channel. The new course of the stream frequently 
 led it over a cliff, resulting in a waterfall. 
 
 Li)-mt>akort6J 
 
 Fig. 101. Vertical section at Tinkers Falls, N. Y. The soft shale bed near 
 the middle of the section disintegrates more rapidly than the other 
 rocks and thus makes the deep notch back underneath the falls. During 
 the dry season the stream of clear water falls at L and does little 
 eroding. During high water, the larger stream carrying sediment 
 falls at H wearing away the lower end of the talus, even wearing a 
 basin in the bed rock at H. 
 
 Beaches. On many rivers like the Genesee in New York 
 and the Yellowstone in the National Park there are several 
 waterfalls separated by more or less graded reaches similar 
 
LAKES 135 
 
 to those which separate the rapids at a later period. (See 
 sec. 69). These reaches may vary in length from a few 
 inches to several miles. 
 
 115. Economic Importance of Waterfalls.— The solar 
 energy that lifts the water from the sea into the atmos- 
 phere is stored in the raindrops and this is concentrated 
 at the waterfalls in such a way that man can utilize it to 
 turn the wheels of his machinery and thus turn it into 
 mechanical energy, heat, or light. ' 
 
 In the early settlements of North America the vicinity 
 of the waterfalls was the point first selected by the 
 pioneer for his home and especially for his villages and 
 towns, because here he found the energy to run the mills, 
 to grind his corn and saw his lumber. Later when steam 
 power was discovered and utilized and the great beds of 
 coal were found in Pennsylvania and elsewhere, steam 
 was used to run the factories and the waterwheels were 
 neglected in many places. 
 
 Recent improvements in electrical appliances, by which the 
 energy in the waterfall can be cheaply transported on metallic 
 wires long distances and turned into mechanical power, heat, 
 or light as desired, emphasize again the importance of water- 
 falls, poetically called "White Coal," and the power is now being 
 used in hundreds of places. Energy from Niagara Palls is 
 carried by wire into central New York to light the cities, run 
 the cars, and furnish power for some of the factories. What 
 other falls can you name that are utilized in a similar way? 
 
 116. The Fall Line.— Along the Atlantic sea coast 
 is a coastal plain of varying width which is underlain by 
 beds of sand, clay, and gravel that are much softer than 
 the crystalline metamorphic rocks in the old Piedmont 
 belt against which they lie. The rivers flowing from the 
 hard rocks of the upland to the softer deposits of the 
 coastal plain, form falls or rapids at the point of contact. 
 Many of the streams have a deep navigable channel 
 
136 
 
 PHYSICAL GEOGRAPHY 
 
 across the plain from the falls to the sea. Naturally these 
 falls were among the first points selected by the early set- 
 tlers as sites for their villages which later grew into the 
 most important cities along the Eastern United States. 
 
 Fig. 102. Fall line on a small stream. The stream flows over 
 a bed of hard limestone in the midst of softer rocks. The 
 falls visible in the background are of the Niagara type and 
 have receded about 200 feet forming the gorge through 
 which the stream is flowing. The falls will soon change 
 to rapids. Why? (E. R. Smith.) 
 
 Besides the useful water power obtained from the falls, 
 other reasons for their selection as sites for cities were 
 the good harbors, connected by navigable water with the 
 open sea, and a good starting point, hence a good trading 
 point, for the pioneers who penetrated the interior of the 
 continent. The river valleys above the falls even where 
 not navigable, furnish the best ways for first the trail, 
 later the wagon road, and finally the railroad into the 
 

 LAKES 137 
 
 interior, and the early town thus grew into the modern 
 city. 
 
 Some of the more important cities whose sites were 
 thus determined by the waterfalls of the type mentioned 
 are Philadelphia, Baltimore, Washington, Richmond, 
 Raleigh, Columbia, and Augusta. A line drawn through 
 these cities is known as the Fall Line.* Trace out the 
 line connecting these cities on a map of the United States. 
 
 A great many prosperous manufacturing cities have 
 grown up inland around waterfalls on the streams because 
 of the valuable power obtainable for running the ma- 
 chinery. Let the class make a list of such cities. 
 
 REFERENCES 
 
 Lakes: 
 
 Russell, Lakes of North America. Ginn & Co., 1895. 
 
 Russell, Lake Lahontan, U. S. Geol. Surv. Mon., XL 
 
 Gilbert, Lake Bonneville, U. S. Geol. Surv., Mon., I. 
 
 Diller, Crater Lake, Oregon. Nat. Geog. Mag., Vol. 8, p. 33, 
 and U. S. Topographic Atlas. 
 
 Fenneman, Lakes of Southeast Wisconsin. Wis. Geol. Surv. 
 Bull. 8. 
 
 Murdock, The Great Salt Lake. Nat. Geog. Mag., Feb., 1903, 
 p. 75. 
 Swamps and Marshes: 
 
 Shaler, 6th An. Report U. S. Geol. Surv. pp. 353-398. 
 
 Shaler, 10th An. Report U. S. Geol. Surv. pp. 255-339. 
 Niagara Falls, Grabau, Bull. 45 N. Y. State Museum, 1901. 
 Niagara Falls, Gilbert, Nat. Geog. Mon., American Book Co. 
 
 * It is thought that some of the falls on this line are due to faulting in the 
 rocks. 
 
CHAPTER IV 
 GLACIERS 
 
 Switzerland has more visitors than any other country 
 of equal area in the world, due chiefly to its beautiful 
 scenery. One of the highest words of praise for the 
 picturesqueness of any portion of our own country is to 
 call it the "Switzerland of America." 
 
 One of the most attractive features of Switzerland's 
 beautiful landscapes is the occurrence of the fields' of 
 perpetual snow on the mountains sending down frozen 
 rivers towards, often into, the green fields of the valleys. 
 These streams of snow and ice, called glaciers, begin in a 
 snow field and end in a river. 
 
 117. Snow Fields.— The temperature of the atmos- 
 phere decreases rapidly in ascending from the lower to 
 the higher altitudes and latitudes. On the very high 
 mountains in the tropics, on lower mountains in the tem- 
 perate regions, and still lower elevations in the polar 
 regions, most of the precipitation is in the form of snow. 
 Where there is not sufficient warmth to melt all that falls, 
 there is an accumulation from year to year which forms 
 a snow field, — the perpetual snow of the snow-capped 
 mountains. 
 
 Small snow fields occur on a few of the higher peaks 
 of the Rocky Mountains in the United States ; larger ones 
 on the high peaks of the Sierras ; still larger ones further 
 north along the Alaskan coast ; and a much larger one 
 in Greenland. In fact, the whole area of Greenland ex- 
 cept a narrow strip along the coast, is covered with snow 
 
 138 
 
GLACIERS 
 
 139 
 
 and ice. Small snow fields occur on the higher peaks in 
 Mexico and Central America. There are snow fields, large 
 
 Fig. 103. Aletsch glacier, the longest glacier in Switzerland. The dark 
 line in the middle is the medial moraine, composed of rock fragments 
 from the distant mountains. Notice the irregular surface caused by 
 the numerous crevasses, and the deep depression on each side of the 
 glacier. (Photograph furnished by Colgate University.) 
 
140 PHYSICAL GEOGRAPHY 
 
 and small, on the higher mountains of the Alps, the 
 Pyrenees, in Scandinavia, the Himalayas, the Andes, and 
 in eastern Africa. The largest snow field in the world 
 at the present time is that on the Antarctic continent. 
 
 There is evidence that in the past there were larger 
 snow fields than at present, one of which covered a large 
 area in North America and another a large area in 
 Europe. 
 
 From Snow to Ice. If the snow continued to fall on 
 the upland regions faster than it melted and there were no 
 other escape for it, the final result would be to have all 
 the water of the oceans, lakes, and rivers piled up around 
 the poles and on the mountain tops. There is, however, 
 another escape for the snow. It gradually changes into 
 a granular mass composed of little pellets of ice, resem- 
 bling coarse salt in appearance, known as the neve. It is 
 similar to the last remnants of snow drifts in the spring. 
 In the snow field under the heat of the sun and the pres- 
 sure of the mass, this granular snow or neve is changed 
 into hard blue ice, which gradually moves or flows away 
 from the snow field. In the continental snow fields, like 
 Antarctica, the ice flows out in a continous sheet around 
 the margin, and in the smaller snow fields on the moun- 
 tain peaks the streams of ice follow the deep valleys, lead- 
 ing down the sides of the mountain. In some instances 
 there is only one ice stream or glacier from a snow field. 
 Sometimes several glaciers flow from the same field. 
 
 There is no sharp separation between a glacier and the snow 
 field which is its source. The ice that moves is properly called 
 a glacier, but the bottom portion of the snow field consists of 
 ice, most of it, probably all of it, in motion. 
 
 Many Alpine snow fields lie in amphitheatre-like basins called 
 cirques, which have been worn out of the solid rock by the ice. 
 Fig. 104 shows several cirques formed in this way from which 
 the glaciers have melted. 
 
GLACIERS 
 
 141 
 
 Classes of Glaciers. (1) A continental glacier is a 
 large field of snow and ice that covers a continent such as 
 Antarctica or a large part of a continent such as the one 
 that covered north central Europe or central North America. 
 
 FiG. 104. Cirques or snow basins in the Rocky Mountains near Ouray, Col. 
 (July, 1906.) 1, a cirque. 2, ridge of moraine, composed of rock carried 
 out of the basin. 3, another smaller cirque on the same ridge. 4, portion 
 of another cirque only the top of which is visible. 
 
 (2) The Alpine, or valley glacier, is the name given to the 
 stream of ice that flows down the mountain valleys. Gla- 
 ciers known as Piedmont are formed by the union of several 
 valley glaciers which flow out on the same plain and unite 
 into one. The Malaspina glacier in Alaska is an example. 
 Cliff glaciers form in depressions on the mountain side, 
 but do not extend down to the larger valleys. (See fig. 105.) 
 118. Glacial Conditions.— Necessary conditions for 
 forming glaciers are (1) heavy snow fall, that is, a greater 
 
142 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 105. Work of a cliff glacier in the Rocky Mountains near Ouray, Col. 
 The darker band across the light streak, just above the middle of the view 
 is a terminal moraine of a cliff glacier that occupied the cirque above it. 
 The talus cone below the moraine is composed of material carried by gravity 
 down the mountain from the moraine. The loose material (2) above the 
 moraine is mostly talus formed by frost action since the melting of the 
 glacier. 
 
 fall in the winter than will melt in the summer, and 
 (2) a cool climate with changes of temperature. In the 
 Himalaya Mountains, the glaciers on the south side, where 
 it is warmer, descend several thousand feet nearer sea 
 level than those on the north side, because of the greater 
 quantity of snow precipitated on the south slope. Changes 
 of temperature are needed both to cause precipitation 
 of moisture and to change it to ice after it has fallen. 
 
GLACIERS 143 
 
 It is warmth that causes the moisture first to find its way 
 into the atmosphere from the ocean and the moist land, 
 and second to rise to the mountain top ; it is the cold that 
 causes the precipitation in the form of snow, then the heat 
 of the sun changes the snow first to neve and finally to ice 
 and causes it to flow down the mountain. 
 
 119. Movements of the Glacier.— It was a long time 
 after the existence of glaciers was known, before it was 
 understood that the ice really moved. Even at the pres- 
 ent time there is some uncertainty as to just why and how 
 it moves, hut the fact that it does move is proven beyond 
 question. After the study of this chapter, the pupil 
 should enumerate all the points of evidence that the gla- 
 ciers move. 
 
 The rate of movement varies in different glaciers and 
 even in the same glacier at different seasons. The move- 
 ment is generally faster in a large glacier than in a small 
 one under the same conditions. It is faster in a warm 
 season than in a cold, faster in the middle than at the 
 sides, faster at the top than on the bottom, faster on the 
 outside of a curve than on the inside., faster on the 
 steeper slopes. Why? 
 
 One of the ways in which the rate of movement of 
 different portions of a glacier was determined was to put 
 a row of stakes across the ice in line with one on the rocks 
 on each side. After a few months the straight line had 
 the position shown in fig. 106. 
 
 In 1821, two men were lost in a crevasse on the Bossons 
 glacier on Mt. Blanc. Professor Forbes, who had been study- 
 ing that glacier made the statement that the remains of these 
 men would appear at the lower end of the glacier in 40 years, 
 the length of time it would take the glacier to move from the 
 crevasse to its lowest point, a distance of about one mile. In 
 1861, when the mangled remains of these men, and some of 
 the instruments carried by them appeared at the end of the 
 
144 
 
 PHYSICAL GEOGRAPHY 
 
 glacier, the forecast of Forbes was recalled and people mar- 
 veled at its accuracy. 
 
 120. Variation in Length of a Glacier.— The snow line 
 is the elevation on the mountains above which the snow 
 lies all the year, and below which it is all melted during 
 the summer season. The glacier must originate above the 
 
 B 
 
 «. & & ® e 
 
 Fig. 106. Diagram indicating one of the ways in which movement of the ice 
 in glaciers was demonstrated. A line of stakes was extended across a 
 glacier continuous with those on the bordering mountain side. At suc- 
 cessive intervals the stakes were observed in the positions shown. B 
 shows the changes in a row of stakes on the vertical side of a glacier. 
 
 snow line and as soon as it crosses that line it begins to 
 waste from melting. The distance it descends below the 
 snow line depends upon the size of the glacier, its rate of 
 movement, and the climate in which it moves. It will- 
 melt nearer the snow line in the tropics and descend 
 further below the snow line in the temperate and frigid 
 climates. 
 
 It is only in high latitudes that the glacier descends 
 as low as sea level. In temperate and tropical regions it 
 descends until the rate of melting just equals the rate of 
 advance. At this point, which is the end or terminus of 
 
GLACIERS 
 
 145 
 
 the glacier, the ice is still moving, but it is melted as fast 
 as it moves and the end of the glacier remains fixed as 
 long as the conditions remain constant. 
 
 One or more warm, dry seasons in which there is less snow- 
 fall and more melting, will cause the end of the glacier to move 
 hack up the valley and establish a new point of equilibrium in 
 accord with the new conditions. In the same way one or more 
 cool, wet seasons in which there is unusually heavy snowfall 
 and less rapid melting, will cause the end of the glacier to ad- 
 vance down the valley a greater distance until conditions are 
 again balanced. In this way the glacier serves as a good indi- 
 cator of climatic variations. With one or two exceptions all 
 the glaciers of the Alps are now retreating. In the early part 
 of the last century they were advancing. 
 
 121. Crevasses. — In the steeper parts of the chan- 
 
 PiG. 107. Snowfield and crevasses, Alpine glacier. Some of the boulders on 
 the surface fall to the bottom through the crevasses. Fresh snow some- 
 times driffs over and closes the top of a crevasse thus forming a death 
 trap for the unwary traveler who steps upon the snow and falls through 
 into the depths of the glacier. (Colgate University.) 
 10 
 
146 PHYSICAL GEOGRAPHY 
 
 nel which would correspond to the rapids and waterfalls 
 in the river, the glacier is very uneven, with many deep 
 cracks or fissures called crevasses. Below the rapids these 
 close up in part by regelation or refreezing and the ice 
 stream passes on, as above the rapids. The crevasses are 
 formed wherever there is a change in the angle of slope 
 of the channel in which it is moving, and on the outside 
 of the curve, where there is a bend in the valley. (Fig. 107.) 
 
 122. Ice Tables and Pinnacles.— A large flat rock on 
 the surface of the glacier protects the ice underneath from 
 the sun's rays so that it does not melt as rapidly as the 
 surrounding ice, the result being that the rock is finally 
 left standing on a column of ice like a pyramid. When 
 the surrounding ice is melted away several feet below the 
 rock, the sun shines underneath the capstone, melting the 
 ice on that side and the rock falls off, leaving a pinnacle 
 or needle of ice. (Will the cap rocks fall on the north 
 or south side of the pinnacle in the northern hemisphere?) 
 
 The ice tables are more apt to occur near the lower end of 
 the glacier. Why? They are more common in a dry, hot sum- 
 mer than a cold one. Why? 
 
 123. Other Surface Irregularities.— In a similar 
 manner the medial moraine protects the ice from melting 
 underneath *it ; so that it frequently forms a prominent 
 ridge of rock fragments along the middle of the glacier. 
 (See fig. 103.) 
 
 The Alpine or valley glaciers, below the snow line, flow be- 
 tween rock walls that are bare of snow in the summer season. 
 The heat, absorbed and radiated on the glacier from the rocks 
 where they receive the direct sunlight, causes the glacier to 
 melt more rapidly on the side than in the middle. Hence, in 
 crossing a glacier in such places one must ascend a hill of ice 
 before reaching the middle of the glacier. (See lower end of 
 Aletsch glacier fig. 103.) 
 
GLACIERS 147 
 
 In the narrower canyons, where the glacier and the rocks 
 bordering it do not receive the direct rays of the sun, the ice 
 may be as high or higher at the side than in the middle of 
 the glacier. 
 
 Small stones and thin patches of dust, instead of forming 
 pinnacles like the large boulders, sink into the ice and make 
 little holes called dust wells that are filled with water which 
 freezes over at night and thaws during the day. 
 
 124. Moraines. — As the glacier moves over the sur- 
 face, it scrapes off large quantities of soil and even 
 some fresh rock, especially where the underlying rock 
 projects above the surface in sharp points or ledges. Be- 
 sides the material pushed and shoved along in front of 
 and underneath the ice there is a considerable quantity 
 frozen in the lower portions of the ice. Where the 
 glacier flows along the base of a cliff, it receives all the 
 rock fragments that fall from the cliff through the action 
 of frost, gravity, and other weathering agencies. As the 
 ice is advancing slowly all the time, the material is mov- 
 ing forward, forming a band of rocky material along the 
 side of the glacier below the cliff, known as the lateral 
 moraine. Where two glaciers unite, the lateral moraines 
 at the point of junction will unite in the midst of the 
 combined glacier and form a medial or middle moraine. 
 (See fig. 103). Where there are many tributaries, there 
 may be many lines of medial moraines. 
 
 In some instances the moraines are so numerous and 
 so large as to entirely cover the surface of the ice, as is 
 the ease of the Unter Aar glacier in Switzerland. The 
 material carried in the bottom and underneath the ice 
 forms the ground moraine. Medial moraines may some- 
 times be formed of material from the ground moraine or 
 material underneath the glacier which is carried upward 
 through the glacier by an upward current in the ice until 
 
148 
 
 PHYSICAL GEOGRAPHY 
 
 it reaches the surface, forming a medial moraine or in- 
 creasing the size of the one already formed. 
 
 All the rock material carried by the ice, the medial, 
 lateral and ground moraines, is dropped at the end of the 
 glacier and there forms the terminal moraine. During 
 the retreat of the glacier if the end remains stationary 
 for a period of time, the material accumulates as in the 
 first terminal moraine, from which it may be distinguished 
 by calling it a recessional moraine or a terminal moraine 
 of recession. (See fig. 105.) 
 
 125. Special Topographic Forms of Glacial Deposit.— 
 
 PiG. 108. Till or boulder clay on Fayette Street, Syracuse, N. Y. 
 It consists of a mass of tough clay interspersed with numer- 
 ous partially rounded, striated boulders. The entire mass 
 was imbedded in the bottom of the ice or pushed along 
 underneath the glacier. 
 
 All of the material carried by the glacier is deposited 
 somewhere, some of it at the end, some of it underneath 
 the ice. That deposited at the end of the glacier, while 
 it is stationary or nearly so, forms the terminal moraine 
 
GLACIERS 
 
 149 
 
 which generally consists of irregular hills and ridges. 
 The moraine in some places consists of a single ridge, 
 while in others it occupies an area covered irregularly with 
 hills of different sizes, sometimes inclosing basin-like de- 
 pressions called kettle holes. When these are filled with 
 water they are called kettle lakes and the whole area 
 called the kettle moraine. Where the glacier retreats 
 regularly, the moraine material is distributed somewhat 
 uniformly over the area. 
 
 Drift is the name given to all the material deposited 
 by a glacier when it disappears by melting. 
 
 Till, or boulder clay, is the unsorted material of the 
 ground moraine consisting of clay, frequently blue clay, 
 interspersed with more or less sand and boulders, the latter 
 frequently striated and facetted by being rubbed against 
 other pebbles or against the bed rock. (See fig. 120a.) 
 
 A kame is a low hill of gravel and sand, partly but 
 irregularly stratified, commonly elongated transverse to 
 
 Via. 109. Kanie topography. Mendon, Monroe Co., N. Y. Kames are 
 composed of gravel and sand in irregular ridges, commonly formed in 
 crevasses near the margin of the glacier. (H. L. Fairchild.) 
 
 the direction of the ice movement. It is thought to have 
 formed in cracks or crevices in the ice near the end or 
 
150 
 
 PHYSICAL GEOGRAPHY 
 
 margin of the glacier, from materials washed in by sur- 
 face streams and the waters from the melting ice and 
 rains. 
 
 An esher is a low winding ridge of sand and gravel 
 generally elongated in the direction of the ice movement. 
 
 Fig. 110. A small esker, near Jamesville, N. T. Probably formed by ihe 
 accumulation of gravel and sand in a stream channel underneath the 
 
 It may vary from a fraction of a mile to many miles 
 in length and is probably formed by the accumula- 
 tions in a sub-glacial stream which at the time would have 
 sides and roof of ice. The esker is in general longer, 
 lower, more winding and extended in a different direction 
 from the kame. (See fig. 110.) 
 
 A drumlin is a rounded egg-shaped hill composed of 
 till or unstratified drift, commonly elongated in the direc- 
 tion of ice movement and usually about 200 or 250 feet in 
 

 GLACIERS 
 
 151 
 
 height, sometimes lower but rarely higher than that above 
 the base. Frequently there are pockets of sand and 
 gravel in the surface of the drumlin, although the greater 
 part of the outside consists of boulder clay. It is 
 
 FiG. 111. Drumlin on Euclid Avenue, Syracuse, N. Y., looking east. 
 The hill is composed of boulder clay deposited underneath the ice. 
 In this case the north end is much steeper than the south end but in 
 some drumlins the two ends are similar. 
 
 probable that the central core of many drumlins is solid 
 rock. Excavations either natural or artificial into the in- 
 terior are so few in number that there is some uncertainty 
 about drawing general conclusions regarding their inter- 
 nal structure. Drumlins are formed underneath the 
 glacier by the heaping up of the ground moraine. There 
 are scores of drumlins along the line of the Erie Canal 
 through central New York from east of Syracuse to west 
 
152 PHYSICAL GEOGRAPHY 
 
 of Rochester. They are abundant in eastern Massa- 
 chusetts, in Wisconsin and Michigan. 
 
 126. Corrading Work of Glaciers.— Glaciers are and 
 have been important geologic agents both in grinding the 
 rock surfaces and in transporting material. In corrading 
 or grinding the surface rocks, the glacier acts like a 
 
 Fig. 112. Glacial scratches (striae) on sandstone on the 
 Catskill Mountains at an elevation of 2,400 feet. (H. D. 
 McGlashan.) 
 
 coarse sandpaper pushed over the area. The continental 
 glacier that covered the Northern United States must have 
 been several thousand feet thick in many places and pushed 
 its rough-shod surface against the rocks with tremendous 
 force. 
 
 Ice weighs over 50 pounds per cubic foot, hence a 
 glacier 5,000 feet thick would press down with a force of 
 more than 250,000 pounds on every square foot, but in 
 many places the ice was 10,000 feet or more in thickness, 
 
GLACIERS 153 
 
 hence its eorrading effect on the rock surface over which 
 it moved must have been very great. 
 
 The eorrading action of the glacier is indicated by the 
 scratching, grooving, and polishing of the rocks of all kinds over 
 which it passed, and by the vast quantities of ground-up fresh 
 rock which it deposited along its course. Pulverized soil and 
 mantle rock are prevailingly yellow, brown or red in color, but 
 
 
 L^l 
 
 
 l^^fi 
 
 
 
 
 -..•■V^v^ 
 
 
 S6W Z^I^K 
 
 
 
 
 
 "■"fcifs. 
 
 
 ^Wtey^f^Q * 'tB 
 
 
 
 
 
 " 
 
 
 ""' .;*""" -■ 
 
 
 
 
 
 ;,"'"'. " : 
 
 
 
 ^^^ 
 
 
 
 
 "jjQMTCflevqH 
 
 
 h," •;'."- 2j^--- • 
 
 - ' 
 
 
 
 ; .__ 
 
 
 
 
 ■ 
 
 ^*i& 
 
 Hsj 
 
 m^HH 
 
 
 
 
 B^m^QF' 
 
 ss?jfc 
 
 rM 
 
 
 
 Hjk*>.< 
 
 MfmBSit *i»L 
 
 
 
 
 
 Fig. 113. Glacial grooves in volcanic rock on the side of 
 Uncompaghre Canyon, near Ouray, Col. Extensive areas 
 in this canyon are bare of any fragmental material and in 
 many places show the abrading action of the glacier. 
 
 ground-up fresh rock is blue. Besides the scratching and 
 grooving of the bed rock, many of the loose boulders in the 
 glacial deposit are striated, grooved, and partly rounded by 
 being rubbed against other rocks. (Where possible, study the 
 rock surface over which the ice has passed and carefully com- 
 pare boulders from the glacial deposit with those from a 
 stream channel, or from a sea or lake beach.) (Fig. 120a p. 161.) 
 The grinding action was of course not uniform over the 
 entire area. In a hilly region . the tendency would be to wear 
 away projections and make a smoother surface. The valley 
 glaciers and the ice tongues of the continental glaciers extend- 
 
154 
 
 PHYSICAL GEOGRAPHY 
 
 ing in valleys, deepen and widen the valley, making a U-shaped 
 glacial valley out of the V-shaped stream valley (fig. 114). How- 
 ever, in passing across valleys transverse to the direction of 
 movement, the tendency would be to deposit material in the 
 bottom of the valley and wear away the top of the hill, thus 
 making the surface more regular than it was before. We 
 might expect also that in passing over a hill, a glacier would 
 
 Fig. 114. A U-shaped glaciated valley near Ouray, Col. Much of the 
 material from this valley was eroded by the glacier. Glacial cirque 
 visible in background. There are three cirques at the head of the 
 valley from which the united glaciers extended down the U-shaped 
 valley in the foreground. 
 
 corrade more on the stoss or thrust side of the hill (the side 
 with which it first came in contact) than on the lee side where 
 it might even deposit material. In places, basin-shaped depres- 
 sions are scooped out in the rock which on the retreat of the 
 glacier are filled with water and become lakes. (See the Silver- 
 ton and Telluride quadrangles of the U. S. Topographic Atlas 
 where scores of these cirque lakes are shown. Fig. 115 is a view 
 in the northwest corner of the Silverton Quadrangle. See also 
 Chap. III.) 
 
 In many places in a flat region the glaciei moves over a bed 
 
GLACIERS 
 
 155 
 
 of sand or clay with almost no corrading action. In fact, in 
 many places the corrasion is just as much on the hard rock as 
 on the soft material and sometimes more. In this respect it is 
 markedly different from the corrading action of a river, which 
 always attacks the softest material first. 
 
 Fig. 115. Silver Lake Basin, near Ouray, Col. The lake in the foreground 
 is formed behind a moraine. The low dark ridge in the middle of the 
 picture is another moraine behind which is another lake similar to the 
 one in the foreground. The whole basin including both lakes is a cirque. 
 
 Over hard massive rocks the glacier frequently erodes 
 the surface in small rounded domes which at a distance re- 
 semble the backs of sheep and are called roches moutonnees 
 (rock sheep). This type of glacial erosion is common on 
 the crystalline rocks of the Canadian highlands and on the 
 granite and volcanic rocks of the Rocky and Sierra Moun- 
 tains. 
 
 Huge pot holes, sometimes 20 feet or more in depth are 
 formed in places underneath the glacier by the grinding of 
 the boulders where they were whirled about by streams de- 
 
156 PHYSICAL GEOGRAPHY 
 
 scending through a crevasse. (See fig. 116.) Glacial pot 
 holes are similar in some respects to those formed by 
 streams on the rapids. (See sec. 72.) 
 
 Fig. 116. Pot holes on grooved and striated rock surface in Glacier Garden, 
 Lucerne, Switzerland. Larger pot holes are shown elsewhere in the same 
 garden. They were formed by streams falling through the ice when the 
 glacier covered the area. (J. 0. Branner.) 
 
 Hanging Y alleys. — The glacier sometimes erodes the 
 main valley much deeper than the tributary valleys and 
 when the glaciers are melted from the area, the streams of 
 water in the tributary valleys enter the main valley over 
 a cliff, forming cataracts. Such tributaries are known as 
 hanging valleys and are common in many glaciated areas. 
 
 127. Glaciers as Transporting Agents.— The glaciers 
 are probably more important transporting agents than 
 corrading ones, since they not only carry all the material 
 they wear off the rocks over which they pass, but large 
 quantities that gain access to the glacier in other ways. 
 

 GLACIERS 157 
 
 It carries material frozen in its under surface and pushed 
 underneath and in front, subglacial material ; material on 
 the surface that falls from cliffs and mountains by which 
 
 Fig. 117. Glacial Hanging Valley in Norway. The streams 
 from the tributary valleys descend by a series of cascades 
 to the floor of the main valley which was worn down by the 
 glacier. 
 
 it passes, and that swept on its surface by avalanches and 
 otherwise — superglacial material; and that in the midst 
 of the ice between the top and the bottom, englacial ma- 
 terial. 
 
 128. The Materials Carried by Glaciers.— The glac- 
 iers carry all sizes of material from the very fine to the 
 very coarse. The coarse and fine are sometimes sorted 
 and separated by the waters associated with the melting 
 ice, but frequently they are deposited in a heterogeneous 
 mass. The bulk of the material in most glacial deposits 
 over northern United States will be found on inspection 
 to consist of rock materials that have come from an area, 
 much of it within one or two miles of the place where it 
 
158 
 
 PHYSICAL GEOGRAPHY 
 
 is deposited. A part of the deposit, however, has been 
 transported for a long distance, sometimes a hundred 
 miles or more. Through central and southern New York, 
 
 Fig. 118. A crystalline glacial boulder transported by the glacier from 
 Canada to Syracuse, N. Y. Shown as it was being moved by man to 
 the cemetery to serve as a monument. 
 
 there are a great many boulders, large and small, that 
 have been moved by the glacier from the Canadian high- 
 lands north of Lake Ontario. One of these, known as the 
 Crouse boulder, now in the cemetery at Syracuse, weighs 
 about 75 tons, and was carried by the glacier from Canada 
 to Central New York. 
 
 The large boulders are mostly carried on or in the 
 glacier and when the ice melts, the boulder is sometimes 
 left on a very insecure foundation. In such positions 
 they are called perched boulders or rocking stones. (Fig. 
 119). Boulders of disintegration that sometimes resemble 
 
GLACIERS 
 
 159 
 
 glacial rocking stones may be distinguished by noting that 
 they are the same kind of rock as that on which they are 
 perched. Fig. 120 shows a boulder of disintegration in 
 the Garden of the Gods. 
 
 Fig. 119. Perched boulder or rocking stone deposited by the glacier near 
 Greensboro, Vt. (C. H. Richardson.) 
 
 The material transported by a glacier is deposited when the 
 ice melts. As the greatest melting takes place at the lower end 
 of the glacier, there the greatest deposits will he formed. In 
 some places the material is spread somewhat evenly over the 
 surface but frequently it is deposited in the form of drumlins, 
 kames, eskers or the irregular mounds of a terminal moraine. 
 
 The drift-covered surface of a region that has been covered 
 by a continental glacier is quite different from the surface of the 
 bed rock on which the drift material rests, and both the surface 
 of the drift and the surface of the bed rock are different from 
 
160 
 
 PHYSICAL GEOGRAPHY 
 
 that of the same area before the glacier passed over it. Hence, 
 the topography of a glaciated region is characteristic and dis- 
 tinct from that of an unglaciated region. 
 
 Fig. 120. Boulder of disintegration in the Garden of the Gods, Colorado. 
 It is the remnant of a bed of sandstone ; the surrounding portions 
 have been carried away by rain and winds. It has not been trans- 
 ported from another locality like the two preceding ones. (G. H. 
 Ashley. ) 
 
 129. Icebergs. — The ice composing the glacier is dis- 
 posed of in two ways. In case of the large glaciers in 
 high latitudes, the ice stream flows into the sea and moves 
 out into the salt water until the end is broken off and 
 floats away as a large cake of ice, called an iceberg. By 
 
GLACIERS 
 
 161 
 
 FIG. 120a. Boulders of different origin. 1 and 2 glacial boulders. 3, 4, 
 and 5, boulders worn and polished by wind-blown sand on the desert. 
 6, boulder of disintegration. 7-11, boulders from a rocky beach. 
 
 the action of ocean currents, icebergs slowly drift towards 
 the equator, gradually melting as they move, until they 
 finally disappear. The largest icebergs in the southern 
 
 Fig. 121. Diagram illustrating how icebergs are formed where glaciers flow in- 
 to the sea. The end of the glacier in the sea is raised and lowered by the 
 tides and waves until it breaks off and floats away in an iceberg. 
 11 
 
162 
 
 PHYSICAL GEOGRAPHY 
 
 hemisphere come from the polar ice cap which covers the 
 Antarctic continent. In the Northern hemisphere the 
 largest ones come from the coast of Greenland. 
 
 130. Melting of Glaciers.— Outside the polar regions 
 glacial ice is disposed of by melting on the land before it 
 reaches the sea. Melting goes on along the whole length 
 of the glacier in the warm season, but is most active at 
 the lower end where the air is denser and warmer. The 
 water melting on the surface of the glacier forms streams 
 which flow along the top until they come to open cracks 
 or crevasses through which they drop to the bottom. 
 
 In the Alpine or valley glaciers, the subglacial streams gen- 
 erally unite under the ice and emerge from the end of the 
 glacier in a single stream which frequently flows from an ice 
 cave. 
 
 In the case of a continental glacier there will be many 
 streams flowing from the margin of the glacier. Where the 
 
 J 
 
 
 
 tei&flii^lB 
 
 ** , - — • '-..:' -■'"-...' ■.■•■ - '-/*\ 
 
 \ *> ,4* , ■*« ,;,. ■ v fi 
 
 
 Fig. 122. View in one of the cross glacial channels, near 
 Manlius, N. Y. The level floor of the channel, an eighth 
 of a mile in width, is bordered by limestone cliffs about 200 
 feet high. The head of the channel is visible in the distance. 
 
 land slopes away from the glacier, streams will run off through 
 every depression or valley, and the vast quantities of rock ma- 
 
GLACIERS 
 
 163 
 
 terial swept along by these streams is distributed down the 
 valleys beyond the margin of the glacier and known as valley 
 trains. In the absence of valleys, it will be spread out over the 
 plain beyond the glacier, forming a glacial apron or an overwasli 
 plain. 
 
 131. Glacial Channels.— Where the land slopes in the direc- 
 tion from which the glacier is moving, there will be an accu- 
 mulation of water in the depression at the end of the ice, form- 
 
 Fig. 123. View at the head of the channel shown in Fig. 122. 
 The former vertical cliff has been partly eroded at the top 
 and the falls are changing to rapids. 
 
 ing a lake. The water from the melting ice here mingles with 
 the water draining from the land, until it fills the depression 
 and overflows at the lowest point. In central New York, 
 where the glacier was moving south and the rivers flowing 
 north, the ice formed a dam across all the north draining val- 
 leys which then filled with water up to the lowest point in 
 the divide, when the water overflowed and often cut a deep 
 channel through into the next valley. Where the water in one 
 of these cross channels flowed over a ledge of hard rock on to a 
 softer layer, waterfalls like Niagara were formed. Some of the 
 streams near Syracuse were probably as large or even larger 
 than the Niagara River. On the further retreat of the glacier 
 
164 PHYSICAL GEOGRAPHY 
 
 the streams disappeared but the pools at the bottom of the 
 waterfalls remained as lakes in the area mentioned. 
 
 There are scores of these east and west cross-valleys formed 
 in this way across the divides between the north-flowing streams 
 in central New York. (For good examples of these cross chan- 
 nels study the Syracuse, Tully and Skaneateles sheets of the 
 contour map. See also maps, diagrams, and descriptions of 
 these channels by Professor Fairchild in the 21st Annual Report 
 of the State Geologist of New York.) (Figs. 122 and 123). 
 
 132. Glaciers Compared with Rivers.— In some ways 
 glaciers are like rivers; in others they are very much un- 
 like them. Alpine or valley glaciers resemble rivers in 
 flowing through valleys or elongated depressions in the 
 surface and along the lowest part of the valley ; in having 
 crooks and turns, and falls and rapids ; in moving faster 
 at the top than at the bottom, faster on the outside of a 
 curve than on the inside; in moving more rapidly and 
 having a rougher surface on the steeper portions of the 
 channel, namely the falls and rapids, than on the level 
 portions; in being fed by moisture precipitated from the 
 atmosphere ; in carrying this precipitated moisture to or 
 towards the sea level; in carrying vast quantities of rock 
 material from higher to lower levels. 
 
 Glaciers differ from rivers in moving much more slow- 
 ly — inches per day instead of miles. Both are fed by 
 rains and snow, but rivers are fed chiefly by rain and 
 groundwater, while glaciers are fed almost entirely by 
 snow. The source of a glacier is always a snow field; of 
 a river it is springs or a spring, a lake, or sometimes even 
 a glacier. Glaciers carry more and coarser material on 
 the surface than a river, which carries all its coarse ma- 
 terial by rolling and pushing it along the bottom. 
 
 Rivers may carry heavy loads down steep slopes, but 
 they drop the greater part of the load on the first flat, 
 while glaciers carry heavy burdens over flats and in many 
 
GLACIEKS 165 
 
 eases even up hill. The river carries most of its burden 
 during the flood season, dropping much of it with the sub- 
 sidence of the flood, while the glacier carries its burden 
 steadily along until it drops it at the end of the ice or 
 until it becomes lodged underneath the ice. Rivers wear 
 away first the softer parts of the rock over which they 
 flow, while glaciers wear away both hard and soft. Gla- 
 ciers form moraines, rivers form flood plains and deltas. 
 Rivers are frequently very important highways of com- 
 merce, while glaciers are obstructions. In what other 
 ways do glaciers and rivers resemble each other and differ 
 from each other? 
 
 Glaciers form an important part in the freshwater circula- 
 tion of the globe — a frozen portion of the circle that checks and 
 retards the rate but fortunately does not stop it entirely. 
 
 The North American Continental Glacier.— In the 
 
 geological age immediately preceding the present, a large 
 part of North America was covered with a great field of 
 snow and ice. There were three centers of accumulation 
 from which the ice moved out radially; one called the 
 Labrador center was east of Hudson Bay, another the 
 Keewatin center was directly west of Hudson Bay and 
 another known as the Cordilleran was in Western Canada. 
 From these three centers the ice spread out until it 
 covered nearly all of Canada and a large part of northern 
 United States. Many of the geographical features of this 
 area are due directly or indirectly to the action of this 
 now extinct glacier. It deepened and widened some of 
 the valleys, it filled and destroyed others, it caused the 
 shifting of many river channels. It changed the form of 
 many of the existing hills and formed some additional 
 ones. It scraped mantle rock from some places and de- 
 posited it in others. 
 
166 
 
 PHYSICAL GEOGRAPHY 
 
 What are some of the other effects produced by the North 
 American Glacier? Try to picture in your mind some of the 
 results from the movement of such a great sea of ice into this 
 
 Fig. 124. Map of North America — the ice age, showing the part covered by 
 the ice and the three centers of accumulation from which the ice moved. 
 (After Chamberlin.) 
 
 country now; its effect on the streams, lakes, hills, soil, vegeta- 
 tion, animals and man; the conditions during the advance and 
 those during the retreat or melting of the glacier. The condi- 
 
GLACIERS 167 
 
 tions several thousands of years after the melting are those we 
 have at the present time. 
 
 To produce this great glacier there was of course a change 
 in the climate, in fact, two changes, one an increase in cold to 
 produce the ice and second a warmer change to cause its melt- 
 ing and disappearance. The probable causes for these changes 
 is a topic too large for discussion here. One cause was the 
 elevation of the area to higher altitudes. Another probable 
 cause was the variation of the amount of carbon dioxide in the 
 atmosphere. (For good discussion see Geology by Chamberlin 
 and Salisbury, page 424.) 
 
 133. The Economic Effects of Glaciation.— After the 
 
 study of glacial phenomena in the preceding pages the 
 reader should draw his own inferences as to the effect of 
 the glacier on the industries of man, on the area of the 
 northern United States. The present soil is markedly 
 different from that before the passage of the glacier. Has 
 it been improved or not? In what respects? The topog- 
 raphy is quite different. Is it better or worse for man's 
 use in agriculture? For transportation? The multi- 
 tude of lakes were formed by the glacier. Are they an 
 advantage or not? How? Most of the waterfalls are 
 the result of glaciation. Are they a benefit or not ? How ? 
 Enumerate other changes caused by the glacier, stating 
 whether they have added to or detracted from the com- 
 mercial value of the region. 
 
 REFERENCES 
 
 Russell, Glaciers of North America, Ginn & Co., 1897. 
 Shaler and Davis, Glaciers, Houghton, Mifflin & Co., 1881. 
 Wright, Ice Age in North America, D. Appleton & Co., 1890. 
 Salisbury, Glacial Geology, Vol. V., Geol. Surv. N. J., 1902. 
 Chamberlin, The Rock Scorings of the Great Ice Invasion, 
 
 7th An. Report U. S. Geol. Surv., p. 155. 
 Upham, Glacial Lake Agassiz, Mon. 25, U. S. Geol. Surv. 
 Geikie, The Great Ice Age, D. Appleton & Co., N. Y., 1895. 
 Tarr, Phys. Geog. of N. Y. State, Macmillan Co., N. Y., 1902. 
 
168 
 
 PHYSICAL GEOGRAPHY 
 
 Davis, The Sculpture of Mountains by Glaciers, Scottish 
 
 Geog. Mag., Feb., 1906., p. 76. 
 Fail-child, Glacial Lake Iroquois, N. Y. State Museum, 20th 
 
 An. Report State Geol., 1900, Albany, N. Y. 
 Fairchild, Drumlins of New York, Bull. Ill, N. Y. State 
 
 Museum. 
 
CHAPTER V 
 
 THE OCEAN 
 
 A few centuries ago the ocean was an impassable bar- 
 rier to man ; now it is the greatest and best of all his high- 
 ways. Commercial products can be transported much 
 cheaper across the ocean than the same distance across the 
 continent, to say nothing of the greater ease and comfort 
 to the traveller. Two of the principal factors in bringing 
 about this change are the use of the mariner's compass 
 and the improvement in steam navigation. 
 
 134. Size of the Ocean.— The ocean is the irregular 
 body of salt water surrounding and separating the con- 
 tinents and containing, it is estimated, about 1,300 quad- 
 rillion, tons of water. It covers about 72 per cent of the 
 earth's surface, or 143,259,000 square miles, of which 
 7 per cent or 10,000,000 square miles lies on the con- 
 tinental shelf. 
 
 135. The continental shelf is the shallow margin 
 of the ocean bordering the continents. It varies in width 
 from a fraction of a mile to more than 100 miles. From 
 the outer or ocean margin of the shelf there is a steep 
 slope or descent down to the ocean depths forming the 
 sides of the basin. In other words, the ocean basins are 
 full to overflowing and the overflow extends out over the 
 border of the land areas forming an irregular belt of 
 shallow water, the continental shelf, which corresponds 
 in a way to an irregular rim of the submerged basin. 
 Owing to elevations and depressions of the earth's crust 
 the width of this shallow water zone varies greatly from 
 
 169 
 
170 
 
 PHYSICAL GEOGRAPHY 
 
 time to time. A depression of the continent causes a 
 further advance of the water on the land and the con- 
 tinental shelf is wider. An elevation of the land area 
 causes the recession of the shore line, the emergence of the 
 shallow sea bottom and the continental shelf is narrower 
 
 r-TTy— Continent 
 
 o 
 ^w Continental sh9lf 
 
 
 Ill 
 
 W/////////M 
 
 Ocean Basin 
 
 ^/y////// 
 
 W////////////A 
 
 ^z^^^^ 
 
 Fig. 125. Vertical section across a continental shelf showing its relation to 
 the continent and ocean basin. It varies from one or two to 100 miles 
 or more in width. 
 
 and the continent larger. Considerable portions of all of 
 the continents have in ages past been covered by the sea 
 and formed part of the continental shelf during their sub- 
 mergence. (See fig. 125.) 
 
 136. Mediterraneans.— Besides the open ocean there are 
 several smaller divisions partially separated from it, the largest 
 of which is the Mediterranean Sea, whose depth is nearly as 
 great as that of the great oceans. It is almost entirely sepa- 
 rated from the open sea, being connected with the Atlantic by 
 the narrow strait of Gibraltar and with the Indian ocean by the 
 Suez canal and the Red Sea. 
 
 Other mediterranean seas are the Gulf of Mexico, the Car- 
 ribbean, China, and Japan seas, the surface portions of which 
 are not as nearly surrounded by land as the Mediterranean Sea, 
 but their deep basins are surrounded by land. 
 
 137. Composition of Sea Water.— Sea water contains 
 much mineral matter in solution, the average being about 
 Sy 2 per cent but it varies considerably in different parts 
 of the ocean. The inflow of a great river like the Amazon 
 or the Mississippi, or excessive evaporation in certain local- 
 ities produces local variations in the percentage of salt. 
 About three-fourths of the mineral matter held in solution 
 
THE OCEAN 171 
 
 is sodium chloride or common salt. The remainder consists 
 largely of magnesium, calcium, and potassium salts. There 
 are minute quantities of other elements. 
 
 Chemical composition of the salts of average sea water: 
 
 Sodium chloride 77.758% 
 
 Magnesium chloride 10.878 
 
 Magnesium sulfate 4.737 
 
 Calcium sulfate 3.600 
 
 Potassium sulfate 2.465 
 
 Calcium carbonate 345 
 
 Magnesium bromide 217 
 
 100.000 
 Besides the solid salts dissolved in the sea water, there is a 
 large quantity of the gases of the atmosphere, which, like the 
 salts, vary greatly in quantity in different parts of the ocean 
 and in the same part at different times. Fishes and other animals 
 of the sea obtain the oxygen necessary for life from the sea water. 
 The carbonate of lime in the limestone beds on the land is 
 dissolved by carbonic acid in the groundwater and carried into 
 the sea in solution. When the corals and other animals se- 
 crete the lime carbonate in their skeletons or shells, the car- 
 bonic acid that was holding it in solution is set free and part of 
 it at least goes back into the atmosphere. 
 
 138. Circulation of Salts of the Ocean.— The water 
 flowing into the sea carries salts in solution, while that 
 which is evaporated is nearly pure water, which would 
 apparently cause an accumulation of salt in the ocean. 
 On the other hand, it is probable that much of the salts 
 carried to the ocean are those that were formerly taken 
 from the ocean. The great beds of rock salt in central 
 New York and elsewhere were formerly in the sea. Nearly 
 all the great beds of limestone over all the continents were 
 deposited in the sea from materials taken from the sea 
 water and are now being returned to the sea to be again 
 extracted from the solution by animals and plants to form 
 new beds of limestone over the sea bottom. Therefore, the 
 
172 
 
 PHYSICAL GEOGEAPHY 
 
 salts, like the water, circulate from the ocean to the conti- 
 nents and back, and it is not possible from our present 
 knowledge to say whether or not the sea water is becoming 
 denser. 
 
 Density of sea water varies with the temperature, the 
 composition and the pressure. There is an increase in dens- 
 ity with decrease in temperature to near the freezing point. 
 It expands and becomes lighter as it freezes. The average 
 density of the surface of the sea water at 60 degrees F. is 
 about 106. There is a slight increase in density to the 
 
 bottom due to the pres- 
 sure of the overlying 
 water. An increased per- 
 centage of salts in solu- 
 tion causes a correspond- 
 ing increase in density. 
 
 139. Sounding and 
 Dredging.— Much defi- 
 nite knowledge concern- 
 ing the sea bottom and 
 the deep portions of the 
 sea has been obtained in 
 the last half century by 
 improved methods of 
 sounding and dredging. 
 The previous explorations 
 had been in delineating 
 the shore lines of the 
 continents and islands. 
 With the adoption of 
 modern sounding lines 
 
 w 
 
 "Q- 
 
 The 
 
 ■ZT 
 
 Fig. 126. Sounding apparatus. 
 
 large ball, B, weighs several hundred and dredges, a new field 
 
 pounds and is mechanically detached q-£ investigation Was 
 from the water bottle, W, when it to 
 
 strikes the bottom of the ocean. opened, namely, the ocean 
 

 THE OCEAN 
 
 173 
 
 bottom, the study of which has given rise to the new science, 
 Oceanography. 
 
 Soundings are made with fine steel wire (why not 
 rope?) to which a sinker in the form of a heavy iron ball 
 like a cannon ball is attached in such a way that it is re- 
 leased when it 
 strikes the bottom. 
 Why are the sinkers 
 left on the bottom 
 of the ocean? Sam- 
 ples of water are 
 obtained from dif- 
 ferent depths by at- 
 taching to the wire 
 at definite intervals 
 brass tubes, called 
 water bottles, so 
 constructed that 
 they remain open in 
 descent but are au- 
 tomatically closed 
 as soon as lifting 
 begins. 
 
 The temperature 
 of the ocean deeps 
 is obtained by self- 
 recording thermome- 
 ters. These like the 
 water bottles may be 
 attached to the line 
 at different places, 
 so that a single 
 sounding may give, 
 besides the depth, 
 
 Fig. 127. Two types of dredges used in collect- 
 ing specimens of the mud and life forms 
 from the bottom of the ocean. The bag 
 is attached to a long wire from the ship, 
 and is dragged along the bottom scooping up 
 material. Some low forms of life are caught 
 in the tangles below the dredge and brought 
 to the surface in that way. 1, Chester rake 
 dredge. 2, Blake dredge. (U. S. Fish Com.) 
 
174 PHYSICAL GEOGRAPHY 
 
 samples of the water and the temperature at several differ- 
 ent places between the surface and the bottom. Moreover, 
 a sample of the bottom mud may at the same time be ob- 
 tained by collecting that which sticks to the water bottle 
 at the end of the wire. 
 
 Specimens of the bottom sediment are generally ob- 
 tained along with specimens of the life in trawls or 
 dredges, consisting of strong nets having an iron rim and 
 laden with weights. These nets when dragged along the 
 sea bottom scoop up masses of the soft mud, ooze, and 
 specimens of such forms of life as there exist. (Fig. 127.) 
 
 There is another method of sounding by means of an instru- 
 ment which records the pressure. One advantage of this 
 method lies in the fact that it can be used without stopping the 
 vessel, as it is independent of the length of line. 
 
 140. The Deeps.— Scattered over the floor of the 
 ocean basins are deep depressions — the so-called deeps or 
 anti-plateaus, which extend below the ocean bottom to 
 about the same extent that the plateaus rise above the 
 general level of the continents. 
 
 The deepest known point in the ocean is the Challenger 
 deep, 31,600 feet, near our insular possession Guam. The 
 Aldrich deep near New Zealand is 30,930; the deepest 
 sounding in the Atlantic is near Porto Rico, 27,930. The 
 Atlantic ocean is generally deeper near the sides, (15,000 
 feet to 18,000 feet) than in the middle, (9,000 to 12,000 
 feet).. The elevated area of the mid-ocean bottom is 
 called the Telegraph plateau and across it extends the 
 several Atlantic cables from North America to Europe. 
 
 The average depth of all the oceans is about 12,000 to 
 15,000 feet, which is nearly six times the average height 
 of the lands above the ocean level. It is estimated that if 
 all the continents and islands were thrown in the sea the 
 average depth would be nearly two and a half miles. 
 
THE OCEAN 175 
 
 141. Temperatures of the Ocean.— The surface of the 
 ocean is heated by the sun's rays, but these probably do 
 not produce any perceptible effect below a few hundred 
 feet. Since water, like air, grows lighter as it is heated, 
 the surface-heated waters do not sink and hence do not 
 reach the ocean bottom or any great depth in the ocean. 
 The surface water in the equatorial region is heated to 
 about 80 degrees P. At the poles it is frozen part of the 
 year and near the freezing point most of the time. Since 
 the colder water becomes heavier and sinks, all the water 
 of the polar oceans is near 28 degrees F., the freezing 
 point of salt water. As there is a slow creep of this water 
 along the ocean bottom towards the equator, the deeper 
 portions of the ocean, even in the equatorial regions, are 
 very cold. Specimens of ooze and mud brought from the 
 ocean bottom in the tropics show temperatures at or near 
 the freezing point. 
 
 The body of the ocean water has a rather uniform tem- 
 perature. Even the surface waters change but little in 
 comparison with the land temperatures, the daily change 
 of the surface rarely exceeding two or three degrees and 
 the yearly maximum range being fifteen degrees. 
 
 Soundings of the Challenger in the Atlantic ocean, 3 J /2 
 degrees south of the equator, show the following temper- 
 atures : 
 
 Surface 78 degrees Fahr. 
 
 270 feet deep 68 
 
 960 " " 50 
 
 1920 " " 41 
 
 9000 " " 36.5 
 
 15200 " " 33 
 
 The temperature of inland seas or mediterraneans is higher 
 than that of the bordering ocean at corresponding depths be- 
 cause they have no connection with the polar waters and do 
 not have a temperature at the bottom lower than that at the 
 
176 
 
 PHYSICAL GEOGRAPHY 
 
 lowest place in the strait connecting them with the open sea or 
 the coldest water formed in the winter season of the area. (See 
 fig. 128.) 
 
 CARIBBEAN SEA 
 
 ATLANTIC OCEAN 
 
 70-80° 
 
 Fig. 128. Diagram showing relation of temperatures in a mediter- 
 ranean sea to corresponding depths in the open sea. The cold 
 waters of the deep sea do not rise and hence do not pass the 
 shallow water of the connecting strait. 
 
 142. Waves. — Waves are formed on the sea or any- 
 body of water by the friction of the wind blowing across 
 it, causing the surface water to move up and down, back 
 and forth, each particle of water traversing an elliptical 
 path. Generally the backward movement equals the for- 
 ward and the water comes to rest where it started, except 
 where the waves curl and break, when the top of the wave 
 is driven forward. Where the wind continues for some 
 time in the same direction, considerable quantities of 
 water are driven forward and heaped up on the windward 
 shores. (Fig. 129.) 
 
 Fig. 129. Diagram illustrating the orbital movement of water particles in 
 waves. The water rises in front of the advancing wave and sinks after 
 the passing of the crest, each particle traversing a circular or elliptical 
 path. A B level of water at rest. C C length of wave from crest to 
 crest. D D' height of wave. 
 
THE OCEAN 
 
 177 
 
 Size of waves. The stronger the wind the larger the waves 
 that are formed. The height of the wave measured from the 
 bottom of the trough to the top of the crest, is sometimes 
 thirty feet or more, rarely reaching a height of fifty feet in the 
 open sea. The length of the wave varies from a few feet to 
 1500 feet or more, much more in the earthquake waves, and the 
 velocity varies from 20 to 60 miles an hour. The visible side of 
 the advancing wave is the front, the opposite side the back of 
 the wave. 
 
 The size of the wave increases with the density, area, and 
 depth of the water; hence the ocean waves are larger than 
 those on lakes or rivers. 
 
 Sie. 130. Breakers and surf on boulder beach. (M. S. Lovell.) 
 
 143. Breakers. — As the waves of the open sea ap- 
 proach the shore, where there is not sufficient depth of 
 water to form the front of the advancing wave the top 
 moves forward, breaks off, and falls as foam to be caught 
 by the advancing wave and carried forward until it breaks 
 again, in this way forming the so-called "breakers" along 
 the shore. It is these breakers that are so destructive to 
 
 12 
 
178 
 
 PHYSICAL GEOGRAPHY 
 
 boats and ether property. Hence, when vessels cruising 
 along the shore find a storm coming, if there is no good 
 harbor near at hand, they sail for the open sea to avoid the 
 destructive breakers of the shallow water. The white foam- 
 ing waters produced by the breakers on the shore are called 
 the surf. The turbulent waters, when not too violent, are at- 
 tractive to the surf bathers. 
 
 144. Undertow. — The undertow is a backward move- 
 ment along the bottom from the shore towards the open 
 sea. The water that is carried forward and heaped up on 
 the shore by the breakers and surf cannot return sea-ward 
 on the surface because of the incoming waves, so it flows 
 back along the bottom, forming the undertow which so 
 often proves dangerous to the surf bathers, who are 
 caught by it and carried out into deep water and drowned. 
 The fine material that is ground up by the waves on the 
 beach is carried back into the deeper water by the under- 
 tow and spread out in beds of gravel, sand, and clay which 
 may later be elevated and form part of the stratified rocks 
 of the continent. 
 
 145. Earthquake Waves.— When an earthquake shock takes 
 place beneath the bed of the sea, it sometimes causes the ele- 
 vation of the surface of the water over a large area, which 
 spreads out in long, low waves, having great velocity. As these 
 waves approach the shore, they decrease in velocity but increase 
 in height, piling up the water on the shore with great force, 
 causing at times enormous destruction of life and property. 
 
 During the disastrous earthquake that destroyed Lisbon in 
 1755, the first shock caused the people who were not killed to 
 leave their houses. Most of them assembled on the new marble 
 quay, when the sea wave, 50 feet or more in height, swept in 
 with great force, destroying nearly 60,000 people. 
 
 The great volcanic eruption and accompanying earthquake 
 shock at Krakatoa in 1883 produced sea waves that spread 
 around the world. On the coasts near the eruption, waves 70 
 feet or more in height rushed on the shore, destroying many vil- 
 
THE OCEAN 
 
 179 
 
 lages and thousands of people. So powerful were the waves 
 that a large ocean vessel was swept a mile and a half inland 
 and left there by the retreating wave. Earthquake waves are 
 sometimes wrongly called tidal waves. 
 
 146. Effects of the Waves. — (1) One of the most con- 
 spicuous effects of the waves is the modification of the 
 shore line produced by their erosive action. In this work 
 
 Pig. 131. Wave eroded shore, Maryland. The indentations are worn by the 
 waves assisted by gullies. The material is diatomaceous earth. (Maryland 
 Geological Survey.) 
 
 the common wind and storm waves are assisted by the 
 tidal and the earthquake waves. They wear away rocks 
 in some places and build up bars and reefs in others. The 
 softer rocks are worn away first, forming bays and inlets 
 between the harder rocks which form the headlands, or in 
 some cases islands. (See Chapter VI). 
 
 (2) The waves aerate the waters of the ocean by stir- 
 ring them up and thus exposing larger surfaces to the 
 action of the atmosphere; also by blowing over the crests 
 of the waves, thus inclosing the air in the waters. This 
 
180 PHYSICAL GEOGRAPHY 
 
 action serves to oxidize the decaying organic matter and 
 thns purify the waters; it also furnishes oxygen for the 
 animals living in the sea. 
 
 (3) The waves exercise enormous mechanical power, 
 part of which is utilized by man to ring the bell and blow 
 
 FlG. 132. Low tide in Bay of Fundy, near Gaspareaux River. See Fig. 
 133. (Roland Hayward, 1903.) 
 
 the whistle on the harbor buoys. This power is some- 
 times used to pump water, or open flood gates. 
 
 (4) The waves are frequently destructive to life and 
 property. During violent storms they destroy sea walls, 
 docks, lighthouses and other property on shore, and fre- 
 quently overwhelm and destroy boats. The destructive 
 effect of the waves on boats in the open sea is materially 
 lessened and often the vessel is saved by spreading a little 
 oil on the water. The disastrous effects of the waves are 
 produced by the breaking of the wave, when the top curls 
 
THE OCEAN 
 
 181 
 
 over and falls upon the boat. A little oil on the water 
 spreads rapidly even in the face of the wind, and decreases 
 the friction enough to permit the crest of the wave to 
 settle back quietly without breaking. Small boats can 
 
 Fig. 133. High tide in Bay of Fundy, same point as Fig. 132. 
 Hayward, 1903.) 
 
 (Roland 
 
 safely ride the largest waves as long as the waves do not 
 break and fall into the boat. 
 
 147. Tides and Tidal Waves.— At all points on the 
 shore of the ocean the water rises and falls twice each day. 
 It rises steadily for about six hours until it reaches its 
 highest level, high tide, and then subsides for about six 
 hours, until it reaches its lowest level, low tide, when it 
 again rises. The period of rising is not always uniform 
 with the period of falling, but the average of the sum of 
 the two is equal to 12 hours and 26 minutes. Pigs. 132 and 
 133.) 
 
182 
 
 PHYSICAL GEOGRAPHY 
 
 Twice each month the tides reach a maximum height, 
 the spring tide, and twice they reach the minimum height, 
 the neap tide. The incoming tide is called the flood tide, 
 the outgoing the ebb tide. Slack water is the interval be- 
 tween the two. 
 
 In shallow harbors the hour of departure of ocean steamers 
 is usually determined by the time of high tide, as they can then 
 float with safety over the bars and shallow places which they 
 could not pass at low tide. Finding the time when high tide will 
 occur at any place is called "establishing the port." 
 
 On the open sea the rise and fall of the tide is not percep- 
 tible, so low and broad is the wave. In bays and estuaries where 
 the tidal wave is confined and restricted, it frequently rises to 
 great heights. In the Bay of Pundy on the coast of Nova Scotia 
 
 Fig. 134. Tidal flats.— Low tide in Basin of Mines, N. S. The area is 
 covered with water at time of high tide. (S. R. Stoddard.) 
 
 the tide rises to a height of 50 feet or more. Similar high tides 
 occur in the Bristol channel. In both places the tide is not con- 
 spicuously high at the comparatively wide mouth of the bay, but 
 as the low, long wave advances up the ever-narrowing channel 
 the waters begin to pile up until they reach a maximum at or 
 near the head of the bay. (Figs. 132 and 133). 
 
 148. Tidal Wave in Rivers.— In certain places the 
 
THE OCEAN 183 
 
 tidal wave meets opposition in the current of a river and 
 at times the waters rise into a high wave commonly known 
 as the bore or eagre which rushes up the river, often with 
 high velocity, causing great destruction along the banks 
 and at times to shipping in the river. On the Amazon 
 River this tidal wave, known as the pororoca, extends for 
 several hundred miles up the river with great destruction 
 to the bordering forests. Similar waves often prove very 
 destructive to shipping on the Hoang Ho (River) in China 
 and the Seine River in France. 
 
 Tidal race. In Long Island Sound a low tide from the east 
 meets a high tide from the west at Hell Gate and six hours later 
 the conditions are reversed. At both times the water rushing 
 through the narrow channel with great velocity proved very- 
 destructive to shipping until the channel was widened by blast- 
 ing away the rocks. Such a current is called a tidal race. 
 
 A somewhat similar but more complex meeting of the tides 
 in the North Sea forms the dreaded Maelstrom off the coast of 
 Norway. 
 
 149. Cause of the Tides.— The close relation existing 
 between the time of the tides and the time of the succes- 
 sive crossings of the meridian by the moon was known 
 for a long time before it was suggested that gravitative 
 attraction was probably the cause of the tides. The at- 
 traction of the moon causes the heaping up of the waters 
 on the side towards the moon, because they are nearer and 
 because the waters respond more readily to the gravitative 
 pull than do the more rigid rocks. For the same reason 
 the waters would rise on the side opposite the moon. The 
 heaping up of the waters on opposite sides of the globe 
 causes a lowering of the waters or low tide at the inter- 
 mediate points. (See fig. 135.) 
 
 The sun also causes a tide, but so much smaller than 
 that caused by the moon that it is rarely noted except 
 
184 PHYSICAL GEOGRAPHY 
 
 when it coincides with that of the moon or is directly op- 
 posed to it. 
 
 Spring and neap tides. The sun tide coincides with the moon 
 tide when the sun and moon are in line with the earth, either 
 
 FlG. 135. Diagram showing position of the sun and moon during spring and 
 neap tides. A spring tide, the result is the same at full moon when the 
 moon is on the oposite side from the sun. B, neap tide. First quarter; 
 the result is the same at the third quarter of the moon. 
 
 on the same side, as at new moon, or on opposite sides, as at 
 full moon. The tides are then equal to the sum of the two, the 
 greatest for the month, and are called spring tides. 
 
 During the moon's quarter the sun and moon are at right 
 angles to each other from any point on the earth, when the tide 
 equals the difference between the two and hence is the lowest 
 for the month, the neap tides, which come at the first and the 
 third quarters. 
 
 Owing to the inertia of the water, it takes some time for the 
 full effect of the moon's attraction to manifest itself, so that 
 high tide is not directly underneath the moon, but some distance, 
 at times some hours behind it. This is the lag of the tides. 
 The regularity of the movement of the wave is disturbed very 
 much by the continental and insular land masses, so that in 
 many places the tidal movements become quite complex. 
 
THE OCEAN 185 
 
 150. Ocean Currents.— The very slow, almost imper- 
 ceptible movements of the ocean waters are called creep; 
 the faster but still very slow movements are called drift; 
 the faster, more conspicuous movements are called cur- 
 rents, and the more rapid currents are called streams. In 
 the waves the movement of the water is mainly up and 
 down, but in the strong wind waves where they break at 
 the top, forming the "white caps," there is a forward 
 motion at the top of the wave which is blown over and 
 driven forward by the wind. A continuation of this 
 movement, as in the belt of constant winds, would pro- 
 duce a surface current. 
 
 151. Causes of Ocean Currents.— The causes given for 
 ocean currents are winds, differences in temperature and 
 pressure, and the rotation of the earth. There is some 
 difference of opinion concerning the relative importance 
 of these. The movement of the winds is probably the most 
 important cause of all. The difference in temperature be- 
 tween the warm tropical waters and the cold polar waters 
 would cause convectional movements. The ultimate cause 
 in both cases is difference in temperature, but in the first 
 case it produces movements of the atmosphere, which in 
 turn cause movements of the water. The rotation of the 
 earth probably produces movement of the ocean waters to 
 some extent. The direction of the movements is influenced 
 by the rotation of the earth and by the outline of the con- 
 tinents. 
 
 152. Currents in the Atlantic— In the Atlantic Ocean 
 there is a current westward, in the equatorial regions, to 
 the South American coast, where part of it is deflected 
 into the South Atlantic and part north. The north 
 branch divides at the West Indies, part of it passing 
 through the Carribbean Sea and the Gulf of Mexico, 
 whence it emerges as the Gulf Stream. After joining the 
 
186 
 
 PHYSICAL GEOGRAPHY 
 
 other portion of the equatorial current east of Florida, it 
 continues northeast across the ocean as the Atlantic drift, 
 dividing again west of Europe where a portion of it con- 
 tinues northeast until it is lost in the Arctic ocean. The 
 other part of the Atlantic drift turns southward along 
 the coast of Spain and Portugal and northwest Africa, 
 
 Chart ol tile Ocean Currents. 
 
 Fig. 136. Map of ocean currents. The solid lines are warm currents; the 
 dotted lines are cold currents. Sargasso seas in each of the eddies. 
 
 until it finally joins the equatorial current to be again 
 turned westward across the Atlantic, thus completing the 
 circuit of the North Atlantic Ocean. Trace out in a 
 similar way from the map the warm currents and then 
 the cold ones of the other oceans. (Fig. 136.) 
 
 153. Sargasso Seas.— The central portion of the North At- 
 lantic, the part surrounded by the current just described, has 
 no continued movement but corresponds to the central portion 
 of a great eddy. It is called the Sargasso sea from the abun- 
 dance of the seaweed Sargassum which, because of the numerous 
 air sacs along the stem, floats on the surface of the ocean. 
 Under the combined action of the eddying waters and the shift- 
 ing winds, this floating weed accumulates in places in such dense 
 
 
THE OCEAN 187 
 
 masses as to seriously retard the progress of ships. It was part 
 of the Sargasso sea that Columbus encountered in his first voy- 
 age, where his sailors became frightened, thinking they might 
 never escape. "Where are the other sargasso seas? 
 
 154. Drift of Cold Waters.— Slow movements of the 
 ocean water are called drift or creep. There is an ex- 
 tensive creep of the cold polar waters toward the equato- 
 rial regions which appears as surface movements only in 
 high latitudes, and only locally does the movement form 
 true currents. When the south-moving cold polar waters 
 meet the north-moving warm currents or drift, they sink 
 underneath the warm waters and continue to creep 
 equatorward along the ocean bottom. Ferrel's law (see 
 index) about the movements of the atmosphere applies 
 equally well to the ocean currents. From the map show 
 or explain the relation. 
 
 155. Effects of Ocean Currents.— (1) The movement 
 into the higher latitudes of large bodies of warm water, 
 like the Gulf Stream in the Atlantic and the Japan cur- 
 rent in the Pacific, carries with it tropical heat which 
 tempers the climate in a marked degree. Likewise the 
 polar currents and the drift bring the cold of the polar 
 regions into the lower latitudes and cool the climate. 
 
 (2) Ocean currents affect navigation by hastening or 
 retarding the speed of vessels, depending upon whether 
 they are going with or against the current. Sometimes 
 they cause vessels to drift from their courses on to dan- 
 gerous coasts, when the current is toward the shore along 
 which the vessel is sailing. Because of these shifting 
 movements, often imperceptible, the navigator must use 
 extra precautions in planning his course and in getting 
 his location by astronomical observations. Nansen at- 
 tempted to reach the north pole by getting in the waters 
 drifting northward and permitting his vessel to be frozen 
 
188 PHYSICAL GEOGRAPHY 
 
 in the ice and carried along with the drift. The lack of 
 definite knowledge concerning the polar drift resulted in 
 failure to reach the pole. 
 
 (3) Ocean currents distribute plant life. The islands 
 of the sea receive seeds which have drifted from distant 
 lands. Many of the verdure-clad islands that would 
 otherwise have remained barren land have received their 
 vegetation in this way. In a similar manner, both lower 
 and higher forms of animal life have been carried long 
 distances by the ocean currents and thus introduced into 
 other lands. 
 
 (4) The transference of water from one part of the 
 ocean to another by the currents prevents stagnation and 
 makes life possible by carrying oxygen and food to the 
 different organisms. The currents are instrumental in 
 causing dense fogs by bringing cold and warm water and 
 hence cold and warm air together in large quantities. 
 
 Explain the cause of the dense fogs that occur so frequently 
 on the fishing grounds of the banks near Newfoundland. Since 
 many of the trans-Atlantic steamers pass over these banks the 
 danger of collision with the fishing vessels is greatly increased 
 by the heavy fogs. Why is London noted for its fogs? Why 
 should there be more fog at San Francisco than at Denver? 
 
 That the colder, heavier polar waters creep along the ocean 
 bottom towards the equator is shown by the low temperature 
 of the water at great depths in tropical regions. This move- 
 ment is probably universal but very slow in all oceans. The in- 
 creeping cold waters replace the warm water carried from the 
 warmer regions by evaporation, and thus complete a general 
 circulation of all the oceanic waters. 
 
 THE OCEAN FLOOR 
 
 156. Topography of the Ocean Bottom.— The broad- 
 er general features of the ocean bottom are not greatly 
 different from those of the land areas, but the details are 
 decidedly different. There are plains, plateaus, and 
 
THE OCEAN 189 
 
 mountains, but there is an almost total lack of valleys and 
 hills that mark the continental land areas. Hence if the 
 sea bottom were exposed to view one would be impressed 
 by the striking monotony of the scenery, the absence of 
 the many varied forms sculptured on the land by rainfall, 
 winds, and streams. 
 
 In places on the continental shelf where portions of the land 
 area have been recently submerged, the buried hills and valleys 
 are not entirely obliterated. 
 
 157. Materials on the Sea Bottom.— The materials 
 on the sea bottom are quite varied in different places, but 
 may be divided into those on the continental shelf and 
 those over the deep sea basins. The first would include 
 those deposited in water less than 600 feet deep and would 
 consist of gravel, sand, and mud; coral, and other organic 
 deposits, the materials of which are derived mainly from 
 the lands. 
 
 The materials eroded from the land by the rivers and 
 from the beach by the ocean waves are carried out and 
 spread over the sea bottom by the river and shore currents, 
 by the undertow and by winds which carry it as dust 
 through the atmosphere. The sand and mud are carried 
 in suspension and dragged along the bottom, while the 
 lime carbonate for the limestones is carried out in solu- 
 tion. 
 
 The mechanical sediments are generally coarser and 
 thicker within a few miles of the shore, thinning out in 
 the deeper waters. The calcareous deposits are formed 
 in the clearer waters which are comparatively free from 
 sediments. 
 
 158. Deep Sea Deposits.— The deeper portions of 
 the sea— the deep basins outside the continental shelf- 
 are covered with organic oozes and fine muds. Some of 
 the oozes are calcareous or limy, and some silicious, that 
 
190 
 
 PHYSICAL GEOGRAPHY 
 
 is, composed of silica. The most common of the calcar- 
 eous oozes, named from the prevailing forms of organic 
 remains, are the globigcrina ooze and the pteropod ooze; 
 the siliceous ones are the radiolarian ooze and the diatom 
 ooze. The first three are minute animal forms; diatoms 
 are microscopic plants of varied and beautiful forms 
 which live in both salt and fresh water. (See sec. 105, 
 chapter III.) 
 
 Fig. 137. Some of the deep sea ooze highly magnified. The minute animals 
 live at or near th surface of the sea but their remains sink to the bottom 
 where it forms ooze. A — foraminiferal ooze magnified 50 diameters 
 from depth of 11,000 feet. B — raliolarian ooze magnified 100 diameters 
 from depth of 26,850 (one of the deeps.) 
 
 The microscopic plants and animals which form the 
 different oozes, live on or near the surface of the sea and 
 as they die, their remains sink to the bottom and accumu- 
 late as the soft ooze. They live at the surface in shallow 
 water as well as in mid-ocean but there is so much other 
 material on the bottom of the shallow seas that the re- 
 mains of the microscopic organisms are generally ob- 
 scured, while in the deep sea they form the bulk of the 
 material on the bottom. 
 
 In many places around the border of the oceanic basins 
 there are extensive areas of fine muds, named from their 
 
THE OCEAN 191 
 
 color blue, red, and green. In the deepest portions of 
 the sea basins, known as the deeps, the bottom is covered 
 with a red clay, the origin of which is uncertain, but it is 
 probably formed in part at least of volcanic and meteoric 
 dust. Glauconite or green sand covers the sea bottom 
 in some places. 
 
 The greater part of the continental areas is covered with 
 rocks that were formed in the sea. Even the greatest mountain 
 ranges and the extensive plateau areas are largely composed of 
 the materials of former sea bottoms. It is quite probable that 
 portions of the present sea bottom over the continental shelf may 
 in the future become land areas not greatly different from the 
 present lands. 
 
 Most of the rock over the continents consists of sand- 
 stones, shales and limestones, the off-shore shallow water 
 deposits ; yet there are representatives of the oozes in the 
 chalk beds of England, France, and portions of the United 
 States. There are diatomaceous deposits of great extent 
 in California, and smaller deposits at Richmond, Virginia, 
 and elsewhere. 
 
 159. Stability of Sea Basins and Continents.— Despite the 
 fact that the continents are for the most part covered with sea 
 bottom deposits, there is good reason for thinking that there is 
 little or no change from sea basin to land area and vice versa. 
 The interchange has been between the continents and the con- 
 tinental shelf. At the present time the area of the continental 
 shelf is about 10,000,000 square miles. From time to time por- 
 tions of it are elevated above the sea level and added to the con- 
 tinents and portions of the continents are depressed and added 
 to the sea area. Diastrophic movements (compare first part of 
 Chapter VIII) of this kind have produced many changes in the 
 land and sea areas during the past geological ages. Through them 
 all the continents have probably been growing larger and the 
 continental shelf smaller: The ocean basins have doubtless 
 been growing deeper but not larger in area. 
 
 160. Life in the Ocean.— The life in the ocean is quite 
 varied and in places very prolific. The varying physical 
 
192 PHYSICAL GEOGRAPHY 
 
 conditions produce three rather distinct life regions: (1) 
 the continental shelf or shallow water area, (2) the bot- 
 tom of the deep sea basins, (3) the pelagic life or that on 
 the surface of the open sea. 
 
 Life on the shore and in the shallow seas. The life of 
 
 Fig. 138. Two of the larger animals of the open ocean. The upper one is a 
 grampus or whale which has been stranded on the beach. The other 
 is a bottle-nosed dolphin. (U. S. Fish Com.) 
 
 the shallow seas includes the greater part of the more 
 familiar forms such as the fishes, molluscs, crabs, lobsters, 
 corals, sea urchins, star fishes, porpoises, and seals, all in 
 great number and variety. In places there is also prolific 
 vegetable life which is necessary for the support of the 
 animal life. The shallower portions of the ocean, known 
 
THE OCEAN 
 
 193 
 
 Fig. 139. Giant squid, Port Otway, W. Patagonia. It frequents the 
 shallow water near shore in cold climates. It is a large and voracious 
 animal belonging to the same class as the devil fish. (U. S. Fish Com.) 
 13 
 
194 PHYSICAL GEOGRAPHY 
 
 as banks, such as the Grand Banks off the coast of New- 
 foundland, are frequented by vessels from distant lands 
 for the cod and other fishes which swarm here in great 
 numbers. The coral reefs, which grow only in shallow 
 water, teem with multitudes of living forms. Indeed, 
 there are few places where life is more prolific than on a 
 coral reef. The littoral or shore life includes the eel grass, 
 marsh grass, mangrove, and other plants, besides the great 
 variety of animal life. (Figs. 138 and 139.) 
 
 Deep sea life. The life on the deep ocean bottom is 
 quite meagre, consisting of a few strange and fantastic 
 forms. The conditions are unfavorable for abundance of 
 life, as it is everywhere dark, cold, — almost at the freezing- 
 point — and there is enormous pressure from the great 
 depth of water. 
 
 Despite the dreary, monotonous, and undesirable con- 
 ditions of deep sea bottom, there is a growth, scanty it is 
 true, of living forms over a considerable portion of it. 
 There is probably no vegetation, as that requires some sun- 
 light, and hence the animals of the sea bottom are de- 
 pendent for their food supply on the remains of the sur- 
 face forms which sink to the bottom. 
 
 Many of the deep sea forms, as they are brought up in 
 dredges, perish as soon as they reach the surface because of 
 the great change in pressure. At a depth of 20,000 feet there is 
 a pressure from the overlying water of over 600 tons per 
 square foot. The animals of the deep sea resist this pressure 
 in the same way that we resist the pressure of the atmosphere, 
 namely, by having a corresponding pressure on the inside. "When 
 they are somewhat suddenly released from the great external 
 pressure, before there is a proper adjustment of the internal 
 pressure, the result is generally disastrous. 
 
 Pelagic life. The life on and near the surface of the 
 open sea — the pelagic life — is nearly everywhere abundant, 
 but especially so in the tropical regions. There is a great 
 
THE OCEAN 195 
 
 variety as well as quantity of forms, varying in size from 
 the multitudes of microscopic plants and animals (see sec. 
 158) to the huge whales which feed upon them. 
 
 The floating vegetation of the sargasso seas attract many 
 forms of animal life which make it their feeding ground, 
 and they in turn form food for carnivorous forms which 
 are thus attracted. 
 
 The different forms of pelagic life, including the floating 
 vegetation, the microscopic animals, whales, fishes, and other 
 free swimming forms, are common also in the surface waters of 
 the shallow water areas of the continental shelf. The range of 
 the different species over the surface of the ocean is limited by 
 the changes in temperature and not by the depth of the water. 
 
 The great part of the pelagic life lies on or close to the sur- 
 face of the ocean, between which and the sparsely inhabited sea 
 bottom is the great bulk of the oceanic waters — dark, cold, 
 dreary, monotonous zones — great, watery desert areas, almost 
 barren of life. 
 
 161. Economic Features of the Ocean.— "Old Ocean's 
 gray and melancholy waste," like many other poetical ex- 
 pressions, is very misleading and untrue if we attempt to 
 apply it literally. It is the greatest and by far the best 
 of all our highways, which, besides being free, extends to 
 nearly every nation and serves to unite the civilized coun- 
 tries into a great commercial family. 
 
 The ocean makes the land habitable by furnishing 
 moisture and tempering the climate. It carries the 
 warmth of the tropical sun to the temperate and polar 
 regions and in turn transports the cold of the poles to- 
 wards the equator. It is the chief factor in the circula- 
 tion of moisture through the atmosphere. 
 
 An important part of the food supply of the world 
 comes from the ocean. Probably most important of all 
 are the fishes of many kinds. Make a list of the names of 
 all the fishes that you know are taken from the ocean for 
 
196 PHYSICAL GEOGRAPHY 
 
 food. Besides the fishes there are oysters, clams, lobsters, 
 crabs, shrimps, walruses, polar bears, whales, porpoises, 
 and seals. Other important products are pearls, coral, 
 sponges, shells, salt, and seaweed. In some countries sea- 
 weed is used extensively for food. What other uses has 
 it? It is estimated that the annual value of the food 
 products taken from the sea is not less than $500,000,000. 
 
 REFERENCES 
 
 Pillsbury, The Guif Stream, the Annual Report, U. S. Coast 
 Survey, 1890. 
 
 Page, Ocean Currents, Monthly Weather Review, August, 
 1902, p. 397. 
 
 Davis, Winds and Ocean Currents, Journal of School Geog- 
 raphy, Vol. II, 1898, p. 16. 
 
 Everman, Strange Fishes of the Deep Sea, The World of To- 
 Day, June and September, 1902. 
 
 Goode, Deep Sea Fishes. 
 
 Thomson, The Depths of the Sea, and the Voyage' of the 
 Challenger; Macmillan Company. 
 
 Sigsbee, Deep Sea Sounding and Dredging, Washington, D. C, 
 1880. 
 
 Tanner, Deep Sea Exploration, U. S. Fish Commission, Wash- 
 ington, D. C. 
 
 Flint, Oceanography of the Pacific, Bull. No. 55, U. S. Natl. 
 Museum. 
 
 Agassiz, Three Cruises of the Blake, 2 vols., Houghton, 
 Mifflin & Company, Boston, 1888. 
 
 Maury, Physical Geography of the Sea. 
 
 Littlehales, Marine Hydrographic Survey of the Coasts of 
 the World, 8th Rept. Int. Geog. Cong. Washington, 
 1904, p. 576. 
 
CHAPTER VI 
 SHORE LINES 
 
 162. The shore line is the line where land and sea 
 areas meet ; the line above and below which there is an 
 abrupt change in the living forms and sometimes a very 
 sudden change in the topographic forms. It is on and 
 near the shore where great numbers of plant and animal 
 remains are buried and preserved in the shore sediments, 
 hence furnishing a key to the life of the geological period. 
 Thus by studying the fossil forms in the shore deposits of 
 the past, one gains a knowledge of the life of previous 
 ages. Animals and plants living during one geological 
 period are different from those of the preceding and fol- 
 lowing periods ; hence the fossil remains in the ancient 
 shore deposits indicate the geologic age in which the de- 
 posits were formed. (See fig. 140.) 
 
 163. Topography. — The shore line has a topography 
 peculiarly its own. The bars, beaches, projections, in- 
 dentations, and deposits are in many respects different 
 from anything inland or on the sea bottom. A knowl- 
 edge of shore forms and shore features aids greatly in the 
 study of the geography of the past, the distribution of 
 land and sea areas in the past ages. 
 
 Besides the lessons taught by the shore features and de- 
 posits, there is a wonderful inspiration in standing on the shore 
 and contemplating the vastness of the ocean and the ceaseless 
 beat and roll of the waves. It appeals to man in his con- 
 templative moods in much the same degree, but in a different 
 manner from that of the grandeur of the mountains, or the soli- 
 tude of the desert. 
 
 197 
 
198 
 
 PHYSICAL GEOGRAPHY 
 
 Like the river, the mountain, the plain, and other natural 
 features, the shore line appears to follow a more or less regular 
 cycle of change and have a life history of its own. But because 
 it is more sensitive to slight changes of elevation or depression 
 and probably more subject to such changes, the shore cycle is 
 liable to be interrupted or broken so frequently that its exist- 
 
 
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 M 
 
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 5=P 
 
 
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 Ky,' 
 
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 ' "•' . 
 
 Fig. 140. Bodkin Point, Md. A buried cypress forest now being uncovered 
 by the waves. Remains of both the ancient forest and the living one are 
 being buried in the sands of the present beach to tell the story in future 
 ages. (Maryland Geological Survey.) 
 
 ence is commonly overlooked and many persons thus fail to read 
 the past history of a shore by studying its present features. Yet 
 the phenomena on any shore line, if properly interpreted, indi- 
 cate many of the changes it has undergone and will undergo. 
 
 164. Shore Erosion. — The erosion on the shore line 
 is done mostly by the waves, which erode the rocks much 
 as the rain and the streams do the upland. The corrad- 
 ing action of the waves is aided by the other weathering 
 
SHOKE LINES 
 
 199 
 
 agencies, such as the frost, wind, chemical action, plants, 
 and animals. The tides assist the wave action by lifting 
 and lowering them to new points of attack. 
 
 Fig. 141. Pacific Coast on the 17-mile drive at Monterey, Cal. Showing 
 breakers and the effect of the waves on hard rocks. Why are the rocks 
 on the beach more rounded than those out in the water ? (Detroit Pub. 
 Co.) 
 
 The active work of the waves is done mostly during a 
 storm, or by the irregular heavy earthquake (so-called 
 tidal) waves that occasionally deluge a coast. The storm 
 waves on the coast . correspond in their corrading effect to 
 the freshet in the river. 
 
 165. Effect of Storm Waves. — The work of the storm 
 waves is confined largely to a vertical range from about 
 50 feet below tide to 100 feet or so above tide. On this 
 comparatively narrow vertical belt their force is frequent- 
 
200 PHYSICAL GEOGRAPHY 
 
 ly terrific and their work is accomplished in several ways: 
 
 (1) The impact of the boulders, shingle, and sand, that 
 are picked up by the waves and hurled against the rocks 
 with great force, loosens more material from the cliff and 
 breaks and grinds up that already loosened. On the 
 Bahama Islands, blocks weighing twenty tons have been 
 hurled by the waves 125 feet from the shore and 25 feet 
 above high water. 
 
 (2) The boulders, gravel and sand torn from the cliff 
 are rolled up and down the sloping beach, being thus worn 
 smaller, while the finer material is swept back into deeper 
 water. 
 
 (3) The spray acts both mechanically and chemically. 
 On the coast of Scotland, light-house windows have been 
 broken at the height of 300 feet. The spray dashing 
 against the rocks, high above the reach of the waves, as- 
 sists in the chemical disintegration of the rock constituents. 
 
 (4) The hydrostatic pressure of the water, and the 
 compression and expansion of the air driven by the waves 
 into the crevices and caves along the shore, are agents of 
 disintegration. 
 
 166. Tidal Waves.— True tidal waves are not very powerful 
 eroding agents on the open shore, but in bays, estuaries, and 
 river channels they are often quite active. The bore or pororoca 
 of the Amazon, the mascaret of the Seine, and similar waves 
 in other rivers, are great tidal waves which sweep with high 
 velocity up the river channel, destroying and tearing away the 
 material along the banks, proving destructive to boats on the 
 river as well as to property on the shore. The so-called tidal 
 wave that destroyed so much property and flooded such ex- 
 tensive land areas at Galveston in 1902 was produced by the 
 hurricane which it accompanied and was in no way related to 
 the tide. 
 
 167. Earthquake Waves.— Sometimes a coast or a 
 portion of a coast is visited by a large and very destruc- 
 
SHORE LINES 
 
 201 
 
 tive wave frequently but wrongly called a tidal wave, as 
 it in nearly all eases accompanies an earthquake or vol- 
 canic disturbance. Such waves are not destructive on 
 the open sea, where they pass as low waves of great length 
 and often unperceived; but as they approach the shore 
 
 Fig. 142. Shore of Lake Ontario, near Oswego, N. Y. A wave-cut cliff which 
 is being undercut and pushed back by the eroding and undermining action 
 of the waves. (Oliphant.) 
 
 and drag the bottom, the water begins to pile up and rush 
 in on the shore in an overwhelming flood that causes 
 enormous loss of life and property and frequently modi- 
 fies the shore-line beyond recognition. 
 
 168. Transportation and Deposition Along the Shore. 
 — The volume of water that is carried in on the shore on 
 the crest of the waves is returned along the bottom in the 
 
202 
 
 PHYSICAL GEOGRAPHY 
 
 undertow which carries back with it the fine material 
 formed by the grinding of the shingle on the beach. This 
 
 material is carried out from the beach and deposited, in 
 the order of the size of the fragments, with the coarsest 
 
SHORE LINES 
 
 203 
 
 nearest the shore and the finest farthest out. Where there 
 are currents at or near the shore, they affect the distribu- 
 tion of the material by moving it along the beach or car- 
 rying it further out in the sea. 
 
 Besides that carried out by the undertow and the cur- 
 rents, there is frequently a movement of material along 
 the beach by the waves and the shore currents produced 
 by the waves where they strike the shore obliquely. It is 
 in this way that bars, cusps, spits, hooks, and wall beaches 
 are formed. (See sections 171 to 173.) 
 
 169. Topographic and Structural Features of Shore 
 lines. — Where the waves beat against a rocky shore, they 
 
 Pig. 144. Diagram showing a wave-cut and wave-built terrace on the shore 
 line. Dotted line A, position of the former shore. B, the portion of the 
 land cut away by the waves. C, the wave-cut terrace. D, the wave-built 
 terrace composed of the fragments worn from the cliff by the waves and 
 carried back by the undertow. 
 
 cut away the rocks near the water-line and the shore-line 
 is carried into the land by the wearing away of the rocks, 
 forming the wave-cut terrace. As the terrace is cut back 
 into higher land the latter is undermined and a vertical 
 or overhanging shore cliff is formed, that recedes as the 
 water undercuts, by the upper portion falling down, to 
 be ground up and carried away. 
 
 The material ground up by the waves at the base of 
 the cliff is carried back into deeper water by the under- 
 
204 
 
 PHYSICAL GEOGRAPHY 
 
 Pig. 145. A chimney rock formed by Shore erosion, Port- 
 land, England. A remnant left by the wearing away 
 of the surrounding rocks by the waves. 
 
 tow and deposited beyond the edge of the wave-cut ter- 
 race, making the wave-built terrace. ( See figs 142 to 144. ) 
 Chimney Rocks. As the waves and the gravel beach 
 cut into the rock cliff, some portions of it are left stand- 
 
 
SHORE LINES 205 
 
 ing, while the waves cut down and carry away the material 
 on all sides. These remnants commonly include portions 
 between joint-planes and are generally for that reason 
 quite angular, sometimes rectangular. From their form 
 they are commonly called chimney rocks (See fig. 145.) 
 
 Fig. 146. Remnant of a sea cave in a chimney rock on the California 
 coast, near San Diego. (J. C. Branner.) 
 
 Effect of dikes on the shore line. Sometimes an intrusive dike 
 of igneous rock (see sec. 236) is more resisting to the weather 
 than the surrounding rock which, crumbling away more rapidly, 
 leaves the dike standing above the surface often like a great 
 row of cord-wood jutting out on the beach, sometimes out into 
 the water. In other places the igneous dike weathers more 
 rapidly than the surrounding rock, and thus forms great chasms 
 extending back into the cliff where the dike material has been 
 torn out by the waves. Sometimes a chasm of this kind is cut 
 across a headland, separating the end from the mainland and 
 thus forming an island. There is one place on the north shore 
 of Lake Superior where from a boat one may see fourteen of 
 these dark-colored dikes cutting the light-colored granite rock 
 within a distance of less than a mile. 
 
 In some places on a narrow neck of land the bottom portion 
 is cut through first, leaving the upper portion standing as a 
 
206 
 
 PHYSICAL GEOGKAPHY 
 
 natural bridge. Several such bridges occur on the coast of Cal- 
 ifornia. (See figs. 146 and 148). 
 
 170. Sea Caves. — Sea caves are formed when the 
 waves undercut the cliff more rapidly at one point. They 
 commonly begin at a soft place in the rock, a fissure, or a 
 
 Fig. 147. Deep chasm formed by a dike of igneous rock disintegrating 
 more rapidly than the harder wall rock. This chasm on the shore of a 
 small lake in the Adirondacks was not formed by the waves but is 
 similar to many that were so formed along the shores of the Great 
 Lakes and the ocean. (S. R. Stoddard.) 
 
 joint-plane. Generally such caves are not very long, be- 
 cause as soon as the opening is made, the inrushing wave 
 blocks the mouth of the cave, when the air is compressed 
 and acts as a cushion to protect the rocks within from the 
 blow of the wave. The compression of the air and the 
 sudden expansion when the wave recedes may tear loose 
 some blocks and thus enlarge the cave. Sometimes the 
 
SHORE LINES 
 
 207 
 
 land side of the cave is worn away, leaving a natural bridge 
 on the shore. (See figs 148 and 149.) 
 
 IIG. 148. Natural bridge formed by action of the waves on the shore of the 
 Pacific near Santa Cruz, Cal. The top of the bridge is part of the uplifted 
 coastal plain that borders the shore. (J. C. Branner.) 
 
 Fig. 149. Shore of the Pacific Ocean at La Jolla, Cal., showing sea caves and 
 other evidences of wave erosion. (J. C. Branner.) 
 
208 
 
 PHYSICAL GEOGRAPHY 
 
 Whistling caves and blow holes are formed in the sea caves, 
 where an opening occurs in the roof that permits the escape of 
 the imprisoned air, which rushes out often with great violence, 
 producing a noise something like a steam whistle. Sometimes 
 these caves are so shaped that not only the air but a column of 
 water is forced out through an opening at the top, forming the 
 spouting cave. (Fig. 150). 
 
 Fig. 150. Spouting Cave in the ice on the shore of Lake Ontario at Oswego, 
 N. Y. Somewhat similar caves occur in the rocks in places on the ocean 
 shore. (M. S. Lovell.) 
 
 171. The Beach. — The beach varies in character at 
 different points. In the smaller coves on the headlands 
 and on the bold, rocky shores, there are great accumula- 
 tions of boulders and gravel. At the head of larger bays 
 and along low, shores the beach is covered with sand or 
 mud. The character of the material on the beach largely 
 depends upon whether there is a shore cliff, the kind of rock 
 in the cliff, the shape of the cliff, the form of the shore 
 adjoining the cliff, and the direction of the winds. 
 
SHORE LINES 
 
 209 
 
 The shingle beaches are formed at the base of rock 
 cliffs where the fragments from the cliff are ground up 
 by the waves. Where the incoming waves strike the shin- 
 gle beach obliquely, the material is moved along the beach 
 beyond the end of the cliff, forming the wall beach or 
 travelling beach, which frequently extends across the mouth 
 cf a stream and forms a lake or causes the stream to shift 
 its course beyond the end of the shingle wall. The wall 
 beach is formed wherever the material is eroded from the 
 cliff faster than it is carried back into deep water. 
 
 Fifi. 151. A hooked sand spit at Dutch Point on Lake Michigan. (U. S. 
 Geol. Survey. ) 
 
 172. Spit, Hook. — Winds and shore currents trans- 
 fer materials along the beach, and frequently, where there 
 is a bend in the shore or a change of direction, the shore 
 current may be deflected out into deep water and the 
 beach accumulation be extended out from the shore as a 
 point or arm, which is known as a spit. When the point 
 is recurved it forms a hook, or hooked spit. The curving 
 
 14 
 
210 
 
 PHYSICAL GEOGRAPHY 
 
 of the hook is commonly due to the action of another cur- 
 rent at an angle to the first one. The second current may 
 be temporary, due to a violent storm; and after it ceases, 
 the spit may continue in the direction first taken until it 
 meets another storm, where another hook may form, mak- 
 ing in this way a series of hooks or barbs on the same spit. 
 Spits are also formed in quiet waters between two cur- 
 rents which carry sediment. (Figs. 151 and 152.) 
 
 
 Fig. 152. A sand spit forming a bar across mouth of Floyd's Creek, Mary- 
 land. (Maryland Geological Survey.) 
 
 173. Bars. — The spit may form at the headland at 
 the opening of a bay, or it may form along the sides of a 
 bay. In time, if it is not checked by a strong river or 
 tidal current through the bay, it may extend entirely 
 across; joining the land on the opposite side, when it is 
 called a bar, sometimes a bay bar to distinguish it from 
 bars formed in other ways. 
 
SHORE LINES 
 
 211 
 
 Small islands along a shore are frequently tied or joined to 
 the shore by a bar which may have started as a spit from the 
 
 FlG. 153. Tie-bars connecting the mainland of Italy with Monte Argen- 
 tario Island. (See Boston Bay, Mass., Sheet U. S. Top. Atlas for 
 similar example on New England Coast. ) 
 
 island or from the shore or from both places. There may be 
 either one or two, sometimes more of these bars tying the island 
 to the shore. They are formed where the islands lie near shore 
 
212 
 
 PHYSICAL GEOGRAPHY 
 
 and there is sufficient rock waste from them. They are some- 
 times called tie-bars because they tie the island to the shore. 
 
 174. Barriers.— Where there is a stretch of shallow 
 water off shore, there is sometimes a violent agitation of 
 the bottom sand and mud by waves which form the break- 
 ers at some distance out from the shore. The meeting, 
 in these muddy waters, of the waves from the sea on one 
 
 Fig. 154. Shore of Lake Champlain, Valcour, N. Y. Sand beach, ueacb. 
 vegetation, small sand barrier, lagoon and long sand spit or cuspate 
 foreland. (H. M. Brock.) 
 
 side and the undertow from the land on the other side, 
 checks the velocity of each, causes a deposit, and builds 
 up an off-shore ridge or bar, which in time reaches the 
 surface, above which it is built by the waves and wind. 
 Such an off-shore bar is called a barrier. The shallow 
 water or lagoon behind the barrier is in time filled by the 
 sediment carried in by the rivers, the sand and dust car- 
 ried in by the winds, both aided materially by the accu- 
 
SHORE LINES 
 
 213 
 
 mulations of vegetable and animal matter. After the 
 filling of the lagoon, the former barrier becomes the beach 
 of the new shore line and another barrier develops, in this 
 way extending the land area into the sea. A barrier beach 
 is formed where the water is too shallow for the waves to 
 attack the shore. (For description of the coral barrier 
 reef see sec. 181). 
 
 175. Shore Terraces. — Terraces are formed along the 
 
 Fig. 155. Sand terraces on the north shore of Lake Superior. Drawn 
 to scale from barometric measurements by the author. The terraces 
 are known to the Indians as "Manabozho's stair steps." 
 
 shore, by the elevations of the land which carry the first 
 beach above high water and expose a new surface on 
 which another beach is formed. The elevated beaches 
 form in some places boulder terraces, in others sand or 
 gravel terraces, in others bed-rock or wave-cut terraces. 
 (See figs 155 and 155a.) 
 
 176. Irregular Shore Lines.— An irregular shore line 
 is generally caused by a migration of the shore line land- 
 ward, due either to subsidence of the land area or to the 
 erosive action of the waves. The beating of the waves on 
 a new shore 'line will first wear away the softer rocks, or 
 the more exposed ones, forming indentations or bays, with 
 
214 
 
 PHYSICAL GEOGRAPHY 
 
 the harder rocks standing out as headlands and promon- 
 tories. Irregularities in the rocks on the headlands cause 
 caves, natural bridges, chimney rocks and islands. (See 
 figs. 156, 157, 146, 148 and 149!) 
 
 
 
 i*'iG. 155a. Shore terraces on the mountain bordering Great Salt Lake, 
 Utah. The terraces mark former shore lines of the extinct Lake Bonne- 
 ville. Notice the desert vegetation in the foreground. Salt Lake 
 visible in the background on the right. (D. T. McDougal. ) 
 
 The most irregular shore lines are produced by the sinking 
 of the land and the advance of the sea, in which case the sea 
 extends up the valleys, sometimes long distances,, forming bays, 
 estuaries or fiords, that is, drowned valleys. The hills bordering 
 the valleys form headlands on the submerged area. What were 
 monadnocks and peaks before submergence, become islands along 
 
SHOKE LINES 
 
 215 
 
 the new shore. In the drowning of the lower portion of the 
 valleys the rivers are dismembered and the tributaries flow di- 
 rectly into the arm of the sea. (Study the Boothbay sheet of 
 the U. S. Top. Atlas.) 
 
 Fig. 156. Irregular shore on the Oregon coast, formed by wave erosion. The 
 more resistant rocks form the headlands and islands, which are the 
 remnants of the land area cut away on each side by the waves. (J. E. 
 Kirkwood.) 
 
 177. Regular Shore Lines.— Regular shore lines are 
 formed in several ways: (1) By the uplift of the land, 
 which causes the shore line to move seaward from the old 
 land border on to the newly uplifted coastal plain, pro- 
 ducing a quite regular coast-line. This regularity of shore 
 line is due to the smoothness of the sea bottom. 
 
 (2) By the building of sand reefs parallel to the 
 shore, causing a movement of the shore outward to the 
 
216 
 
 PHYSICAL GEOGRAPHY 
 
SHORE LINES 217 
 
 reef. This filling in of the lagoon and marshes inside the 
 bar, removes the inequalities. 
 
 (3) By the waves cutting off the headlands and filling 
 up the bays, thus making a more regular coast line. 
 
 (4) By delta deposits at the mouth of a river flowing 
 into a bay finally filling the bay and thus straightening 
 that portion of the coast. The extension of the bay-bars 
 across the bay and the tie-bars between the islands and 
 the mainland tend to straighten the coast line. 
 
 SHORE LINES MODIFIED BY LIVING FORMS 
 
 The shore line is sometimes greatly modified by the 
 accumulation of organic matter, both vegetable and ani- 
 mal. . 
 
 178. Vegetable. — In tropical regions one of the most 
 important plants that affect the shore line is the Mangrove 
 tree, one of the very few trees that flourishes in salt water. 
 The seed often sprouts while still attached to the branch, 
 and sends forth a long radicle or root stem which fre- 
 quently extends to the mud at the bottom, takes root and 
 from the top a new stem or trunk is formed. Prom the 
 trunk many spreading roots extend to the bottom, and many 
 branches form at the top, some extending downward to 
 start new roots and new trunks, until a single parent tree 
 is surrounded by a small grove. Some of the fruit drops 
 off and floats away on the water with the long radicle ex- 
 tending towards the bottom until it finally becomes at- 
 tached to the bottom mud and starts a new tree and a new 
 grove. 
 
 The network of roots catches and holds drift material 
 and mud, until a solid embankment is built up. The shal- 
 low lagoon between it and the mainland in time fills with 
 accumulated vegetable and animal matter and mud de- 
 
218 PHYSICAL GEOGRAPHY 
 
 posits. A continuation of this process extends the shore 
 line seaward wherever the building up is faster than the 
 destruction by the waves. The shore plain built in this 
 way is apt to be wet and marshy. The mangrove is very 
 abundant on the coast of Florida. ( See fig. 158. ) 
 
 Fig. 158. Mangrove trees on the shore of a lagoon at low tide. Gilbert Group 
 of coral islands in the Pacific Ocean. The area is covered by the sea at 
 high tide. (U. 8. Fish Com.) 
 
 Eel and marsh grass. The mangrove does not grow north of 
 Florida, but the low-lying plains bordering the shallow water 
 along the northern shore of the United States are extended sea- 
 ward in a somewhat similar manner by another kind of vegeta- 
 tion. The eel grass grows over the shallow bottom below low 
 tide, where it acts as a trap to catch the mud stirred up by the 
 waves, until the bottom is raised to low tide surface-level, when 
 the marsh grass takes possession and aids in the upbuilding 
 process up to or sometimes above high tide. The repetition of 
 this process causes the extension of the marsh grass plains 
 seaward. 
 
 179. Coral. — One of the most prominent of all the 
 land builders along the shores is the coral polyp, an ani- 
 
SHORE LINES 
 
 219 
 
 mal which secretes carbonate of lime that it extracts from 
 sea water. It grows in such multitudes that even though 
 a single coral polyp secretes but a small quantity of lime 
 
 1 
 
 fitter * 
 
 
 3$^ 
 
 
 *;'~d'*&$'- 
 
 Fig. 159. A coral colony showing the polyps opened. The polyps 
 somewhat resemble flowers. (Smith. Inst.) 
 
 the aggregate is something astounding. The Great Bar- 
 rier Reef off the coast of Australia is more than 1,000 
 miles long and contains a mass of limestone probably 
 
220 PHYSICAL GEOGRAPHY 
 
 equal to any of the great limestone beds extending through 
 the central and eastern United States. 
 
 The reef-building coral flourishes only in tropical seas where 
 the winter temperature of the waters does not fall below 68 de- 
 grees F. It does not grow above the surface of the salt water 
 at low tide nor at depths greater than one hundred feet. It does 
 
 Fig. 160. Coral Head or Mushroom. Beach north of Hepuhepuama, 
 Makemo atoll, in the Pacific Ocean. (U. S. Fish Com.) 
 
 not grow in muddy waters, hence is not found at the mouths of 
 rivers. It grows best in waters that are violently agitated by 
 the waves and currents, hence, it is not found in great abun- 
 dance inside the atolls, but flourishes on the outside in the midst 
 of the surf and breakers. The reason for this is that it needs a 
 constant supply of food, oxygen, and carbonate of lime, which 
 is soon exhausted in the lagoon, but is constantly renewed by the 
 moving waters in the breakers. 
 
SHORE LINES 
 
 221 
 
 Thick coral beds. While the coral does not grow at 
 depths greater than 100 feet, some of the reefs appear to 
 be several thousand feet deep ; at least the dredge brings 
 up dead coral from that depth off the shore of the reefs. 
 This is accounted for in two ways : ( 1 ) The coral grow- 
 ing outward from the reef at the top forms overhanging 
 masses which break off from their weight or are broken 
 off by the waves and slide down the steeply inclined 
 sea-bottom into the deep water; or (2) the bottom sub- 
 sides as the coral is growing and the coral that grows 
 
 Fig. 161. Illustrating the development of an atoll from a fring- 
 ing coral reef. ss, former sea level. F, fringing reef. 
 s' s', subsequent level of the sea after sinking of the island. 
 BB, barrier reef, s" s", sea level after further subsidence 
 when AA is a coral atoll surrounding a lagoon. (Darwin.) 
 
 near the surface is carried down into deep waters by the 
 sinking of the bottom. This may continue indefinitely 
 without killing the coral at the top, providing the sinking 
 does not take place more rapidly than the coral grows. It 
 may be slower, but not faster. (See fig. 161.) 
 
 180. Coral reefs.— The coral deposits attached to the 
 shore form fringing reefs, such as those on the Bahama 
 Islands. Those that occur out from the shore at dis- 
 tances varying from a fraction of a mile to several miles, 
 form barrier reefs, such as the keys off the coast of Flor- 
 
222 
 
 PHYSICAL GEOGRAPHY 
 
 ida. Such reefs are separated from the mainland by a 
 lagoon which is frequently deep enough for a ship channel. 
 By subsidence of the island a fringing reef may be- 
 come a barrier reef and in time an atoll, or circular reef 
 inclosing a body of salt water or lagoon. Atolls may al- 
 so be formed by coral growth on the rim of an extinct 
 volcano or on any sea bottom less than 100 feet deep. 
 Whitsunday, Caroline and many other islands in the Pa- 
 cific are atolls. (See fig. 162.) 
 
 Fig. 162. Portion of Pinaki Atoll and barrier reef. Paumotu group, 
 Pacific Ocean. The semi- circular light band of breakers marks the 
 position of the barrier reef surrounding the atoll. (U. S. Fish Com.) 
 
 181. Fossil Reefs.— There are fossil coral reefs in the 
 limestone beds at Syracuse, New York, at the falls of the 
 Ohio River at Louisville, Kentucky, at Chicago, Illinois, 
 and many other places in the United States, signifying 
 that these areas were at one time covered by the sea, with 
 conditions favorable to coral growth. What does this in- 
 dicate regarding the climate of central and northern United 
 States in times past ? 
 
 
SHORE LINES 
 
 223 
 
 182. Limestone from Other Animals than Coral.— 
 
 Growing in the same waters with the corals, is a great 
 variety of other animals and plants, many of which secrete 
 carbonate of lime, while others deposit silica. Such are 
 
 *mr—** 
 
 -;. 
 
 :>' 
 
 
 ►at, 
 
 
 Fig. 163. Shell beach, Lagoon of Pinaki, Paumotu group, Pacific 
 Ocean. The beach is composed of shells of mollusks which in 
 time will form a bed of limestone similar to many that now 
 occur on the continents. (U. S. Fish Com.) 
 
 the different kinds of molluscs, crinoids and sponges. 
 There are also many microscopic forms. The aggregate 
 remains of the multitude of different forms are mingled 
 with the corals in the formation of the coral limestone 
 beds. In many places extensive beds of limestone or sili- 
 cious rock are formed by the molluscs and other forms of 
 life without any reef -building coral. (Fig. 163.) The 
 
224 PHYSICAL GEOGRAPHY 
 
 coquina limestone now forming in this way along the Flor- 
 ida coast is used to some extent for building stone. 
 
 183. Lake Shores. — Lake shore lines are similar to 
 ocean shore lines in many ways. The lake waves are 
 neither so large nor so strong as the ocean waves, hence 
 the erosion is not so rapid. The water, except that in 
 the salt lakes, is not so dense, hence sediment is not car- 
 ried as freely as in the salt waters. In the northern lati- 
 tudes the lakes, except a few of the largest ones, freeze 
 over in the winter season, and are not subject to active 
 erosion on the shore by the winter winds. The ice, while 
 protecting the shore from the winds, becomes an active 
 agent of erosion in itself. The expansion of the ice due to 
 changes in temperature causes it to push against the shore 
 with great force. When the frozen surface is broken up by 
 warm weather the blocks are driven on the shore by storm 
 winds. 
 
 There is no coral in fresh water, and most of the other forms 
 of life common in the ocean do not occur in the lakes, which 
 have a fauna and flora of their own. In the larger lakes the 
 living forms affect the shore life very little; but in many small 
 lakes, vegetation accumulates along the shore and forms marshy 
 plains which in time cover the whole lake basin. Some of the 
 small lakes are bordered by plains composed of marl, which con- 
 sists of the remains of animals and plants that grew in the lake 
 in sufficient quantities to partly, sometimes entirely, fill it. 
 
 184. Fossil Shore Lines.— How may we recognize a 
 former shore line after the body of water which caused 
 it has disappeared? Many of the features explained on 
 the preceding pages are characteristic of shores and not 
 found elsewhere ; hence a recognition of these features 
 means the recognition of a former shore line. 
 
 North of Lake Superior, at different elevations on the hills, 
 are boulder beaches similar to those at the water's edge to-day. 
 At other points are the wave-built sand-terraces, similar to those 
 
SHORE LINES 
 
 225 
 
 forming on the present shore. These old beaches are at differ- 
 ent elevations above the lake, some less than one hundred, some 
 more than three hundred feet above the water. (See fig. 155.) 
 
 Fig. 164. Chazy limestone, Chazy, N. Y. Showing the fossil shells, that 
 are the remains of animals buried in the mud in the margin of the 
 shallow sea that covered that area millions of years ago. (H. M. Brock.) 
 
 Along the coast of California in several places are wave-cut 
 terraces many feet above the sea, indicating a recent elevation 
 of the land that carried the former shore line high above the sea- 
 level. (See fig. 148.) 
 
 Besides the cobble beaches and sand terraces, other shore 
 features that may often be recognized on fossil lakes are wave- 
 cut cliffs, terraces, bars, spits, hooks and deltas. 
 
 Examples. Surrounding Great Salt Lake, in places 
 some miles from the lake, is a prominent shore line, or 
 rather a series of them indicating the levels of a former 
 great lake which has been called Lake Bonneville. (See 
 fig. 155a.) 
 
 Lake Agassiz in central North America, Lake Passaic 
 
 15 
 
226 
 
 PHYSICAL GEOGRAPHY 
 
 in New Jersey, and Lake Iroquois in New York are other 
 fossil lakes which have been recognized by their shore 
 lines. (See fig. 86.) 
 
 FlG. 165. Fossil boulder beach on north side of Adirondack Mountains, Covey 
 Hill, Canada, 480 feet above tide. Similar boulder beaches bordered by 
 shore cliffs occur at lower levels. (H. M. Brock.) 
 
 185. Sand Dunes. — On sandy shores where the pre- 
 vailing winds are from the water, the sand forms great 
 ridges or dunes, varying in height from a few feet to sev- 
 eral hundred feet. In an open country the sand ridges 
 are generally formed at right angles to the direction of 
 the winds. Where there are local obstructions, the small 
 dunes are parallel with the direction of the winds. The 
 blowing inland of the sand from the shore often aids ma- 
 terially the cutting back of the shore line by the waves. 
 
 On the coast of southwestern France the prevailing west 
 winds have blown the sand inland, forming dunes several miles 
 in width, which have covered farms and villages as they were 
 
SHORE LINES 227 
 
 driven forward by the winds. The further progress of these 
 dunes has been checked by planting trees over and in front of 
 them, which in some places not only stop the drifting dunes but 
 even form productive forests. (Fig. 167.) 
 
 Fig. 166. Sand dune at Biggs, Oregon, covered with wind ripples. Which, 
 way was the wind blowing that formed the dune ? Notice the alluvial 
 terraces in the background. (U. S. Geol. Survey.) 
 
 The eastern and southern shores of Lake Michigan contain 
 many sand dunes of great size, which have in places made in- 
 roads on the fertile farm land. Attempts have been made to 
 check their further progress by the growth of grass and trees. 
 Similar but smaller dunes occur in large numbers in New York 
 State at the east end of Lake Ontario. They are very abundant 
 in many places along the Atlantic coast, especially in the Caro- 
 linas. 
 
 Sand dunes vary greatly in height. On the coast of Holland 
 some are two hundred and sixty feet; on Cat island, one of the 
 Bahamas, nearly four hundred feet; and on the western coast of 
 Africa near Cape Bajador, more than five hundred feet high. 
 
 Sand dunes are also common features on many sandy areas 
 
228 
 
 PHYSICAL GEOGRAPHY 
 
 remote from and independent of shore lines. They are very 
 abundant in desert and semi-arid areas and along many river 
 flood plains in humid areas. (See fig. 222.) 
 
 Fig. 167. Diagram showing method of checking drifting sand. A solid 
 barrier, A, causes a dune in front of it. An open but rigid barrier, B, 
 causes the dune to form in and finally over it. An open flexible barrier. 
 C, causes the dune to form behind. The sand moves from left to right 
 in the diagram. (After the U. S. Dept. of Agriculture.) 
 
 186. Harbors. — The most important economic fea- 
 tures along the sea coast are the harbors, or places of 
 shelter for vessels in time of storm. In some places there 
 
SHORE LINES 
 
 229 
 
 Fig. 168. Dune Park, Ind. Advancing front of a moving dune, bury- 
 ing forest and swamp vegetation. (H. C. Cowles.) 
 
 Fig. 169. Dune Park, Ind. Roots of the cottonwood cree exposed by the 
 action of the wind. In time the tree will be completely undermined 
 and overthrown. (H. C. Cowles.) 
 
230 
 
 PHYSICAL GEOGRAPHY 
 
 are long stretches of coast line without any cities, because 
 there is no harbor for the vessels. 
 
 The conditions necessary for a good harbor are: (1) 
 protection from incoming heavy waves, (2) an open, deep 
 channel extending from the anchorage to the open sea, (3) 
 water deep enough to permit the vessels to approach close 
 
 Fig. 170. Fiord Harbor on coast of Norway. Many such harbors lie well 
 inland, sheltered from the winds by high hills. Naero Fiord, Norway. 
 
 to the shore line to facilitate loading and unloading, (4) 
 location convenient to natural highways into the interior, 
 (5) roomy enough to accommodate many vessels without 
 interference, (6) good bottom for anchorage, and (7) 
 absence of strong river or tidal currents. 
 
 (1) Delta harbors, on the delta of a great river, have the ad- 
 vantage of access by water to the great fertile plains of the in- 
 terior of the continent, but they are often hampered by the 
 difficulty of keeping a ship channel open and free from the 
 mass of the mud carried in by the river. 
 

 SHOKE LINES 231 
 
 (2) Estuary delta harbors are on drowned rivers where the 
 sea has entered the lower part of the valley and a new delta has 
 formed at the head of the bay or estuary. 
 
 (3) Fiord harbors differ from the preceding in being deeper, 
 and generally lying in rock depressions with less soil on the 
 bordering hills than commonly occurs along the bays or estua- 
 ries. The fiords represent the deep ice-worn channels of glacial 
 origin, and hence are found only in high latitudes where the 
 glacial streams run into the sea. Their origin accounts for the 
 bare rock walls and scarcity of mantle rock. They are abundant 
 on the coast of Norway. (Fig. 170.) 
 
 (4) Mountain ranges that project into the sea frequently 
 have troughs or depressions below sea level which may be util- 
 ized as harbors. Such is the western end of the Pyrenees in 
 Spain, and the peninsula and islands of Greece. Sometimes the 
 mountains are parallel to the coast, and the harbor or harbors 
 may lie inside the first range, as San Francisco Bay and many 
 similar land-locked areas along the coast of Washington and 
 Alaska. 
 
 (5) Glacial moraine deposits along a sea coast sometimes 
 form protected harbors. 
 
 (6) . Lagoon and sand-bar harbors occur on almost all sandy 
 shores where there is a long stretch of shallow sea bordering 
 the coast. The waves build up a barrier at some distance off 
 shore, and the lagoon between the bar and the shore, where deep 
 enough, furnishes safe anchorage for vessels. Most of the la- 
 goons of this kind are not deep enough for the modern ocean 
 steamship, unless deepened artificially by dredging, but they 
 serve a useful purpose for the smaller coasting vessels. 
 
 (7) Sand-spit harbors are similar in some respects to the last 
 mentioned, but in the spit the sand is drifted along the shore 
 until in drifting past the headland at the entrance of a bay the 
 spit is carried part way or perhaps entirely across the bay, thus 
 making a safe anchorage in the bay behind it. Provincetown, on 
 Cape Cod is an example of this class. 
 
 (8) Volcanic crater harbors are formed by a breach in the 
 rim of a volcanic crater that occurs near sea level on an island 
 or the border of a continent. The accompanying view (fig. 171) 
 shows such a crater at the village of Ischia, on the island of 
 Ischia, near Naples. The notch in the rim of the crater permits 
 
232 
 
 PHYSICAL GEOGRAPHY 
 
 small vessels to enter and find a snug harbor in the crater of 
 the extinct volcano. 
 
 (7) Coral reefs and atolls furnish many much-needed harbors 
 in the tropics. The lagoon inside of the barrier reef or on the 
 interior of an atoll frequently furnishes a good harbor for large 
 as well as small vessels. Often the entrance to the coral har- 
 bor is narrow, intricate and dangerous. Biscayne bay, on the 
 east coast of Florida, is an example of a coral barrier-reef har- 
 bor; and Hamilton, on the Bermudas, is an example of an atoll 
 harbor. Both of these types are much more numerous in the 
 Pacific than in the Atlantic ocean. 
 
 Fig. 171. A volcanic crater harbor on the Island of Tschia in the Bay 
 of Naples, Italy. A notch in the rim of the crater forms an opening 
 through which boats pass to the open sea. 
 
 187. Economic Importance of Harbors.— The pres- 
 ence or absence of good harbors has much to do with the 
 location of cities and the commercial prosperity of the 
 adjacent region. The location of San Francisco is not an 
 accident. It has one of the best harbors on the Pacific 
 

 SHORE LINES 233 
 
 coast, which is at the same time a connecting link between 
 the ocean and the great fertile interior valley of Califor- 
 nia. New York City on the east coast is the metropolis of 
 the United States mainly because of its good harbor, lo- 
 cated at the natural doorway into the interior of the con- 
 tinent through the Hudson Valley and the Great Lakes. 
 Boston, Philadelphia, Baltimore, Washington, and all the 
 prominent cities on the eastern coast owe their locations 
 mainly to their good harbors. 
 
 In a few places there are sufficient attractions to cause 
 the growth of a town or city where there is no harbor, and 
 the commerce is carried on under great difficulties. Nome 
 City on Cape Nome, Alaska, is an example. Great quan- 
 tities of gold are found in the sands and gravels of the 
 sea shore and the inflowing streams. People come to get 
 the gold and must have food, clothing, houses, machinery, 
 etc., which are brought by ships on the ocean, but they 
 cannot get close to the shore because of the shallow water. 
 The goods and passengers are unloaded by lightering, that 
 is, a lighter vessel or boat takes a portion of the freight 
 through the breakers and shallow water to the shore. 
 Sometimes horses and cattle are thrown into the water and 
 made to swim ashore. In time of a storm the lighter can- 
 not get through the breakers, and the large vessels must 
 wait until the storm subsides, which may be several days. 
 In a violent storm it must put out to sea to avoid being 
 driven aground in the shallow water and destroyed by 
 the waves. 
 
 In the absence of a natural harbor, sometimes an arti- 
 ficial harbor is constructed at a great expense. This is 
 done by building a wall or breakwater out from the shore, 
 inclosing water deep enough to float the vessels. The 
 breakwater is so-called because on it the heavy storm- 
 waves from the open sea break and lose their power to 
 
234 PHYSICAL GEOGEAPHY 
 
 injure a vessel lying safely in the calm waters behind the 
 wall. The harbor for the city of Los Angeles at San 
 Pedro on the Pacific Coast is a type of this class. See the 
 Oswego sheet of the U. S. Topographic Atlas for example 
 of artificial harbor at Oswego. 
 
 REFERENCES 
 
 Shaler, Beaches and Tidal Marshes, Natl. Geog. Mon., Amer. 
 
 Book Co. Natural History of Harbors, 13th An. 
 
 Rept. U. S. Geol. Survey. 
 Gulliver, Shore Line Topography, Proc. Am. Acad. Arts and 
 
 Sci., Vol. 34, Jan., 1899. 
 Gilbert, Features of Lake Shores, 5th An. Rept. TJ. S. Geol. 
 
 Surv. p. 75. 
 Darwin, Structure and Distribution of Coral Reefs, Appleton 
 
 & Co., New York, 1889. 
 Dana, Corals and Coral Islands, Dodd, Mead & Co., New 
 
 York, 1895. 
 
CHAPTER VII 
 
 THE LAND 
 
 The land or solid portion of the earth, has many fea- 
 tures in strong contrast with the water, or liquid portion, 
 and the atmosphere, or gaseous portion. It is subject to 
 change like the other parts. The mountains, the plains, 
 and even the rocks themselves undergo cycles of change, 
 each with its own life-history, extending over a very long 
 period of time. 
 
 So slow are the changes that to the casual observer the 
 mountains were always mountains and will ever remain 
 such, but the geographer sees the mountains and hills in 
 process of growth and decay, and to him they are living 
 objects of interest as he studies their varied changes. So 
 with the plains, plateaus, valleys, volcanoes and other 
 natural features. He studies carefully the variations 
 going on and learns that by properly interpreting these 
 he can trace out the birth, growth, maturity, decay and 
 disappearance of even the "everlasting hills." Their 
 previous history is recorded and preserved in the rock 
 strata which have been wisely compared to the stone 
 leaves in the book of nature from which the geologist reads 
 the history of the earth and its development. The study 
 of this history is properly the province of Geology. It is 
 the province of Geography to interpret the elements of 
 this history and study the ways in which it is made and 
 recorded. 
 
 188. Divisions.— The two main continents have been 
 named the Eastern, comprising Eurasia and Africa, and 
 the Western, comprising North and South America. 
 
 235 
 
236 PHYSICAL GEOGRAPHY 
 
 Australia is a third continent much smaller than either of 
 the other two ; and probably Antarctica, of which little is 
 known, may prove to be a fourth. Continents are dis- 
 tinguished from islands ; first, by size, being much larger ; 
 and second, by structure, since, except the coral atolls, 
 the interior of islands is high land sloping to the sea, while 
 the interior of the continents is lowland consisting of 
 great river basins. The high land and great mountain 
 ranges occur mostly on or near the margin of the continent, 
 and not in the interior, as in the case of islands. 
 
 189. Islands. — Islands may be divided into two 
 classes, continental and oceanic ; the first includes those 
 that lie near the continents on the continental shelf and 
 hence are surrounded by comparatively shallow water ; 
 the second, those that rise out of the deep waters of the 
 ocean basins. 
 
 Continental islands are of two kinds; (1) those built 
 up on the shallow ocean bottom by corals or by currents, 
 waves, and wind, such as the sand barriers along the 
 Atlantic coast; (2) Remnants of the continent left above 
 the sea level by an advancing shore line. The hills of the 
 old shore become islands along the new shore. Such are 
 the islands along the coast of Maine. Those formed in 
 the first way are low and sandy with sandy shores. Those 
 in the second are generally rocky and bordered by rock 
 cliffs. 
 
 190. Distribution of the Land.— It may be observed on a 
 globe or a map of the continents that much more than half of 
 the land area lies north of the equator. If we should divide the 
 globe into two hemispheres by taking London, the greatest crty 
 in the world, as a center of one of them, it would be seen that 
 nearly all of the land (about nine-tenths) is included in the Lon- 
 don Hemisphere, while the other is largely a water-area. Is 
 there any significance in the location of London in the center 
 of the land hemisphere? 
 
THE LAND 
 
 237 
 
 Since it is the land masses that divide the ocean into its 
 different parts, the unequal distribution of the land causes an 
 unequal division of the oceans; thus the Pacific ocean which lies 
 mainly in the water-hemisphere is much larger than any of the 
 other oceanic divisions. 
 
 191. Importance of the Land.— To the existence of 
 dry land is due the possibility of all forms of land life. 
 
 Water Hemisphere. Land Hemisphere. 
 
 Fig. 172. Division of the earth into two hemispheres, one of which contains 
 nearly all the land. London is near the center of the land hemisphere. 
 Where is the center of the water hemisphere ? 
 
 It is possible that a large part of the life in the sea is 
 dependent on the occurrence of land, since much of the 
 material to supply the marine life comes from the land. 
 To the land areas are due likewise the direction, intensity, 
 and in large measure the existence of the ocean currents 
 so important to life both in the sea and on the land. 
 They also influence in large measure the movements of the 
 atmosphere and the distribution of moisture in the form of 
 rain and snow. Imagine what a monotonous and dreary 
 planet this earth would be if the entire surface were cov- 
 ered with water as it would be if the rock surface were free 
 from elevations and depressions. 
 
238 
 
 PHYSICAL GEOGRAPHY 
 
 192. Topography of the Land Compared With the 
 Sea Bottom. — In its broad, general features, the land 
 areas somewhat resemble the ocean floor in reverse order. 
 The continents correspond in a way, above the ocean level, 
 to the ocean basins below except that they are smaller. 
 The great plateaus on land have their opposites in the anti- 
 plateaus or deeps of the ocean. Here the analogy ceases, 
 as there is no erosion over the ocean bottom to correspond 
 to the multitude of valleys and steep hillsides on the land. 
 The widespread monotony of the ooze-covered plains of 
 the ocean bottom is replaced on the land by an ever vary- 
 ing diversity of landscape produced by the carving action 
 of the rainfall and the streams on the uplifted plateau and 
 mountain masses. 
 
 Potassium I . /■> 
 All others not I ./> 
 
 Fig. 173. Diagram showing the approximate percentage of the common ele- 
 ments that form the known part of the earth. More than half of the 
 oxygen is combined with the silicon. (Hessler and Smith.) 
 
 193. The Composition of the Earth's Crust.— The 
 solid portion of the earth contains a greater variety of 
 chemical elements than the atmosphere or the hydro- 
 sphere. About eighty different elements have been recog- 
 nized by the chemists, but only a few of these form an 
 
THE LAND 239 
 
 appreciable part of the rocks and the minerals of the 
 earth's crust. One element, oxygen, forms about half of 
 all the known part of the earth, including the air, water 
 and land. The other most common elements are silicon, 
 aluminium, calcium, magnesium, iron, sodium, potassium, 
 carbon, hydrogen, and nitrogen. The elements enter into 
 many different mineral and rock combinations, but again 
 the bulk of all the rocks is made up of a comparatively 
 small part of the hundreds of known minerals.* (See fig. 
 173.) 
 
 194. Minerals. — A mineral is a portion of inorganic 
 homogeneous material produced by natural means, having 
 a definite or nearly definite chemical composition and gen- 
 erally having a crystalline structure. Most minerals are 
 crystalline and many have a definite crystal form, but 
 many occur in rock masses where the crystal form does not 
 appear, while some few have not even crystalline texture. 
 
 Minerals are distinguished from each other by a care- 
 ful comparison of all the physical properties such as hard- 
 ness, color, color of the powder or streak, crystal form and 
 habit, cleavage, luster, optical, electrical, and magnetic 
 properties, all of which can be learned satisfactorily only 
 by the study of the mineral specimens. They may also be 
 distinguished by their chemical properties which may be 
 tested by the use of the blowpipe with different reagents. 
 Minerals are classified commercially according to their 
 uses, and scientifically according to their composition. 
 
 Suggestions : In studying the hardness of minerals it is cus- 
 tomary to select a certain number, generally ten, and arrange 
 them in the order of relative hardness, as a scale for com- 
 
 *It is not necessary to study all the minerals described in the following 
 pages. The student should study the minerals in his laboratory collection 
 and use these pages for reference. Do not study the text on minerals with- 
 out the minerals, but in connection with them. 
 
240 PHYSICAL GEOGRAPHY 
 
 parison. The ones commonly selected are (1) talc, (2) gypsum, 
 (3) calcite, (4) nuorite, (5) apatite, (6) orthoclase, (7) quartz, 
 (8) topaz, (9) corundum, (10) diamond. By comparing any other 
 mineral with these its hardness can be designated by a number 
 corresponding to that given fi the mineral with which it agrees 
 in the scale. For example, a mineral that would scratch calcite, 
 but not fluorite would be marked 4 in the .scale commonly writ- 
 ten H (=) 4. The powder or streak may be obtained by rub- 
 bing the mineral on unglazed porcelain or by scratching it with 
 a file. 
 
 All crystal forms of materials may be divided *into six groups 
 or systems, but the determination of these involves more knowl- 
 edge of crystallography than can be given here. Compare the 
 crystals as to the number of faces, the number of the same kind, 
 the shape of the faces and the arrangement of them. The dif- 
 ferent kinds and degrees of cleavage and luster can be learned 
 by comparison of the different minerals. 
 
 Rock-forming minerals. The most important rock- 
 forming minerals are quartz, the feldspars, micas, horn- 
 blende, augite, calcite, dolomite, serpentine and kaolin. 
 
 195. Quartz, the oxide of silicon (SiO ), forms one of 
 the essential minerals in granite, the bulk of the grains in 
 most of the sandstones, and a part of some other rocks. It 
 is one of the hardest of the common minerals, 7 in the 
 scale, readily scratching glass. It crystallizes in six-sided 
 prisms with pyramids (See fig. 174). It has a conchoidal 
 fracture, and commonly a vitreous luster, some varieties 
 have a waxy luster and others a dull luster. While it 
 occurs in nearly all the different colors, in the granites 
 and sandstones it Is usually gray, white, or colorless. The 
 streak, difficult to obtain, is white or gray. In the mineral 
 form it is used commercially in the manufacture of glass 
 and porcelain. Some varieties, as rock crystal, amethyst, 
 jasper, and chrysoprase are used as gems. Some sand- 
 paper is made from ground quartz. Compare quartz with 
 calcite, feldspar, fluorite, and selenite. 
 
/ Cube 
 (jtaletia, Halite, 
 /fr/te. 
 
 /L fjritohedron. 
 Rrite 
 
 3 Octahedron. 
 Magnetite, ffrite, 
 Fluorite. 
 
 Heyaaonaf 
 4. FPismanct/yramid. S. Quartz Crystal. 
 Quartz. 
 
 C~l\ 
 
 6. uca/enohed'ron. 
 Catcite-Uoatooth Sjaar. 
 
 0- Monoclinic 
 Qrthoclase 
 
 fe/Jsp, 
 
 wr. 
 
 y. Irafjezohedtvn. 
 Garnet. 
 
 7. Rhornbohectroti. 
 Cleavage form ofCalcite. 
 
 Fig. 174. Some of the common crystal forms. The same mineral may occur 
 in different forms, as pyrite in the first three above, but for the same 
 mineral these are always in the same one of the six systems. The three 
 forms given for pyrite are in the isometric systems. The two forms for 
 quartz, Nos. 4 and 5 are in the hexagonal system. 
 16 
 
242 
 
 PHYSICAL GEOGRAPHY 
 
 196. Feldspars are divided into two classes, ortho- 
 clase and plagioclase. The first occurs in granites and 
 syenites, the other in the diorites and gabbros. The ortho- 
 clase contains potash combined with silica and alumina, 
 
 
 
 
 ' 4^9C3teP*sff 
 
 Sttkfea.-^. 
 
 gHV^ 
 
 ^sjh^ SB 
 
 
 '^^^■(■•(■f^wJIMM 
 
 ' «3NH 
 
 ^H|^^ 
 
 
 ^jgSgjj^v-., _ --"'Sa 
 
 ,'\W"~ . '? ." ", 
 
 *> ■ • '■ " '"■«%*m^3/Q5!9Ss*& k -^' 
 
 f ; ■•■-*. 
 
 '"•■'~ . /. ' ~" ' " - V , . 
 
 .■ %:. *^ 
 
 •"?;y> •gpA ■ 
 
 r 
 
 ^ 
 
 ■ ■ - - '• '. - ..v i 
 
 , s ■ . -■•* - -• - 
 
 ' ' ' -> -'^ 
 
 
 
 r <^Hk. ••-.';. v'- 
 
 V ■' 
 
 FiG. 175. Half of a large feldspar (albite) crystal from Cabot, Vt., 4 feet 
 long 2Vs feet wide. The feldspars and quartz sometimes form very- 
 large crystals. (0. H. Richardson, Vt. Geol. Survey.) 
 
 while plagioclase contains soda or lime or both in place of 
 the potash. The feldspars are not quite so hard as quartz 
 being one less in the scale, but are still hard enough to 
 scratch glass. They differ from quartz in having bright 
 cleavage surfaces in two directions at right angles or 
 nearly so. Feldspar becomes dull on weathering as it 
 disintegrates and finally crumbles into a soft, clayey mass. 
 Feldspar is commonly white, gray, or pink in color. It 
 is quarried in New York, Pennsylvania, New Hampshire, 
 and elsewhere and is used in the manufacture of porcelain 
 and chinaware. (See fig. 175). 
 
THE LAND 243 
 
 197. Micas are characterized by the extremely thin 
 plates or scales into which they may be separated, due to 
 the perfect cleavage. There are several different varieties, 
 of which muscovite and biotite are the most common. 
 
 ]?IG. 17G. Feldspar quarry near "Elam, Pa., August, 1898. Feldspar 
 occurs in commercial form in veins or dikes in igneous or metamorphic 
 rocks. It forms a large part of the granite rocks. 
 
 Muscovite, the so-called isinglass, is colorless in thin pieces 
 when pure. It is used for electrical purposes, lanterns, 
 stove and furnace doors, as a lubricant and for decorative 
 purposes. It occurs in granite, syenite, and in some 
 schists, and sandstones. Biotite is black or dark green in 
 color and occurs in granite, syenite, and some schists, also 
 in diorite and some of the other dark-colored igneous rocks. 
 Muscovite has a composition somewhat similar to that of 
 
244 PHYSICAL GEOGRAPHY 
 
 orthoclase ; in biotite, iron and magnesia replace the potash 
 of the muscovite. 
 
 198. There are several varieties of amphibole, the most com- 
 mon of which is hornblende, a black mineral occurring in 
 syenite, diorite, some granites and schists. It may be dis- 
 tinguished from biotite by not separating in thin scales. One 
 form of the fibrous mineral, asbestos, is a variety of hornblende. 
 Another form of asbestos is a variety of serpentine. It is the 
 latter that is used extensively for making fire-proof cloth, and 
 covering steam pipes and boilers. 
 
 199. Augite, (the most common of the pyroxenes) is a dark 
 green mineral which occurs in diabase, basalt, and gabbro. 
 Augite and hornblende are important rock-making minerals com- 
 posed of silicates of iron, magnesia, and lime. Varieties of each 
 differ in color but where they form a large part of the rock mass, 
 the augite is dark green and the hornblende is black. The 
 augite is commonly in short, thick crystals or irregular masses, 
 hornblende usually in long, slender crystals, sometimes finely 
 fibrous. 
 
 200. Calcite is composed of the carbonate of calcium 
 (CaCO) and forms the bulk of the limestones, marbles, 
 and chalk deposits. It forms a large part of marl, of 
 shells of all kinds, most of the coral, extensive deposits in 
 caves and about lime springs and occurs in veins or fissures 
 in different kinds of rocks. The limestones and marbles 
 besides having extensive use as building and ornamental 
 stone are used for making quicklime and cement and hence 
 they form the base of most of the mortars in building 
 operations. Calcite is one of the most useful of all the 
 minerals and fortunately is very widely distributed. 
 Compare calcite with dolomite, quartz, and fluorite and 
 point out the differences, telling how you would distin- 
 guish them. When pure it is colorless to white; impure 
 varieties occur in all colors — red, black, blue, gray, and 
 yellow are abundant. It cleaves readily in three direc- 
 tions into rhombohedrons. Clear forms, Iceland spar, 
 
THE LAND 
 
 245 
 
 show double refraction. It effervesces freely in dilute 
 acid. (See figs. 177 and 174.) 
 
 201. Dolomite is the double carbonate of lime and 
 magnesia, and hence differs from calcite in having part 
 
 Fig. 177. Travertine quarry at Bagru, near Rome, Itaiy. The 
 rock is calcite deposited from solution in the spring water. 
 From this quarry the rock was obtained for the Coliseum, 
 St. Peters, and other buildings in Rome. (J. C. Branner.) 
 
 of the lime replaced by magnesia. It frequently resembles 
 calcite so closely, especially in many limestones and 
 marbles, that it is difficult to distinguish from it. It may 
 commonly be distinguished by adding quite dilute cold 
 hydrochloric acid, in which the calcite will effervesce 
 vigorously and the dolomite but little, if at all, until the 
 acid is heated. 
 
 202. Kaolin when pure is white and forms China 
 clay. It is formed by the decomposition of the feldspars 
 and the other silicates by the action of the groundwater 
 leaching out the metallic bases, leaving the insoluble sili- 
 cate of alumina, which combined with water forms kaolin. 
 It is used in the manufacture of china and porcelain ware, 
 
246 PHYSICAL GEOGRAPHY 
 
 encaustic tile, and as a filler for paper. Mixed with other 
 materials it probably forms the bulk of all the clays and 
 shales, and a considerable portion of all the soils. 
 
 ORES 
 
 The ores are the minerals from which the metals are 
 obtained. A few of the metals such as gold and copper 
 occur in the metallic state in nature and are called native 
 gold, native copper; but most commonly the metals in 
 nature occur combined with one or more other elements, 
 forming compounds known as ores. The most common 
 combinations are with oxygen, forming oxides; sulphur, 
 forming sulphides; and carbonic acid, forming carbonates. 
 
 203. Iron, the most useful of all the metals, occurs in 
 nature in all three of the above compounds in its different 
 ores. 
 
 Hematite (red hematite, fossil ore, specular ore) is at 
 present the most important ore of iron in the United States 
 and from it more than four-fifths of our iron is manu- 
 factured. , It occurs in several varieties, some of a bright 
 red color, some steel gray, and some almost black. What- 
 ever the color of the mass, the streak or powder is always 
 red. Hematite consists of ferric oxide, the higher oxide 
 of iron. (Fe O ). The most productive locality for this 
 ore is the region about Lake Superior from which much 
 of the ore is shipped by boats on the Great Lakes. It is 
 mined extensively in Alabama and in smaller quantities 
 in New York, Tennessee, Virginia, Missouri, and other 
 states. 
 
 Limonite (brown hematite, bog ore, yellow ochre) the 
 hydrous ferric oxide (FeO, 2HO) differs in composition 
 from the hematite by having water combined with 
 the iron oxide. It has the same composition as the iron 
 
THE LAND 
 
 247 
 
 FIG 178 Map of Lake Superior iron ore district and markets. More than 80 
 per cent, of the iron ore mined in the United States comes from the Lake 
 Superior mines. Much of it is shipped by boat over the Great Lakes. 
 The district second in importance is in Alabama. The shaded areas are 
 the coal fields. Cities underlined are the principal shipping and receiving 
 points. Ore districts at Lake Superior and in Alabama in black. 
 
248 PHYSICAL GEOGRAPHY 
 
 rust that forms on iron objects exposed to the air. It 
 varies in color from yellow ochre to very dark brown, al- 
 most black, but the streak is always brown or yellow. It 
 forms the yellow and brown coloring matter in nearly all 
 the soils and mantle rock. It is deposited in bogs form- 
 ing the bog ore, and occurs in many places in the mantle- 
 rock, especially in that resulting from decayed limestone. 
 It has been mined in hundreds of places along the lime- 
 stone areas in the Great Valley of the Appalachians and 
 elsewhere. 
 
 Magnetite, the third oxide of iron, consists of the union 
 of the ferric and ferrous, or the higher and the lower iron 
 oxides, (Fe O , FeO) and contains a higher percentage 
 of iron when pure than any of the other ores. It differs 
 from the other oxides and from all other minerals by its 
 strong magnetic properties. Three other minerals, one 
 variety of hematite and the bronze-colored iron sulphide, 
 pyrrhotite, and franklinite are slightly magnetic, but no 
 other minerals are attracted as strongly by a magnet as 
 magnetite. Magnetite is black in color and the streak is 
 black which distinguishes it from the other iron ores. It 
 occurs in the Adirondack Mountains, in southeastern New 
 York, along the east side of the Appalachians and else- 
 where. One of the largest magnetite mines in the world 
 is at Cornwall near Lebanon, Pennsylvania. 
 
 Iron pyrites is a yellow, brass-colored mineral, the sul- 
 phide of iron, (FeS 2 ) sometimes called "fool's gold," be- 
 cause so frequently mistaken for that precious metal. The 
 name is appropriate because despite the resemblance in 
 color it may be so easily and surely distinguished from 
 gold. When placed in the fire or on a hot stove, it turns 
 black, gives off the odor of burning sulphur and becomes 
 magnetic. It is hard and brittle while gold is soft and 
 
THE LAND 249 
 
 malleable. While commonly classed with the iron ores, 
 pyrites are not used for the manufacture of iron in the 
 United States because the sulphur would injure the quality 
 of the product. It is used for the sulphur in the manu- 
 facture of paper, phosphates, etc. (See fig. 174.) 
 
 Siderite, the carbonate of iron, (FeCOs) is formed by tbe 
 combination of carbonic acid with the oxide of iron. It varies 
 in color from gray to brown and sometimes black as in the black- 
 band ore. It occurs associated with coal beds and as black 
 nodular masses in the shale beds, where it forms the clay iron- 
 stone. It is used extensively in England and formerly in this 
 country for the production of iron, but it is used very little in 
 the United States at present. 
 
 204. Copper Ores.— In the Lake Superior district 
 copper occurs in the metallic state, native copper, but in 
 the western areas it occurs mostly in the compounds of 
 the metal with carbonic acid or with sulphur. 
 
 Chalcopyrite, the most common copper sulphide, is yel- 
 low in color and is frequently mistaken for iron pyrite. 
 It differs from pyrite in being softer, hence more easily 
 scratched, having a more golden yellow color and giving 
 a blackish green color in the powder. Bornite, another 
 sulphide, varies in color, being blue, purple, and yellow. 
 There are two carbonates of copper — malachite, having a 
 bright green color and azurite, a deep blue, both of which 
 beside their use as a source of copper are sometimes used 
 for ornamental purposes. 
 
 205. Lead Ores. — The most common ore of lead is galena, a 
 sulphide of lead (PbS) which looks much like the metal. It crystal- 
 lizes in cubes, and has a cubical cleavage, that is, when broken it 
 parts along planes parallel to the faces of the cube. Its cleavage 
 combined with its brittleness distinguish it readily from the 
 metallic lead which it resembles in color. Its color, cleavage, 
 and specific gravity (6-7) distinguishes it from other minerals. 
 Galena frequently contains silver, and most of the silver mines 
 
250 PHYSICAL GEOGRAPHY 
 
 produce large quantities of lead as a by-product. Some lead is 
 obtained from cerussite, the carbonate of lead. 
 
 206. Zinc Ores. — The chief zinc ore is sphalerite or zinc 
 blende, a sulphide of zinc, (ZnS) called "jack" by the miners. It 
 has usually a brown color, nearly black at times, and a resinous 
 luster. The most productive localities are Missouri, Kansas, 
 and Wisconsin. In New Jersey much zinc is obtained from 
 franlclinite, a bluish-black mineral resembling magnetite, and 
 from sincite, a red-colored oxide of zinc. Willemite, a silicate of 
 zinc, occurs with the New Jersey ores. 
 
 207. Aluminium Ores.— Bauxite, mined in Alabama and Ar- 
 kansas, is practically the only ore of aluminium at the present 
 time, although the metal occurs abundantly in many other min- 
 erals. Cryolite, formerly used almost entirely as a source of 
 aluminium, was at one time shipped in in large quantities from 
 Greenland. Corundum is nearly pure alumina, that is, the oxide 
 of the metal; emery, ruby, and sapphire are varieties of corun- 
 dum. Aluminium forms a part of the clay in all the great clay 
 and shale beds, but it is too difficult to separate from the silica 
 in the clay to make the clay a source of the metal. 
 
 208. Amongst other useful minerals are halite, gyp- 
 sum, sulphur, graphite, talc, magnesite, fluorite, and apatite. 
 
 Halite, or rock salt is mined from strata deep below 
 the surface in New York, Michigan, Ohio, Kansas, Louis- 
 iana, and elsewhere. It is frequently obtained by drilling 
 wells down to the bed of salt, running in water which dis- 
 solves the salt, then pumping out the water and evaporat- 
 ing it. At Syracuse, N. Y., the salt is already in solution 
 by groundwater, so that it is only necessary to pump out 
 the salt water and evaporate it. In places in Utah, 
 Nevada, and southern California, salt occurs in great 
 abundance on the surface, ready to be gathered up and 
 utilized. In some localities it is mined like coal from 
 underground workings. In some places it is obtained by 
 evaporating the sea water. It is distinguished from all 
 other minerals by its taste. (See fig. 179.) 
 

 
252 PHYSICAL GEOGRAPHY 
 
 Gypsum is the sulphate of lime combined with the 
 water of crystallization. H z =2 ; luster, pearly to dull. 
 Compare with calcite. When heated enough to drive off 
 some of the water it forms the plaster of Paris. It is 
 
 1\IG. 180. Gypsum quarry, Lyndon, N. Y. The upper 15 feet are limestone. 
 The lower part (60 feet) of the quarry consists of gypsum. It is quarried 
 for use in the manufacture of Portland cement, wall plaster, and land 
 plaster. 
 
 used in making 1 wall-plaster, stucco work, as a fertilizer 
 for soil and in the manufacture of Portland cement. 
 Alabaster, a variety of gypsum, is used for ornamental 
 purposes. Gypsum occurs in beds separated by layers of 
 shale and associated with salt beds in many places. It is 
 quarried in New York, Michigan, Kansas, Iowa, and many 
 of the more western states. (Fig. 180.) 
 
 Sulphur is obtained in Utah, Nevada, California, and Louis- 
 iana, but much of that used in the United States is imported 
 
THE LAND 
 
 253 
 
 from the Island of Sicily. It is used for making matches, gun- 
 powder, and sulphuric acid and as a disinfectant. 
 
 Graphite, sometimes called black lead, is a soft, black mineral 
 composed of nearly pure carbon. It occurs in the Adirondack 
 Mountains, N. Y., and in Pennsylvania, and in several of the 
 western states, but the best quality is imported from the island 
 of Ceylon. It is used in the manufacture of lead pencils, cruci- 
 bles, paint, stove polish and as a lubricant. (Fig. 181.) 
 
 Fig. 181. Interior of Dixon's graphite mine, four miles west of Hague, N. Y. 
 The graphite is scattered through the rock which is quarried, crushed, 
 and the graphite separated. (U. S. Geol. Survey.) 
 
 Talc is mined in St. Lawrence county, N. Y., in Virginia, 
 Pennsylvania, New Hampshire, and Vermont. It is composed 
 of the hydrous silicate of magnesia, is one of the softest (H=l) 
 of all the minerals, and has a characteristic greasy or soapy feel. 
 It is used as a filler in paper manufacture; the soapstone variety 
 is used for switch boards in electrical work, table tops in chem- 
 ical laboratories, for household purposes it is used for sinks, 
 laundry tubs, cake griddles, foot warmers, etc. Compare speci- 
 
254 PHYSICAL GEOGRAPHY 
 
 mens of soapstone with foliated talc, describing the differences. 
 
 Magnesite, the carbonate of magnesia, is used in making car- 
 bonic acid for soda fountains, as a filler for paper, and for lining 
 furnaces. It is quarried to some extent in California but much 
 of that used in the United States is imported. 
 
 Phosphates. The phosphate of lime used so extensively as a 
 fertilizer ccnsists of the mineral apatite. The purer mineral 
 form is quarried in Canada and the more massive rock form is 
 quarried in Florida, South Carolina, Tennessee, Alabama and 
 elsewhere. 
 
 Fluorite. Fluorite is the mineral formed by the chemical 
 union of fluorine and calcium. It crystallizes in cubes and 
 octahedrons, but it cleaves more commonly into octahedrons; 
 the color is generally green or purple, but it is sometimes color- 
 less. It is used as a furnace flux and for the manufacture of 
 hydrofluoric acid which etches glass. 
 
 Four of the lime minerals are but one degree apart in the 
 scale of hardness and, being common minerals, are usually 
 selected as types in the scale: gypsum, 2; calcite, 3; fluorite, 4; 
 apatite, 5. 
 
 Besides the minerals mentioned above, there are a hundred 
 or more common ones somewhat widely distributed, a number 
 of them having some economic importance. There are also 
 more than a thousand that are much less common and many of 
 them exceedingly rare. 
 
 Make a list of the minerals you have studied with the char- 
 acteristic properties of each. 
 
 ROCKS 
 
 The minerals, either singly or in various combinations, 
 make up most of the rocks on the exterior of the earth. 
 Some rocks, as limestone, or serpentine, are composed of 
 a single mineral, while others, as granite or diabase, are 
 composed of several different ones. In the glassy vol- 
 canic rocks there are no separate minerals, although they 
 consist probably of fused minerals which in the glass have 
 lost their identity. 
 
 Rocks are commonly grouped in three general classes, 
 
THE LAND 
 
 255 
 
 based on origin, namely, sedimentary, igneous, and meta- 
 morphic. 
 
 209. Sedimentary rocks are formed by the accumula- 
 tion of sediments in water, and are therefore stratified. 
 Included in this class are certain wind-formed deposits 
 that might be distinguished as eolian. The sedimentary 
 rocks are divided into the following groups based on the 
 chemical composition of the rock mass: 
 
 Fig. 182. Micro-photograph of brown sandstone. The white particles are 
 nearly all fragments of quartz. The black part is iron oxide, which gives 
 the red or brown color to the rock and acts as a cement to bind the sand 
 grains together. 
 
 1. Siliceous. Most of the sand and gravel deposits 
 are siliceous and largely, sometimes entirely, composed of 
 ground-up fragments of quartz. Along with the quartz 
 
256 
 
 PHYSICAL GEOGRAPHY 
 
 grains there are frequently variable quantities of frag- 
 ments of other common minerals. In sandstones the 
 grains are cemented together by some substance, most 
 
 FIG. 183. Brecciated limestone, Highgate Falls, Vt. The angular fragments 
 of limestone are held together by calcite. A rock in which the fragments 
 are rounded is called conglomerate. (U. S. Geol. Survey.) 
 
 commonly clay, iron oxide, calcite, or silica ; sometimes 
 two or more of these substances may act as cement in the 
 same rock. In the process of weathering of sandstones, 
 the cementing substance is the first to give way and when 
 destroyed the sandstone crumbles to sand, from which it 
 was first formed. (See fig. 182.) 
 
 Pebbles or gravel may be cemented in the same way 
 
THE LAND 
 
 257 
 
 and by the same means as the sand and form conglomerate 
 or puddingstone. If instead of the rounded pebbles of 
 the conglomerate, the fragments are angular, like broken 
 rock, and cemented together, it forms a breccia. 
 
 Fig. 184. Limestone quarry in the Alleghany Mountains at Bellefonte, Pa. 
 The limestone layers are nearly vertical due to the folding of the strata 
 in the uplift of the mountains. The limestone is here used for making 
 quicklime and as a furnace flux in smelting iron ores. In other places 
 it is quarried for building stone. One of the best limestones for build- 
 ing purposes is quarried extensively in Indiana. 
 
 2. Argillaceous. The argillaceous or clayey rocks in- 
 clude the beds of clay or mud as well as the hardened! 
 forms of these which form the shale beds. Clay may 
 grade imperceptibly into shale and this in turn through 
 shaly sandstones into sandstones or through calcareous 
 
 shale' into limestone and by metamorphism into slate. 
 17 
 
258 
 
 PHYSICAL GEOGRAPHY 
 
 Some of the varieties of clay are china clay, brick clay, 
 potters clay, and fire clay. 
 
 3. Calcareous. The calcareous rocks are composed 
 of the minerals calcite and dolomite, and include the many 
 varieties of limestone and marble. Some of the common 
 varieties of limestone are shell limestone : coral limestone : 
 
 PiG. 185. Exposure of a bituminous coal bed near Columbus, Nevada. The 
 man's hand is on the top of the coal seam at the contact with the over- 
 hanging shale. Coal is a sedimentary rock, and the most important one of 
 the fuels. See also Figs. 69 and 231. (U. S. Geol. Survey.) 
 
 chalk; travertine, including the stalactites and the stalag- 
 mites of the caves, and the tufa deposits about springs ; 
 hydraulic limestone or waterlime ; marl; and lithographic 
 limestone. Gypsum, the sulphate of lime, might also he 
 added to the calcareous group. (See figs. 184, 177 and 180.) 
 
 4. Carbonaceous. The carbonaceous rocks include those 
 composed of carbon and the hydrocarbon compounds, as bitu- 
 minous and anthracite coal, lignite, peat, asphalt, petroleum, and 
 natural gas. (Fig 185.) 
 
THE LAND 
 
 259 
 
 Ferruginous rocks include the great beds of iron ore. 
 
 Saline rocks include the beds of rock salt. 
 
 Alkaline rocks include the borax and soda deposits occurring 
 in arid districts. 
 
 210. Igneous rocks may be divided into the crystal- 
 line or granitoid division, sometimes called plutonic; and 
 
 Fig. 186. Granite Quarry, near Barre, Vt. Compare with Figs. 184 and 185. 
 Granite contains joint planes but it is not stratified like limestone and 
 coal. (C. H. Richardson.) 
 
 the volcanic or glassy and stony division, to which is some- 
 times added a third or intrusive, sometimes called porpliy- 
 ritic, class. 
 
 The granitoid rocks include those that cool slowly 
 under pressure, hence they are crystalline and occur only 
 in large masses that were formed deep below the surface 
 and are now exposed because of the erosion of the over- 
 
260 PHYSICAL GEOGRAPHY 
 
 lying rock. They are composed of masses of interlocking 
 crystals of different kinds. The granitoid rocks are : 
 
 1. Granite which consists of quartz, orthoclase feld- 
 spar, and one, two, or all three of the minerals, mica, 
 hornblende, and angite. The micas are more common in 
 granite than the other two. (Fig. 186.) 
 
 2. Syenite, which consists of orthoclase and horn- 
 blende, angite or mica. It differs from granite in the 
 absence of quartz. 
 
 3. Diorite is composed of plagioclase feldspar, and 
 hornblende, and thus differs from syenite in the presence 
 of plagioclase in place of orthoclase. 
 
 4. Gabbro is composed of plagioclase, augite, and 
 commonly magnetite and olivine. It differs from diorite 
 in having augite in place of hornblende. It is darker 
 colored than diorite, which in turn is generally darker 
 than granite and syenite. Diabase is more finely crystal- 
 line than gabbro. Basalt which is still finer grained, 
 belongs to the volcanic or intrusive class. The last two 
 form most of the trap rock which is used so extensively 
 for making good roads. One of the best known exposures 
 is in the Palisades on the Hudson. 
 
 The principal volcanic rocks are: (1) obsidian, volcanic 
 glass; (2) pumice, rock froth, the very porous material from the 
 surface of a volcanic outflow; (3) amygdaloid, the vesicular or 
 coarsely porous form with the vesicles, (holes formed by the 
 escaping gas), filled with other minerals; (4) trachyte and (5) 
 andesite are the two principal stony varieties; (6) porphyry con- 
 sists of a fine matrix with imbedded crystals; (7) tufa or tuff is 
 composed of fragments such as volcanic ashes or cinders par- 
 tially cemented or hardened. 
 
 Pumice is used for grinding and polishing, numbers 4, 5, 6, 
 and 7 are used for building stone, and some varieties of porphyry 
 form a valuable ornamental 'stone. 
 
 211. Metamorphic rocks are formed from either sedimentary 
 
THE LAND 
 
 261 
 
 or igneous rocks by a process known as metamorphism, the chief 
 agents of which appear to be water, heat, and pressure. Marble 
 is metamorphic limestone and is more crystalline and generally 
 harder and brighter colored than the original limestone. Slate 
 is metamorphic clay or shale rendered much harder, stronger, 
 
 FlG. 187. Crumpled gneiss, a highly metamorphosed rock. The metamor- 
 phism is caused in large part by the lateral pressure which produced the 
 wrinkling of the layers. Metamorphic rocks commonly occur in regions 
 of folded rocks, that is, in mountains or the eroded remnants of moun- 
 tains. (U. S. Geol. Survey.) 
 
 and finely crystalline. Anthracite is thought to be a metamor- 
 phic form of bituminous coal produced by pressure and heat. 
 Quartsite is a metamorphic sandstone with silicious cement. 
 Other metamorphic rocks are gneiss, serpentine, and schists of 
 many kinds. (Fig. 187.) 
 
 Selected specimens of the different rocks should be carefully 
 studied and compared, and all rocks found in the field trips 
 should be named and classified. In many places in the northern 
 
262 PHYSICAL GEOGRAPHY 
 
 United States specimens of nearly all the rocks described above 
 may be obtained from the deposits left by the glacier. 
 
 SOIL 
 
 Soil is produced from the different rocks by a variety 
 of processes known as weathering. The principal wea- 
 thering agencies are heat and cold, moisture, vegetation, 
 wind, and the chemical and mechanical effects produced 
 by these. 
 
 212. Disintegration of Rocks.— The heating of the 
 rock under the rays of the sun causes it to expand, often 
 enough to produce cracks and the breaking off of frag- 
 ments. The sudden cooling of the heated rock by a shower 
 of rain may produce fracture by contraction. Freezing 
 of water held in pores and cavities in the rock breaks and 
 fractures it by the expansion of the ice crystals. 
 
 The chemical action of the rain water and the ground 
 water breaks up hard minerals, such as feldspar and mica, 
 causing them to crumble into clay and sand. Portions 
 of the limestone are dissolved leaving other portions in fine 
 fragments in the soil. 
 
 The roots of plants penetrate cavities, cracks, and - 
 joints in the rocks and expanding in growing, act like 
 wedges to split the rock asunder. Both the living and 
 decaying plants furnish organic acids, which, like other 
 acids, act on the minerals to dissolve portions of them and 
 cause the remainder to crumble to fragments. 
 
 Winds carry sand and dust against the hard rock, 
 grinding off the surface. This agency is most conspicuous 
 in dry seasons and in dry climates. 
 
 Gravity acts as a disintegrating agent especially on 
 cliffs and steep slopes by pulling down boulders and frag- 
 ments, causing a further breaking and crushing in the 
 falling, and at the same time exposing fresh surfaces to 
 
THE LAND 263 
 
 the action of the weather. Gravity carries down large 
 quantities of loose mantle rock in the landslide or some- 
 times by a very slow process known as creep. (See figs. 
 188 and 189.) 
 
 Streams grind away the solid rock along their courses 
 and distribute the finely ground-up material over the 
 
 PiG. 188. View near Columbia, Pa., showing creep due to the action of 
 gravity on weathered slate. In the upper half of the picture the vertical 
 layers are broken and creeping down the hill to the right. (U. S. Geol. 
 Survey. ) 
 
 flood plain, and delta, forming alluvium or alluvial soil. 
 The fine sediment carried by the streams into lakes settles 
 on the lake bottom and after the disappearance of the lake 
 forms lacustrine soil. 
 
 Glaciers in cold climates are active agents in breaking, 
 
264 
 
 PHYSICAL GEOGRAPHY 
 
 grinding, and disintegrating rock material and transport- 
 ing it to other localities. 
 
 213. Mantle Rock.— All of the loose material, fine 
 and coarse, that covers the solid bed rock produced by any 
 
 
 
 
 
 1 .' •■ ' 
 
 
 
 ^^■^^^^^^^^B 
 
 
 ■ • ■,-**>?"-":. .'',, . ■ 
 
 
 
 Fig. ±89. Creep in glacial clay soil due to gravity. The Ciay when saturated 
 with water in a wet season is liable to creep down the hillside, as shown 
 in the photo. Sometimes on a steep slope a large mass breaks loose and 
 descends rapidly as a landslide. (E. R. Smith.) 
 
 of the above agencies, is known as mantle rock, which 
 everywhere rests upon the solid massive rock similar to 
 that exposed in the different rock quarries and on the face 
 of rock cliffs. 
 
 The change from solid rock to soil is frequently a 
 gradual one in which there is no sharp line of separation 
 between the two. In fig. 190 the surface is fine soil resting 
 upon the subsoil which contains partially disintegrated rock 
 
THE LAND 
 
 265 
 
 fragments increasing in number and size down to the solid 
 rock at the bottom of the quarry. 
 
 The thickness of the mantle rock varies greatly in different 
 places. In many places on steep hillsides there is none; in 
 other places it is as much as three or four hundred feet deep. 
 
 Fig. 190. Peerless slate quarry, Cambria, Md. Showing the change from soil 
 at the surface through partially disintegrated rock to the fresh unweathered 
 slate at bottom. (Maryland Geological Survey.) 
 
 In the city of Washington the granite rock is disintegrated to a 
 depth of more than 80 feet. In places in Brazil, South America, 
 the mantle rock is 400 feet deep. Such great thicknesses as 
 that are not known in cold climates except where the material 
 has been transported as along stream courses in filled valleys, 
 alluvial fans, talus slopes, or deposits made by the glacier. 
 
 Mantle rock changed to soil. The surface portion of 
 the mantle rock which has been subject to weathering 
 agencies longest, is more minutely divided and broken up 
 
266 
 
 PHYSICAL GEOGRAPHY 
 
 than the underlying portions. The completely decayed sur- 
 face portion which supports plant growth, is called soil and 
 the partially disintegrated underlying material is subsoil. 
 
 iTiG. 191. Weathered surface of granite in Oklahoma. The mantle rock is 
 carried away by wind and rain as rapidly as disintegration takes place. 
 (U. S. Geol. Survey.) Compare with Figs. 192 and 193. 
 
 The most productive soils contain more or less decaying 
 vegetable matter or humus. Probably an important con- 
 stituent of productive soils is the bacteria or microscopic 
 organisms which hasten the decay of the dead plant and 
 the growth of the living one. 
 
 Soils are not very productive until they contain some humus 
 or organic material. It may be questioned whether the mantle 
 rock is truly soil until it receives this admixture of organic mat- 
 ter. This mixing of the organic with the inorganic is accom- 
 plished in several ways. The roots of many plants extend to 
 considerable depths and leave their substance to decay on the 
 death of the plant. Ants, earthworms, and many other burrow- 
 ing animals carry vegetable material down and fresh rock mater- 
 ial to the surface, thus mixing and fertilizing the soil. The 
 farmer assists in this process by the use of the plow and the 
 cultivator with which he mixes the organic with the inorganic. 
 
THE LAND 
 
 267. 
 
 214. Varieties of Soil.— The body of nearly all the 
 soils is made up of clay and sand. If the sand is absent 
 it is clay soil, liable to be cold and wet. The bogs are al- 
 ways on clay soils. If the clay is entirely absent the land 
 will be sandy, dry, and crops are liable to be burnt out by 
 the sun. 
 
 FlG. 192. Hunter ore bank, Center Co., Pa. Residual soil on limestone. 
 Part of the soil has been removed to obtain the limonite iron ore which 
 is mixed through it. Remnants of the limestone show in the view project- 
 ing through the mantle rock. 
 
 There are many grades of soil between pure clay at one ex- 
 treme and pure sand on the other. Probably the best soil is 
 produced by a somewhat equal mixture of the two called loam or 
 loamy soil. The soil in which the sand prevails is best adapted 
 to root crops like potatoes and carrots. The clayey soils are 
 better suited to grass and similar plants, and are generally 
 improved by either surface or tile-draining. 
 
 Along with the clay and sand is a small percentage of the 
 elements that give fertility to the soil. The plant derives the 
 greater part of its food from the atmosphere, but some of it 
 comes from the soil. The nitrates, phosphates, lime, potash, 
 and other alkalies, along with organic matter, give fertility to 
 
268 
 
 PHYSICAL GEOGRAPHY 
 
 the soil by their presence or render it barren by their absence. 
 The decaying vegetation and the work of earth worms and other 
 animals are important if not essential elements of fertility. 
 
 In many places the soil becomes poor and ceases to produce 
 good crops because of the loss of one or more of the above con- 
 stituents. The fertility may be renewed by the addition of 
 manure or some of the commercial fertilizers. 
 
 FlG. 193. Residual soil resting on marble, Chester, Co., Pa. Part of the soil 
 has been removed in order to quarry the marble. The surface of the soil 
 is nearly a level plain, but the rock surface underneath is quite irregular. 
 The rock surface underneath the soil in Fig. 192 is still more irregular. 
 
 The black lands in many places are composed of a soil that 
 is nearly all vegetable material with sometimes a commingling 
 of animal remains. This is the muck which is partially decayed 
 vegetation and which forms a soil very rich in the elements of 
 fertility, but one lacking in body. 
 
 Residual soil occurs in the place occupied by the orig- 
 inal rock from which it was formed. (Figs 192 and 193.) 
 
THE LAND 269 
 
 Transported soils have been carried from the place of 
 disintegration by some agency as water, wind, or ice. The 
 principal kinds of transported soil are : 
 
 1. Alluvial soils which are among the most produc- 
 tive of all soils. There is the happy commingling of sand 
 and clay base with the elements of fertility, all of which 
 are renewed in the periodic overflow of the stream. 
 
 2. Lacustrine soils which are formed on former lake 
 beds and are of three kinds : ( a ) The black muck such as 
 the black lands of New York, formed by vegetable accumu- 
 lations generally in small lakes; (b) the fine muds washed 
 from the lands and filling in the lake basin. The great 
 wheat lands of the northwest belong to the second class, 
 (c) Marls formed largely of remains of small shell animals. 
 
 3. Glacial soil. Most of the soil of the northern 
 United States is glacial soil and it varies greatly in qual- 
 ity. The average productiveness of the whole area has 
 been greatly increased by the glacial action, which mixes 
 the soil from different localities. In some places, the soil 
 is very poor because of too much clay, too much sand, or 
 too many boulders, but the average is much better than in 
 regions of similar rocks where the soil has not been mixed 
 by the glacier. 
 
 215. Life History of Sedimentary Rocks.— The dffferent 
 changes which rocks undergo have already been mentioned. It 
 remains now simply to connect these stages in the history of 
 the rocks to see that the rock material is moving in cycles on 
 the earth much as the water is doing. 
 
 As soon as the rocks are exposed on the surface, the weather- 
 ing agencies begin the work of disintegration. Some of the 
 materials go into solution and are quickly carried back to the 
 sea. Other portions are broken up into fragments large and 
 small, which are washed by the rains into streams and carried 
 into the sea or lake, where they form beds of gravel, sand, and 
 clay. In time these are changed to beds of conglomerate, sand- 
 
270 PHYSICAL GEOGRAPHY 
 
 stone, and shale or slate, and elevated above the water to be 
 again attacked by the weathering agencies and go once more 
 through a similar circuit. 
 
 Similarly the limestone beds on the continents are taken into 
 solution by the groundwater and through the springs poured 
 into the streams and thence carried to the sea where they are 
 taken up by the corals, crinoids, shell fish, etc., whose accumu- 
 lated remains again form great bedded deposits of limestone 
 which are lifted above the sea level to begin a similar cycle over 
 again. 
 
 The sand grains and the mud particles in a recently-formed 
 rock may have formed part of an indefinite number of similar 
 beds of rock in the past. When a bed of rock is weathered, dis- 
 integrated, and carried away, the material is only changed in 
 position but not destroyed. The first rock may disappear as a 
 rock but the material reappears elsewhere, forming parts of 
 other rocks. 
 
 Hardening of the Bocks. The induration or harden- 
 ing of the material into solid rock, as the sand to sand- 
 stone, lime-mud to limestone, mud-beds to shale, is caused 
 partly by the pressure of overlying materials, partly by 
 horizontal pressure, and largely by cementing materials 
 deposited between the grains by the circulating ground- 
 water. The induration may take place before, during, or 
 after the elevation, and in some instances never takes 
 place at all, as in the case of soft clays that occur in the 
 midst of the hard rocks of ancient geological periods. 
 
 216. The Geographic Cycle.— The life history of a 
 land area — the geographic cycle — cycle of erosion — or to- 
 pographical cycle, refers to the successive changes in the 
 surface features of an area from the time it is elevated 
 above sea level until it is worn down to sea level again, 
 /preparatory to beginning a new cycle. 
 
 Since the development of a river system is at the ex- 
 pense of the land area which it drains, the stages of the 
 
THE LAND 271 
 
 land-area's history are similar to those of the river history 
 previously described. 
 
 Youth. Many land areas, when first elevated, have a 
 fairly level surface, which is soon made irregular by the 
 development and trenching of numerous valleys over the 
 area. This incision or deep trenching of the streams dis- 
 tinguishes the very early youthful stage of the cycle from 
 the final old age stage of the preceding cycle before the 
 uplift. The youthful stage is further characterized by 
 broad stretches of undrained areas between the streams, 
 frequently containing many lakes and swamps. 
 
 Maturity. As the cycle advances from youth towards 
 maturity, tributaries to the stream develop in great num- 
 bers until all the inter-stream areas are drained. In the 
 mature stage (study the Charleston, W. V., sheet) the 
 valleys are numerous and deep. Consequently the hill- 
 sides are steep and likely to have many bold, rocky cliffs 
 and steep talus slopes. The divides consist of narrow 
 ridges devoid of lakes and swamps. 
 
 Old Age. The area passes from maturity into old age 
 and again approaches a plain in regularity, but a lowland 
 plain of old age instead of the upland plain of youth. 
 The tops of the hills are lowered by erosion, the talus 
 slopes extend to the tops of the hills and spread out 
 farther at the base. As the tops of the hills are worn 
 down, the level of the valley plain rises, the two approach- 
 ing a common level. Finally the harder and more resistant 
 rocks which do riot erode so rapidly, stand up as knobs 
 or prominences, called monadnocks, on the nearly level 
 plain-area called a peneplain (pene, almost). (See fig. 194.) 
 
 The erosion continues on the peneplain until the entire 
 area is brought to base level, and, in fact, does not wholly cease 
 until it is brought to sea level; but the erosion during the pene- 
 plain stage proceeds with such comparative slowness, that in 
 
272 
 
 PHYSICAL GEOGRAPHY 
 
 most cases the topography of the peneplain is overtaken by one 
 of the movements, either of depression, which causes drowning 
 by carrying it below the sea, or of elevation, which causes re- 
 juvenation or renewal of youth. 
 
 Fig. 194. Mt. Pony, south of Culpepper, Va. A monadnock on a peneplain. 
 The surrounding rocks, have been worn down to a lower level than the 
 harder, more resistant rocks which form the monadnock mountain. (U. 
 S. Geol. Survey.) 
 
 The length of the geographic cycle is determined by a num- 
 ber of more or less complex factors, such as: 
 
 (1) The initial elevation, whether great or small, whether it 
 is accompanied by metamorphic change or not. Thus an ele- 
 vation of metamorphic rocks to great altitudes like the Rocky 
 and Sierra Nevada Mountains, will take a much longer period 
 of time to be reduced to base level than a low elevation of soft 
 material, like 'the coastal plain of New Jersey or Maryland. 
 
 (2) The vigor of the eroding agents which is determined 
 largely by climatic conditions, such as amount and distribution 
 of rainfall and changes of temperature. An area in which the 
 rainfall is concentrated in heavy showers will be eroded much 
 more rapidly than one in which the rain is more evenly dis- 
 tributed throughout the year. 
 
THE LAND 273 
 
 The annual rain fall in the Bad Lands of Western Nebraska 
 is much less than in the fertile districts of Eastern Nebraska. 
 Yet the erosion is much greater because the rain is concentrated 
 in a few heavy showers separated by long intervals of drouth. 
 
 (3) The resistance offered by the rocks — for example, beds 
 of unconsolidated sand and clay may pass through the youthful 
 and mature stages to old age in a small fraction of the time re- 
 quired by the hard crystalline rocks; in fact, the cycle may be 
 completed in the first case before it is scarcely begun in the 
 second. 
 
 The length and stage of the cycle are clearly not a question 
 of years at all. A pile of soft earth in the laboratory under a 
 vigorous shower may be made to pass through all the stages of 
 an erosion cycle in a few hours, while an area of hard rocks 
 might take many hundreds of thousands of years. 
 
 REFERENCES 
 
 Dana, Manual of Mineralogy and Lithology, Wiley & Sons. 
 
 Kemp, A Study of the Rocks, Scientific Publishing Co., New 
 York. 
 
 Crosby, Common Minerals and Rocks. 
 
 Howell, Washington School Collection of Rocks and Min- 
 erals. 
 Soils : 
 
 Shaler, Origin and Nature of Soils, 12th Annual Report 
 U. S. Geological Survey, Part 1. Also the last chap- 
 ter in "Aspects of the Earth" by the same author. 
 
 Hilgard, Soils and Their Properties, Macmillan Co. 
 
 Hilgard, Relations of Soil to Climate, Eull. No. 3, Weather 
 Bureau, U. S. Department of Agriculture. 
 
 Whitney, Some Physical Properties of Soils, Bull. No. 4, 
 Weather Bureau, U. S. Department of Agriculture. 
 
 Whitney, Soil Fertility, U. S. Department of Agriculture, 
 Farmer's Bulletin No. 257. 
 
 Many of the other publications of the Department of Agri- 
 culture contain valuable information on the subjects of soils, 
 and would be a great aid to the teacher in this subject. 
 
 18 
 
CHAPTER VIII 
 
 PHYSIOGRAPHIC AGENCIES 
 
 Diastrophic Movements, Volcanoes, Earthquakes 
 
 Among the most active and important physiographic 
 agencies are those of rainfall, weathering, and the work 
 of streams and waves described in previous chapters. 
 However, one can readily see that the continued action of 
 these eroding agencies on the upland areas would in time 
 carry all the mountains and plateaus to sea level unless 
 some new force or forces should work in opposition to ele- 
 vate new land areas or re-elevate old ones from time to 
 time. Such a force exists in the heated interior of the 
 earth and is manifested in volcanoes and in the elevation 
 and depression of plains, plateaus, and mountains. The 
 force is shown in several ways: there is (1) Diastrophism, 
 a very slow movement affecting large areas; (2) Vulcan- 
 ism, a rapid outpour of material from the interior of the 
 earth to the surface through volcanoes; (3) Seismic move- 
 ments, the uplift and depression of large areas by the 
 force which produces earthquakes.- 
 
 These three phenomena are possibly more or less re- 
 lated to each other, yet each may act independently. 
 
 217. Diastrophism (literally, a twisting or warping) 
 is the term used to designate the movements of large por- 
 tions of the earth's crust and includes both the movements 
 of elevation and depression. An upward movement of 
 any portion of the earth's surface is probably accompanied 
 by a considerable depression elsewhere ; that is, the sur- 
 face is warped or twisted by the action of the internal 
 
 274 
 
PHYSIOGRAPHIC AGENCIES 275 
 
 forces. Diastrophism includes both epeirogenic and 
 orogenic uplifts. An uplift of a plateau in which there is 
 little or no disturbance of the strata is called an epeiro- 
 genic movement in contradistinction to an orogenic move- 
 ment in which the strata are folded and wrinkled. The 
 epeirogenic movement produces plains and plateaus in 
 which the strata are horizontal or but slightly inclined. 
 The orogenic movement produces mountain ranges in 
 which the strata are folded, wrinkled and frequently- 
 broken. 
 
 Evidence of elevation and depression. That many of the plains, 
 plateaus, and mountains have been elevated to their present 
 position by some dynamic force and have not always been at 
 this level is proven by the great numbers of fossil-animal and 
 plant remains of organisms that live only in the sea, showing 
 that these rocks were formed on the sea bottom and then raised 
 to their present height. In many places in the rocks there are 
 fossil ripple marks that were made in the shallow water of the 
 sea. 
 
 On the coasFal plain at Pozzuoli near Naples, the Romans 
 erected a temple to Jupiter Serapis. Later the land was de- 
 pressed by diastrophism until the building was nearly sub- 
 merged in the Mediterranean Sea. This plain was afterwards 
 elevated above sea level, and both the elevation and depression 
 were so gradual as not to overthrow the temple, three columns 
 of which are still standing. They show the effect of their 
 former submergence in the sea by the borings of the Lithodomi, 
 a species of rock-boring shells that live in the Mediterranean 
 Sea. Here is a positive historic example of a depression of a 
 coastal plain 25 feet or more and re-elevation of the same, all in 
 a period of about 2,000 years. Many other examples, historic 
 and geologic, might be cited of both elevation and depression. 
 Can the student mention any from his own observation or 
 reading? (See fig. 195.) 
 
 218. Cause of Crustal Movements.— The cause of 
 the diastrophism is thought to be the shrinkage of the in- 
 terior of the earth due to the loss of heat. Except from 
 
276 
 
 PHYSICAL GEOGRAPHY 
 
 changes due to the seasons, the surface rocks have a nearly 
 uniform temperature, but the interior of the earth which 
 has a much higher temperature is thought to be cooling, 
 
 FiG. 195. Remains of a Roman temple near Pozzuoli, Italy. Since the temple 
 was erected about 2000 years ago, the area has been below sea level and 
 the three marble columns on the right were perforated by rock-boring 
 molluscs. A few feet at the base of the columns were buried in the mud 
 and hence not perforated. 
 
 and as it cools it grows smaller. The outer crust, which 
 is not losing heat and, consequently, not shrinking, must 
 settle down on the decreasing interior portion which causes 
 depressions and elevations over the surface. 
 
 Another cause probably acting conjointly with the pre- 
 ceding, is the extrusion or transfer of solid, liquid and 
 gaseous material and of heat from the interior of the earth 
 to the surface through fissures and volcanoes. 
 
 219. Results of the Crustal Movement.— The results 
 
PHYSIOGRAPHIC AGENCIES 277 
 
 of the crustal warpings are the depressions of great seg- 
 ments of the crust, forming the ocean basins, and the ele- 
 vation of other portions, forming the great continental 
 land masses or portions of the same, the crumpling and 
 elevation of mountain chains, the elevation and depres- 
 sion of plains and plateaus. 
 
 The elevations may be apparent, not real. That is, 
 if the ocean bottom should sink deeper toward the center 
 of the earth than the continental masses, the effect would 
 be the same as if the land masses were elevated. There 
 are some very perplexing problems connected with the 
 origin of the continents and ocean basins. 
 
 220. Isostacy.— The principle of isostacy assumes that the 
 surface portions of the earth are in temporary equilibrium due 
 to equality of gravitative pressure. That is, the continents, 
 plateaus, and mountains, stand above sea level because they are 
 lighter than rocks beneath the ocean bed which are heavier and 
 hence depressed. A disturbance of this equilibrium by mov- 
 ing a large quantity of material from one portion of the surface 
 to another causes corresponding movements of elevation and 
 depression. The erosion of the rocks from the continent and 
 the deposition of the material in the margin of the sea causes 
 a rising of the continent because of the removal of the land, 
 and a sinking of the marginal sea bottom because of the addi- 
 tional load. The movement continues until isostatic equilibrium 
 is again established or some other force or agency intervenes. 
 
 The great movements which approximately fixed the position 
 of the ocean basins and the continental masses, probably took 
 place very early in geological history. But since that time, 
 changes of level less extensive have been going on from time 
 to time which tend to modify the outline and surface features 
 of the land areas. 
 
 221. Changes in the Shore Line.— The ocean basins 
 are now overflowing, and the overflow laps up over the 
 border of the continents on the continental shelf. The 
 shore line, or the meeting of the land and sea, may be ex- 
 
278 
 
 PHYSICAL GEOGRAPHY 
 
 pected to shift from time to time owing to several differ- 
 ent causes : 
 
 (1) Primarily the warping or diastrophic movements 
 described above. 
 
 I'iG. 196. General view of Mt. Vesuvius from across the Bay of Naples. City 
 of Naples at base of the mountain. Eruption of 1872. Note the great 
 volumes of steam from the center of the mountain and from the streams 
 of lava on the sides. Torrents of rain descend from the condensing 
 vapors. 
 
 ^2) The cutting away of the land by the waves on the 
 shores and the consequent advance of the sea on the land. 
 (Chapter VI.) 
 
 (3) Filling-in of the sea bottom by the material car- 
 ried from the land by the rivers. 
 
 (4) The infilling from the materials thrown out by 
 volcanoes in the sea and from the accumulated organic 
 deposits. 
 
PHYSIOGRAPHIC AGENCIES 
 
 279 
 
 VOLCANOES 
 
 Volcanic eruptions are among the most vivid and im- 
 pressive phenomena of nature. The effect produced by 
 them on the surface features of the earth are much less 
 than those produced by the erosive agencies, yet because 
 of the greater intensity of the volcanic forces manifest 
 for a short period of time, they make a much stronger im- 
 pression on the mind of the observer. 
 
 Fig. 197. Near the summit of Mt. Vesuvius previous to the great eruption 
 of 1906, showing the surface of a lava flow in foreground, the great 
 ash cone composed of fragments of lava thrown out of the crater, and a 
 small cinder cone formed on the surface of a lava stream on the left. This 
 part of the mountain was destroyed in the recent eruption. 
 
 222. Mt. Vesuvius.— Mt. Vesuvius, one of the best 
 known of all active volcanoes, was considered to be extinct 
 at the beginning of the Christian era. In the year 79 
 A. D., there was a violent eruption which threw out vast 
 
280 PHYSICAL GEOGRAPHY 
 
 quantities of fine fragments and water vapor which con- 
 densed as rain and fell in torrents. The city of Pompeii 
 was deeply buried under the ashes and dust of the erup- 
 tion from which it is now being excavated by the Italian 
 government. Herculaneum was buried at the same time 
 by the ashes and torrents of mud formed by the heavy 
 rainfall with the ashes. (See figs. 196, 197 and 198.) 
 
 Fig. 198. Crater of Mt. Vesuvius, a few years previous to the great eruption 
 of 1906. Part of a second crater is visible encircling the inner one. 
 There was a part of a third, not shown in the picture. 
 
 Following the great eruption of '79, Mt. Vesuvius remained 
 quiet for many years, the next outburst occurring in 203, the 
 next in 472, again in 512, 993, 1036, 1049, 1138, and 1139, after 
 which it remained quiet for nearly 500 years. But during this 
 period of quiescence volcanic activity was manifest in the smaller 
 volcanoes in the vicinity. 
 
 In 1631 Vesuvius again became violently active, no less than 
 
PHYSIOGRAPHIC AGENCIES 281 
 
 seven streams of lava flowing out from the crater, partially 
 destroying the villages of Ressina, Portici, and Torre del Greece. 
 In 1737 there was a stream of lava from the mountain estimated 
 to contain 300,000,000 cubic feet. 
 
 Probably one of the most violent eruptions of the mountain 
 since 1737 was the recent one in April, 1906, when the vast quan- 
 tity of ashes thrown out destroyed the village of Ottajano, while 
 great streams of lava extended into and partially destroyed the 
 village of Boscotrecasse. Many lives were lost and a great deal 
 of property destroyed. 
 
 Besides the many violent eruptions of Mt. Vesuvius since 
 '79 and in the preceding ages, there has been a great deal of 
 volcanic activity in the region surrounding the mountain, some 
 of which is recent and some in times prehistoric. Monte Nuovo, 
 a symmetrical volcanic cone, was built upon the coastal plain 
 in three days' time in September, 1538. The Solfatara near by 
 has been emitting sulphur and arsenic fumes and carbon dioxide 
 for centuries. 
 
 On the island of Ischia, there are 12 volcanic cones, one of 
 which is now utilized as a harbor for small vessels. The city 
 of Sorrento on the other side of the Bay of Naples is built on 
 part of a volcanic crater. 
 
 223. Mt. Pelee, Martinique.— There are numerous 
 volcanic mountains on several of the West Indies. In 
 fact, many of these islands are composed of volcanic rocks, 
 but previous to 1902 the volcanoes were thought to be ex- 
 tinct. The last eruptions had been in 1718 and 1812 and 
 had been forgotten. In 1851 there were earthquakes on 
 Martinique and some fine ashes were thrown out of Mt. 
 Pelee. 
 
 On April 25, 1902, a great cloud of smoke poured out 
 of Mt. Pelee and for several days there were rumbling 
 noises accompanied by steam and clouds of dust. On May 
 3, there was an eruption which destroyed a sugar factory 
 at the base of the mountain and killed a number of peo- 
 ple. At 7:50 A. M., May 8, occurred the eruption that 
 proved the most destructive to human life of any in 
 
282 
 
 PHYSICAL GEOGRAPHY 
 
 America. The city of St. Pierre with its population of 
 30,000, 17 ships in the bay, and all the country places be- 
 tween the Eoxelane and the Eiviere Blanche were des- 
 
 FiG. 199. View of Mt. Pelee, Martinique, some months after the great erup- 
 showing the spine from a distance. Notice the absence of vegetation in the 
 vicinity of the mountain. (E. O. Hovey, Am. Mus. Nat. Hist.) 
 
 troyed almost instantaneously by an explosion which shot 
 a great volume of hot gas and dust from the top of the 
 mountain over the doomed city and harbor. (See figs. 
 199 to 202.) 
 
 On July 9th, there was another eruption, thought to 
 be similar to the one that destroyed the city of St. Pierre. 
 The following graphic account is given by an eye witness* 
 of the second eruption: 
 
 "As the darkness deepened, a dull red reflection was seen 
 in the trade wind cloud which covered the mountain summit. 
 This became brighter and brighter, and soon we saw red-hot 
 
 *Tempest Anderson in Smithsonian Report, 1902, p. 328. 
 
PHYSIOGRAPHIC AGENCIES 
 
 283 
 
 stones projected from the crater bowling down the mountain 
 slopes, and giving off glowing sparks. Suddenly the whole 
 cloud was brightly illuminated and the sailors cried, 'The moun- 
 tain bursts!' In an incredibly short space of time a red-hot 
 avalanche swept down to the sea. We could not see the sum- 
 mit, owing to the intervening veil of cloud, but the fissure and 
 
 « vis - Vi ' 
 
 Fig. 200. St. Pierre and Mt. Pelee after the eruption, June, 1902. View 
 looking north. Note the great number of north- south walls, where the 
 east-west ones have been destroyed by the blast from the volcano. (Am. 
 Mus. Nat. Hist.) 
 
 the lower parts of the mountain were clear, and the glowing 
 cataract poured over them right down to the shores of the bay. 
 It was dull red, with a billowy surface, reminding one of a 
 snow avalanche. In it there were larger stones which stood 
 out as streaks of bright red, tumbling down and emitting 
 showers of sparks. In a few minutes it was over. A loud, 
 
284 
 
 PHYSICAL GEOGRAPHY 
 
 angry growl had burst from the mountain when this avalanche 
 was launched from the crater. It is difficult to say how long 
 an interval elapsed between the time when the great glare 
 shown on the summit and the incandescent avalanche reached 
 
 Fig. 201. Ejected block of lava thrown out of Mt. Pelee Aug. 30, 1902. 
 Photographed March, 1903. This block is on the plateau about one mile 
 from the crater. (Am. Mus. Nat. Hist.) 
 
 the sea. Possibly it occupied a couple of minutes; it could not 
 have been much more. Undoubtedly the velocity was terrific. 
 Had any buildings stood in its path they would have been utterly 
 wiped out, and no living creature could have survived that blast." 
 "The most peculiar feature of these eruptions is the ava- 
 lanche of incandescent sand and the great black cloud which 
 accompanies it. The preliminary stages of the eruption, which 
 may occupy a few days or only a few hours, consist of outbursts 
 of steam, fine dust, and stones, and the discharge of the crater 
 lakes as torrents of water or as mud. In them there is noth- 
 ing unusual, but as soon as the throat of the crater is thor- 
 
PHYSIOGRAPHIC AGENCIES 
 
 285 
 
 oughly cleared and the climax of the eruption is reached, a mass 
 of incandescent lava rises and wells over the lip of the crater 
 
 Fig. 202. Near view of the huge spine protruding from the crater of Mt. 
 Pelee. Height about 1200 feet above the rim of the crater. View on 
 March 25, 1903. (See Fig. 199) (Am. Mus. Nat. Hist.) 
 
286 PHYSICAL GEOGKAPHY 
 
 in the form of an avalanche of red-hot dust. It is a lava blown 
 to pieces by the expansion of the gases it contains. It rushes 
 down the slopes of the hill, carrying with it a terrific blast 
 which mows down everything in its path. The mixture of dust 
 and gas behaves in many ways like a fluid. The exact chemical 
 composition of these gases remains unsettled. They apparently 
 consist principally of steam and sulphurous acid. There are 
 many reasons which make it unlikely that they contain much 
 oxygen, and they do not support respiration." 
 
 A unique feature of the activity of Mt. Pelee was the 
 growth in the crater of a monstrous spine or monolith of 
 volcanic rock which extended about 1200 feet above the 
 rim of the crater (see fig. 202) at its maximum. This great 
 spine was an object of absorbing interest and considerable 
 speculation on the part of the observers. 
 
 224. Soufriere.— Mt. Soufriere on the island of St. Vincent 
 became violently active about the same time as Mt. Pelee and 
 on May 7, 1902, a great eruption of this mountain destroyed a 
 large amount of property and many lives. 
 
 225. Krakatoa.— In 1883, on the island of Krakatoa, 
 in the East Indies, occurred one of the most violent vol- 
 canic eruptions known to mankind. For many weeks 
 previous there had been great disturbance by earthquakes 
 and eruptions of vapor and dust. In such quantities was 
 this dust thrown into the air that for 100 miles around 
 the island the darkness of midnight prevailed at midday. 
 
 At 10 o'clock Monday morning, Aug. 27, came the cul- 
 mination of this disturbance in what was probably the 
 loudest noise that has ever been heard on this earth, a 
 noise recognized almost 3,000 miles away. Two-thirds of 
 the island was blown into the air, some of it to a height of 
 17 miles, and some of it pulverized so finely that it was 
 three years or more before it all settled out of the atmos- 
 phere. Where part of the island stood before the explo- 
 sion, the sea was 1000 feet deep afterwards. The enorm- 
 
PHYSIOGRAPHIC AGENCIES 287 
 
 ous force exerted in such an eruption is almost beyond 
 human comprehension. 
 
 226. Definition. — A volcano proper is a pipe-like or 
 chimney-like opening in the earth's crust through which 
 molten rock, rock fragments, vapor, or gases escape from 
 the interior to the surface. Much of the solid material 
 so ejected is commonly deposited around the opening, thus 
 building up a cone-shaped mountain. The volcanic cone 
 has a basin or funnel-shaped depression, the crater, at the 
 top which leads into the pipe or neck of the volcano, 
 through which the materials are ejected. The cone is not 
 an essential part of a volcano, but is generally a product 
 of one. (Fig. 203.) 
 
 v 
 
 Fig. 203. Ideal section of volcanic cone, a, Crystalline rocks, b, c, Sedi- 
 mentary rocks, v, Crater of volcano, s, Remnant of a former crater. 
 
 227. Volcanic Cones. — The cones are of three types: (1) 
 They may be composed of volcanic ashes, cinders, or lapilli, ma- 
 terials which have been blown out in a fragmental condition 
 and much of which falls around the mouth of the opening, 
 building up an ash cone as steep as the fragmental material will 
 lie. Mt. Nuovo near Naples is an example. (2) The material 
 may come out through the opening quietly and flow away in 
 streams or sheets, sometimes a great many miles. The shape 
 of the cone in this case depends on the amount, and the tem- 
 perature of the material ejected, but generally it has a very 
 gentle slope on the exterior, almost flat compared with the ash 
 cone. This may be called the lava cone of which the Hawaiian 
 volcanoes, Kilauea and Mauna Loa, are type examples. (3) The 
 eruptions may vary in the same volcano at different times; at 
 one time lava may flow out in streams, and again be blown out 
 in fragments; the cone will be built up in part of one and in 
 part of the other, forming a mixed lava and ash cone. Vesuvius 
 and Etna are examples. 
 
288 
 
 PHYSICAL GEOGRAPHY 
 
 228. Phenomena of a Volcanic Eruption.— The dif- 
 ferent kinds of eruptions might be grouped into two classes, 
 the explosive and the non-explosive or quiet, with numer- 
 ous modifications of each. Both classes are frequently 
 but not always preceded by rumblings and earthquakes, 
 which continue sometimes for several months before a 
 
 Fig. 204. Driblet cones built of scoria and volcanic bombs on the lava field 
 at Cinder Butte, Idaho. Tumuli or small volcanic cones. (See also Fig. 
 197.) (U. S. Geol. Survey.) 
 
 great eruption. In the explosive type these disturbances 
 are apt to increase in intensity up to the time of explosion. 
 The eruption is frequently preceded by the escape of puffs 
 of steam and other gases, all terminating finally in a tre- 
 mendous explosion which generally destroys the top of 
 the volcanic cone. 
 
 In the non-explosive eruption there is a gradual swell- 
 ing up and rising of the lava in the crater until it over- 
 flows the rim and descends the cone in one or more great 
 
PHYSIOGRAPHIC AGENCIES 289 
 
 streams. In the great eruption in Iceland in 1783, two of 
 these streams flowed down the valley forty-five and fifty 
 miles respectively from the source. In the Hawaiian vol- 
 canoes, the streams sometimes flow to the edge of the island 
 and pour the molten lava into the sea. 
 
 In the very high volcanic mountains the pressure of the 
 great vertical column of lava in the crater is sufficient at times 
 to burst the cone and form one or more openings in the side, 
 through which the lava pours out, building up new cones. 
 Sometimes great cracks or fissures form in the side of the cone 
 through which the lava flows, and after hardening, forms dikes, 
 cutting the sides of the cone. Sometimes on the surface of the 
 lava streams or floods there are small cones or craterlets built 
 up, through which gas and sometimes lava poured out. These 
 are driblet cones. (Fig. 204.) 
 
 229. Materials Ejected.— The materials from a vol- 
 cano consist of: (1) gases and vapors; (2) solid materials; 
 (3) molten lava. 
 
 The gases consist of water vapor, chlorine, sulphur, 
 carbon dioxide, carbon monoxide, arsenic and mercury, 
 frequently carrying great clouds of fine dust which ap- 
 pears like smoke. 
 
 The solid materials consist of fine fragments called dust 
 or ashes ; small pieces, lapilli ; large, irregular masses torn 
 from the neck of the opening; and large, rounded masses 
 somewhat elongated and pointed, called volcanic bombs. 
 The latter are formed by small masses of lava that are 
 thrown out while molten, cooling in the passage through 
 the air. (Fig. 205.) 
 
 Forms of lava. The hardened lava, free from gas pores, is 
 obsidian, which is generally a colored glass resembling cinder 
 or slag from an iron furnace. If the lava contains water vapor 
 and other gases escaping as it cools, it forms vesicular lava, 
 named from the vesicles or bubbles; or if there is an excess of 
 
 19 
 
290 
 
 PHYSICAL GEOGRAPHY 
 
 the gas, so that the product is very porous and light, it forms 
 pumice. Dark, heavy lava forms basalt on cooling. 
 
 Tufa and dust. The fine fragmental material is sometimes 
 cemented by the percolating waters, forming volcanic tufa, a 
 soft, porous rock that is used extensively for building stone in 
 central and southern Italy, and to some extent in California. 
 The volcanic dust is sometimes carried long distances. Large 
 deposits of it on the plains of western Nebraska are supposed 
 
 1 
 
 SHI 
 
 
 ^. ..'.'- « -*>' «-. **** - . .. 
 
 !FlG. 205. Elongated volcanic bomb, 13 feet long, on the lava plains at Cinder 
 Buttte, Idaho. The bombs are generally shorter than this one. (U. S. 
 Geol. Survey. ) 
 
 to have blown from the Rocky Mountain area or beyond. Con- 
 siderable falls of volcanic dust which have come from some 
 distant, but perhaps submarine explosion, are sometimes met 
 by vessels at sea. A volcanic eruption is sometimes accom- 
 panied by a heavy downpour of rain caused by the condensation 
 of the ejected vapors which falling with the dust and ashes, 
 forms great streams of volcanic mud, to be changed to tufa as 
 
PHYSIOGRAPHIC AGENCIES 291 
 
 the mud dries. It was the downpour of mud that overwhelmed 
 Herculaneum, while Pompeii was buried under the volcanic 
 dust. 
 
 230. Commercial Products of Vulcanism.— Some of 
 the material from volcanoes has economic importance : ( 1 ) 
 
 Fig. 206. Volcanic butte, San Luis Obispo, Calif. Remnant of a volcanic 
 mountain. The prophyritic lava is quarried for building stone. 
 
 extensive sulphur deposits occur in Sicily, Italy, and Ice- 
 land; (2) the pumice is used for grinding and polishing 
 material; (3) lava and tufa are used for building stone; 
 (4) the fine ■ volcanic ash on Mt. Vesuvius and vicinity 
 furnishes excellent soil which supports many flourishing 
 vineyards; (5) lava is used for road-metal in some places 
 and sometimes as ballast for railways; (6) Pozzuolana, a 
 fine volcanic ash, is used in making cement in Italy ; val- 
 uable ores are sometimes found in volcanic rocks. The 
 
292 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 207. Muir's Butte, Cal. A volcanic cone on which eroding agencies have 
 done little work. Note the symmetry of the cone. (Detroit Publishing 
 Co.) 
 
PHYSIOGRAPHIC AGENCIES 
 
 293 
 
 rich gold mines at Cripple Creek and in the San Juan 
 Mountains are in volcanic rocks. 
 
 231. Active and Extinct Volcanoes.— Some volcanoes 
 are always active, some quiet for years, and some for cen- 
 turies. The first are called active, the last are commonly 
 classed as extinct, and those in the second class are dor- 
 
 FiG. 208. Mt. Shasta, California. A volcanic mountain more deeply eroded 
 than the preceding. (Detroit Publishing Co.) 
 
 mant. It is not always possible to tell when a volcano 
 passes from the dormant to the extinct class. In fact, some 
 that were thought to be extinct have become active. Mt. 
 Vesuvius was supposed to be extinct previous to the great 
 eruption in the year 79 which destroyed Herculaneum and 
 Pompeii. Mt. Pelee had not been active since 1851 until 
 the great eruption in 1902. 
 
 There are 300 active volcanoes, that is, 300 have been 
 active during recent years. How many of the so-called 
 extinct and dormant ones may become active at any time 
 is not known. 
 
294 
 
 PHYSICAL GEOGEAPHY 
 
 232. Effect of Erosion on Volcanoes.— The eroding agencies 
 are always at work on the volcanic cones, even while they are 
 erupting, but each eruption generally obscures the effects of 
 previous erosion. After activity ceases the effects of erosion 
 are soon manifest. The cone is dissected by streams and car- 
 ried away through radiating valleys much like any other moun- 
 
 FiG. 209. Devil's Tower, Wyoming. Remnant of an eroded volcanic moun- 
 tain. By some this is thought to be the remnant of a laccolite (Fig. 211) ; 
 others consider it the throat of a volcano from which the surrounding ash 
 cone has been eroded. (U. S. Geol. Survey.) 
 
 tain peak. (Mt. Shasta should be studied as a type of volcanic 
 cone in youthful stage of erosion. See Folio 2, Top. Atlas, U. S. 
 Geol. Surv., study figs. 207, 208, and 209.) 
 
 Sometimes the cone is composed largely of ashes and the 
 throat-opening is filled with rock cooled from a molten state. 
 
PHYSIOGRAPHIC AGENCIES 295 
 
 In such a case the softer exterior will be eroded rapidly, and 
 leave the harder, more resistant rocks of the neck or plug stand- 
 ing as a prominent elevation. (See fig. 209.) 
 
 233. Calderas. — Sometimes the bottom of the crater 
 subsides as activity ceases, leaving a large and often deep 
 depression, called a caldera, which when filled or partly 
 filled with water forms a crater lake. Crater Lake near 
 Mt. Hood in Oregon is an example. (Study Crater Lake 
 topographic sheet and explanation in Folio 2 of Top 
 Atlas.) (See figs. 75 and 76.) 
 
 Part of the calderas, at least, are thought by some to 
 be formed by the bottom, and part of the rim being blown 
 away by a violent explosion instead of by subsiding. 
 Sometimes an eruption terminates the existence of a crater 
 lake, as was the case on Mt. Pelee where the small lake 
 that was there previous to the eruption was entirely 
 destroyed. 
 
 234. Distribution of Volcanoes.— The greater num- 
 ber of active volcanoes are located around the border of 
 the Pacific Ocean. There is a chain of them extending 
 from Cape Horn at the extremity of South America along 
 the western border of both Americas, across the Aleutian 
 Islands to Asia, and down the Asiatic coast. There are 
 several groups in the Pacific Ocean, a number in the At- 
 lantic Ocean, some on Iceland and the West Indies, and 
 another great group in the Mediterranean Sea around the 
 south end of Italy. 
 
 There is good reason for thinking that there are many vol- 
 canic peaks scattered over the sea bottom. The Hawaiian Is- 
 lands and many other islands are but the tops of volcanic moun- 
 tains, built up on the sea bottom, while no doubt there are many 
 others whose tops are below the surface of the sea. 
 
 In 1867, among the Tonga Islands in the Pacific, a shoal 
 was discovered surrounded by water 6,000 feet deep. Ten years 
 later steam was observed rising from this shoal and in eight 
 
296 PHYSICAL GEOGRAPHY 
 
 years more there was an island of volcanic ashes two miles 
 long and 200 feet high. Unless there is further activity the 
 island will soon be cut away by the waves and again form a 
 shoal. 
 
 During the time of, or immediately following the San Fran- 
 cisco earthquake, a new volcanic island appeared in the Bogoslof 
 group among the Aleutian Islands. 
 
 235. Life History of a Volcano.- The life history of 
 a volcano begins with some changes deep below the surface 
 and beyond our observation. Although the outbreak is 
 frequently preceded by earthquakes, the first visible evi- 
 dence is a crack or opening extending downward indefinitely 
 through the solid rocks. Through this opening are ejected 
 gases, molten lava, and heated rocks, part of which accu- 
 mulate around the top of the opening, building up in time 
 a cone-shaped mountain. This period of up-building may 
 be called the period of youth and growth. The volcano in 
 its maturity is a lofty mountain peak which finally ceases 
 to erupt and becomes extinct. The eroding agencies which 
 have been overshadowed in this upbuilding process now 
 show the effect of their activity in wearing away the top 
 and sides of the mountain. The first step is to carry away 
 the soft fragmental, cinder portion of the cone, leaving the 
 harder central core or neck which is finally worn down to, 
 or below, the level of the original area on which it started. 
 
 236. Fissure Eruptions. — Sometimes eruptions take place 
 through elongated openings, or fissures, instead of through 
 chimney-like rpenings or craters, and are then called fissure 
 eruptions. They do not build craters, but spread out over the 
 adjoining region in ' great sheets or floods, sometimes many 
 hundred feet thick. Such are the great lava fields over parts 
 of Washington, Oregon, Idaho and California, covering an area 
 of 200,000 square miles, thousands of feet in thickness. 
 
 Ther is no sharp separation between eruptions through 
 craters and through fissures. In fact, small fissure eruptions 
 occur frequently on volcanic cones where the pressure from the 
 interior frequently forms cracks or fissures in the side or base 
 
PHYSIOGRAPHIC AGENCIES 
 
 297 
 
 of the cone, through which the lava may flow to the surface in- 
 stead of overflowing the rim of the crater. The hardening of 
 the material in the fissure forms a dik?. 
 
 Dikes of igneous rocks may form likewise in places remote 
 from any volcanic cone, such as those in the city of Syracuse, 
 
 Fig. 210. Devil's Slide, Colorado. A dike of igneous rock. The 
 central portion disintegrated more rapidly, causing the de- 
 pression. The outer portions of the dike are more durable 
 causing them to stand up as walls above the surface. 
 
 N. Y., and in the vicinity of Little Falls, Ithaca, and elsewhere 
 in New York State, in many places along the Appalachian 
 region, also around Lake Superior and in many other localities. 
 The Palisades on the Hudson are composed of igneous rocks 
 that came up in a molten state through great fissures or were 
 forced out between layers of other rocks. (Pig. 210.) 
 
 237. Laccolites. — Sometimes the molten material rising 
 through fissures does not reach the surface but pushes up the 
 overlying rock and spreads out between the layers in a mushroom- 
 
298 
 
 PHYSICAL GEOGRAPHY 
 
 shaped mass called a laccolite. (See fig. 211.) It is called, a 
 sheet or sill if it spreads out between the strata in flat sheets 
 without arching the overlying rock. 
 
 238. Causes of Vulcanism.— There are some features 
 connected with volcanic eruptions that are not well under- 
 
 FiG. 211. Laccolites in Henry Mountains, Utah. Upper figure shows section 
 through laccolite as first formed. Lower figure shows by dotted lines part 
 removed by erosion. (After Gilbert). 
 
 stood. The source of the heat that melts the rock is not 
 known certainly ; it may in part be produced by pressure 
 and gravity, in part by chemical action, in part by residual 
 heat of the earth. The force that lifts the huge column of 
 molten rock 10,000 feet or more above the level of the sea 
 may be due to expansion of the rocks by heat, and espe- 
 cially the expansion of the gases and vapors included in 
 
PHYSIOGRAPHIC AGENCIES 299 
 
 them, aided by the gravitative downward pressure of sur- 
 rounding heavier material. The cause of violent explo- 
 sions that blow out such vast quantities of fragmental 
 material is probably the expansion of the gases, especially 
 water vapor. 
 
 EARTHQUAKES 
 
 Earthquakes are important geographic factors in their 
 effect on topography, on life, and in their relation to vol- 
 canoes. There have been at least three destructive earth- 
 quakes in the United States during the past century be- 
 sides hundreds of minor ones, of which there is little or no 
 record. 
 
 239. Mississippi Valley Earthquake, 1811.— The first of the 
 great earthquakes in this country, of which there is any written 
 account, began in the Mississippi Valley between St. Louis and 
 Memphis on December 16, 1811, and continued at intervals for 
 several months. It began at two o'clock in the morning, when 
 the people awoke to find chimneys falling, furniture thrown 
 about and the earth rocking and trembling. 
 
 "At 7 o'clock a rumbling like distant thunder was heard and 
 in an inftant the earth was convulsed so that no one could 
 stand. Looking at the ground the terrified people saw it rise 
 and fall, as earth waves like those upon the sea rushed past, 
 waving the trees until the branches interlocked, and causing 
 yawning cracks to open. Giant forest trees were split for 40 
 feet up, half standing on one side of the fissure, the remainder 
 on the other. Some of the earthquake rents were of great 
 size, having widths of 30 feet or more, while some are reported 
 as many as five miles in length. Others were circular in form. 
 Into some of the cracks rushed the waters from swamps and 
 bayous, while elsewhere small streams or even rivers left their 
 old beds and made new channels through the cracks. 
 
 "In some places there was a blowing out of the earth, bring- 
 ing up coal, wood, sand, etc., trees being blown up, cracked and 
 split, and falling by thousands at a time. 
 
 "Many of these great fissures are still open at the surfaee, 
 and steep banks formed by landslips are still visible. Several 
 
300 
 
 PHYSICAL GEOGRAPHY 
 
 lakes were formed on river bottoms. Reelfoot Lake, in western 
 Tennessee, formed at this time, is five miles wide, twenty-five 
 miles long and twenty-five feet deep. 
 
 Fig. 212. Earthquake fissure 8 to 10 feet deep on the hill east of Keelfoot 
 Lake, Tenn., formed in 1811. (M. L. Fuller.) 
 
 "During the three months following December 16, there 
 were recorded in the Mississippi Valley 1,874 earthquake 
 shocks, of which eight were violent, ten severe, and thirty -five 
 alarming."* (See figs. 212 and 77.) 
 
 240. Charleston Earthquake.— On August 31, 1886, 
 the city of Charleston, S. C, and the surrounding region 
 were severely shaken by an earthquake, the effects of which 
 were felt as far north as New England and as far west as 
 Minnesota. Nearly every building in the city of Charles- 
 ton was injured to some extent, many of them severely in- 
 
 *M. L. Fuller, Pop. Sci. Mon., July, 1906. 
 
PHYSIOGRAPHIC AGENCIES 
 
 301 
 
 ISOSEISMALS OF THE 
 
 CHARLESTON EARTHQUAKE 
 
 RQSSI-FORO. SCALE 
 St Jc of Mdis. 
 
 - 
 
 ■- ■■■>" 
 
 ^--.■: 
 
 Fig. 213. Map showing area of disturbance by the Charleston Earthquake, 
 1886. The concentric lines are the Isoseismals which converge around the 
 centre, near Charleston. The intensity was greatest near Charleston, and 
 least in Vermont and Minnesota, beyond which it was not perceived. 
 (U. S. Geol. Survey.) 
 
302 
 
 PHYSICAL GEOGRAPHY 
 
 jured and some totally demolished. There was consider- 
 able loss of property and life in the area surrounding 
 Charleston. Fissures were opened in the earth, springs 
 ceased flowing in some places, and broke out in other places, 
 
 m 
 
 
 
 ■ .. _ 
 
 , 
 
 Fig. 214. San Francisco earthquake, April, 1906. Earthquake fracture near 
 Olema, California. The part on the left of the bank has been thrust away 
 from the observer. The fence was built after the earthquake. (J. F. New- 
 som.) 
 
 railway tracks were twisted and distorted and in one in- 
 stance a locomotive was thrown from the track. 
 
 241. San Francisco Earthquake.— Every year there 
 are many earthquakes in California, but most of them are 
 not perceptible to the senses and rarely are any of them 
 very destructive. In 1872 an earthquake destroyed the 
 village of Lone Pine and formed a great fissure through 
 the Sierra Mountains for 200 miles. 
 
PHYSIOGRAPHIC AGENCIES 303 
 
 The earthquake which destroyed more lives and prop- 
 erty in California than any other was the one that took 
 place in the early morning of April 18, 1906. There were 
 a number of minor shocks at intervals for several days, 
 but nearly all the damage was done in 65 seconds time. 
 
 PlG. 215. San Francisco earthquake. On the railway between Los Gatos and 
 Santa Cruz. The rails were stretched so much that a piece had to be cut 
 out before the road could be straightened. (J. C. Branner. ) 
 
 A large part of the city of San Francisco was destroyed 
 by the earthquake and the fires which were caused by it. 
 Great damage was done at Santa Rosa, San Jose, Stanford 
 University, and many other towns in the area of destruc- 
 tion. A great many buildings were thrown down or other- 
 wise wrecked. Nearly all chimneys were shaken down. 
 Water pipes, sewers and bridges were rent apart. Trees 
 were uprooted in large numbers, some were snapped off, 
 leaving the stumps standing. Fissures were opened in 
 
304 
 
 PHYSICAL GEOGRAPHY 
 
 the earth and closed again ; in one place it was reported 
 that a cow was engulfed. Line fences were moved. Roads 
 and railways were twisted and shifted. In one place the 
 steel rails were stretched so that it was necessary to cut out 
 a piece several inches long before they could be replaced. 
 (See fig. 215.) 
 
 Fig. 216. San Francisco earthquake. A vertical drop of seven feet east of 
 Watsonville, California. The foreground was on a level with the orchard 
 before the earthquake. Note the craterlets in the foreground near the 
 break. (J. C. Brainier.) 
 
 The earthquake was caused by a great fissure or crack 
 extending 375 miles from Point Arena on the north to 
 Mount Pinos on the south, along which the earth was frac- 
 tured and shifted horizontally a distance varying in dif- 
 ferent places from six to twenty feet. The area of destruc- 
 tion following this line extended over 400 miles long and 
 fifty miles wide, but the shock was felt as far north as 
 
PHYSIOGRAPHIC AGENCIES 305 
 
 Coos Bay, Oregon, and eastward into Nevada. The passage 
 of the earthquake was recorded by delicate instruments as 
 far away as Sitka, Alaska ; Washington, D. C. ; Tokio, 
 Japan, and Potsdam, Germany. It probably passed around 
 the globe (Figs. 214 to 217.) 
 
 Fig. 217. San Francisco earthquake. View on a road across alluvial lands 
 near Salinas, California. The stair-step appearance is due to the breaking 
 and sinking down along the fractures. This is not on the main fracture or 
 fault plane which produced the earthquake. (J. C. Branner.) 
 
 This earthquake was probably no more violent than the 
 one mentioned in 1872 and probably others, and much less 
 violent than the one in 1811, but the fact that it occurred 
 in the most densely populated part of California made the 
 destruction of human life, and property much greater than 
 any other recorded in the United States. 
 
 242. Kingston Earthquake.— There have been a great many 
 destructive earthquakes in Central and South America and the 
 
 20 
 
306 PHYSICAL GEOGRAPHY 
 
 West Indies. One of the most disastrous in recent times was 
 that which destroyed the city of Kingston, Jamaica. The first 
 shock came at 3:30 P. M., January 14, 1907, and was followed by 
 fifteen severe shocks during the following week. More than one 
 thousand persons were killed and nearly every building in the 
 city was injured; many of them were totally destroyed. 
 
 The area affected by the Kingston earthquake was much 
 smaller than the others mentioned. There seems to have been 
 little damage done outside of a radius of ten miles from the city. 
 The old city of Port Royal, just across the bay, was severely in- 
 jured during the earthquake in 1682, when part of the city sank 
 beneath the ocean. The remnant of the old city was injured in 
 the recent quake. 
 
 243. Earthquake of Lisbon.— One of the most destructive 
 earthquakes recorded in human history, was that on November 
 1, 1755, when the city of Lisbon was destroyed and over 60,000 
 persons perished in a few minutes. It began with noise like 
 heavy thunder which was immediately followed by a most violent 
 agitation of the surface, in which the ground rose and fell like 
 the waves of the sea; the neighboring mountains were shaken 
 like reeds and rent asunder in many places. Great chasms 
 opened in the city into which large buildings tumbled and dis- 
 appeared from view. The waters of the ocean retreated at first 
 and then returned in a great sea wave, fifty feet high, which 
 rushed over the doomed city, completing the ruin caused by the 
 shaking. The area of destruction extended as far away as the 
 Alps Mountains and across into northern Africa where several 
 villages were destroyed. 
 
 Japan is now the foremost nation in the scientific investiga- 
 tion of earthquake phenomena. It was aroused to action by the 
 severe earthquake of October, 1891, in which 7,000 people were 
 killed, 17,000 injured, and 20,000 buildings destroyed. 
 
 244. The Cause of Earthquakes.— Anything that pro- 
 duces a violent jar or concussion in the earth will produce 
 an earthquake. The explosion of a heavy blast in a mine 
 causes a trembling of the earth. The explosion of the 
 chemical works near San Francisco some years ago was 
 felt forty miles away. In nature the following agencies 
 produce earthquake waves: (1) A sudden fracturing of 
 
PHYSIOGRAPHIC AGENCIES 307 
 
 the rocks or the slipping or shifting of a large mass of 
 rock along a fissure or fracture in the earth's crust pro- 
 ducing a geological fault; (2) the explosion of a large 
 volume of gas or steam ; ( 3 ) the slumping off of a large 
 mass of sediment from the edge of the continental shelf 
 into the deep ocean basin. 
 
 245. Distribution of Earthquakes.— Earthquakes are 
 common in volcanic regions, and in mountainous countries, 
 especially in young and growing mountains. They are 
 numerous and destructive around the Pacific Ocean, fol- 
 lowing the volcanic zone; but they are not limited to vol- 
 canic regions as shown by the fact that the most severe 
 earthquake recorded in the United States. took place in the 
 Mississippi Valley as remote from mountains and volcanoes 
 as is possible in this country. 
 
 Earthquakes may occur anywhere at any time, but they 
 are not likely to be either severe or abundant in eastern 
 or central United States in comparison with the Pacific 
 border. 
 
 REFERENCES 
 
 Volcanoes : 
 
 Russell, Volcanoes of North America, Macmillan & Co., 1897, 
 $4. 
 
 Hull, "Volcanoes Past and Present, Scribner's Sons, N. Y., 
 1892, $1.50. 
 
 Judd, Volcanoes, D. Appleton & Co., N. Y., 1881, $2. 
 
 Bonney, Volcanoes, Putnam's Sons, N. Y., 1899, $2. 
 
 Geikie, Ancient Volcanoes of Great Britain, The Macmillan 
 Co., N. Y., 1897, $11.25. 
 
 Diller, Mt. Shasta, National Geographic Monographs, Amer- 
 ican Book Co., 1895. 
 
 Dana, Characteristics of Volcanoes, Dodd, Mead & Co., N. Y., 
 1891, $5. 
 
 Dutton, Hawaiian Volcanoes, 4th An. Rept. U. S. Geol. Sur- 
 vey, p. 8. 
 
308 PHYSICAL GEOGRAPHY 
 
 Heilprin, Mt. Pelee and the Tragedy of Martinique, Lippin- 
 
 cott, Phila., 1903, $3. 
 Phillips, Vesuvius, The Macmillan Co., 1869. 
 Lobley, Mount Vesuvius, London, 1889. 
 Hovey, Eruptions of 1902, of La Soufriere, St. Vincent and 
 
 Mt. Pelee, Amer. Jour. Sci., Nov., 1902, vol. 14, p. 319. 
 Earthquakes : 
 
 Arland, Great Earthquakes, New York, 1887. 
 
 Dutton, Earthquakes in the Light of the New Seismology, 
 
 London, 1904. 
 Charleston Earthquake, 9th An. Rept. U. S. Geol. Survey. 
 Milne, World-Shaking Earthquakes, Scottish Geog. Mag., Oct., 
 
 1902. 
 Perrine, Earthquakes in California, Bull. 161, U. S. Geol. Surv. 
 San Francisco Earthquake, National Geog. Mag., May, 1906, 
 
 Pop. Sci. Mo., Aug., 1906. 
 
CHAPTER IX 
 PHYSIOGRAPHIC FEATURES OR FORMS OF RELIEF 
 
 Plains, Plateaus, Mountains 
 
 If one should travel westward across the United States 
 from Atlantic City on the eastern coast to San Francisco 
 on the western, he would traverse a succession of plains, 
 plateaus and mountains. The same would be true on any 
 other continent, but the order, relative size and features 
 of detail would be different. The surface of all the con- 
 tinents and islands consists of these three natural features 
 with endless variety in each. 
 
 The line of separation between mountains and plateaus 
 or between plateaus and plains is not always sharply 
 marked. In travelling west across the Appalachian plateau 
 it would be difficult for any one to locate the exact spot 
 where he passes from the plateau to the Mississippi plains. 
 
 A desert is a specified form of one of the ether physio- 
 graphic features, a form based on a difference in climate. 
 It may be part or all of a plain or plateau and may contain 
 mountains. 
 
 PLAINS 
 
 246. Plains are areas of low relief, comparatively 
 smooth surfaces, generally at no great elevation above sea 
 level. However, the Great Western Plains rise towards 
 the west to heights several thousand feet above that of 
 some plateaus. Why are they called plains instead of 
 plateaus ? 
 
 The greater part of the food of the world is raised on 
 
 309 
 
310 
 
 PHYSICAL GEOGRAPHY 
 
 plains, and for that and other reasons (what other reasons 
 can you give?) the greater part of the population of the 
 world lives on the plains. They are therefore important 
 geographic features from an economic standpoint. 
 
 Fig. 218. Banded coastal plain. The strata dip towards the sea. The hard 
 layers form ridges with steep face towards the interior. The consequent 
 streams flow towards the sea. The subsequent streams develop along the 
 edges of the soft layers at right angles to the first streams. Conditions 
 are favorable for artesian wells. 
 
 A coastal plain is an uplifted portion of the continental 
 shelf which has been added to the former land area as the 
 shore line receded seaward. A coastal plain may be nar- 
 row and composed of one kind of material, resulting in a 
 simple consequent drainage in which the main streams 
 
PHYSIOGRAPHIC FEATURES 311 
 
 flow in the general direction of the slope of the land; or it 
 may be broad and composed of successive layers of differ- 
 ent kinds of rocks which, if they differ in hardness, result 
 in parallel ridges, and belts of different kinds of soil par- 
 allel to the shore. Such a plain may be distinguished from 
 the preceding by calling it a belted or banded coastal plain. 
 Study carefully fig. 218 and explain the significance of the 
 name. 
 
 If some of the layers are more porous than others, as 
 is generally the case, the conditions are favorable for 
 artesian wells. Long Island, Southeastern New Jersey, 
 and Eastern Maryland are portions of a belted coastal 
 plain composed of beds of sand and clay dipping towards 
 and underneath the sea. The rain that falls on the out- 
 cropping edges of the sand layers is carried down as 
 groundwater underneath the overlying clay beds which 
 prevent its escape to the surface, and hence causes accumu- 
 lation under pressure and consequent rise of the water in 
 the artesian-well opening. Artesian wells may be sunk 
 on the extension of such a plain under the shallow sea as 
 well as on the land plain. (See figs. 219 and 35.) 
 
 An embayed coastal plain is one which, after elevation and 
 erosion, has been depressed, causing the shore line to again ad- 
 vance on the land. The sea will now advance far up the river 
 valleys forming bays and estuaries, thus drowning the lower val- 
 leys and dismembering many of the streams. In the case of the 
 belted plains, there may be one or more lagoons parallel with the 
 shore over the eroded surface of the softer layers which had 
 been worn down nearly to sea level before the depression. The 
 higher, harder rocks then form peninsulas or islands. 
 
 There are many ancient coastal plains now in the interior of 
 the continents and remote from the sea, because since their first 
 uplift there have been successive additions to the plain. In 
 some instances even mountain ranges have been elevated be- 
 tween the old coastal plain and the present sea shore. 
 
 Most of the ancient coastal plains that are now far inland 
 
312 
 
 PHYSICAL GEOGRAPHY 
 
PHYSIOGRAPHIC FEATURES 313 
 
 are more diversified than the recent ones. The rocks are gener- 
 ally harder and more resistant and frequently the surface is 
 more rugged. 
 
 The greater part of New York State has been in times past 
 part of a coastal plain. The sea surrounded the Adirondack 
 Mountains and by successive uplifts of the land the shore-line 
 retreated south and west, exposing additional strips of coastal 
 plain. Study a geological map of New York. 
 
 Economic features of coastal plains. Coastal plains are 
 generally covered with a good soil, they have a good water 
 supply, and commonly a fairly regular surface, all of 
 which favor an extensive agricultural industry. Road 
 construction is for the most part easier than in the hill 
 country, which fact favors both agriculture and commerce. 
 Sometimes the commerce by water is hampered by the lack 
 of- good harbor facilities, but generally there is consider- 
 able water traffic both in the coast trade and on the rivers 
 which flow across the plain. They also favor manufactur- 
 ing industries where there are good harbors or navigable 
 streams, because of the favorable position for distributing 
 the products of the factory. 
 
 247. Alluvial Plains.— Flood plains occur along the 
 older portions of nearly all rivers. As soon as the river 
 has cut down to grade, it begins cutting at the cliffs, some- 
 times on one side and sometimes on the other. Part of 
 this material and part of that brought from the head 
 waters is spread out over the floor of the valley, building 
 up a flood plain over which the river takes a meandering 
 course. During high water when the river overflows its 
 banks, sediment is deposited over all the area flooded, 
 but in greater quantities along the immediate banks of the 
 stream, building up embankments or natural levees, which 
 grow higher from flood to flood until finally the river 
 breaks through and takes a new course on the lower part 
 
314 
 
 PHYSICAL GEOGRAPHY 
 
 of the plain which in turn is built up in a similar manner. 
 (See figs. 220, 221, 54, 55, 58 and 67.) 
 
 One effect of the upbuilding of the natural levee is to cause 
 the surface of the plain to slope away from rather than towards 
 
 ■-WEL-W <i^>^- 
 
 Fig. 220. View on the flood plain of the Bitterroot river in Montana, 
 alluvial soil is very productive. (U. S. Geol. Survey.) 
 
 The 
 
 the river channel, so much so that in some places small streams 
 develop on the levee bank and flow directly away from the chan- 
 nel into the river swamp. (See Donaldsonville topographic sheet.) 
 Furthermore, the levee forms an obstruction to the junction of a 
 tributary with the main stream. On the lower Mississippi river 
 flood plain, some of the tributaries flow along the outer margin 
 of it for many miles before they find an opening through the 
 levee into the main river. (See fig. 221.) 
 
 On the delta, where there are no bordering bluffs, portions 
 of the main stream break through or overflow the levee and flow 
 directly to the sea as distributaries. 
 
 The delta plain forms the continuation seaward of the river 
 
PHYSIOGRAPHIC FEATURES 
 
 315 
 
 flood plain. The delta plain of the Nile has for many centuries 
 been one of the most populous portions of the globe. 
 
 The greater part 
 of a flood plain is 
 fertile land, well 
 adapted to agricul- 
 ture because: (1) It 
 is covered with rich 
 humus carried from 
 the uplands and hill- 
 sides; (2) the fertil- 
 ity is renewed from 
 time to time by the 
 overflows, which de- 
 posit a new layer of 
 fertile soil; (3) the 
 water-table lies so 
 near the surface that 
 the area does not suf- 
 fer from drouth so 
 much as the upland; 
 and (4) transporta- 
 tion and communica- 
 tion, save in the flood 
 season, are easy by 
 road, railway and 
 river. For these rea- 
 sons a large part of 
 the food products of 
 the world is raised 
 on alluvial river 
 plains and deltas. 
 
 Fig. 221. Map of a portion of the lower Miss- 
 issippi River flood plain showing effect on 
 the tributaries of the up-building of the flood 
 plain along the channel. Note how many of 
 the tributaries run nearly parallel with the 
 river for long distances. The dark lines along 
 the river are artificial levees. (U. S. Geol. 
 Survey. ) 
 
 The greatest drawbacks to prosperity on the flood plains 
 are (1) destruction of life and property from the floods, 
 
316 PHYSICAL GEOGRAPHY 
 
 and (2) malarial climate from the many mosquitoes which 
 breed in the stagnant water. Many attempts have been 
 made to remedy the danger from floods by building higher 
 embankments on the levees to keep the water in the chan- 
 nel. But the exceptionally high flood finally overflows 
 and causes injury to both life and property. In a dry 
 
 FiG. 222. Brazos Island, opposite Point Isabel, near Brownsville, Texas. 
 The effect of grass in holding the drifting sand. River flood plain in an 
 arid region. (W. L. Bray.) 
 
 climate, a shallow river sometimes deposits much sand in 
 and along the channel. Strong winds spread the sand 
 over the adjoining fertile areas. (See fig. 222.) 
 
 248. Lacustrine Plains.— A lacustrine plain is one 
 that was formerly covered with a lake. The plain may 
 represent the entire area of the former lake or only a por- 
 tion of it and may be produced by : ( 1 ) the filling of the 
 lake; (2) the draining of it by the cutting down of the 
 
PHYSIOGKAPHIC FEATURES 317 
 
 outlet; (3) the evaporation of the water by a change in 
 climate; (4) diastrophism elevating a portion or all of 
 the lake bottom ; or sometimes a combination of two or 
 more of the above ways. 
 
 The famous celery and onion black land areas over the north- 
 ern United States are almost all lake plains formed by the filling 
 partially or completely of small lake basins with vegetable and 
 animal matter. The numerous vlies or meadows of the Adiron- 
 dacks are similarly formed. 
 
 The great wheat lands of the northwest, in Dakota, Montana 
 and Canada are lake plains on the bottom of large extinct lakes. 
 Lacustrine plains are almost universally fertile, since they con- 
 tain so much organic matter and the rock material is so very 
 finely disintegrated. 
 
 In places around the margin of extinct or fossil lakes, there 
 are sand and gravel deposits corresponding to the sand and 
 gravel beaches now forming in many places along the shores of 
 the larger lakes. These are lacking in fertility and have little 
 value for agriculture, but in the vicinity of cities they furnish 
 sand and gravel for building purposes. Nearly all the sand and 
 gravel used in Syracuse, New York, are obtained from the old 
 beaches of an extinct lake on the bed of which a considerable 
 portion of the city is built. 
 
 249. Salt and Alkali Plains.— Lacustrine plains in arid 
 regions are sometimes covered in part at least with salt or 
 alkalies, sometimes in such quantities that they can be 
 shovelled into cars and shipped to market. Shipping salt 
 in this way was an important industry at Salton, Cali- 
 fornia, before the Colorado River broke loose and covered 
 the area with water. Travel over the extensive alkali plains 
 west of Great Salt Lake in Utah and Nevada is disagree- 
 able in dry weather because of the alkali dust. 
 
 250. Glacial Plains.— A continental glacier, such as 
 that which covered the northern United States in former 
 times, leaves many plains, large and small, on the area 
 which it covered. Probably the glacier does not produce 
 
318 PHYSICAL GEOGRAPHY 
 
 many plains, but it modifies the surface of those already in 
 existence, possibly increasing the size of some of them. 
 
 The glacial plains may be covered with, glacial till or boulder- 
 clay or with sand and gravel as in the overwash plains and 
 glacial aprons. In some places they are partly covered with 
 large boulders. Many of the lacustrine plains of the northern 
 United States are indirectly glacial, as it was the glacier that 
 formed the lake basin and sometimes helped to fill it. 
 
 251. Peneplains.— Some plains are formed by exten- 
 sive erosion of a former plateau or mountain area. As the 
 rivers with their tributaries cut the upland plateau or 
 mountain down nearly to base level, the divides between 
 the valleys are finally lowered to near the valley levels 
 until the entire area approaches a plain surface which is 
 called a peneplain, meaning almost a plain. The harder, 
 more resistant rocks on the area remain as hills or eleva- 
 tions on the peneplain, and the more prominent ones are 
 known as monadnocks. 
 
 Nearly all of New England was at one time reduced by ero- 
 sion to a peneplain, which was then elevated. The streams 
 deepened and widened their valleys until the uplifted plain or 
 plateau was much dissected. The upland areas between the 
 streams are all that is left of the former peneplain. (See "The 
 New England Plateau" by W. M. Davis, one of the National 
 Geographic Monographs.) 
 
 Around the base of high mountains there are fre- 
 quently plains, large and small, that have been built up by 
 the material carried down the mountain and spread on the 
 low ground at the base. They are conspicuous topographic 
 features in the arid and semi-arid mountainous regions of 
 the west and southwest United States. Fig. 223 is a view 
 on one of these intra-montane (among the mountains) 
 plains near Acton in southern California. Such areas 
 have been called plains of aerial aggradation. 
 
a 
 
 H 
 
 
 
 
 c. 
 
 0) 
 
 CO 
 
 ft 
 
 s 
 
 a; 
 
 CJ 
 
 -c 
 
 C] 
 
 CJ 
 
 & 
 
320 
 
 PHYSICAL GEOGRAPHY 
 
 252. Prairies. — The prairies or treeless plains are 
 nearly everywhere covered with a fertile soil, and in a 
 moist climate in the wild state they are covered with a 
 dense growth of prairie wild grass which formerly sup- 
 
 Fig. 224. View on the Great Western Plains. The plains are mostly treeless 
 and have only a light rainfall. The chief industry is grazing herds of 
 cattle, sheep, and horses. Tilling the soil is profitable where the surface 
 is irrigated. The depression is a buffalo wallow. (U. S. Geol. Survey.) 
 
 ported great numbers of buffaloes, antelopes, wild horses, 
 and other animals. Much of the prairie land of central 
 North America is now under cultivation and includes part 
 of the famous corn belt of the central region and the wheat 
 belt of the north and northwest. 
 
 In the semi-arid region of the middle west, the area just east 
 of the Rocky Mountains, the rainfall is not sufficient to grow 
 farm products without irrigation, but enough to produce a scanty 
 growth of a short but very nutritious grass, which formerly sup- 
 ported vast herds of buffalo and which now furnishes food for 
 
PHYSIOGRAPHIC FEATURES 321 
 
 the great herds of cattle, sheep, and horses grazing on this area 
 which extends from the Gulf of Mexico entirely across the United 
 States far into Canadian territory. 
 
 Somewhat similar plains occur in the interior of other con- 
 tinents. Such are the great wheat lands and grazing plains of 
 Argentina in South America, and the great steppes or treeless 
 plains of Russia and southern Siberia. 
 
 253. Tundras.— In the far north in both America and the 
 Eurasian continent are vast stretches of treeless plains covered 
 with a dense growth of mosses and other plants in the short sum- 
 mer season. A few feet below this growing vegetation and con- 
 tinuing for depths sometimes of a hundred feet or more, the 
 ground is perpetually frozen. These frozen plains are known as 
 tundras. 
 
 PLATEAUS 
 
 254. Many upland plains are called plateaus. What 
 is it that distinguishes a plateau from a plain? It is not 
 height alone, for the area of the Great Western Plains east 
 of the Rocky Mountains is higher than either the Ozark or 
 the Alleghany plateau. 
 
 In passing across the Great Western Plains in any 
 direction there is nothing to indicate their elevation, noth- 
 ing that appeals to the senses. The higher portions are 
 nowhere bordered by land at a perceptibly lower level. 
 Even the large rivers flow on the top of the plain. The 
 Rocky Mountains and the Black Hills stand high above 
 them. Despite the fact that on the plains east of the 
 Rocky Mountains the land is several thousand feet above 
 sea level, it is much lower than the mountains which border 
 them. 
 
 As one crosses the eastern margin of the Alleghany 
 plateau, he finds an abrupt descent to the deep valleys 
 separating it from the Alleghany ridges. The rivers which 
 flow across the plateau flow in deep valleys, and hence by 
 comparison the land appears to be high. A plateau is an 
 
 21 
 
322 
 
 PHYSICAL GEOGRAPHY 
 
 inland plain bordered in part at least by a perceptibly 
 lower area, that causes the plateau to appear higher by 
 comparison. 
 
 Fig. 225. View in Ausable chasm, New York. A deep chasm cut by the 
 Ausable river in a hard sandstone rock. (H. W. Brock.) 
 
 255. Canyons.— Plateaus have one characteristic topo- 
 graphic feature not common to plains, namely, deep nar- 
 row valleys ealled canyons in the western United States 
 and gorges, chasms and glens in the east. The Colorado 
 Canyon in Arizona, the Niagara gorge, Ausable Chasm and 
 Watkins Glen in New York are alike in being narrow and 
 deep. 
 
 The western canyons are generally deeper than the eastern 
 gorges because the plateaus are higher, and hence there is a 
 greater thickness of rocks through which the stream can cut be- 
 fore reaching its grade. Yet there are many small canyons in 
 the west on tributaries of the great rivers that are not as deep 
 as Niagara Gorge or Watkins Glen. (See figs. 225, 226 and 97.) 
 
 The western canyons are generally narrower in proportion 
 
PHYSIOGRAPHIC FEATURES 323 
 
 to the depth than the eastern valleys, because (1) the arid 
 climate is less favorable to the action of frost and other weather- 
 ing agencies which wear away the cliffs and widen the valley in 
 the moist climate. (2) The absence of vegetation, due to aridity, 
 
 Fig. 226. Entrance to Grand Canyon of the N. Platte in Wyoming. The 
 canyon has a depth of 1000 feet in places in hard sandstones, limestones, 
 and granite. 
 
 and the concentration of the rainfall in a few heavy showers, 
 favors corrasion in the stream channel, thus deepening the valley 
 at the expense of weathering on the sides. (3) The western 
 area has been elevated higher and more rapidly. 
 
 Tributary canyons develop in time, and as they increase in 
 number, length and size, the plateau is dissected into first table- 
 lands, commonly called mesas in the west. The table lands are 
 further dissected or worn down to smaller remnants forming 
 hills or peaks, called buttes in the west. Name the necessary 
 conditions for the formation of canyons. (Figs. 227 and 228.) 
 
 256. Faults.— The rock layers of a plateau may be 
 fractured or broken, the plane of fracture being a fissure 
 or crack. It frequently happens that the rocks on one side 
 
324 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 227. View west of Sheep Mountain, S. Dakota. Mesa in background. 
 Cactus flats in the foreground. How does the vegetation indicate dry 
 climate? What indication is there of considerable rainfall? (U. G. 
 Cornell.) 
 
 Fig. 228. Alkali Buttes, Weston Co., Wyoming. — Mesa in the far background. 
 The mesa at one time extended over the entire area. The buttes are 
 remnants of the former extension. (U. S. Geol. Survey,) 
 
PHYSIOGRAPHIC FEATURES 
 
 325 
 
 of a fissure are elevated more than those on the other side. 
 Such a displacement of the rocks along a fissure is called 
 a fault, and the plane of the fissure becomes a fault plane. 
 The direction of this fault plane on the surface is the 
 fault line. The projection of the uplifted portion above 
 the other side is called the fault scarp. Where the rocks 
 are much broken and the fault scarps are numerous, the 
 surface of the plateau may be made very irregular. The 
 Block Mountains are supposed to be formed in this way 
 by the fracturing of the plateau and tilting of the great 
 earth blocks along the fault planes. 
 
 
 £iKl 
 
 
 / ^??. : :';'y 
 
 
 / — 
 
 
 / — 1 1 
 
 
 / ILKI | 
 
 
 
 
 ;■"_ • y*-"-""- = — 
 
 W ^ ^ L ^ 
 
 -T-+W 
 
 N- N- N- 
 
 
 Fig. 229. Diagram of fault. AB, fault plane. AC, fault scarp which is 
 worn back to DC in 11. 1 is a normal fault. 11 a reverse fault. 
 
 Faults occur in mountains and plains as well as on the 
 plateaus, but in many cases they are not noticeable on the surface, 
 as after the elevation of the fault scarp the eroding agencies 
 wear down the uplifted portion until the two sides are again on 
 the same level. A fault line is sometimes indicated on the sur- 
 face by a succession of springs which emerge along the line of 
 displacement. (Figs. 229 and 230.) 
 
 257. Economic Importance of Plateaus.— The plateaus 
 are generally not so productive and populous as plains. 
 First, they are likely to suffer more for want of water, as 
 the water plane is not so near the surface. Second, the 
 soil is frequently not so fertile as in the valley or on the 
 
326 
 
 PHYSICAL GEOGRAPHY 
 
 low plain. Third, transportation is generally more ex- 
 pensive than on the plains, due to distance from the sea 
 coast, absence of navigable rivers, and the cost of bridging 
 the numerous canyons. 
 
 Fig. 230. Fault at Jamesville, 1ST. Y. Locate the fault plane and determine 
 from the way the rocks are bent and broken whether the rocks on the left 
 moved up as in 229 1 or down as in 229 11. 
 
 The climate is generally more healthful on the plateau 
 than on the low plains, as the air is lighter, purer, and 
 freer from malaria. The arid plateaus have and probably 
 always will have a scanty population, because of the dif- 
 ficulty of getting water. In a moist climate the plateau 
 
PHYSIOGRAPHIC FEATURES 
 
 327 
 
 may have a prosperous farming population, which, how- 
 ever, is generally less dense than on the low plains. 
 
 Fig. 231. Entrance to coal mine in the Alleghany Plateau, Allegany County, 
 Md. In a plain country like Illinois coal is lifted to the surface through 
 vertical shafts. Here the coal is drawn to the surface on cars on a nearly 
 level roadway, extending from the sides of the deep valleys in under the 
 plateau. (See also Figs 69 and 185) (Md. Geol. Survey.) 
 
 The Alleghany plateau through Pennsylvania and southward 
 is underlain by numerous beds of coal and fire-clay. Many deep 
 valleys cut through these beds, and expose them to view on the 
 hillsides in favorable position for mining. (See fig. 231, also 
 fig. 69.) 
 
 in nearly all plateaus, beds of sandstone, limestone and other 
 rocks suitable for building purposes are exposed on the steep 
 slopes bordering the valleys, where many quarries have been 
 opened for the purpose of obtaining the stone. 
 
328 
 
 PHYSICAL GEOGRAPHY 
 
 DESERTS 
 
 258. The desert is such a striking contrast to the grass- 
 and-forest-eovered plains and plateaus of the humid areas 
 as to seem like a new world. Frequently the first impres- 
 sion on visiting a desert is that one is in dreamland where 
 things are not what they seem. Lakes appear where there 
 
 PiG. 232. On the Mojave desert near Bagdad, California. There is a great 
 scarcity but not absence of life and water. (Detroit Publishing Co.) 
 
 is no water and sometimes seem to run over the moun- 
 tains into the sky. Rocks, hills and mountains appear dis- 
 torted and unreal. Grave and sombre tints have replaced 
 the green leaves and bright flowers. One seems to be look- 
 ing through a yellow or brown glass. 
 
 One of the most impressive features of the desert is 
 the absence of noise, the apparent absolute stillness. One 
 is surprised to hear the ticking of his watch in his pocket, 
 
PHYSIOGRAPHIC FEATURES 329 
 
 the beating of his heart, and other sounds which in our 
 wave-disturbed atmosphere are never heard. (Fig. 232.) 
 
 Sombre, dreary and desolate as the desert may appear 
 at first sight, its solitude has charms that often prove ir- 
 resistible. No peoples are so wedded to their native soil 
 as the nomads of the desert. Rarely indeed do they emi- 
 grate either singly or collectively. 
 
 Definition. If it is the absence or scarcity of life due 
 to unfavorable conditions that makes a desert, then there 
 are three classes of deserts : 
 
 (1) The dry desert, barren for want of sufficient rain; 
 (2) the cold desert, barren because of the low temperature 
 and excess of snow which occurs in polar regions and high 
 mountains; (3) the wet desert, in mid ocean, where the 
 barrenness is caused by the darkness, cold, and pressure. 
 The surface of the ocean teems with life, and there is some 
 life in the bottom of the deep sea, but the great body of 
 the ocean included between these two zones is almost barren 
 of life and in that respect it is a great desert. 
 
 The dry deserts, although smaller than the others, are 
 the ones commonly meant when the word is used; that is, 
 in addition to the idea of barrenness or scarcity of life, 
 the word desert conveys frequently the idea of aridity or 
 scarcity of water. Used in this sense, the second and third 
 classes of deserts mentioned disappear. 
 
 In the broader sense, a desert is a region conspicuous 
 for the scarcity or absence of life, especially vegetable life. 
 In a more limited sense, the barrenness is due to scarcity 
 of moisture. 
 
 259. Dry Deserts. — The definition sometimes given 
 for a desert, that it is a rainless region, is a faulty one as 
 no region is entirely rainless and generally there ' is no 
 sharp line of separation between a desert and a semi-arid 
 region. Ordinarily less than 20 inches annual rainfall 
 
330 PHYSICAL GEOGRAPHY 
 
 means a region too dry to be cultivated and hence classed 
 as semi-arid and used for grazing purposes, unless it can be 
 irrigated. But other factors than annual rainfall must be 
 
 Fig. 233. Big Bad Lands, S. D. Erosion by heavy rains on soft material. 
 The annual rainfall is light but concentrated. The region is desert be- 
 cause of the irregular distribution of the rainfall. (U. S. Geol. Survey.) 
 
 considered. Much depends on the distribution of the rain, 
 whether it falls in the growing season or not, whether it all 
 falls in one or two heavy downpours, or is distributed 
 through the year. (Pig. 233.) 
 
 The rains of the desert are generally violent, often accom- 
 panied by cloud bursts. The effect produced on the surface is 
 to form raging torrents which erode deep gullies or channel-ways 
 known as wadies in the Sahara, and as arroyos or barrancas in 
 the desert areas of the southwest United States. (See sec. 94.) 
 These watercourses, strewn with boulders, sand and driftwood, 
 are characteristic features of aridity. (Figs. 234 and 72a.) 
 
 Wind is an important sculpturing and transporting agent in a 
 desert region. Hot and dry atmosphere produces a dry sur- 
 face to the soil. The absence or scarcity of vegetation causes 
 a bare surface susceptible to the action of the winds which blow 
 
PHYSIOGRAPHIC FEATURES 
 
 331 
 
 the dust and sand from place to place. The accumulation of the 
 sand forms dunes not unlike those in moist climates. (See sec- 
 tion 185.) 
 
 The fine sand and dust carried by the winds against or 
 across the surface of the bare rocks acts as a sand blast in 
 grinding and wearing the surface, even the hardest of rock sur- 
 
 FiG. 234. Arroyo or stream channel in Arizona. The channel is dry nearly 
 all the time, but occasionally it is swept by a torrent. (D. T. McDougal.) 
 
 faces. (Fig. 120a shows some quartz pebbles, among the hardest 
 of common rocks, that were worn by the desert sand blast. Com- 
 pare them with the stream pebbles and the glacial pebbles.) 
 
 The hard granite rocks of the desert are frequently worn in- 
 to weird shapes by the wind-blown sands. (See fig. 191.) 
 
 260. Desert Life. — The life of the desert is in strong 
 contrast to that in a humid area. One of the most prom- 
 inent characteristics of the life is its scarcity, but not often 
 
332 
 
 PHYSICAL GEOGRAPHY 
 
 is it wholly absent. Sombre colors prevail in both animal 
 and vegetable forms. 
 
 "The life on the desert is peculiarly savage. It is a show of 
 teeth in bush and beast and reptile. At every turn one feels the 
 
 Fig. 235. Desert vegetation. Cacti and mesquite near Torres, Sonora, Mex. 
 (See also Fig. 227.) (D. T. McDougal.) 
 
 presence of the barb and thorn, the jaw and paw, the beak and 
 talon, the sting and the poison thereof." (The Desert, Van Dyke, 
 Page 27.) 
 
 The more common plants of the American desert are the sage 
 brush, greasewood, cactus, yucca, bunch grass and mesquite. 
 
 The animals are the coyote, jack rabbit, antelope, prairie 
 dog, rattlesnake, horned toad and Gila monster. (See figs. 235, 
 236, 237 and 227.) 
 
 261. Distribution of Deserts.— Probably the largest 
 of all the dry deserts is the Sahara of Africa. Extensive 
 desert areas occur in central Asia, and in central and west- 
 ern Australia. There is a narrow strip of desert on the 
 west coast of South America, a region that is probably as 
 nearly rainless as any on the globe. 
 
PHYSIOGRAPHIC FEATURES 
 
 333 
 
 There are several desert areas in the west and south- 
 west United States, areas of considerable extent but grow- 
 ing smaller each year. In the older books the Great West- 
 
 FiG. 236. Sage brush (Artemisia tridentata), the most common plant of the 
 arid plains of Western United States. View near Elko, Nevada. Snow- 
 capped Ruby Mountains in the distance. (D. T. McDougal.) 
 
 ern Plains between the Missouri river and the Rocky Moun- 
 tains were called the ' ' Great American Desert. ' ' The area 
 now supports a large and increasing population. The title 
 was next applied to the area west of the mountains, includ- 
 ing at first all that vast area between the Rocky Mountains 
 and the Sierra Nevadas ; but as it became better known the 
 desert portion of this area decreased so rapidly that it does 
 
334 
 
 PHYSICAL GEOGRAPHY 
 
 not now appear on the United States map at all. There 
 are several desert areas of appreciable size in Utah, Nevada, 
 New Mexico, Arizona, and southern California, but they 
 are separated by productive or partially productive areas 
 which are gradually increasing in size at the expense of 
 the barren ones. 
 
 Fig. 237. Knight's Temple in Bates Hole, Wyoming. Life in a region of 
 slight but concentrated rainfall. Trees along the creek, scanty grass in 
 foreground. The hills in the background are nearly devoid of plant life. 
 (U. G. Cornell.) 
 
 The desert areas have been greatly diminished by irrigation, 
 and other portions have been brought under cultivation by tilling 
 the soil. The process known as dry farming is now carried on 
 1 extensively in areas formerly considered barren. In these ways 
 a thrifty and industrious population is gradually encroaching up- 
 on and thus diminishing the desert areas of the western United 
 States. The relatively small portions of the great desert areas 
 that have not been thus brought under subjection have been 
 
PHYSIOGRAPHIC FEATURES 335 
 
 robbed of their former terrors by the horse, the steam and elec- 
 tric railways and the automobile. 
 
 MOUNTAINS 
 
 262. Mountains are the most conspicuous features of 
 the earth's physiography. We can see part of the ocean 
 or part of a large plain, but we cannot see as much of 
 either as we can of a mountain. Hence the mountains 
 impress us with ideas of vastness, sublimity, and Omni- 
 potent power. 
 
 Long ago man, in his imagination, peopled the moun- 
 tains with giants, goblins, and dragons so that they were 
 objects of dread and were avoided by all. A mountain 
 range was then a practically impassable barrier. But in 
 the 18th century the ghosts and goblins that had been hov- 
 ering in the shadows of superstition began to disappear be- 
 fore the bright headlight of scientific discovery and inves- 
 tigation and the mountains became objects of attraction 
 and study rather than of distrust. People are attracted 
 to the mountains in different ways: some for the scenery, 
 as nowhere else do we get such grand and inspiring pan- 
 oramas ; others for the exhilerating atmosphere and the 
 fresh, sparkling waters ; others for the mineral wealth ; 
 others for the timber ; others for the fish and game products. 
 
 While mountains are interesting features to all, they are 
 especially so to the geologist and the geographer because they 
 whisper to him many of the secrets of nature that on the plains 
 are concealed beneath the heavy cloak of mantle rock. In the 
 mountains this mantle is rent and torn in many places, revealing 
 the history of the past in the structure of the underlying rocks. 
 The geologist also observes that while the mountains are now 
 the highest portions of the earth, they were born in the ocean 
 and are truly children of the sea. 
 
 There is no well-defined line of separation between mountains 
 and hills or between mountains and plateaus. Mountains are 
 
336 
 
 PHYSICAL GEOGRAPHY 
 
 higher and larger than hills, but the elevations are comparative. 
 Thus the Fourche Mountains at Little Rock, Arkansas, are less 
 than 400 feet above sea level, but they are much higher than any 
 other area between them and the Gulf. The Black Hills in South 
 Dakota are many times higher than the Fourche Mountains, 
 much higher even than the Alleghany Mountains, but they are 
 dwarfed by the lofty Rocky Mountains to the west and are pop- 
 ularly called hills. 
 
 Pig. 238. An anticline, Hancock, Md. formed by the upward bending of 
 the strata. (U. S. Geol. Survey.) 
 
 Mountains may be caused by diastrophism, folding, 
 faulting, uplifting with erosion, or volcanic action. The 
 uplift accompanied by folding is called orogenic to distin- 
 guish it from an uplift without folding, epeirogenic. The 
 former produces mountain ranges, the latter plateaus which 
 
PHYSIOGRAPHIC FEATURES 
 
 337 
 
 are dissected by streams into mountains. Volcanic erup- 
 tions also build up. mountains. (See Volcanoes.) 
 
 263. Folded Mountains.— Most of the great mountains 
 are caused by orogenic movements. The foldings are fre- 
 
 Fig. 239. Syncline, three miles west of Hancock, Md. A trough- shaped 
 downward bending of the strata. (U. S. Geol. Survey.) 
 
 quently complex and after the surface has been subject to 
 erosion for a long time, it is much diversified by the more 
 rapid cutting away of the soft layers, which causes the 
 hard layers to stand above the surface as mountain ridges 
 and hills. 
 
 The crumpling of the layers produces anticline, syn- 
 cline and monocline folds. The upward bending forms 
 the anticline, the downward bending or trough forms the 
 syncline, while a single bending from one level to another 
 
 22 
 
338 PHYSICAL GEOGKAPHY 
 
 is a monocline. (Study the diagrams, figs 240 and 242, and 
 figs. 238 and 239.) 
 
 After the bending of the rocks, the tops of the anticlines 
 form the tops of the mountains or ridges where erosion begins 
 most actively, because they are the higher points, and possibly 
 also because the rocks there are more shattered and broken. 
 Thus valleys form along the anticlines which are cut down more 
 rapidly than the first valleys in the synclinal troughs, until in 
 time the synclines (the first valleys) are left as mountains high 
 above the level of the eroded anticline which now forms the val- 
 ley. The accompanying diagrams indicate how erosion has cut 
 off the tops of the anticlines until the synclines stand at higher 
 levels and form mountains. Many of the present ridges of the 
 Alleghany and other mountains are synclines. When first up- 
 lifted the mountain ridges were on the anticlines. (Fig. 240.) 
 
 Fig. 240. Diagram illustrating crumpling of the strata in mountain-making. 
 A, anticline ; S, syncline ; M, monocline. Dotted lines represent portions 
 eroded after the crumpling. 
 
 Parallel ridges and terraced mountains. During the 
 erosion of the top of a large anticline which contains alter- 
 nating layers of hard and soft rocks, parallel valleys de- 
 velop on the softer layers which leaves the harder layers 
 standing up as parallel ridges between the valleys. In this 
 way there may be formed a succession of ridges, a half 
 dozen or more, on a single anticline. Sometimes one hard 
 layer is more resistant than another and will therefore 
 form a higher ridge, the less resisting layer forming a 
 lower parallel ridge which to the observer at a distance 
 appears like a terrace on the side of the higher mountain. 
 These are called terraced mountains and occur in a num- 
 ber of places among the Alleghany ridges. Tussey Moun- 
 
PHYSIOGRAPHIC FEATURES 
 
 339 
 
 tain along the south side of the great Nittany Valley in 
 central Pennsylvania is a terraced mountain. (See fig. 
 241.) 
 
 Fig. 241. Tussey Mt., Center Co., Pa. View of a terraced mountain. 
 The first ridge or terrace is several hundred feet lower than the one in 
 the background and is separated from it by a valley eroded on the softer 
 sandstone between the ridges. The stream from the dividing valley flows 
 through the water gap in the middle of the picture. 
 
 Canoe Mountains. — Canoe mountains are formed in anticlinal 
 and synclinal folds by the ends of the axis dipping below the 
 surface, as shown on the accompanying diagrams. They receive 
 their name from their resemblance to a large upturned canoe in 
 the anticline and an upright canoe in the syncline. After the 
 erosion of the top of an anticlinal fold it resembles a canoe with 
 the bottom worn off. Deep erosion in the central portion of such 
 a fold produces some unique basins or coves cut off or isolated 
 from surrounding regions by a mountain-rim. People dwelling 
 in such isolated localities are likely to retain habits and customs 
 which have disappeared years before in more cosmopolitan 
 localities. (Fig. 242.) 
 
 A great mountain range, such as the Alleghany, consists of 
 a series of simple and complex folds with often a bewildering 
 
340 
 
 PHYSICAL GEOGRAPHY 
 
 number of ridges, all of which go to make up the mountain range. 
 
 264. Domed Mountains.— Domed mountains are 
 formed by the uplift of a broad, dome-shaped arch instead 
 of an elongated one ; that is, the layers dip from a point 
 
 Fig. 242. Canoe Mountain which occur among the Alleghany 
 mountain ridges. H, H, hard rock strata wnicii form ridges 
 when intervening softer layers are removed by erosion. The 
 upper figure is a syncline in which the hard layers resemble 
 a nest of canoes. The lower figure is an anticline in 
 which the canoes are inverted and the bottom worn off. 
 (After Willis.) 
 
PHYSIOGRAPHIC FEATURES 341 
 
 or center, instead of from a line as in the anticlinal folds. 
 Domed mountains may be simple or complex with the cen- 
 tral mass more or less intricately folded or faulted. The 
 Adirondack Mountains are an example of complexly 
 crumpled domed mountains. They consist of crystalline 
 metamorphic and igneous rocks surrounded by sedimen- 
 tary layers which dip away from the mountains in all di- 
 rections. 
 
 265. Laccolites. — A laccolite or laccolithic mountain is formed 
 by the intrusion of a mass of igneous rock which does not reach 
 the surface but spreads out between the layers in a mushroom- 
 shaped or umbrella-shaped mass, at the same time pushing or 
 bulging up the overlying layers into a dome-shaped mass. 
 
 Like all other mountains, the laccolites generally have a very 
 irregular and diversified surface due to the action of eroding 
 agents. The Henry Mountains in Utah are good examples of 
 laccolites or simple domed mountains. (See fig. 211.) 
 
 266. Block Mountains are caused by fracturing of the earth's 
 crust into huge blocks which are then tilted or set on edge, 
 thus giving the newly formed mountain a steep slope on one side 
 and a quite gentle slope on the other. They are the fragments 
 of a broken-up plateau. They occur in the great interior basin 
 east of the Sierra Nevada Mountains. 
 
 267. Mountains of Circum-Erosion.— Mountains may be 
 formed from a plateau without fracturing by the eroding action 
 of streams and their tributaries, which cut the plateau into 
 fragments that are called mountains. The larger ones are likely 
 to be flat-topped and form table mountains. They are very irre- 
 gular in shape and size. Such are the Catskill Mountains, and 
 the mountains of western Pennsylvania and West Virginia. (See 
 Fig. 299.) 
 
 268. Volcanic Mountains.— Volcanic mountains con- 
 sist of the cinder and lava cones built up around the crater 
 of a volcano. Some of the loftiest mountain peaks in the 
 world are formed in this way. While the volcano is still 
 active the cone may be quite symmetrical, but as soon as 
 it becomes extinct the effects of the eroding agencies are 
 
342 PHYSICAL GEOGRAPHY 
 
 shown in the gullies and valleys that form on the slope. 
 When the other portion of the mountain is worn away the 
 central neck or core of the volcano may still form a prom- 
 inent mountain mass. (See figs. 207, 208, and 209.) Mt. 
 Shasta, Mt. Hood, Mt. Baker and many other high moun- 
 tain peaks of the western United States are volcanic 
 mountains. 
 
 269. Life History of Mountains. — All the great mountain 
 ranges are born in the sea, having a beginning in the accumula- 
 tion of a great mass of sediments on the ocean bottom bordering 
 the continents. Since the margin of the ocean is shallow, in 
 order to have a great thickness of deposits, it follows that the 
 bottom is sinking while the sediments accumulate. After a long 
 period of subsidence the uplift or movement in the opposite di- 
 rection begins, when the sea bottom sediments are folded and 
 elevated as mountains high above the sea. Then the agencies 
 of erosion, the sculpturing agencies, begin their work. The accu- 
 mulation of the thick bed of sediments might be called the 
 embryonic stage of development. 
 
 The youthful stage is that immediately following the eleva- 
 tion above the sea in which the mountain has the regular 
 slopes of the first uplift. The rain and the other weathering 
 agencies soon start gulches and valleys which change the smooth 
 slopes into very rugged ones. The more rapid erosion of the 
 softer strata causes the harder layers to stand out as hills, ridges 
 and irregularities on the surface. During this stage waterfalls, 
 rapids, canyons, gorges, steep cliffs, and talus slopes are formed. 
 In the higher mountains, snow fields with accompanying glaciers 
 and glacial erosion modify the surface, while avalanches, land- 
 slides and earthquakes are accompanying features. (See figs. 
 104, 114, and 115.) 
 
 Mature stage. The mountains pass from youth to maturity 
 as the softer parts are worn away, as the streams are established, 
 as the ridges and peaks reach great elevation and ruggedness, 
 and as the divides become narrow and well defined. The valleys 
 are still deep but wider than in the youthful stage, while flood 
 plains are forming on the short grade-level stretches, talus slopes 
 are becoming larger and extending nearer the tops of the cliffs, 
 waterfalls are fewer, and caves are forming in the limestone 
 
PHYSIOGRAPHIC FEATURES 343 
 
 strata. The larger streams form water gaps where they cut 
 through the ridges and the shifting of the smaller streams leaves 
 many wind gaps which serve as passes for highways. 
 
 Old age begins when the talus slopes extend to the tops of 
 the ridges and peaks, which are crumbling and being washed 
 down into the valleys, when the flood plains are expanding and 
 the streams meandering in their courses. The heights of the 
 mountains are lowered by erosion from the summit and the hill- 
 sides are made less steep by erosion at the top and filling in at 
 the bottom. The talus slopes increase in size until they reach 
 and cover the tops of the cliffs. The rocky, barren cliffs of 
 maturity give way to soil-covered, farm-covered slopes in old age. 
 
 The region about New York City, Philadelphia and Balti- 
 more represents extreme old age of mountains, where they have 
 all been cut down to low hills or even plains in places. The final 
 stage of mountain erosion, like that of plains and plateaus, is the 
 peneplain (Sec. 216) which may in time be brought to base level. 
 Over the peneplain the harder and more resistant rocks stand 
 forth as relict mountains or monadnocks, the remnants of the 
 former high peaks and ridges. (See fig. 194.) 
 
 Height. The height of a mountain or mountain range 
 at any time depends upon a number of factors, such as the 
 rate of elevation, the character of the rocks in the moun- 
 tain mass, the age of the mountains, and the climate. 
 
 In many places in the Alleghany Mountains, a thick- 
 ness of several miles of rock has been eroded, but it does 
 not follow that the mountains were several miles higher 
 than at present, because erosion was taking place while 
 elevation was going on. Whether the mountains were ever 
 higher than at present and how much higher depends on 
 the relative rate of activity of the eroding and elevating 
 forces. 
 
 In general the young and mature mountains are the 
 higher mountains, higher because they are young and ma- 
 ture. The age of mountains is commonly reckoned from 
 the time of their first uplift from the sea bottom, which is 
 indicated by the age of the upper strata or the newest sedi- 
 
344 PHYSICAL GEOGRAPHY 
 
 ments that take part in the folding of the mountains. It 
 should be considered that some of the mountain ranges 
 have been worn down and re-elevated one or more times 
 since the first uplift. There is good reason for thinking 
 that the Alleghany Mountains have been re-elevated at 
 least twice. 
 
 270. Mountains ap Barriers.— Mountains act as barriers in 
 the distribution of moisture. In crossing high mountains, 
 moisture-laden winds lose most of the water on the windward 
 side and pass down the lee side as drying winds. Thus the west 
 slope of the Andes in the trade wind belt receives almost no 
 moisture, as it is nearly all precipitated on the east side of the 
 mountains and helps to form that greatest river in the world, the 
 Amazon. 
 
 The higher the mountain, the more effectual barrier is it to 
 the vegetation and the lower forms of animal life. Very few of 
 the plants that grow on the plains or in the valleys could by 
 natural means cross such mountains as the Rocky Mountains or 
 the Andes. Hence the native plants — the wild flowers, shrubs 
 and trees — are quite different on the two sides of these moun- 
 tains. The same is true of many animal forms. Some of the 
 hardier and more roving forms of life find the mountains an 
 obstruction, but like man they can and do cross them. 
 
 The difficulties attending the crossing of mountains are 
 frequently a decided check to the free intercourse of the peo- 
 ple on both sides and the partial isolation in sequestered moun- 
 tain valleys is liable to cause a very provincial community, in 
 which habits and customs of past decades are preserved. In 
 many of the deep valleys or coves in the Alleghany Mountains 
 one may see the customs of fifty years or more ago with little 
 change or modification. In some places the old style wagons with 
 wooden axles, linch pins and tar buckets are still in use. These 
 wagons were in common use fifty years ago, but probably none 
 of the readers of this book ever saw one unless he has been visit- 
 ing in some of the sequestered mountain valleys. 
 
 271. Mountain Climate.— The climate of the moun- 
 tains is different from that of the surrounding plains and 
 valleys. So marked are the differences on mountains of 
 
PHYSIOGRAPHIC FEATURES 345 
 
 even moderate height from surrounding lowland areas 
 as to cause a difference of plant and animal life. The cli- 
 mate is likely to prove more moist than on the lowlands, 
 but in the region of prevailing winds this may prove true 
 of only the windward side of the mountains while the lee 
 side may be dry and barren. The east side of the Andes 
 in the trade wind belt has a very heavy precipitation 
 while the west side is rainless. In the Himalayas the north 
 slopes are dry and are bordered by an arid region, while 
 the south slopes have an exceptionally heavy precipitation, 
 the heaviest in the world. 
 
 The heavy rainfall and snow fall of the mountains are 
 being used in many localities in the western United States 
 to furnish water for irrigating the surrounding semi-arid 
 plains and plateaus. The mountains and plateaus are im- 
 portant factors in inducing rainfall over the continents. 
 The winds passing over the ocean and plains are warmed 
 and absorb moisture ; in climbing the mountains they are 
 cooled and precipitate the moisture. 
 
 The change in temperature found in ascending moun- 
 tains is quite marked. Not only is the average tempera- 
 ture lower, but the daily range of temperature is greater. 
 Night on the mountains is always cool and on the highest 
 mountains is always cold even in the summer season. 
 
 272. Economic Features of Mountains.— The moun- 
 tains are the great health resorts, furnishing sites for sum- 
 mer homes, and hotels, where fresh air, pure water, and 
 wholesome exercise are obtained by multitudes from the 
 crowded cities and towns. 
 
 Timber supply. Some of the mountains are utilized 
 as forest preserves and more of them should come under 
 government control for this purpose. The most rugged 
 mountains can never be cultivated to advantage and where 
 forests are not preserved or cared for, the mountains be- 
 
346 PHYSICAL GEOGRAPHY 
 
 come fire-swept, barren wastes instead of profitable and 
 attractive woodlands. . 
 
 The forests may not only be a profitable and continued 
 source of lumber supply, but at the same time furnish 
 game preserves where wild game and fish may flourish. 
 They may at the same time furnish the much needed regu- 
 lator of water supply to the streams, prevent disastrous 
 floods in one reason and dry stream beds in another, by 
 conserving the heavy rainfall and distributing it through 
 the dry season. 
 
 Mineral wealth. Mountains are the sources of much 
 of the mineral wealth, due in part to the fact that deep 
 erosion has exposed the deep seated rocks, thus causing 
 the exposure of a great thickness and range of rocks to 
 the view of the miner. It is also in large measure due to 
 the fracturing and metamorphism of the rocks during the 
 mountain-making process, thus producing more veins and 
 greater concentration of valuable minerals in veins. Most 
 of the mines of gold, silver, quicksilver, and other metals 
 are located in the mountains, occurring in old mountains 
 as well as in young or mature ones. 
 
 Building stone. There are large exposures of rocks of 
 many kinds in the mountain areas because of the folding 
 and erosion, and hence they furnish sites for stone quar- 
 ries. However, the largest and most .productive rock quar- 
 ries are not in the mountains. The limestone quarries of 
 Indiana and Illinois, the sandstone quarries of Ohio and 
 Connecticut, the granite quarries of eastern Massachusetts 
 and Southern Maine are all remote from mountains. 
 What reasons can you give for such a condition ? 
 
 REFERENCES 
 
 Plains : 
 
 Johnson, High Plains of the United States, 21st An. Rept. 
 U. S. Geol. Survey, Pt. VII, p. 601. 
 
PHYSIOGRAPHIC FEATURES 347 
 
 Johnson, High Plains of the United States, Natl. Geog. Mag., 
 
 Vol. IX, p. 493. 
 Salisbury, The Physical Geography of New Jersey, N. J. 
 
 Geol. Survey, Trenton, 1895. 
 Darton, The Great Plains of the Central United States, An. 
 
 Rept. U. S. Geol. Surv., also Scottish Geog. Mag., Jan., 
 
 1906. 
 Deserts: 
 
 Van Dyke, The Desert, Chas. Scribner's Sons, 1901. 
 MacDougal, Desert Vegetation, Publication of Carnegie Insti- 
 tute. 
 National Geographic Magazine, April, 1904, The American 
 
 Deserts. 
 Davis, A Temporary Sahara, Jour. Sch. Geog., Vol. IV, 1900. 
 Piatt, The Sahara, Jour. Sch. Geog., Vol. IV, 1900. 
 Herbertson, Man and His Work. 
 Plateaus : 
 
 Powell, Canyons of the Colorado, Flood & Vincent, Meadville, 
 
 Pa. 
 Dutton, The Colorado Canyon, Mon. II, U. S. Geol. Survey. 
 Campbell and Mendenhall, Plateau of West Virginia, 17th 
 
 An. Rept. U. S. Geol. Surv. 
 Hodge, The Enchanted Mesa, Natl. Geog. Mag., Vol. VIII, 
 
 1897, p. 273. 
 Mountains : 
 
 LeConte, Theories of the Origin of Mountain Ranges, Jour. 
 
 Geol., Vol. I, p. 542. 
 Willis, Mechanics of Appalachian Structure, 13th An. Rept., 
 
 Pt. II, U. S. Geol. Survey, p. 217. 
 Willis, Northern Appalachians, Natl. Geog. Mon., Am. Book 
 
 Co., 1895. 
 Hayes, Southern Appalachians, Natl. Geog. Mon., Am. Book 
 
 Co., 1895. 
 Davis, Southern New England, Natl. Geog. Mon., Am. Book 
 
 Co., 1895. 
 Davis, Rivers and Valleys of Pennsylvania, Nat. Geog. Mag., 
 
 Vol. I, p. 183. 
 Geikie, Classification of Mountains, Scot. Geog. Mag., v. 17, 
 
 Sept., 1901. 
 Lubbock, Scenery of Switzerland, MacMillan Company, 1896. 
 Cross, Laccolitic Mountain Groups, 14th An. Rept. U. S. Geol. 
 
 Surv., Pt. II, p. 165. 
 
CHAPTER X 
 THE ATMOSPHERE 
 
 273. The atmosphere is the gaseous portion of the 
 earth which surrounds the liquid and solid portions. 
 Floating in suspension in the atmosphere are large but 
 variable quantities of moisture in the form of invisible 
 vapor and also condensed vapor in the form of clouds, fog 
 or mist, along with many dust particles and microscopic 
 organisms. All this material while in the atmosphere may 
 be considered as a part of it, in the same way that the por- 
 tions of the gases which penetrate the water and the land 
 may be considered as portions of the water and land- 
 spheres for the time. The air is as truly a part of the 
 earth as the water or the land. It even approaches, pos- 
 sibly exceeds them in volume, although it is less in mass. 
 
 The science which treats of the atmosphere, its posi- 
 tion, functions, phenomena and laws governing them is 
 called meteorology. 
 
 274. Origin of the Atmosphere.— According to the nebular 
 hypothesis, all portions of the earth were at one time in a gas- 
 eous condition, but as the gases cooled and contracted, the 
 greater part became liquid, most of which on further cooling be- 
 came solid. The air is the portion which still remains gaseous. 
 The physical state of matter is partly a question of temperature. 
 At 32 degrees F. (F.=Fahrenheit, the thermometer in com- 
 mon use) water freezes and becomes solid; at 212 degrees it 
 boils and becomes a gas. Some substances, as metallic mercury, 
 freeze at a much lower temperature,— 40 degrees F., while many 
 of the common rocks freeze solid at temperatures as high as 
 3,000 degrees to 5,000 degrees F. Portions of the present at- 
 mosphere have been reduced to a liquid by lowering the tempera- 
 
 348 
 
THE ATMOSPHERE 349 
 
 ture and increasing the pressure, but at ordinary temperatures 
 it remains gaseous. 
 
 275. Function of the Air.— In the economy of the 
 earth the atmosphere serves many important functions, 
 such as (1) diffusing light; (2) conducting sound; (3) 
 retaining heat; (4) supporting life in many ways; (5) 
 supporting combustion; (6) moving ships; (7) driving 
 windmills; (8) reducing the weight of bodies submerged 
 in it, thus making it possible for some animals to walk and 
 others to fly ; ( 9 ) producing waves and ocean currents ; 
 (10) moving sand and dust and wearing away rock; (11) 
 distributing moisture and heat. What other functions 
 can you name? Can you see the air? Can you feel it? 
 Can you weigh it? 
 
 276. Composition of the Atmosphere.— The atmos- 
 phere consists of a mixture of nitrogen and oxygen in the 
 proportion of nearly four parts of nitrogen to one of oxy- 
 gen along with small but variable quantities of carbonic 
 acid gas, water vapor, argon, crypton, helium, and prob- 
 ably other rare but yet unknown gases, besides variable 
 quantities of dust particles. 
 
 Nitrogen, which forms about four fifths of the bulk of the 
 atmosphere, is one of the most inert of the gases and so far 
 as life is concerned its chief function appears to be to dilute 
 the oxygen. It has little or no tendency to combine with the 
 other elements under normal conditions, but certain plants, such 
 as clover, have the power of secreting it in their roots in the 
 form of nitrates which greatly enrich the soil. Nitrogen com- 
 bined chemically with oxygen and water forms nitric acid. If 
 this comes in contact with soda or potash it combines with them 
 forming compounds called nitrates. 
 
 Oxygen forms about one fifth of the atmosphere and is much 
 more active and aggressive in its character than the nitrogen. 
 It is the chief agent in combustion; in fact nearly all burning 
 consists of the chemical union of oxygen with carbon, forming 
 carbon dioxide and other gases, whether it be in fires, where it 
 
350 PHYSICAL GEOGRAPHY 
 
 produces heat and light, or in our own bodies where it forms 
 heat, but not light. Oxygen is ever active also in combining 
 with metals and minerals in the rocks of the earth. A knife left 
 on the ground in a few days is covered with rust; in a few 
 months it crumbles to fragments, eaten up by the rust, in other 
 words, by the oxygen of the atmosphere. Oxygen forms half of 
 the rocks of the earth's crust, and eight-ninths of the water. It 
 is being taken from the atmosphere by animals, by fires, by the 
 rusting of rocks and minerals. It is being returned by plants 
 which take the carbon dioxide gas from the air and separate it 
 into the elements, carbon, which makes new compounds forming 
 part of the plant, and oxygen, which is returned to the air. It 
 is also set free by certain chemical changes in the rocks. 
 
 Carbon dioxide or carbonic acid gas (CO2) forms a small but 
 important part of the air. The proportion varies greatly at 
 different places and times but averages about 0.03%. 
 
 It is one of the chief heating agents in the atmosphere and 
 thus has considerable influence on the climate, owing to a varia- 
 tion in the proportion present from time to time. It is a 
 denser, heavier gas than nitrogen or oxygen and absorbs and 
 holds the heat from the sun's rays, thus serving as a blanket 
 to warm the earth. It is directly necessary to plant life, furnish- 
 ing the most important article of food for the plant and indirectly 
 necessary to animal life. Why? When dissolved in water it 
 becomes an active agent of solution and disintegration in the 
 rocks, especially the limestones. 
 
 Carbonic acid is added to the atmosphere by the breath of 
 animals, by the decay and combustion of all animal and vegetable 
 matter, by volcanoes, by carbonated springs and from the sea 
 water. It is extracted from the air by plants which fix the car- 
 bon in their tissue and give the oxygen back to the air, by the 
 disintegration of the rocks in which it combines with other ma- 
 terials to form carbonates, and it is absorbed by the sea water 
 and fresh waters where these are not already saturated with it. 
 Owing to this circulation through the rocks and the sea, the 
 proportion of this gas in the air varies sufficiently from one geo- 
 logic age to another, it is thought, to affect the climate materially. 
 
 Water vapor is a small, variable, but very important consti- 
 tuent of the air. The water in an invisible gaseous condition is 
 absorbed by the atmosphere from the surface of the ocean, otber 
 
THE ATMOSPHERE 351 
 
 bodies of water, and the moist land. The gases ejected from 
 volcanoes also supply large quantities of vapor to the air. An- 
 other source of supply is in combustion and as exhalation from 
 the lungs of animals. 
 
 The water in the invisible gaseous state is carried by the 
 winds over the continents, where, condensing in clouds, it is pre- 
 cipitated in the form of rain or snow to fall on the earth and 
 flow back to the ocean again to start on a similar circuit. The 
 circulation of water in this way is essential to all life — in the 
 ocean, in the air, and on the land. A large per cent of all living 
 plant and animal matter consists of water and there must be a 
 constant renewal of the water supply in order to retain the life. 
 
 Dust is another important constituent of the air which is 
 everywhere present but most abundant over the land areas near 
 the surface in dry weather. Why? It consists of exceedingly 
 fine particles of pulverized rock carried up by the winds or 
 blown out from volcanoes, of particles of unconsumed fuel in the 
 smoke, of living germs in the form of bacteria and microbes, or 
 of decayed plant and animal tissue. In a ray of sunshine passing 
 through a small opening into a dark room, one can see a vast 
 number of the dust particles, but there is a much larger number 
 invisible because so very small. 
 
 The dust of the air is thought to be an important aid in the 
 precipitation of moisture. The dust particle becomes a center 
 of condensation of moisture until there is sufficient to form the 
 raindrop or the snowflake, which then falls to the earth. It acts 
 with the carbonic acid and the moisture in heating the air, as 
 each little dust particle becomes a little furnace or reservoir of 
 heat which -it radiates in all directions. The bacterial portion 
 aids decomposition and the spread of disease. It influences the 
 color of the sky, the brilliant red sunset being due largely to the 
 dust particles in the air. 
 
 Dust is sometimes classed as an impurity in the atmosphere, 
 but since it is always present, and serves a useful if not a neces- 
 sary purpose for the support of life, it is properly one of the 
 constituents of the air. 
 
 277. Pressure of the Air.— Because the pressure of 
 the air is exerted equally iu all directions, it long remained 
 unperceived. If we should exhaust all the air from under- 
 neath a scale pan, we would find a weight of air on the 
 
352 
 
 PHYSICAL GEOGRAPHY 
 
 pan of about fifteen pounds to the square inch or a little 
 more than a ton to the square foot, that is, provided the 
 weight were taken at sea level ; with change of temperature 
 or change of elevation the pressure would change. It 
 would increase if taken below sea level and decrease if 
 taken above. It would decrease with an increase in the 
 temperature and increase with a decrease in temperature 
 because the warm air expands and is therefore 
 lighter than the same volume of cold air subject 
 to the same pressure and the cold air contracts 
 and is hence heavier than a similar volume of 
 warm air. 
 
 
 Fig. 243. 
 
 Mercury 
 barometer, 
 
 common 
 form. 
 
 Weight on the earth is the effect of gravity 
 which tends to draw all bodies toward the center of 
 the earth, hence the weight of the atmosphere at 
 any point is its vertical pressure, but owing to the 
 extreme mobility, this pressure due to weight is 
 exerted equally in all directions, so that under ordi- 
 nary conditions we do not find the scale pan pressed 
 downward by air, because there is the same pressure 
 underneath as on top. The pressure of ten tons or 
 more on the outside of the human body is not felt 
 because there is a corresponding pressure on the in- 
 side. The weight of a cubic foot of air at sea level 
 at a temperature of 60 degrees is .075 lbs., while the 
 pressure exerted by this cubic foot would be more 
 than a ton on each side. 
 
 278. Barometer.— The instrument com- 
 monly used in weighing the air, that is, de- 
 termining the pressure, is a barometer, which in 
 its simplest form consists of a glass tube closed 
 at one end, filled with mercury and inverted in 
 a cup of the same metal. If this is done at 
 sea level the mercury will settle in the tube until 
 the top of it is about 30 inches above the level 
 of that in the cup. Now a column of mercury 
 
THE ATMOSPHERE 353 
 
 30 inches high weighs 15 pounds per square inch at the 
 base of the column, hence the weight of the air pressing 
 on the surface of the cup outside of the tube must be equal 
 to 15 pounds per square inch, since the two balance each 
 other. Why is mercury used? Why not some other 
 liquid? If water were used how long a tube would it 
 require ? 
 
 An aneroid barometer differs from a mercurial one in substi- 
 tuting for the column of mercury a small corrugated metallic 
 box from which the air has been exhausted as 
 nearly as possible. The surface of this box is 
 connected through a series of levers to a needle 
 in such a way that when the sides of the box 
 are pressed in, as would be the case with an 
 increase of pressure in the air, the needle will 
 turn around on a dial like the hand of a watch, 
 and when the pressure decreases the needle 
 moves in the opposite direction. The dial of 
 the aneroid is marked so that movements of F ,. 
 
 the needle will indicate the number of feet the YO i& barometer 
 
 barometer has been taken up or down, or it for measuring 
 
 may be marked in inches to correspond to the elevations. See 
 
 movements of the mercury in the other baro- VlG / 246 for m " 
 
 „ , tenor construc- 
 
 meter; in fact it generally has both scales. ti 
 
 Because it can be carried in the pocket like a 
 watch, and is much more convenient for ordinary use than the 
 bulky mercurial barometer. 
 
 279. Density of the Air.— If a barometer were car- 
 ried up a mountain the mercury would gradually fall m 
 the tube, because of decrease in the pressure of the atmos- 
 phere, until at an elevation of 3.4 miles above the sea there 
 would be only 15 inches in the tube ; that is, at that height 
 the air would be only half as dense or heavy as at sea 
 level. At greater elevations the density has been esti- 
 mated as follows : 
 
 23 
 
354 
 
 PHYSICAL GEOGRAPHY 
 
 Elevation 6.8 miles, density % and barometer 7.5 inches 
 
 10.2 " . " % " 3.75 
 
 13.6 " " & " 1-87 
 
 17.0 " " 3V " -95 
 
 This estimate is based on the assumption that the den- 
 sity decreases in the upper atmosphere at the same rate 
 that it does in the lower atmosphere ; that is, a decrease of 
 one-half for every 3.4 miles ascent. 
 
 280. Height of the Atmosphere.- The upper limit of 
 the atmosphere is not known, but various estimates have 
 placed it at heights varying from 50 to 500 miles. It prob- 
 ably extends much higher than either figure ; in fact, there 
 is good reason for thinking that it extends as far as the 
 outer limit of the zone of control of the earth's gravity. 
 But if the decrease in density approximates that indicated 
 in the above table it becomes so rare as to be difficult of 
 detection by any available means far short of 200 miles. 
 
 281. Pressure Curve.— If the barometer readings are 
 recorded at any point for several days it will be seen that 
 there is considerable variation. If the barometer should 
 be read for several different hours each day for several 
 
 Fig. 245. A barogram or pressure curve made by a barograph during the 
 passage of a cyclone followed by a cold wave. Notice the rapid fall and 
 rise of pressure. 
 
 days and the results plotted on cross-section paper, the re- 
 sult would be the pressure curve. This pressure curve is 
 plotted even more accurately by an instrument called the 
 
THE ATMOSPHERE 
 
 355 
 
 barograph. (See fig. 246.) The curve made by the baro- 
 graph is called a barogram. (Fig. 245.) 
 
 282. Barograph.— The barograph used by the U. S. Weather 
 Bureau is based on the principle of the aneroid instead of the 
 mercurial barometer. It consists of a corrugated iron box (B) 
 from which the air has been exhausted so that an increase in the 
 
 Fig. 246. A barograph. The pen traces a line on the paper which is moved 
 by clockwork. If the pressure were uniform the line traced would be 
 parallel to the horizontal lines on the paper. 
 
 pressure of the air depresses the surface of the box and a de- 
 crease in the pressure causes a corresponding elevation in the 
 surface produced by a spring inside the box. These movements 
 of the surface are magnified by a series of compound levers to 
 which is attached a pen so adjusted as to leave its trace on 
 the roll of cross-ruled paper which is moved by clockwork. 
 This shows conclusively that the pressure at any place at any 
 one time is dependent on the condition of the weather. If the 
 effect of the weather on the barometer is known, then the process 
 may be reversed and the record of the barometer may be taken 
 as the indication of the weather conditions; and if along with 
 
356 PHYSICAL GEOGRAPHY 
 
 this, the regular movements of the atmosphere are considered, 
 the weather conditions may often be foretold for some time 
 ahead. 
 
 283. Isobars.— In order to compare barometer read- 
 ings from different localities to determine probable weather 
 conditions, it is necessary to make corrections for the dif- 
 ferences in elevation of the places and another for the dif- 
 ferences in temperature. Tables have been made out for 
 this purpose so that having the reading of the barometer 
 and the thermometer, and knowing the elevation of the 
 point above sea level, it is only necessary to turn to the 
 tables and make the necessary additions or subtractions to 
 reduce the readings from different places to a common 
 plane, which by common consent is taken as sea level. The 
 records that are given on the government weather maps 
 are all the corrected sea-level readings at the temperature 
 of 32 degrees F. 
 
 In order to bring out graphically the results obtained 
 from barometric readings at many different stations, lines 
 representing variations in pressure of one-tenth of an inch 
 are drawn through points having the same barometric 
 pressure. Such lines are called isobars (meaning equal 
 pressure), and are shown on the daily weather maps by 
 continuous black lines. Compare carefully several daily 
 isobaric charts or weather maps with each other and with 
 the isobaric chart of the world for the year. (See fig. 254.) 
 
 284. Barometric Gradients.— On the daily weather map most 
 of the isobars are more or less concentric around centers, some 
 of which are marked high and some marked low, meaning high 
 pressure and low pressure. The barometric gradient is the rate 
 at which the air pressure changes from place to place and 
 particularly between the high and the low. It indicates the 
 direction in which the atmosphere tends to move, namely, 
 from the high to the low, and the steeper the grade, that is, 
 the greater the number of the isobars, the more rapidly the 
 
THE ATMOSPHERE 357 
 
 air moves and hence the stronger is the wind. Test this by 
 comparing current weather maps on a windy day and a calm one. 
 
 285. Temperature and Heat.— Temperature is the 
 measure of the heat energy of any body. The instrument 
 used for recording the temperature is called a thermometer 
 (heat measure). In the common house-thermometer mer- 
 cury rises and falls through a capillary tube from expan- 
 sion and contraction with increasing and decreasing tern* 
 perature, and generally indicates increase and decrease of 
 heat. However, many bodies are capable of absorbing or 
 giving off considerable heat without any perceptible change 
 of temperature. Thus when heat is applied to ice, the 
 temperature does not vary until all the ice has been changed 
 to water. The heat required to change a pound of ice to 
 water at the same temperature would raise the pound of 
 water from 32 degrees to 174 degrees F. This is called 
 latent heat of fusion, and will be given off again before 
 the water will freeze. It requires a large increment of 
 heat to change water from a liquid at 212 degrees to a 
 vapor at the same temperature, the latent heat of vapori- 
 zation. (This is technically expressed in heat units called 
 calories. A calorie is the amount of heat required to raise 
 a gram of water one degree Centigrade. The latent heat 
 of vaporization of water is 536.6 calories.) "Why does 
 sprinkling the lawn or the street on a hot summer day cool 
 the air? Why is it generally warmer in winter and cooler 
 in summer on the sea shore than in the interior? Why is 
 it sometimes warmer after a rain than before? 
 
 286. Thermometer.- The temperature of the air is 
 usually measured by a mercury thermometer, which con- 
 sists of a small bulb filled with metallic mercury that is 
 attached to a capillary tube in which the mercury rises 
 when it is heated and in which it sinks when it is cooled. 
 On the tube or on a flat surface to which the tube is at- 
 
358 
 
 PHYSICAL GEOGRAPHY 
 
 tached is a scale marked off in degrees from which is read 
 the number corresponding to the height of the mercury in 
 the tube. The mercury thermometer may be used for 
 measuring temperatures between —40 degrees, the freezing 
 point of mercury, and 648 degrees F., the boiling point. 
 For lower temperatures some other liquid as alcohol or 
 ether is used ; for higher temperatures some more resistant 
 metal or metals or some other device is used. Describe a 
 maximum and a minimum thermometer and the Fahren- 
 heit, Centigrade, and absolute scales for grading ther- 
 mometers, if these instruments are at hand. 
 
 287. Temperature Curve. — The variation in temper- 
 ature at any place from time to time may he represented 
 by a temperature curve as shown in fig. 247. The curve 
 
 Fig. 247. Thermogram, a temperature curved formed by the thermograph. 
 
 may be constructed for any period of time for which the 
 thermometer readings have been taken. The thermograph 
 automatically records such a curve with greater accuracy 
 of detail than can be shown on one drawn from thermo- 
 meter readings. Study curves of this kind if available, 
 and note the time of day when the maximum and mini- 
 mum temperatures occur. Each student should plot a 
 temperature curve for a week or a month from data ob- 
 tained by reading the thermometer and recording the tem- 
 perature 3 or more times each day. 
 
THE ATMOSPHERE 
 
 359 
 
 A thermograph is an instrument for recording automatically 
 the temperature for a fixed period of time in much the same way 
 as a barograph records pressure. The record of the thermograph 
 is a thermogram or temperature curve. (See fig. 247.) 
 
 Fig. 248. Thermograph, an instrument for recording temperature changes. 
 
 288. Sources of Heat.— The three sources of heat sup- 
 ply on the earth are (1) the sun, (2) the stars and other 
 heavenly bodies, (3) the internal heat of the earth. In 
 quantity the last two are insignificant when compared with 
 that from the sun, which is the source of not only nearly 
 all the heat, but the light, and other forms of energy as 
 well. The radiant energy that comes from the sun is 
 known as insolation, which manifests itself on the earth in 
 part as heat, in part as light, and probably in several other 
 forms of energy. The earth receives about one two-bil- 
 lionth portion of the sun's insolation and a large part of 
 that received is not retained but is reflected or radiated 
 off into space. 
 
360 PHYSICAL GEOGRAPHY 
 
 A small portion of the sun's rays, as they pass through the 
 atmosphere, are intercepted by the dust particles and the heavier 
 gases and changed to sensible heat, but the greater part passes 
 directly through to the surface of the earth, where a portion is 
 absorbed by the rock-and-water-surface and changed to latent, or 
 radiant heat and a portion is reflected back through the atmos- 
 phere. The proportion of rays absorbed to those reflected, varies 
 greatly with different surfaces. More are reflected from a water 
 surface than from rock and more from light-colored rocks than 
 from dark-colored ones. There is likewise a wide variation de- 
 pending on the angle of inclination of the rays to the surface. 
 The greatest percentage of insolation is absorbed under the ver- 
 tical rays and as they vary from the vertical there is an increas- 
 ing proportion reflected until the tangent rays, such as those at 
 sunrise and sunset, are nearly all either reflected or else pass 
 directly through the atmosphere into space beyond. 
 
 289. Temperature of the Air. — The atmosphere is 
 warmed (1) by the direct insolation of the sun, (2) from 
 the heated surface of the earth by radiation, by conduc- 
 tion, and by convection, and (3) by compression as shown 
 when pumping air into a bicycle tire. When the air 
 descends from altitudes of less pressure to regions of greater 
 pressure it is compressed and warmed, as in the high pres- 
 sure areas and where the air flows from the mountain top 
 into the valley or plain; (4) by precipitation. The great 
 quantity of heat required to change water to vapor remains 
 latent in the vapor and is given off when the moisture is 
 precipitated. 
 
 The air is cooled (1) by radiation of its heat into space ; 
 (2) by conduction when it comes into contact with the 
 cooler earth or body of water; (3) by expansion as when 
 it flows out of a bicycle tire or when it rises from a region 
 of greater to one of less pressure as in ascending the moun- 
 tain or in the rising currents in the low pressure areas; 
 (4) by convection, as by the descent of the cold currents 
 to replace the rising currents of heated air; (5) by evapor- 
 
THE ATMOSPHERE 361 
 
 ation. How? The heating of the air by compression and 
 the cooling by expansion is known as adiabatic heating and 
 cooling. 
 
 290. Elements Affecting the Temperature of the Air. 
 
 — The distribution of solar heat is determined by the suc- 
 cession of day and night and of the seasons. The atmos- 
 phere and the earth underneath it receive heat directly 
 from the sun during the day, receiving the greatest quan- 
 tity at midday when the rays are most nearly vertical. 
 The temperature, however, is the highest from one to two 
 hours after noon. Why? There is more or less regular 
 decrease in the heat received from the sun, as one goes 
 from the tropics toward the poles. Why? 
 
 Effect of pressure. In areas of high pressure, the air is being 
 warmed because it is under pressure and in areas of low pres- 
 sure, it is being cooled because it is rising and expanding. How- 
 ever, the temperature of the air near the earth is higher in the 
 low pressure areas than in the high; in fact, that is the reason 
 why it is low, because the temperature is higher and hence the 
 air is lighter and is crowded up by the inward pressure of the 
 surrounding heavier air; the temperature is kept high because 
 the air moves into the center along the surface of the earth, 
 where it is warmed by conduction and frequently by precipita- 
 tion of the moisture; it cools by expansion as it rises, but it is 
 then beyond the reach of our senses. The air is cooler and feels 
 cooler in the high centers because it is descending from the 
 higher altitudes, where it is much colder. The clear air of the 
 high center favors radiation of heat and in that way lowers the 
 temperature. Cold waves come with the high centers in the 
 winter. The fact that the air is warmed in the high and cooled 
 in the low is shown in two ways, by comparing the temperature 
 taken at high altitudes, by means of a kite or balloon, and second 
 by noting that in the highs the air is clear and generally free 
 from clouds and rain, while in the lows, it is cloudy and fre- 
 quently precipitates rain or snow. Cooling the air condenses the 
 moisture and warming it increases its capacity for moisture, 
 causing it to dissolve the clouds instead of condensing them. 
 (See Sec. 296 and 314 for explanation of high and low pressures.) 
 
362 PHYSICAL GEOGRAPHY 
 
 Effect of latitude. The seasonal changes are most marked at 
 and near the poles and least at and near the equator, due to the 
 fact of less variation in the inclination of the sun's rays in the 
 tropics and greater uniformity in the distribution of sunlight 
 and darkness. 
 
 The temperature decreases with an increase of latitude at 
 the average rate of about 1 degree F. for 1 degree or about 70 
 miles of latitude. 
 
 Effect of altitude. The temperature decreases with altitude 
 at the average rate of about 1 degree F. for every 300 feet of 
 ascent; hence, at the equator one would find about the same 
 change in temperature by ascending a mountain six miles high 
 as in going north or south 1000 times this distance. The reason 
 for the rapid decrease in temperature in ascending the moun- 
 tain is that the air is less dense, and contains less carbon dioxide, 
 water vapor, and dust particles that serve to warm the air at 
 lower altitudes. 
 
 Effect of Water. — Bodies of Water tend to equalize 
 the temperature of the region bordering them, because they 
 absorb heat less rapidly than the land, do not become so 
 hot during the day or during the summer season, and 
 since they part with their heat less rapidly than the land, 
 they do not cool as quickly; hence the water is cooler than 
 the land in the summer and warmer in the winter and ex- 
 ercises a corresponding effect on the atmosphere that comes 
 in contact with it Therefore points along the sea coast 
 have a more uniform climate than inland points. The 
 same thing is true in a less degree of the lakes, especially 
 the larger lakes. Even the Finger lakes of central New 
 York temper the climate on their shores, but their influence 
 does not extend so far away as is the case with larger 
 bodies of water.- 
 
 The chief reasons for the tempering influence of the 
 water on the air are (1) the greater specific heat of water 
 so that it requires about twice as much heat to raise a 
 given volume of water one degree as it does a similar vol- 
 
THE ATMOSPHERE 363 
 
 ume of earth; (2) being more mobile the water warmed 
 in one place is carried by currents to another and colder 
 part of the ocean, and since cold water is denser and 
 heavier, the water cooled at the surface sinks to the bot- 
 tom and the surface is not frozen until the whole body of 
 water is reduced to the point of greatest density which is 
 near the freezing point ; hence large bodies like the ocean 
 are never frozen in our latitude but the deeper portions 
 are always cold ; ( 3 ) part of the heat received on the water 
 is expended in producing evaporation and hence does not 
 raise the temperature; (4) clouds and fog which check 
 radiation of heat are more common over water than over 
 land areas. 
 
 Effect of Clouds. — Cloudiness retards loss of heat by 
 radiation. In the spring and autumn when the tempera- 
 ture is near the freezing point one frequently hears the 
 remark, "If it clears off to-night, there will be a frost." 
 On a clear night the heat received from the sun during 
 the day is rapidly radiated out into space. If the clouds 
 are present this radiation is checked in a large degree, be- 
 cause they do not permit the heat to pass through as readily 
 as through clear atmosphere and they also radiate and re- 
 flect heat back to the earth. 
 
 Prevailing winds affect the temperature in some places. 
 In India for about half the year, the winds blow from the 
 Indian Ocean warm and moist. During the other half 
 they come from the Thibetan Plateau and Himalaya 
 Mountains dry and cold. 
 
 Influence of topography. In high latitudes where the sun's 
 rays are quite slanting even at midday, there is great difference 
 in the quantity of heat received on the warm south slopes, which 
 may be at nearly right angles to the noonday sun, from that on 
 the cool north slopes where the rays may be nearly tangent or 
 in some cases never strike even at noonday. Slopes facing west 
 or southwest are warmer than those facing east or south- 
 
364 
 
 PHYSICAL GEOGRAPHY 
 
 east. The difference may be manifest in a region moderately 
 hilly, but is still more pronounced in a mountainous country, 
 especially so where the mountains extend east and "west. Are 
 there any spots in your vicinity where the spring flowers bloom 
 first? Where the early fruits first ripen? What is the relation 
 of such spots to the sunshine? (See fig. 249.) 
 
 Fig. 249. Diagram showing different effects of the sunshine on the two 
 sides of a valley. The north side of the valley receives the nearly 
 vertical rays of the sun at noonday, while the south side is in the 
 shadow. In the winter season this causes more frequent thawing and 
 freezing, and hence more rapid weathering on the north side, and in 
 the spring it causes earlier vegetation. 
 
 291. Isotherms. — The thermometer is read and re- 
 corded twice daily, at 8 o'clock morning and evening, at a 
 great many stations in the United States and Canada and 
 the results distributed by telegraph to certain places where 
 they are recorded on maps and lines drawn connecting 
 points having the same temperature ; such lines are called 
 isotherms, meaning equal temperatures. By consulting a 
 number of daily weather maps for successive days, it will 
 be seen that there is considerable variation in the position 
 of the isotherms from day to day. These may all be 
 averaged and a map constructed showing the mean for 
 the month. Fig. 250 shows an isothermal map for July, 
 one for January and another for the year. Compare these 
 carefully and account for the different positions of the 
 same isotherms. 
 
Fig. 250. Isothermal chart for January, July and for the year. 
 Note how the isotherms move southward in the northern win- 
 ter, and north in the summer. Why ? Why are they deflected 
 so much more in North America in the summer and in the 
 north Atlantic in the winter ? 
 
366 PHYSICAL GEOGRAPHY 
 
 292. Temperature Gradient.— On some of the weather maps, 
 there are more isotherms than on others, showing at times a 
 much greater difference or range of temperature. In general, 
 great differences in temperature are found associated with great 
 differences in pressure; in fact extremes of temperature cause 
 extremes of pressure. The difference between the high and low 
 temperatures is called a temperature gradient and the gradient 
 is higher when the isotherms are most numerous and closest to- 
 gether. Steep temperature gradients are associated with steep 
 or decided pressure gradients. Compare figs. 245 and 248 and 
 note that high pressure is associated with low temperature and 
 vice versa. The gradients are high in each case. 
 
 293. Temperature Zones.- In the isothermal chart of 
 the world, it is shown that the isotherms of 70 degrees lie 
 some distance on each side of the equator but at different 
 distances in the January and in the July charts. These 
 isotherms inclose the warm or hot zone through the midst 
 of which runs a line of highest temperature, the heat 
 equator, which lies north of the true equator in July and 
 south of it in January; that is, it shifts north and south 
 following the sun. The temperature belt inclosed between 
 the isotherms of 70° and 30° is called the temperate zone, 
 while the region around the poles outside of the thirty de- 
 gree isotherm has a frigid temperature. All of these zones 
 it will be observed shift north and south following the 
 movements of the heat equator. (Study fig. 251.) 
 
 All of the temperature zones are more nearly uniform in the 
 southern hemisphere than in the northern, and more uniform on 
 the southern oceans than on the southern continents. Why? 
 The student should be able to state the reasons from the data in 
 the preceding pages. 
 
 MOVEMENTS OP THE ATMOSPHERE 
 
 294. Winds, Currents and Calm?.— The direct cause 
 of the movements of the air is difference in pressure, which 
 in turn is due to difference in temperature. Thus, when 
 
THE ATMOSPHERE 
 
 367 
 
 Fig. 251. Climatic zone map based on isotherms. Point out some of the varia- 
 tions from a zonal map based on the tropical and polar circles. Compare 
 with Fig. 250 and note how the zones may shift with the seasons. 
 
368 PHYSICAL GEOGRAPHY 
 
 the air at any place becomes heated it expands and is 
 pushed up by the surrounding air crowding in to take its 
 place, which in turn is replaced by air descending at some 
 other place. So winds and air currents are produced. 
 The movements more or less horizontal, where rapid enough 
 to be perceptible, are called winds. The vertical move- 
 ments, both up and down, are not ordinarily perceptible 
 and are known as calms. The equatorial calms are formed 
 by rising currents of air and the tropical calms by descend- 
 ing currents, while the movement from the tropical calms 
 to the equatorial calms forms the trade winds. 
 
 Classification of the winds. The winds may be grouped 
 for classification into terrestrial or planetary, cyclonic or 
 eddying, and continental. The wind is named from the 
 point of the compass from which it is blowing, hence a 
 west wind means a movement of the air from the west to- 
 ward the east. 
 
 295. Terrestrial or planetary winds are those due to 
 the condition of a rotating planet heated from an external 
 source, and occur on all planets that have an atmosphere. 
 There is an excessive heating in the region of the equator, 
 which causes the air to expand and flow off aloft, thus pro- 
 ducing a low pressure belt of calms known as the doldrums 
 or the equatorial calms and a high pressure near the tropics 
 known as the horse latitudes or tropical calms formed by 
 descending air. 
 
 Trade winds. The warm air in the doldrums is forced 
 upwards by the air which crowds in from the trade winds 
 on both sides. The trade winds do not move directly north 
 and south to the equator but are deflected to the west be- 
 cause of the rotation of the earth, which according to Fer- 
 rel's law causes a deflection of all winds, cyclonic as well 
 as terrestrial, to their right in the northern hemisphere 
 and to their left in the southern hemisphere. It is be- 
 
Regular Winds / / / / 
 
 Monsoons _ _ _ // \t // 
 
 S \ \ \ \ \ \ 
 
 NORTH-WESTERLIES 
 
THE ATMOSPHERE 
 
 369 
 
 cause of the regularity with which these winds blow that 
 they are called trade winds. While they are still im- 
 portant factors in commerce they were much more so when 
 all the vessels were sailing vessels before the days of 
 steam navigation. 
 
 wind:} and Raln3 of July — Northern Snmmfa? 
 
 Fig. 253. Planetary wind belts in summer and winter. The heat equator lies 
 in the midst of the equatorial rain belt. 
 24 
 
370 PHYSICAL GEOGRAPHY 
 
 Since the doldrum belt shifts north and south following 
 the sun during the change of seasons, the trade wind belts 
 shift with it. (See fig. 253.) 
 
 The antitrades are caused by the ascending air at the 
 equator overflowing out toward the poles in the higher 
 atmosphere, above the trade winds and in an opposite di- 
 rection. In the vicinity of the tropics, the antitrades 
 descend in part to the surface, but since the descent is 
 vertical or nearly so, they form belts of calms known as the 
 horse latitudes or tropical calms. 
 
 The prevailing westerlies are the winds blowing from 
 the horse latitudes towards the poles, but like the trade 
 winds and all other atmospheric movements, they follow 
 Ferrel's law and are deflected to the right in the northern 
 hemisphere and to the left in the southern hemisphere, 
 thus becoming northwest winds in the southern hemisphere 
 and southwest winds in the northern. They are much less 
 regular in their movement than. the trade winds, frequently 
 shifting direction to take part in the great spiral whirls 
 known as cyclones and anticyclones. They are also sub- 
 ject to many local disturbances such as land-and-sea breezes 
 and the mountain and valley breezes. Beyond the belt of 
 the prevailing westerlies, the movements of the atmosphere 
 are not so well known; the winds are thought to circle 
 around the poles forming the circumpolar whirl or eddy. 
 
 296. Cyclonic Winds.— A second class of winds more 
 local and variable than the terrestrial ones are the cyclones, 
 in which the winds move inward and upward in a spiral 
 whirl or eddy around a region of low barometric pressure. 
 In temperate climates, cyclones occur in the belt of the pre- 
 vailing westerlies where they cover large areas, sometimes 
 1,000 miles or more in diameter. 
 
 There are two movements of the air in a cyclone, a 
 horizontal one towards the center and a vertical one at 
 
THE ATMOSPHERE 
 
 371 
 
 and near the center. The origin of the movement is prob- 
 ably due to the increase in temperature at the center which 
 causes the air to expand and overflow in the upper atmos- 
 phere, producing a downward pressure on the surrounding 
 
 Fig. 254. Cyclone (low) and anticyclone (high) areas in United States. 
 Line of arrows show path over which the central low has passed. Shaded 
 areas indicate where rain has fallen during preceding 24 hours. Dotted 
 lines, isotherms, continuous lines, isobars. Arrows show direction of "wind. 
 Black circle on the arrow, cloudy, open circle, fair weather. The great 
 storm of Feb., 1902 which caused excessive floods in the Ohio valley. 
 (U. S. Weather Bureau.) 
 
 area. The crowding towards the center by this downward 
 pressure pushes the expanded air up and the movement is 
 continued until equilibrium is again restored. The area 
 is variously designated a cyclone, a low pressure area or a 
 low. It should be noted that the violent whirling storms 
 which prove so destructive to life and property, called 
 cyclones in the newspapers, are properly called tornadoes, 
 
372 
 
 PHYSICAL GEOGRAPHY 
 
 and are described below. One or more cyclones pass 
 across the United States nearly every week. (Figs. 254 
 and 255.) 
 
 An anticyclone is an area of high pressure or a high, 
 where the air is descending and the winds blow out along 
 the surface from the center. As the name indicates it is 
 the opposite of a cyclone, the winds blowing from the anti- 
 cyclone or high, to the low. The higher or steeper the 
 pressure gradient, that is, the greater the difference be- 
 tween the pressure in the center of the low and the high, 
 the stronger will be the winds. The air flows down the 
 pressure slope at a rate proportional to the steepness of 
 the slope. 
 
 The weather in the United States is in a large measure 
 determined by the "highs" and "lows" which move across 
 the country in the general direction of the prevailing 
 winds. (See sec. 319.) 
 
 Fig. 255. Mean tracks of the high and low pressure areas across the United 
 States and the average daily movement of the same. (U. S. Weather 
 Bureau. ) 
 
THE ATMOSPHERE 
 
 373 
 
 Movements of cyclones in the United States. Cyclones some- 
 times enter the United States from the northwest into Montana 
 or Dakota and travel southeast to near the middle of the Missis- 
 sippi valley and then northeast to and sometimes across the 
 Atlantic Ocean. Sometimes they develop in the southwest in 
 New Mexico and Texas and then move northeast off the con- 
 tinent. Sometimes they come in from the Pacific Coast. Some- 
 times they pass out of the United States in the southeast. The 
 rate of advance differs somewhat, but is generally faster in the 
 winter, averaging about 800 miles per day, and slower in the 
 summer, about 500 miles per day. (See fig. 255.) Test this by 
 actual measurement from a series of weather maps for successive 
 days. 
 
 297. Hurricanes. — The tropical cyclones or hurricanes 
 are great whirling storms from 100 to 300 miles in dia- 
 meter, in which the winds frequently become very violent 
 
 
 FiG. 256. Map showing track of the Galveston hurricane. From the dates 
 the rate of movement can be estimated. (U. S. Weather Bureau.) 
 
374 
 
 PHYSICAL GEOGRAPHY 
 
 and destructive near the center. In the very center, how- 
 ever, the winds die away leaving a calm with a clear sky, 
 known as the ' ' eye of the storm ' ' which is said to vary from 
 10 to 20 miles in diameter, while immediately around it 
 the winds are most violent, decreasing in intensity further 
 
 iM.G. 257. Map showing track ot the Oalveston hurricane through a forest in 
 Texas. The trees nearly all lie parallel with each other. (W. S. Bray.) 
 
 from the center. The hurricanes originate on the oceans 
 within the tropics. The South Atlantic ocean, however, 
 appears to be free from them. In the North Atlantic they 
 start near the West Indies and are known as West India 
 hurricanes. They generally move in a northwesterly direc- 
 tion to the coast of Florida and thence northeasterly across 
 the Atlantic occasionally reaching the coast of Europe be- 
 fore they are dissipated. Sometimes they move up the 
 east coast of the United States, causing great destruction 
 
THE ATMOSPHERE 
 
 375 
 
 to the shipping. Occasionally one of the hurricanes passes 
 into the Gulf of Mexico and thence into the Gulf States. 
 It was one of these tropical hurricanes that passed over 
 
 I'iG. 258. Photograph of a tornado. Note the funnel shaped cloud around 
 which the winds move with great velocity. (W. E. Seright. ) 
 
 the city of Galveston in the year 1900 and destroyed the 
 greater part of the city, besides doing much damage in the 
 country farther north. Similar storms in the Pacific Ocean 
 
376 PHYSICAL GEOGRAPHY 
 
 are called typhoons and often prove very destructive in 
 the region of the Philippines and Japan. (Figs. 256 and 
 257.) 
 
 298. Tornadoes are cyclonic whirlwinds of small area 
 and great intensity that originate in the region of the pre- 
 vailing westerlies. They are associated with thunder- 
 storms in the summer season and are most common on 
 the plains of the west and southwest. It is not often that 
 a violent tornado occurs east of the Alleghany Mountains, 
 yet it does sometimes. 
 
 They are generally marked by a dark funnel-shaped 
 cloud suspended from the black mass of the thunder cloud 
 (see fig. 258). The storm generally moves east or north- 
 east at a rate varying from 20 to 40 miles an hour but the 
 rotary velocity of the wind in the whirl may reach 500 
 miles or more. It is the most violent class of storms known 
 in the United States and some of the effects produced are 
 almost incredible, such, for instance, as plucking the feath- 
 ers from a chicken, tearing the tires from a wagon, tearing 
 the lath from a house and driving them through the roof 
 of a barn. 
 
 When a tornado occurs on a lake or the ocean, a column of 
 water is often formed in the vortex and it is then called a water- 
 spout. A vessel caught in one of these waterspouts is liable to 
 severe injury if not total destruction. It is thought that the 
 water in the waterspout is mostly condensed from the clouds 
 rather than drawn up from the sea. 
 
 299. Hot Waves.— The warm, south winds drawn 
 northward into a low pressure area, when unseasonably 
 warm and dry, are called siroccos. The typical siroccos 
 occur in Italy and are caused by the hot, scorching winds 
 of the African desert flowing towards a low pressure area 
 in central Europe. Similar but not such strongly marked 
 siroccos occur at times in the Mississippi Valley, where 
 
THE ATMOSPHERE 377 
 
 they are known as hot waves and cause drouth in the sum- 
 mer season and thaws in the winter. In Australia such 
 winds are known as brickfielders. 
 
 The chinook is the warm, drying wind that descends the east- 
 ern slope of the Rocky Mountains to the great plains. The 
 moisture has been precipitated on the west slope and summit of 
 the mountains and the air descends on the plains as dry, hot 
 winds. 
 
 300. Cold Waves.— A cold wave signifies a sudden 
 fall of the thermometer resulting in temperatures extreme- 
 ly low for the season in any given locality. For the winter 
 season in central New York a cold wave is defined as a 24 
 hour temperature fall of 20 degrees or more to a minimum 
 of 10 degrees or lower, while in the warmest portions of 
 the United States a fall of 16 degrees to a minimum of 32 
 degrees only is required. It follows a cyclone, precedes 
 an anticyclone, and is produced by the cold winds from 
 the plains of the west and northwest moving towards a low 
 to the east. It is commonly accompanied by fair weather 
 but occasionally there is a fine drifting snow and high 
 winds forming the much dreaded blizzard of the western 
 plains. The Norther of Texas, the buran of Siberia and 
 the northeaster of western Europe are local names for a 
 cold wave in the different countries. The last is produced 
 when a low pressure swings a little farther south than 
 usual and the cold winds are drawn down from the plains 
 of northern Europe. The northeaster in the United States 
 is much dreaded along the Atlantic coast as it is frequently 
 the border of an advancing hurricane from the south, 
 which means danger to coasting vessels. 
 
 301. Continental Winds.— A third class of winds, 
 caused by local differences in the rate of radiation and ab- 
 sorption over land and water areas, is called continental 
 winds, the most marked type of which is the monsoon. 
 
378 PHYSICAL GEOGRAPHY 
 
 302. Monsoons.— The monsoons are best developed in 
 India where the sea breeze in the summer is so strong as to 
 reverse the northern trade winds and cause the southeast 
 trades to continue across the equator and over India as 
 southwest winds. In the passage across the tropical seas, 
 the air is heavily charged with moisture, which is precipi- 
 tated on the south slopes of the Himalayas, producing an 
 enormously heavy rainfall, in places as high as 35 feet per 
 year. In the winter the winds are reversed, the cold winds 
 from the plateau of central Asia blowing across India to 
 the sea. The winds, warming as they descend the moun- 
 tains, blow across India as dry winds, taking up instead 
 of precipitating moisture and when they are prolonged they 
 produce drouth and famine in the land. The monsoons 
 are caused by unequal heating of land and water, the land 
 being warmer than water in the summer and cooler in 
 winter. (See fig. 252.) 
 
 303. Land and Sea Breezes.- The daily changes be- 
 tween land and sea are similar but less pronounced than 
 the seasonal. The land is heated during the day, causing 
 the air to expand; the inflow from the sea produces the 
 sea breeze during the middle of the day but dies out in the 
 night. At night the land cools more rapidly and the 
 wind is reversed to the land breeze blowing from the land 
 to the sea during the night and in the early morning. This 
 reversal of the winds is utilized by the fishermen who sail 
 out on the land breeze in the early morning and return on 
 the sea breeze in the evening. 
 
 304. Mountain and Valley Breezes have a similar origin. The 
 mountain radiates heat more rapidly at night than the valley, 
 hence the heavy and cool air (heavy because cool) flows down 
 the mountain and down the valley forming the mountain oreeses. 
 In the daytime the reverse takes place when the valley Ireese 
 blows up the valley and up the mountain. The mountain breezes 
 
THE ATMOSPHERE 
 
 379 
 
 are generally stronger than the valley breezes because in blowing 
 down the slopes they are aided by gravity. 
 305. Wind Velocity.— The velocity of 
 the wind is recorded by an anemometer 
 (anemo, wind; meter, measure). The 
 style used by the Weather Bureau is 
 shown by the accompaning figure. The 
 wind blowing into the cups causes them 
 to revolve rapidly about the vertical axis, 
 the rate of movement being indicated in 
 miles per hour by an index at the base of 
 the standard. The winds are roughly 
 classified according to velocity as follows : 
 
 1. Calm signifies no movement or 
 less than one mile per hour. 
 
 2. Light wind, less than 10 miles per 
 hour, moves leaves on trees. 
 
 3. Moderate, 10 to 15 miles per hour, moves small branches. 
 
 4. Brisk, 15 to 25 miles, sways branches, raises dust. 
 
 5. High wind, 25 to 40, sways trees. 
 
 6. Gale, 40 to 60, breaks branches, uproots trees. 
 
 7. Hurricane and tornado, above 60, sometimes 500 miles per 
 hour, destroys houses. 
 
 The direction of the wind is indicated by a wind vane which 
 consists of an arrow with two broad divergent flanges on the 
 opposite end, free to rotate on a vertical axis. The arrow points 
 in the direction from which the wind is blowing. The arrows on 
 the weather maps point the direction in which the wind is 
 blowing. 
 
 FlG. 259. An anemometer 
 or wind gauge for meas- 
 uring the velocity of the 
 wind. 
 
 HUMIDITY AND PRECIPITATION 
 
 306. Absolute and Relative Humidity. — The atmos- 
 phere always carries some moisture in the form of invisible 
 water vapor which is obtained by its contact with the sur- 
 face of the ocean and the moist land. The amount of 
 moisture in the atmosphere varies at different places, and 
 at the same place at different times. The quantity of 
 water in a given volume of air at any time expressed in 
 
380 PHYSICAL GEOGRAPHY 
 
 grains per cubic foot denotes its absolute humidity. The 
 amount of vapor present in the air, compared with wnat 
 might be present if the air were saturated with moisture, 
 gives the relative humidity and is expressed in per cent. 
 If the air were perfectly free from moisture, which it never 
 is, the relative humidity would be zero ; when it is satur- 
 ated, the relative humidity is 100 per cent. 
 
 While the absolute humidity may remain constant, the rela- 
 tive humidity varies with the temperature. The capacity of the 
 air for moisture increases with an increase in temperature. 
 Thus the air may be saturated, the relative humidity 100 per 
 cent at one temperature, say 60 degrees, and if the temperature 
 be raised to 80 degrees the relative humidity will fall consider- 
 ably below 100. On the other hand, should the temperature be 
 lowered when the relative humidity is 100, precipitation will take 
 place, that is, rain or snow will fall. When you hear the expres- 
 sions, "The air is raw," "It is penetrating," what can you infer 
 concerning the humidity? Why does cold, moist air feel colder 
 and warm moist air warmer than dry air at the same tem- 
 peratures? 
 
 307. Dew Point.— The temperature at the point of 
 saturation is .known as the dew point, and may be deter- 
 mined experimentally by placing some ice in a cup of 
 water and stirring it with a thermometer until moisture 
 begins to form on the outside of the cup. The reading of 
 the thermometer at that time will be the dew point of the 
 atmosphere at that instant. By trying this experiment at 
 several different times, it may be noticed that this varies 
 considerably in air even at the same temperature. 
 
 308. Instruments. — There are several different instru- 
 ments used for measuring the humidity of the air. The 
 essential part of a common hygrometer consists of human 
 hair deprived of its oil, which changes in length with the 
 percentage of moisture in the air. It is called the hair 
 hygrometer. 
 
 The sling psychrometer consists of two standard ther- 
 
THE ATMOSPHERE 381 
 
 mometers attached to a board, one of which has the bulb 
 covered with wet muslin. They are whirled through the 
 air for a short time to 
 hasten the evaporation 
 from the muslin. If the 
 air is saturated with 
 moisture, the two ther- 
 mometers will read the g 
 same, but if the relative fj 
 humidity is low, there < 
 
 Will be rapid evapora- Fig. 260. Hygrometer. An instrument for 
 .• r> ,i t recording the relative humidity of the at- 
 
 tion from the muslin , s . . , , '. 
 
 mosphere. A wet and dry thermometer 
 Covering the Wet bulb, is commonly used and the results com- 
 
 causing the mercury to pare ' 
 
 fall. The difference between the wet and dry bulb readings 
 
 will increase as the relative humidity decreases. 
 
 A hygrodeil- is a form of hygrometer in which the result is 
 shown directly by adjusting two sliding pieces to the height of 
 the mercury in the wet and the dry bulb thermometers, in such 
 a way that they control the position of an index which points 
 out the number indicating the relative humidity in per cent. 
 
 309. Dew and Frost.— When rapid radiation from 
 objects on the surface of the earth causes the temperature 
 of the air in contact to be lowered to the point of satura- 
 tion, the moisture begins to condense, the point of satura- 
 tion being commonly known as the dew point. Dew is 
 formed on a clear night by the rapid radiation of the heat 
 from the surface after the sun goes down. The air com- 
 ing in contact with the cooled and cooling surface is chilled 
 by conduction, when some of the moisture condenses as 
 dew; or, if below 32 degrees P., it condenses in the crystal 
 form as hoar frost. Dew or frost, is formed most rapidly 
 on the surface of substances which are the best radiators of 
 heat, such as stone, grass and leaves. 
 
382 
 
 PHYSICAL GEOGRAPHY 
 
 Less clew is formed on a cloudy than on a clear night because 
 the clouds check radiation and prevent the surface from being 
 sufficiently cooled. Dew is not formed on a windy night, because 
 the air does not remain long enough in contact with the cool 
 surface to be lowered to the dew point. 
 
 310. Clouds.— The condensation of the moisture in the 
 air produces clouds of many different shapes and sizes. 
 A cloud at the surface of the earth is called fog, or, if very 
 light, mist. In the fog or cloud, the moisture has been suf- 
 ficiently condensed to form small particles large enough to 
 intercept the rays of light. 
 
 311. Classification of Clouds.— The more common 
 forms of clouds are: (1) the cumulus which often resem- 
 
 ii'JG. 261 Cumulus cloud. Common in the summer season, 
 cedes a thunder storm. 
 
 Frequently pre- 
 
 bles great masses of snowy wool or cotton. They com- 
 monly have a flat or nearly regular base but a very irre- 
 gular and changing top and are among the most common 
 cloud forms in the summer season. They are formed by 
 the ascending currents of warm air from the heated land 
 surface. They are also called thunderheads and commonly 
 
THE ATMOSPHERE 
 
 383 
 
 precede a thunderstorm. The base is generally half a 
 mile to a mile above the surface of the earth. 
 
 Fig. 262. Plumed cirrus cloud. Height 8000 meters in -winter, 9700 meters 
 summer. (K. E. Howell.) 
 
384 
 
 PHYSICAL GEOGRAPHY 
 
 (2) The cirrus cloud is a feathery, plume-like form 
 that occurs at a height of five to ten miles above the surface 
 and often consists of fine ice or snow crystals, owing to its 
 great height. It forms in the front of an advancing cy- 
 clone or low pressure area and, moving ahead with the 
 ''low," is a pretty good indication of the advance of a 
 storm center. It has been called a "weather-breeder" be- 
 cause it is frequently followed by rain or snow. 
 
 (3) Stratus clouds occur in layers or strata near the 
 surface and frequently accompany rainstorms. They 
 sometimes fall to the surface and form fogs. They are 
 common in the early morning, but may occur at other 
 hours. 
 
 Fie. 263. Cirro cumulus cloud. 
 Howell.) 
 
 Height 6500 meters summer. (E. B. 
 
 (4) Nimbus is a rain cloud, consisting of a dark grey 
 to black mass generally covering the whole sky and from 
 which the rain falls. (The term "nimbus" refers to a 
 
THE ATMOSPHERE 385 
 
 condition rather than to a form of cloud and is usually 
 understood to be any mass, of cloud from which rain or 
 snow is falling.) Any of the other clouds, especially the 
 stratus or cumulus, may rapidly change to a nimbus. This 
 is the most common cloud form in New York State during 
 the winter, lasting at times for several weeks with the rain 
 falling at intervals. 
 
 The different cloud forms mentioned may form many 
 combinations, as cirro-cumulus, cirro-stratus, cumulo-stra- 
 tus, strato-cumulus. 
 
 312. Precipitation.— Rain occurs when the moisture 
 condenses into drops which fall to the earth. If the 
 condensation takes place at temperature below 32 degrees 
 F. it forms snow, which bears the same relation to the rain 
 in the clouds that frost does to dew on the surface of the 
 earth. The moisture may condense as snow in the higher 
 air and, in falling through warmer currents near the sur- 
 face, may melt and reach the surface as rain. But if the 
 rain should freeze while falling through the lower air it 
 would not form snow but sleet. Sleet may also be half- 
 melted snow. 
 
 Hail is thought to be a mixture of snow and frozen rain. 
 It is formed during thunder- 
 storms in the summer season 
 probably by the passage of 
 the descending moisture through 
 several air currents with tem- 
 peratures alternately above and 
 below the freezing point. Hail 
 storms, coming as they do in the 
 summer season often cause great 
 damage to vegetation. 
 
 oho ~ ... „ ,» . r~, Fig. 264. Tipping rain gauge. 
 
 313. Quantity Of Rain.-The Measures and records auto- 
 
 amount of rainfall is determined matically the rainfall. 
 25 
 
386 
 
 PHYSICAL GEOGRAPHY 
 
 by measuring the depth of water in a vessel known as a rain- 
 gauge. A section of the rain-gauge used by the U. S. Weather 
 Bureau is shown in fig. 264. Snow and hail are melted and the 
 result given in the amount of water as though it had fallen as 
 rain. It takes about 8 or 10 inches of snow to equal an inch of 
 rain, but this differs with the kind of snow. 
 
 Most all the rainfall may be included under the three 
 heads : cyclonic, tropical and monsoon. 
 
 314. Cyclonic Rains.— In the region of the prevail- 
 ing westerlies, most of the rainfall comes from the cyclonic 
 or low pressure areas. As the cyclone moves east across 
 the country, the warm, moist winds, drawn in from the 
 south and east, ascend in the atmospheric whirl and are 
 
 Fig. 265. Rainfall map of the United States showing the mean annual rainfall 
 in different portions of the country. Give your reasons for the great vari- 
 ation. More of the zonal lines run north and south than east and west. 
 Account for the maximum and minimum in the same latitude. (U. S. 
 Weather Bureau.) 
 
 cooled as they rise ; the moisture they carry is condensed 
 and falls as rain or snow. The greater part of the rain 
 
THE ATMOSPHERE 387 
 
 falls to the east or the southeast of the cyclone center. 
 Verify this by study of the weather maps. 
 
 Thunderstorms. In the summer season the cyclones 
 are frequently accompanied by thunderstorms which are 
 most frequent to the east and south of the cyclone center, 
 but are not limited to these parts. They are produced by 
 rapidly ascending warm air currents which produce a 
 heavy cumulus cloud, the downward pressure of which 
 causes reversed air currents to spread out on the surface 
 in the midst of the ascending warm currents in front of 
 the rapidly moving clouds. The outrushing blast of cool, 
 refreshing air is generally followed closely by a downpour 
 of rain which may continue for a few minutes or for sev- 
 eral hours. Thunderstorms are most frequent in the latter 
 part of the afternoon or night. The lightning is caused 
 by the passage of the electric spark from cloud to cloud or 
 between the earth and the cloud. Thunder is the sound 
 caused by the violent agitation of the air along the flash. 
 Since the velocity of light is nearly instantaneous for 
 short distances and sound travels about twelve miles per 
 minute, the distance of a lightning flash may be roughly 
 estimated in miles by dividing by five the number of sec- 
 onds that elapse between the flash of lightning and the 
 sound of the thunder. Much of the rain in the summer 
 season in the Mississippi Valley comes from the thunder- 
 storms. 
 
 Cloudbursts associated with thunderstorms and torna- 
 does are thought to be caused by ascending air currents so 
 violent that they hold up the condensed moisture for some 
 time, until the accumulation finally breaks through and 
 the water falls' in a mass or sheet, frequently causing dis- 
 aster on the surface where it falls. Cloudbursts are most 
 frequent in dry or semi-arid regions, often proving destruc- 
 tive in the mountains of Arizona, New Mexico and Col- 
 
388 PHYSICAL GEOGRAPHY 
 
 orado. Many persons have been drowned from the cloud- 
 bursts in these states and on the Sahara and other deserts. 
 The tropical rains in the doldrum belt are of almost 
 daily occurrence. The clouds begin to form near the mid- 
 dle of the day and heavy rains, generally accompanied by 
 thunderstorms, follow in the early afternoon. The sky 
 clears at night and the morning is fair. These rains con- 
 tinue throughout the year shifting north and south, fol- 
 lowing the movements of the heat equator. (See fig. 253.) 
 
 WEATHER AND CLIMATE 
 
 315. Weather refers to all the atmospheric conditions 
 that can be seen or felt, such as (1) the temperature, 
 whether hot or cold, or growing warmer or colder; (2) pre- 
 cipitation, whether rain or snow and how much ; ( 3 ) Cloud- 
 iness, whether fair, partly or wholly cloudy, and the rela- 
 tive humidity of the air; (4) winds, direction and velocity, 
 and changes. 
 
 316. Climate is the sum total of the average weather 
 conditions for a series of years ; its consideration should 
 include also a statement of the extremes or variations from 
 the normal, and would have the same elements of temper- 
 ature, moisture and winds as the weather. The whole area 
 of the earth is sometimes divided into five climatic zones, 
 separated by certain parallels of latitude, but if all the 
 elements of climate are considered, the zones would be more 
 irregular and might have a number of subdivisions such as 
 those indicated in fig. 251. 
 
 The controlling factors of the climate are : 
 (1) Latitude. Outside of the tropics the sun's rays 
 become more and more inclined as one advances towards 
 the poles and the climate becomes correspondingly cooler, 
 hence the division into torrid, temperate and frigid cli- 
 mates. 
 
THE ATMOSPHERE 389 
 
 (2) Altitude.- Since the density of the air and hence 
 the temperature decreases with the altitude, cooler climates 
 will be found in ascending the mountains and plateaus. 
 
 (3) Distance from the ocean or other large body of 
 water affects the uniformity of temperature and frequently 
 the moisture or precipitation. 
 
 317. Effect of Mountains on Climate. — The relation of moun- 
 tains to an area often has a marked effect on its climate, an 
 effect most pronounced in the region of prevailing winds, where 
 they blow across the mountains. In the trade wind belt in South 
 America, there is a heavy rainfall on the east or windward side 
 of the Andes Mountains, while on the lee side there is a very 
 light rainfall. In southern India in the monsoon belt, there are 
 heavy rains during the part of the year when the summer mon- 
 soons are blowing, while the remainder of the year is dry. 
 
 318. The terrestrial wind belts are factors of prime impor- 
 tance in determining the climate. The doldrum belt has its al- 
 most daily rains and uniformly moist climate. The trade wind 
 belt has a generally uniform fair weather on the seas and fre- 
 quent rains on the lands, where the winds blow over considerable 
 elevations, but dry on the lee side of the mountains. Most of the 
 deserts occur in this belt. The subtropical belt over which the 
 horse latitudes migrate have prevailingly fair weather, but an 
 area lying in this belt is swept by the trade winds in one season 
 and by the prevailing westerlies at another. It is an area of dry 
 summers and rainy winters. (See fig. 251.) 
 
 319. The cyclone and anticyclone paths are controlling 
 factors of the weather in the belt of the prevailing wester- 
 lies, and determine the weather changes, from day to day. 
 These should be studied carefully from the daily weather 
 maps published by the government, and should be studied 
 on groups of maps for several different months in differ- 
 ent seasons. 
 
 The following weather conditions* may be looked for 
 in association with the lows and highs in the United States : 
 
 "High winds with rain or snow usually precede the low. In 
 advance of the low the winds are generally southerly and con- 
 
 * Quoted from the Chief of the Weather Bureau. 
 
390 PHYSICAL GEOGRAPHY 
 
 sequently bring high temperatures. When the center of the low 
 passes to the east of a place, the wind at once shifts to the west 
 or northwest, bringing low temperature. The temperature on a 
 given parallel west of a low may be reasonably looked for on the 
 same parallel to the east when the low has passed. Frost will 
 occur along the north of an isotherm of about 40 if the night is 
 clear and there is little wind. Following the low usually comes 
 an area of high, bringing sunshiny weather, which in turn is fol- 
 lowed by another low. 
 
 "The cloud and rain area in front of a low is generally about 
 the size of the latter and oval, with the west side touching the 
 center of the low in advance of which it progresses. 
 
 "When the isotherms run nearly east and west no decided 
 changes in temperature will occur. If the isotherms directly west 
 of a place incline northwest to southeast it will be warmer; 
 if from northeast to southwest it will be colder. 
 
 "An absence of decided waves of high or troughs of low 
 pressure indicates a continuance of existing weather, which will 
 last until later maps show change, usually first appearing in the 
 west." 
 
 320. Weather Maps.— At eight* o'clock each morn- 
 ing and evening at many places in the United States, 
 Canada, Mexico and the West Indies, observations are 
 made on the weather conditions. A record is made of 
 the barometric pressure, temperature, velocity and direc- 
 tion of the wind, condition of the sky, relative humidity, 
 and amount of precipitation, and within the hour these 
 data in a condensed cipher dispatch are sent by telegraph 
 to the Weather Bureau in Washington. The data are 
 rapidly tabulated and transferred by appropriate symbols 
 to a weather map, which is in turn engraved and a large 
 edition printed and delivered to the mails all within a 
 remarkably short period of time. Smaller editions of a 
 less elaborate map are printed at the local stations in dif- 
 ferent cities outside of Washington. 
 
 *Eight o'clock by the 75th meridian time, which means 7 o'clock at St. 
 Louis, 6 o'clock at Denver, and 5 o'clock at San Francisco. 
 
THE ATMOSPHERE 391 
 
 The data shown on the weather map consist of (1) iso- 
 bars, represented by solid black lines drawn through points . 
 having the tame atmospheric pressure, a line for each tenth 
 of an inch on the barometer; these lines curve around and 
 enclose the lows and the highs. (2) red lines (on the local 
 maps, dotted lines) are drawn for the isotherms, one for 
 each 10 degrees difference in temperature. (3) Heavy, 
 broken red lines enclose areas where there has been a de- 
 cided change in temperature equal to a rise or fall of 20 
 degrees or more in 24 hours. (4) Shaded areas (on the 
 "Washington map but not shown on the local map) indi- 
 cate the area over which there has been rain or snow dur- 
 ing the past 24 hours. (5) The condition of the sky is 
 indicated by a small circle, which is black for cloudy sky 
 and open for clear sky. The arrow on the circle indicates 
 the direction of the wind. R signifies rain and S snow. 
 
 Besides the graphic representation by lines and sym- 
 bols, all the data are printed in tabulated form on the 
 margin of the map. Daily weather maps from the nearest 
 "Weather Bureau office or from Washington can generally 
 be secured on application and should be studied along with 
 the text. 
 
 Many thousands of the weather ma^J are distributed daily 
 through the mails and by messengers. Besides the maps there 
 are thousands of cards sent out from the local stations which 
 contain simply the weather forecasts for the next 24 hours. 
 These cards are sometimes distributed in large numbers by busi- 
 ness firms and are displayed in stores, post offices, railway sta- 
 tions, elevators, and other public places-. In some places the 
 rural mail carriers display weather signals on the mail carts and 
 in places the signals are displayed on some prominent point as 
 a steeple, flagpole, or some tall building. 
 
 The flag signals are as follows: A square white flag for fair 
 weather; a square blue flag for rain or snow; a triangular black 
 flag above the white or blue flag indicates followed by warmer 
 ■weather; if below, by colder; a square white flag with a square 
 
FiG. 266. Daily weather map. Note the movements of the lows and highs 
 for the two days. On February 3rd, the intervening day, the one low 
 was central over southern Maine, the other over the Pan Handle of Texas. 
 (U. S. Weather Bureau.) 
 
THE ATMOSPHERE 393 
 
 black center indicates a cold wave coming. There is another set 
 of flag signals in use for wind storms on the lakes or sea shore. 
 
 321. Benefits from Weather Forecasts.— Some of the 
 many benefits that may be derived from the widespread 
 distribution and heralding of the weather forecasts are sug- 
 gested in the following : Knowledge of a tropical hurricane 
 in the West Indies arrives by cable and storm signals are 
 placed in all the harbors along the Atlantic coast from 24 
 to 36 hours ahead of its arrival, by which many vessels are 
 saved from destruction. Similar forecasts of storms save 
 a great many boats on the Great Lakes. Some of the in- 
 surance companies recognize the value of this branch of 
 the service by refusing all risks on vessels that go out 
 against the warnings. 
 
 The news of a decided cold wave coming from the northwest 
 causes quite a flutter in many lines of business, the ice com- 
 panies, the coal dealers, the railway employees in charge of 
 perishable goods, the fruit commission merchants, stock raisers, 
 and many others who take such precautions as they can to pre- 
 vent loss. An important branch of the service consists in the 
 warnings of floods along the larger rivers in which the fore- 
 knowledge is often the means of saving a great deal of property. 
 
 The student may enumerate other ways in which benefit may 
 be derived from the foreknowledge of the weather changes. 
 
 The weather forecast is given for 24, sometimes 48 hours 
 ahead. There has been considerable study in trying to find some 
 scientific basis of foretelling the weather conditions some weeks 
 or months ahead, but no definite results have been obtained. 
 The weather conditions published in certain pamphlets and 
 almanacs for the entire year have little if any scientific value. 
 
 322. Climatic Zones.— The surface of the globe is 
 commonly divided into five climatic zones, based on an 
 arbitrary division of so many degrees of latitude. Thus 
 the torrid zone includes all the area between the tropics, 
 the two temperate zones the areas between the tropics and 
 the polar circles, while the remainder is in the frigid zones. 
 
394 PHYSICAL GEOGRAPHY 
 
 It has been shown, however, that the unequal distribution 
 of land and water causes a distribution of winds, rains, 
 and temperature that does not follow the parallels. In 
 comparing the isothermal chart of the world for the year 
 and for the winter and summer seasons it will be seen that 
 the temperature inside of the tropics in one place is quite 
 different from that in the tropics in another place. A 
 comparison of the rainfall in different areas shows even 
 more marked differences. (See sec. 293, fig. 251.) 
 
 A more practical division of the surface into tempera- 
 ture zones would be based on isotherms rather than on 
 parallels. Some of the rather well defined climatic types 
 that occur in different areas are (1) the doldrums of the 
 tropics with warm, moist climate and persistent rainfall; 
 (2) the trade wind belt which is warm and wet on the 
 east side of the continents and generally dry, sometimes a 
 desert, on the west side of the continent ; ( 3 ) the monsoon 
 belt with the wet and dry seasons; (4) the subtropical 
 belts over which the dry tropical calms, the frequently pre- 
 cipitating trade winds and the prevailing westerlies mi- 
 grate at different seasons. The temperate zone may be 
 divided into two parts, (5) that nearer the tropics char- 
 acterized by warm summers and mild winters, and (6) 
 the outer portions, by hot summers and cold winters. 
 
 There is a marked difference between the climate on 
 the seashore and that of the interior, between the eastern 
 and western shores of both the continents and the oceans. 
 Likewise between the plain, plateau, and mountain cli- 
 mates. Find some examples of each. 
 
 323. Changes in Climate. — One frequently hears the 
 statement that the climate is changing — that there is not 
 so much snow and that the winters are not so cold as they 
 used to be. Such remarks apply to the weather rather 
 than to the climate. There are frequently quite marked 
 
THE ATMOSPHERE 395 
 
 changes between successive seasons, but the official weather 
 records do not indicate any marked changes in the climate 
 back as far as the record has been kept. 
 
 324. Geological Climates.— The geological record which ex- 
 tends over millions instead of a few tens of years, shows many 
 pronounced climatic changes. For instance, some few thousand 
 years ago the climate was enough colder than that at present in 
 the northern hemisphere, to cause an accumulation of snow and 
 ice in the form of great glaciers over all the north central parts 
 of North America and Europe. This condition continued ap- 
 parently for thousands of years. In a preceding geological period 
 it was warm enough for the growth of tropical plants as far 
 north as the Arctic Circle. 
 
 In still earlier geological times, a very long time ago, the 
 climate of central New York and southern Michigan was ex- 
 ceedingly dry, possibly as dry as that of Utah to-day. This is 
 shown in the record by the great beds of rock salt in this region. 
 
 325. Electric and Optical Phenomena.— Lightning is 
 caused by the electric discharge in the form of a vivid flash 
 or spark between clouds or between a cloud and the earth. 
 The lightning is associated with a heated atmosphere and 
 is common in the hot summer season but Is absent in the 
 winter season, except rarely when the air becomes unsea- 
 sonably warm. It appears also to be associated with move- 
 ments of the warm air currents and hence accompanies 
 the violent air movements of thunderstorms and tornadoes. 
 Probably the moisture in the cloud is also an important 
 element in the electric discharge. The energy, or electro- 
 motive force, manifest in a violent thunderstorm, is far in 
 excess of that produced by any artificial means. It takes 
 several different forms, known as zig-zag or chain light- 
 ning, heat lightning and sheet lightning. 
 
 The passage of the electric current from the earth to the 
 cloud, or the cloud to the earth, is likely to be from some ele- 
 vated point as a tree, a church steeple, or some tall building, 
 yet this is not always the case as lightning has been known to 
 
396 
 
 PHYSICAL GEOGRAPHY 
 
 strike animals and other objects in the near vicinity of trees 
 and buildings without injury to the tall object. (Fig. 267.) 
 
 The thunder is caused by the inrushing air to fill the partial 
 vacuum produced by the lightning flash. The interval of time 
 between the flash of the lightning and the sound of the thunder 
 is an indication of the distance of the flash. 
 
 Fig. 267. Lightning flash, Lincoln, Neb. (U. G. Cornell.) 
 
 326. St. Elmo's Fire is a brush discharge of electric- 
 ity often observed during electric storms on steeples, 
 masts of vessels at sea, and other high points. It is un- 
 accompanied by the noise or danger of the lightning flash. 
 
 327. The aurora oorealis is presumably an electric 
 phenomenon, the cause of which has not been satisfactorily 
 explained. Since in the northern hemisphere it is always 
 observed in the north it is commonly called the northern 
 lights. It is occasionally observed as far south as New 
 York, but it is much more frequent and spectacular in the 
 higher latitudes where it is an object of much interest dur- 
 
THE ATMOSPHERE 397 
 
 ing the long northern winter. It consists of a great areh 
 or sheets of light stretched across the northern sky, from 
 which great streamers of many and fantastic forms ex- 
 tend to, or towards, the zenith. It possibly has some rela- 
 tion to the magnetic poles of the earth. 
 
 328. The rainbow is an- arch of prismatic color that is 
 produced by the refraction and reflection of the light from 
 the interior of the raindrops; the light emerging from the 
 drop is separated into the prismatic colors. Frequently 
 a second bow appears and even a third and fourth have 
 been reported. A rainbow usually shows less than half a 
 circle. Under what conditions does it appear a half circle 1 
 If one could see the rainbow from a balloon how much of 
 the circle would appear? 
 
 329. Coronas or rings around the moon, sun dogs, moon dogs, 
 and halos are other phenomena due to refraction and reflection 
 of the light in the upper atmosphere, sometimes from the little 
 ice or snow crystals, sometimes from drops of moisture. Cor- 
 onas are due to diffraction and interference. Halos are caused 
 by reflection and refraction of the light in the small ice crystals. 
 
 The different colors of the sky are due to refraction and 
 selective scattering of the different prismatic rays. When there 
 is much dust in the atmosphere the bright red and yellow colors 
 are reflected to the eye at sunrise and sunset. 
 
 330. The mirage is caused by the turning of the rays 
 of light from their original direction, causing objects to 
 appear to be out of place. It is produced by the atmos- 
 phere occurring at times in layers of different density. The 
 light rays which have already been bent from their original 
 course are reflected to the eye from the surface of one of 
 the layers, causing the object to appear out of position and 
 frequently out of proportion. 
 
 The desert mirage occurs over hot, dry land areas, by the 
 reflection from the layers near the earth to the eye, giving the 
 appearance of the reflection of trees from a smooth water sur- 
 face. Many a person has been lured to destruction by following 
 
398 PHYSICAL GEOGRAPHY 
 
 these phantom lakes across the scorching sands of the desert. 
 The stratification of the lower layers of air is due to the intense 
 heating of the air near the ground, which causes it to expand, 
 but the air being quiet, there accumulates considerable pressure 
 before convectional currents are started. Sometimes the flight 
 of a bird is sufficient to disturb this unstable equilibrium and 
 start the uprush of heated air which frequently produces a whirl- 
 wind. Sometimes a half dozen or more of these whirlwinds are 
 visible at one time on the sandy plains of the desert on a hot 
 summer day. 
 
 The mirage is sometimes visible on the sea, where the reflec- 
 tion is from the upper atmosphere down to the eye of the ob- 
 server, causing ships and other objects below the horizon to 
 appear in the sky sometimes upright and sometimes inverted. 
 This form of mirage is known as the looming. 
 
 331. The zodiacal light is a disk of faint light sur- 
 rounding the sun. It may be seen as a triangular column 
 of light, rising from the western horizon shortly after twi- 
 light in the winter and spring and in the east before day- 
 break from September to January. It is thought to be 
 sunlight reflected from a cloud of meteorites revolving 
 around the sun. Another theory for the zodiacal light is 
 that it is caused by particles electrically discharged from 
 the poles of the sun and condensed along the plane of its 
 equator. 
 
 332. The Gegenschein (counter-glow) is a faint patch of light 
 on the ecliptic directly opposite the sun. One hypothesis for its 
 occurrence is that it is caused by meteors which tend to con- 
 dense directly opposite the sun. Another explanation is that it 
 forms a tail to the earth similar to the tail of a comet composed 
 of particles of helium and hydrogen escaping from the earth. 
 
 REFERENCES 
 
 1. Davis, Elementary Meteorology, Ginn & Co., Boston, 1894. 
 
 2. Waldo, Modern Meteorology, Scribner's Sons, New York, 
 
 1893. 
 
 3. Ward, Practical Exercises in Elementary Meteorology, 
 
 Ginn & Co., Boston, 1896. 
 
THE ATMOSPHERE 399 
 
 4. Ferrel, Popular Treatise on the Winds, Wiley & Sons.. 
 
 New York, 1889. 
 
 5. Annual Reports, Monthly Weather Review and Daily 
 
 Weather Map by the U. S. Weather Bureau, Wash- 
 ington, D. C. 
 
 6. Harrington, Rainfall and Snowfall of the United States, 
 
 Bulletin C, U. S. Weather Bureau, Washington, D. C. 
 
 7. Greely, American Weather, Dodd, Mead & Co., New York, 
 
 1903. 
 
 8. Ward, Hann's Handbook of Climatology, MacMillan & Co., 
 
 New York, 1903. 
 
 9. Harrington, Weather Making, Ancient and Modern, An. 
 
 Rept. Smithsonian Institution, 1894, pp. 249-271. 
 
 10. Davis, Practical Exercises in Geography, Nat'l Geog. Mag. 
 
 Vol. XI, p. 62. 
 
 11. Garriott, West Indian Hurricanes, Nat'l Geog. Mag., Vol. 
 
 X, p. 343, and Vol. XI, p. 384. 
 
CHAPTER XI 
 GEOGRAPHY OF PLANTS, ANIMALS, AND MAN 
 
 333. Influence of Environment on Life.— All forms 
 of life are of necessity influenced by their physical en- 
 vironment. The kind, the abundance, the variety of living 
 forms on any area largely depends upon the geographical 
 conditions of soil, climate, and topography on the land ; and 
 temperature, depth, and clearness of the waters in the 
 sea. This has been suggested from time to time in the pre- 
 ceding chapters, but it seems fitting now in conclusion to 
 consider the subject directly in reference to the life rela- 
 tions. 
 
 Man is probably as nearly independent of his geo- 
 graphical surroundings as any other form of life, but that 
 in his migrations, civilization, industries, and mental as 
 well as physical development, he has been greatly influ- 
 enced by geographical conditions is apparent to all. Many 
 of the lower forms of life are more susceptible than man 
 to their surroundings and hence occupy only a few limited 
 areas, while man ranges over the earth from the equator 
 nearly to the pole and is making strenuous efforts to reach 
 that hitherto inaccessible point. 
 
 334. Effect of Climate.— There are striking differ- 
 ences in the kinds of life and the habits of the living forms 
 in the different climatic zones. In the warm, humid 
 region, life, death, and decay go on with striking uniform- 
 ity and rapidity throughout the year and the years. In 
 the cold temperate zones there is a warm season of rapid 
 growth, and a cold season of rest, when the trees and shrubs 
 
 400 
 
Longitude from Greenwich 140 
 
YfllGNT I90S Br ATON&ON, MENUEft 4 GRQi/Ea 
 
GEOGRAPHY OF LIFE 
 
 401 
 
 shed their leaves and fruit, and the herbs and grasses die 
 and disappear all but the roots, bulbs, and seeds. Many 
 of the animals hibernate. Man, the domestic animals, and 
 some of the wild animals remain active during the cold 
 weather of the winter months, but the lower forms of 
 life,— many of the animals, and all the vegetable forms — 
 lie dormant and inactive until the return of warm weather. 
 The winter in cold climates is characteristically a sea- 
 son of silence. At a distance from human habitations al- 
 most the only sounds are those of inanimate nature. 
 
 "With the coming of the spring there is a marvellous awak- 
 ening and unfolding. The brooks, swollen to overflowing by the 
 
 Fig. 268. Winter in cold climates is a season 01 silence, 
 evergreen forest in the United States. 
 
 Winter scene in an 
 
 melting of the snow, make music as they run. The northward 
 flight of the birds brings to every grove a chorus of song. A 
 host of batrachians and reptiles bestir themselves after a long 
 26 
 
402 PHYSICAL GEOGRAPHY 
 
 winter sleep and vociferously proclaim their presence. The in- 
 sect world, with its unnumbered legions, takes wing. The air 
 vibrates with millions of voices. The trees put forth their leaves, 
 each a harp-string which responds to the touch of the fingers of 
 the wind. The organ-notes of the thunder again startle the hiber- 
 nating echoes. As the winter is the silent season, so the spring 
 is the time of music." (Russell's North America, pp. 296-297.) 
 
 Make a list of the birds and wild animals you see or 
 know to be alive in our fields and forests in the winter. 
 Note the date when you see the first birds in the spring 
 and the ones that come first. What animals hibernate or 
 sleep during the cold season? (See fig. 268.) 
 
 This seasonal renewal of the activities of the varied 
 forms of life is probably one of the reasons why man has 
 made his greatest advancement in the temperate zones. 
 
 PLANT GEOGRAPHY 
 
 The number and kinds of plants on any area not under 
 cultivation are determined largely by the condition of the 
 soil, water, air, and temperature. 
 
 335. Soil. — Most land plants have roots which find 
 anchorage in the soil from which they derive sustenance 
 both in water and mineral matter. While but a small part 
 of the plant is formed by the mineral matter in the soil, 
 that small part is so important that if the materials are 
 not in the soil the vegetation does not flourish. Thus a 
 grain of wheat that would sprout and grow a spindly stalk 
 a foot high with no grains on poor soil, would grow a lusty 
 stalk four feet high, with many good grains, on a fertile 
 soil. 
 
 The kind of soil has much to do with the variety and quan- 
 tity of vegetation. Thus the vegetation on a sand soil will be 
 different from that on a rock, clay, loam, humus, or alkaline soil. 
 Much depends on the relation of these soils to each other; thus 
 a humus on sand would be different from a humus on clay. More 
 
GEOGRAPHY OF LIFE 
 
 403 
 
 important than the chemical proportions are the physical ones, 
 such as, the fineness of the particles and the porosity of the mass 
 as affecting the circulation, absorption, and retention of moisture. 
 Some forms of life are independent of the soil, such as floating 
 vegetation, which derives sustenance, wholly from the water and 
 air. A few land plants live without contact with the soil and 
 
 j<ta. 269. Spanish moss on live oak tree, Columbia, Texas. 
 A common epiphyte in the southern United States. 
 
 (W. L. Bray.) 
 
 derive sustenance wholly from the air. Such are called epiphytes, 
 because they grow upon the stems and branches of other plants. 
 They are most abundant in the tropics. Fig. 269 shows the 
 Spanish moss an epiphyte that grows in great abundance in the 
 southern and southwestern United States. The mistletoe is a 
 common epiphyte widely distributed through the United States 
 and Europe. 
 
 336. Water.— Water forms a large part of the material 
 of nearly all plants and hence is essential to their existence. 
 The kind of water, whether fresh, salt, or alkaline, and the 
 quantity of it, whether an excess as in the marsh, a dearth 
 
404 
 
 PHYSICAL GEOGRAPHY 
 
 as in the desert, a limited supply as in the semi-arid dis- 
 tricts, or a generous amount as in the humid districts ; and 
 the temperature, whether hot, temperate, or cold, determine 
 in a large degree the kind as well as the quantity of the 
 vegetation. The distribution of the rainfall throughout 
 the year is important; whether it falls in the winter or in 
 the growing season. The relation of the water table to 
 the surface soil is also an important factor. 
 
 Fig. 270. Some types of water plants growing in a swamp of northern 
 United States. Some float on the surface, others extend several feet above 
 the surface, while others grow in the bottom entirely under water. "View 
 in the Montezuma Swamp, N. Y. (E. B. Smith.) 
 
 337. Classification of Plants Based on Water Supply. 
 
 — On a basis of humidity plants may be divided into (1) 
 water plants, (Hydrophytes) ; (2) drouth or desert plants 
 (Xerophytes) ; (3) intermediates (Mesophytes). 
 
 1. Some water plants grow on the surface of the water, 
 
GEOGRAPHY OF LIFE 
 
 405 
 
 others on the bottom. Another class includes those with 
 roots on the bottom and leaves and branches above the sur- 
 
 
 
 ^^^JJuJ^r-^^ 
 
 Fig. 271. niustrating the function of cypress knees. A, level of water in 
 the growing season. B, lowest level of swamp water; a, cypress tree with 
 part of the roots under water; b, tree with all roots under water; c, tree 
 with none of the roots under water; dd, cypress knees through which the 
 roots breathe; ee, knees not yet grown to serviceable height; ff, abortive 
 knees not needed by the tree. (After Shaler.) 
 
 Fig. 272. Cypress trees and knees in the Great Dismal Swamp of Virginia. 
 The knees are protuberances on the roots extending sometimes to several 
 feet above the surface of the water. (U. S. Geol. Survey.) 
 
 face, such as the mangrove tree in Florida, water lilies, cat- 
 tails, splatter dock,, reeds, and cane in the lakes and 
 swamps. The water hyacinth is a floating plant that grows 
 
406 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 273. Papago Indian, Sonora, Mexico, crushing the pulp of tne interior 
 of a barrel cactus in order to squeeze the water out of it. Sometimes a 
 gallon or more of water is obtained in this way from a single plant. 
 (D. T. McDougal.) 
 
GEOGRAPHY OF LIFE 407 
 
 in such quantities on the rivers and lakes of Florida as to 
 be a serious menace to navigation and the fishing industries 
 on the inland waters, (Fig. 270.) 
 
 Cypress trees that grow sometimes in the water and some- 
 times on dry land develop a unique method of getting air to the 
 roots that grow under water, by having a knob or process grow 
 up through the water to and above the surface until it is in con- 
 tact with the air. These knobs which are known as "knees," 
 stand above the surface, looking much like stumps. (See figs. 
 271 and 272.) After the drainage of the swamp the new growth 
 of cypress on the dry land is devoid of knees. 
 
 The Sargassum that occurs so abundantly out in mid-ocean 
 has numerous small air sacs which serve as floats or life-pre- 
 servers to keep it at the surface. The Bladderroot, a fresh water 
 plant, has similar floats. The bladders or air sacs serve to 
 aerate the plant as well as float it. The duckweed, a small green 
 floating plant has numerous air chambers through the body of 
 the plant. There is another class of water plants, microscopic 
 in size, that occurs in vast quantities in both salt and fresh water. 
 The best known forms in this class are the diatoms which 
 secrete a wall of silica and hence are preserved in great deposits 
 in the bottom of the sea and lakes. (See sec. 105.) 
 
 2. Desert plants which have the opposite condition 
 from the water plants, have many ways for collecting, re- 
 taining and conserving the moisture and prolonging their 
 existence in the absence of rain. The scarcity of leaves 
 is one device, as it is from the leaves that evaporation 
 takes place. Some of the cacti have no leaves. A hairy 
 covering over the leaves in some plants serves to shade them 
 from the rays of the sun. Thorns and brambles serve to 
 protect many of them from being eaten by animals. The 
 cactus, sagebrush, greasewood and yucca are among the 
 most common plants on our western deserts. The semi- 
 arid regions, which are subject to drought at regular or ir- 
 regular periods, have a greater variety and number of 
 plants than the desert. In such areas some of the plants 
 store water in reservoirs provided for that purpose in 
 
408 
 
 PHYSICAL GEOGRAPHY 
 
GEOGRAPHY OF LIFE 
 
 409 
 
 the leaves and stems. Others conserve moisture by curling 
 the leaves and thus exposing a smaller surface. (Figs. 
 273, 274, and 275.) 
 
 Fig. 275. Oasis of palms, (Neo Washingtonia filifera) in the Colorado Desert, 
 near Indio, Cal. (See Fig. 79.) Any part of a desert area with water at 
 or near the surface is an Oasis. It is a green spot in the midst of the 
 brown waste. (D. T. McDougal.) 
 
 3. The intermediate plants that grow on dry land sup- 
 ported by a fairly abundant rainfall are the most numerous 
 and comprise about 80 per cent of the total flora. They 
 are called mesophytes because they occur midway between 
 the very dry and the very wet conditions. They include 
 most of our cultivated plants and most of the forest trees. 
 They occur in the same rain belts as the water plants but 
 under different physiographic conditions, that is, where 
 there is sufficient rainfall but the water does not stand on 
 the surface as in the case of the hydrophytes. 
 
 They occur in different rain belts from the desert plants. 
 The dividing line is about 15 inches annual rainfall. It varies 
 
410 
 
 PHYSICAL GEOGRAPHY 
 
 considerably with, the distribution of the rainfall and other con- 
 ditions. It requires about 20 inches of annual rainfall to support 
 forest growth, but under certain conditions some coniferous trees 
 exist in cold climates on less than that. 
 
 The slopes of the Rocky Mountains are covered with forests 
 (where they have not been destroyed) which form a belt between 
 
 FlG. 276. View at the timber line in the Rocky Mountains, Ouray County, 
 Colo. The upper portion of the mountains are void of trees. The forests 
 are dense towards the base of the mountain. Snow lies on the high moun- 
 tains nearly all the year. 
 
 the plains at the base, treeless from lack of rainfall, and the tree- 
 less peaks at the top made so from excess of snow. On all very 
 high mountains even in the tropics there is an upper limit to 
 tree growth known as the timber line. (See fig. 276.) 
 
 The upper limit of trees is not due directly to cold but to 
 excess of snow, as shown by the occurrence of trees on the nar- 
 row ridges much higher than in the depressions. It is in the 
 depressions where the snow accumulates and remains long after 
 it has melted from the ridges, so that the growing season when 
 the ground is free from snow is too short for trees to develop. 
 
 In respect to their association, there are two great groups of 
 the intermediate plants that have a very pronounced effect on 
 
GEOGRAPHY OF LIFE 
 
 411 
 
 the surface. The one group consists of grasses and herbs and 
 forms the meadows, prairies, pastures, and tundras. The other 
 consists of shrubs and trees and forms the thickets and forests. 
 "With change of conditions each of these may encroach upon the 
 territory of the other. Fig. 277 shows an area in Texas where 
 the forest trees are now advancing over the grass plains. The 
 axe and forest fires have been instrumental in changing thousands 
 of acres of forest area to grass land, or in some cases to waste 
 land. 
 
 '" ->■ '* •. 
 
 wipl^**.'-.-- > 
 
 '* • , 
 
 
 Fig. 277. Forest growth advancing on the prairie, Tarkington Prairie, Liberty 
 County, Texas. (W. L. Bray.) Where the prairies are bordered by forests, 
 the tendency is in some places for the forests to advance on the prairie. 
 
 338. Air and Light.— The chief supply of raw ma- 
 terials for the plants is derived from the air and consists 
 largely of carbonic acid, which in the cells of the green 
 plant is decomposed, the carbon with some oxygen and 
 hydrogen forming compounds which make up the plant 
 tissue, while some of the oxygen is set free. The nitrogen 
 of the plant comes from the soil but the soil probably ob- 
 tained it originally from the air. 
 
Fig. 278. Sequoia Gigantea. (U. S. Geol. Survey.) The big trees, small 
 trees, and shrubs grow in different light zones. The big trees shade the 
 smaller ones, and both shade the shrubs and ground plants. 
 
GEOGRAPHY OF LIFE 413 
 
 All green plants require light. Green cells are food 
 factories where water, materials from the soil, carbon 
 dioxide and other gases of the air are combined to produce 
 food for animals or material for other plants. The sun- 
 light and the green material (called chlorophyll) of the 
 plant cell seem to be the most important factors in this lit- 
 tle organic laboratory where the inorganic air and mineral 
 matter are changed to the organic vegetable compounds. 
 The plant tissue which is eaten by animals undergoes 
 further changes in the chemical laboratory of the animal 
 which devours it, and it is there transformed to animal 
 tissue. Some plants known as light plants require more 
 light than others which are known as shade plants. In a 
 forest there are several zones or strata based on the rela- 
 tive amount of light. The tall trees form the upper zone 
 and receive the most light, below this is a stratum of 
 shrubs, then herbs, and next to the ground the green mosses 
 and lichens. (See fig. 278.) 
 
 339. Temperature.— The extremes of temperature be- 
 tween which nearly all plants grow are 32 and 122 degrees 
 F. Some forms of alga? live in the Hot Springs of Yel- 
 lowstone Park at a temperature as high as 199 degrees. 
 By a special adaptation to change of conditions, plants 
 lying dormant pass- through cold winter seasons having a 
 temperature much below 32 degrees. The distribution of 
 the temperature throughout the year, and the relation of 
 the temperature to moisture are important factors to con- 
 sider. 
 
 A general subdivision of the land area into plant zones based 
 on temperature is as follows: 
 
 1. Boreal, polar or cold zone, with mean annual temperature 
 below 30 degrees F., contains lichens, mosses, gentians, willows, 
 etc. It includes the greater part of North America north of the 
 United States and high mountain areas in the United States. 
 
414 
 
 PHYSICAL GEOGRAPHY 
 
 u 
 
 
 
 w^ 
 
 
 |yy 
 
 i>= 
 
 .'7 
 
 i 
 
 .7 
 
GEOGRAPHY OF LIFE 415 
 
 2. Transition, or cold temperate, mean annual temperature 
 30 to 40 degrees F., contains evergreens, such as spruce, fir, hem- 
 lock, pine, etc. This zone forms a fainy wide belt along the 
 northern United States, southern Canada, and along the Alle- 
 ghany, Rocky, and Sierra Nevada mountain ranges, between the 
 boreal on the mountain top and the austral of the bordering 
 plains. 
 
 3. Upper Austral, or warm temperate, mean annual tempera- 
 ture 40 to 60 degrees F., contains deciduous trees such as oak, 
 maple, beech, chestnut, etc. It covers the central United States, 
 including the greater part of the plains and prairies and portions 
 of the Alleghany plateau. It may be divided into the arid plains 
 region of the west and the humid areas of the middle and east. 
 
 4. Loiver Austral, or sub-tropical, mean annual temperature 
 60 to 72 degrees F., contains broad leaved evergreens, magnolia, 
 holly, cactus, pines, palmettos, and cypress. It includes the At- 
 lantic coastal plain south of the Potomac, the Gulf plains, lower 
 Mississippi Valley, Texas east of the staked plains, part of 
 Arizona, and the low areas of southern and central California. 
 
 5. Tropical, mean annual temperature 72 to 82 degrees F., 
 has a luxuriant vegetation, containing great numbers of climb- 
 ing and air plants. It occurs in southern Florida and Cuba. 
 
 Local Zonation. Besides the broad planetary zones of tem- 
 perature just described, there are many local zones in each, some 
 based on temperature, some on moisture, some on dependence 
 upon other plants, some on light, and others on the kind of soil 
 or rock. 
 
 Most all large hills, and mountains are belted with different 
 kinds of plants or trees, the belts being very irregular in many 
 places, as the zones are determined in part by the temperature 
 due to elevation, in part by light and wind, in part by the kind 
 of soil. 
 
 Most all swamps and some lakes have concentric zones based 
 upon the depth of water. (See figs. 85, 90 and 92.) 
 
 340. Control of Plant Distribution by Methods of 
 Migration.— On areas in which the temperature and 
 humidity favor vegetation, the plants must be distributed 
 over the area in some way. In the first uplift of a lake 
 bed, a coastal plain, or an island area there may be no veg- 
 
416 PHYSICAL GEOGRAPHY 
 
 etation. Seeds of land plants may spread over it in va- 
 rious ways as follows: 
 
 1. Some are carried by the wind. Some seeds like 
 those of the thistle and dandelion have feathery floats 
 which serve as little balloons to buoy up the seed so that it 
 may be carried long distances before it falls to the earth 
 to sprout and start a new center of distribution. 
 
 2. Some seeds have spines or sharp prongs by which 
 they are attached to the fur or hair of animals and thus 
 carried to distant points. Such are the burdocks, and 
 Spanish needles. 
 
 3. Edible seeds or seeds in edible fruit are often car- 
 ried by birds or other animals to distant points, and there 
 grow and multiply. 
 
 4. Some plants have explosive seed pods that fly open 
 with force and throw the seeds some distance away. A 
 repetition of this process from year to year carries the 
 plants over wide areas. Study the common witch hazel. 
 
 5. Seeds and sometimes plants are carried long dis- 
 tances by rivers and ocean currents. Many oceanic islands 
 obtain their plants in this way. The seeds of the cocoa 
 palm are thought by some to be widely distributed by the 
 ocean currents among the coral islands of the tropical Pa- 
 cific Ocean. 
 
 6. Man is one of the most important agents in dis- 
 tributing plants. He transplants them to distant parts of 
 the world, over mountains and across oceans or deserts. 
 The food and flowering plants are carried to all lands for 
 cultivation, and the seeds of weeds and other undesirable 
 plants are unavoidably carried with them. The railroads 
 and automobiles are important agents in this distribution. 
 Many plants migrate or spread by sending out shoots, run- 
 ners or underground stems. The strawberry is a good 
 example. 
 
GEOGRAPHY OF LIFE 
 
 417 
 
 Certain plants at times show a very peculiar distribution. 
 The Hart's-tongue fern (Fig. 280) occurs in Onondaga county, 
 N. Y., in a few places only on the Onondaga limestone. It is not 
 known to grow on any other rock in the county; nor is it known 
 to occur in any other place in eastern United States except one 
 place in Tennessee. It occurs in Ontario and is common in 
 North Africa and Southern Europe. 
 
 341. Barriers.— It seems probable that the different 
 
 FlG. 280. Hart's Tongue fern {Scolopendrium oflicinarum) occurs in Onon- 
 daga County, N. Y., only on Onondaga limestone. Tennessee is the only 
 other locality where it is known to occur in the United States. (J. E. 
 Kirkwood. ) 
 
 27 
 
418 PHYSICAL GEOGRAPHY 
 
 species of plants and animals had each a starting point on 
 one of the continents from which it spread over the sur- 
 rounding region until it met some barrier which checked 
 or stopped its further advance. Owing to the varied habits 
 of different species, what would prove a barrier to one 
 form might be no barrier to another. 
 
 The question of barriers which check the spread of 
 animals or plants from the center of origin is one of great 
 interest but involved in too many complexities for thorough 
 discussion here. 
 
 Animals or plants that live on the bottom of the shallow 
 portions of the sea on the continental shelf, find a barrier 
 in the land on one side and the deep ocean on the other. 
 Between these two barriers the species range along the 
 shore until stopped by an obstruction of some other kind, 
 the most common one being a change in temperature. Some 
 forms can live only in cold water, others only in warm 
 water, and others only in temperate water. Thus the reef- 
 building coral polyp which cannot stand a temperature be- 
 low 68 degrees F. is limited by the temperature to tropical 
 regions. 
 
 To most of the plants and animals that live in the sea, 
 fresh water is a barrier, and they do not enter the river 
 however deep and wide the channel may be. The opposite 
 is true for many fresh-water forms ; that is, the salt water 
 at the mouth of a river is an effective barrier that prevents 
 the spread into other rivers. There are a few forms, how- 
 ever, that live in either fresh or salt water. To such forms 
 the shore line is not a barrier, and they may pass along the 
 shore from river to river until they reach a temperature 
 barrier. 
 
 The shore line of a large body of water is a barrier to 
 most animals and plants that live on the land as well 
 as to those that live in the water. Many of the land ani- 
 
GEOGRAPHY OF LIFE 419 
 
 mals can cross a river or small lake by swimming bnt they 
 find the ocean an effective barrier. 
 
 Mountains, especially high mountain ranges, are effective bar- 
 riers to most of the forms of land life both plant and animal. 
 For that reason the indigenous life on the two sides of such a 
 mountain range as the Rockies or the Alps is likely to be quite 
 different. To most forms of plants of the austral and transition 
 zones the boreal area of a high mountain range is an insurmount 
 able barrier. Seeds with balloon attachments like the thistle 
 may sometimes be carried over by the wind, and burs and other 
 seeds with hooks may be carried across in the fur of animals, 
 but most of the plants at the base of the mountains have no 
 natural means of getting over the crest. 
 
 Deserts, especially large deserts such as the Sahara or those 
 of Central Asia, are effective barriers to most forms of life. The 
 aridity of the desert is as destructive to life as the cold tem- 
 perature of the mountain tops. Man, by provident forethought, 
 may carry sufficient supplies of food and water to enable him to 
 cross to supplies on the other side, but not so the plant or the 
 wayward animal, which perishes for want of water. 
 
 Plains are barriers to certain forms of life that flourish only 
 on the mountains. The broad stretches of prairies, the treeless 
 plains of the Mississippi Valley, prove a more effective barrier 
 than the great rivers to denizens of the forests and the hills. 
 
 Life of one kind may prove a very effective barrier to other 
 forms of life. 
 
 A forest is a barrier to certain kinds of plants and animals, 
 while its shade is necessary for the life of others. So a thicket 
 is a barrier to some forms and a protection to others. To some 
 the meadow or the grassy prairie is a decided check. 
 
 Some forms of life are dependent on others and cannot 
 flourish without them. To such dependent forms the absence of 
 the godfather on which they depend is a serious negative barrier 
 to their advance. 
 
 Certain insects are necessary for the fertilization of certain 
 plants, and destruction of either the plants or the insects would 
 cause a destruction of the other. 
 
 Some forms are enemies to others and where they occupy 
 an area they prove a decided barrier to the advance or spread 
 of the new form in that direction. 
 
420 PHYSICAL GEOGRAPHY 
 
 342. Effect of Vegetation on Physiography.— Some 
 of the effects of vegetation on shore lines have been described 
 in Chapter VI. The growth of the mangrove, the eel grass, 
 marsh grass and other water plants frequently produces 
 very marked changes on the position of the shore line and 
 in the case of small lakes, their results are not limited to 
 the shore but they fill the entire lake or marsh and make 
 a fertile, dry land area of it. 
 
 The drifting vegetation frequently lodges and forms an 
 obstruction on the course of a stream where later, sand and 
 gravel are deposited, sometimes turning the river from its 
 channel. 
 
 343. Indigenous and Existent Vegetation.— One 
 should keep in mind constantly the distinction between ex- 
 istent vegetation and the indigenous. The latter refers to 
 the plants which are native to the area through geographic 
 influences independent of man. The existent vegetation 
 is often in large measure the result of man's influence. 
 
 The potato, the maize or Indian corn, and tobacco are 
 indigenous to America but are now widely distributed over 
 the world. The peach, fig, grape, and orange are indigen- 
 ous to the European continent but are now distributed in 
 all countries. 
 
 Not only are fruits, grains and vegetables widely dis- 
 tributed by man, but many weeds and flowers as well. The 
 thistle, for instance, has become so abundant in many local- 
 ities as to cause laws to be made prohibiting any one from 
 permitting it to grow on his land. 
 
 The beautiful scarlet geranium, cultivated in our gar- 
 dens and greenhouses, is indigenous to South Africa, but it 
 has been transplanted by man to all parts of the world. 
 It is now growing wild in great luxuriance in California, 
 Australia and elsewhere. 
 
 The following is a list of plants with the name of the country 
 
GEOGRAPHY OF LIFE 421 
 
 in which they are indigenous. From this make a list of such as 
 you know to be growing where you live, stating in each case the 
 way or ways in which you think it may have been transplanted 
 from its original habitat. 
 
 Fruits, etc. Apple — Europe. Apricot — America or China. 
 Banana — S. Asia. Black Currant — Europe. Cherry — Asia Minor. 
 Gooseberry — England. Mango — S. Asia, Malay Peninsula. Oranges 
 and Lemons — Cochin China, Indo-China. Pear — Australia, all over 
 Europe. Plum — common, Mt. Elbons, N. Persia. Pineapple — 
 Brazil, Mexico, Guiana. Pomegranate — Persia, Afghanistan, Bel- 
 uchistan. Quince — N. Persia. Raspberry — Temperate Europe 
 and Asia. Red Currant — England and Normandy. Strawberry — 
 Europe, Asia, N. America. Tomato — Peru. Half a century or 
 more ago they were considered poisonous and raised for orna- 
 ment. Used to frighten the slaves before the war. Fig — Mediter- 
 ranean Basin. Grape — Cultivated first probably in Asia, wild in 
 N. America, Europe and Asia. Date Palm — Narrow zone from 
 Euphrates to Canaries. Peanut — Brazil. Cloves — Moluccas. Red 
 Pepper — America. 
 
 Vine fruits. Cucumber — West Indies. Gourd — Coast of Mal- 
 abar and Abyssinia. Musk Melon — Asia, Mexico, or California. 
 Pumpkin — Mexico or Texas. "Water Melon — Egypt. 
 
 Nuts — fruits. Cocoa-nut palm — America. Chestnut — Temper- 
 ate America, Europe, Japan. Hickory — 10 species all in E. North 
 America, Canada, Mexico. Walnut— North America, temperate 
 Asia, S. E. Europe. Occurs fossil in Tertiary and Quaternary in 
 North America. 
 
 Miscellaneous fruits. Cactus, Prickly Pear — Native in Mexico, 
 used for fruit and fodder, spineless variety now being cultivated 
 in arid areas in United States. Hops — Eurasia. Lima Bean — 
 Peru. Introduced in United States about 1820. Poppy — Shores 
 of Mediterranean. 
 
 Boots and tubers. Jerusalem Artichoke — Canada and United 
 States. Beet — Canary Islands, Mediteranean Basin. Carrot 
 — Europe and West Temperate Asia. Potato — United States 
 of Columbia and Peru. Radish — W. Temperate Asia. Sal- 
 sify — Borders of Mediterranean. Sweet Potato — America, some 
 say Asia. Turnip — Europe, Siberia. 
 
 Grains and seeds. Barley — Eurasia. Buckwheat — Manchuria, 
 near Lake Baikal. Maize (Indian corn) — America. Oats — Europe 
 
422 PHYSICAL GEOGRAPHY 
 
 and Tartary. Rice — India or China. It was used in China 2,800 
 B. C. Rye — Between Austrian Alps and Caspian Sea. Wheat — 
 Uncertain, very ancient, probably Euphrates Valley. Antedates 
 historic records. Known in China 2,700 B. C. Found in Pyra- 
 mids of Egypt of date thought to be 2,700 B. C. Durum Wheat 
 ■ — Long used in Russia and Southern Europe. Introduced in 
 U. S. and Canada about 1900. Much more productive on the dry 
 lands of the wheat belt than common wheat. Coffee — Abyssinia. 
 
 Fibers. Cotton — South Asia. Flax — Borders Mediterranean, 
 Caspian and Black seas. Hemp — Central Asia, Siberia. 
 
 Plants used for stems or leaves. Artichoke (true) — Borders of 
 Mediterranean. Asparagus — Europe, England, W. Temperate 
 Asia. Alfalfa — Brought to the United States from Chile. Prob- 
 ably from Asia Minor or Arabia. Celery — Europe and Asia. 
 Cabbage — Europe. Clover, Purple — Asia, Aryan Nations; crim- 
 son — around Pyrenees. Lettuce — S. Europe, Canary Islands, 
 Algeria, E. Asia. Millet — Egypt, Arabia. Parsley — S. Europe, 
 Algeria, Lebanon. Rhubarb — Central Asia. Saffron — Asia Minor. 
 Sorghum — Tropical Africa. Spinach — Empire of Medes and 
 Persians. Sugar Cane — S. Asia. Tea — Indo-China. Tobacco — 
 America, perhaps Mexico, Bolivia, Venezuela. Onion — Persia, 
 Afghanistan. Garlic — Europe. 
 
 344. Uncertainty of Origin.— The original habitat of 
 some of the plants is uncertain, owing to lack of definite 
 precision in the ancient records. Most of the wild plants 
 and many of the cultivated ones antedate definite historic 
 records. Early man, ages before even the primitive stages 
 of civilization, was instrumental in distributing many of 
 the plants. It should be noted that many of the cultivated 
 plants are varieties produced by cultivation, and new 
 varieties are constantly appearing. 
 
 The attempt to trace out the original habitat of the different 
 plants has been by means of (1) Geographical Botany which deals 
 with the distribution of plants, supplemented by the aid of (2) 
 Archeology and Paleontology, (3) History, (4) Philology. Con- 
 clusions are reached only after carefully sifting the data from 
 all the above sources. 
 
 The table given above was compiled mainly from the follow- 
 ing sources: (1) Origin of Cultivated Plants by de Candolle, (2) 
 
GEOGRAPHY OF LIFE 
 
 423 
 
 Our Plant Immigrants by David Fairchild. (National Geog. Mag., 
 April, 1906.) (3) Cyclopedia of American Horticulture by L. S. 
 Bailey. 
 
 With the aid of the United States Census report on agricul- 
 tural products, the student should now plot on a map of the 
 United States the corn belt, wheat, cotton, sugar, and rice belts, 
 and endeavor with the aid of the teacher to give geographic rea- 
 sons for their location. It is not a coincidence that corn is the 
 chief product in one locality, rice in another, tobacco in another, 
 etc. 
 
 FORESTS 
 
 One of the most important topics now before the Amer- 
 ican people is that of the present, past and probable future 
 conditions of the forests. When this country was first 
 settled by white men, a large part of it was covered by 
 dense forests. The early settlers chopped down the trees 
 
 Fig. 281. Log jam at Glen's Falls, N. '£. This is one of the ways in which 
 our forests are disappearing. (Natl. Geog. Mag.) 
 
424 
 
 PHYSICAL GEOGRAPHY 
 
 and burned them in order to clear the land for their farms. 
 Later the lumbermen cut the trees by millions to furnish 
 the lumber to build the cities, villages, factories, etc. So 
 rapidly has cutting of the forests been carried on that ex- 
 tensive areas are now bare and barren wastes, for the 
 destruction begun by the chopper has been completed by 
 the fires. (Fig. 282.) 
 
 345. Effects of Forest Destruction.— On most of the 
 plateau, plain, and valley areas, after the cutting of the 
 forest the land was brought under cultivation, and is now 
 
 PiG. 282. North Sugar Loaf Mountain, N. H. 
 a barren waste. 
 
 Once heavily timbered, now 
 
 covered with prosperous farms, but in the rocky portions 
 of the mountainous and hill country, the soil is so thin or 
 so poor that it cannot be cultivated, and the result is that 
 unproductive and unsightly barren waste areas now mark 
 the sites of former stately forests. 
 
GEOGRAPHY OF LIFE 
 
 425 
 
 In the virgin forests there was an accumulation of de- 
 caying vegetation that furnished a rich soil for the forest 
 trees. The fires following the cutting of the trees burned 
 up the vegetable mould leaving bare rocks in place of the 
 former deep, rich carpet of moss and shrubs. 
 
 The vegetable carpet of the forest acts like a great 
 sponge which absorbs and holds the rainfall, which serves 
 to keep the area moist in the rainless season. The destruc- 
 tion of the vegetable sponge causes most of the rainfall to 
 
 Fig. 283. Vegetation on the surface of a forest acts like a great sponge, pre- 
 venting the rapid run-off of the rainfall. Yellow pine forest in the Sierra 
 Nevada Mountains. 
 
 run over the rock surface, and thus wash into the streams 
 and carry away the residue left by the fire and drought. 
 The absence of the forest permits more of the rainfall 
 
426 
 
 PHYSICAL GEOGRAPHY 
 
 to run directly into the streams producing great floods, 
 which means destruction to property in the valleys and 
 great decrease in farm products from drought in the dry 
 seasons. (See fig. 284.) 
 
 Fig. 284. The destruction of the forest permits the rapid erosion of the soil 
 by heavy rains. Near Marion, N. C. (U. S. Geol. Survey.) 
 
GEOGRAPHY OF LIFE 
 
 427 
 
 The preservation and protection of forest areas on the 
 hills, mountains, and plateaus are of vital importance to 
 the prosperity of the farms in the valleys as well as the 
 farms on the upland. 
 
 The chief products obtained from the great forests are 
 lumber, wood pulp, bark for tanning, pitch, tar, and tur- 
 
 FiG. 285. Forest preserves (in black) in the Western United States in 
 1902. Some have been added since that time. The shaded areas are 
 Indian reservations. (U. S. Geol. Survey.) 
 
 pentine. The smaller trees furnish telegraph and tele- 
 phone poles, ties for railways, pulp for paper and wood 
 for charcoal. All of these materials are necessary in our 
 great commercial industries, but the method of obtaining 
 them has been wasteful and extravagant in the extreme. 
 
428 
 
 PHYSICAL GEOGRAPHY 
 
 Now, when it is almost too late to remedy it, we are begin- 
 ning to realize that these products could have been obtained 
 without the enormous waste. 
 
 State and National Legislatures have at last been aroused to 
 the importance of preserving or conserving the remnants of our 
 former great forests for the welfare, not only of the future gen- 
 
 Fig. 286. Forest areas (in black) on the Western United States in 1902. 
 Part of the area has since been deforested by lumbermen and fires. 
 Shaded areas contain a scanty growth of small trees. (U. S. Geol. 
 Survey. ) 
 
GEOGRAPHY OF LIFE 
 
 429 
 
 erations, but of the present as well. We now have considerable 
 areas of forest land owned and controlled by the nation and the 
 different states, from which the lumber and other products of 
 the forest will be obtained, without the destruction of the forest. 
 The accompanying map shows the location of the present forest 
 preserves, and it is to be hoped that these preservations will 
 increase in size and number from year to year. Schools of For- 
 estry have already been established for the training of men to 
 properly care for these forests. (Fig. 288.) 
 
 Fig. 287. Sequoia Gigantea, Mariposa Grove of Big Trees, Cal. (See also 
 Fig. 278.) 
 
 The principal districts of the United States from which enor- 
 mous quantities of lumber have been obtained, and which still 
 contain forest remnants of great value are — 
 
 I. New England, including Maine, New Hampshire, and 
 Vermont, with their great forests of pine, hemlock, 
 spruce, and cedar, and smaller forests of oak, maple, 
 birch, elm, etc. 
 
 II. The Adirondacks, with its pine and spruce. 
 
 III. The Great Lake region, especially northern Michigan 
 and Wisconsin, rich in pine and hemlock. 
 
430 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 288. 
 IV. 
 
 VI. 
 VII. 
 
 Forest rangers at work in the Texas pine forests. (W. U. Bray.) 
 
 The Alleghany Mountains and plateau with white pine, 
 
 hemlock, hardwood in the north, and yellow pine and 
 
 hardwood in the south. 
 
 The Gulf region with yellow pine, cedar, cypress and 
 
 oak. 
 
 The Rocky Mountain region with bull pine and spruce. 
 
 The Pacific region, the richest of all at present, with its 
 
 great forests of redwood, pine, hemlock, spruce, and 
 
 cedar. (Figs. 278, 286 and 287.) 
 
 ANIMAL GEOGRAPHY 
 
 346. Zoological Provinces and Faunas.— In general, 
 animals have a greater freedom of movement than plants. 
 The fact that they have the power of shifting quickly from 
 
GEOGRAPHY OF LIFE 431 
 
 place to place makes them less dependent on their surround- 
 ings. Most of the forms of animal life can by their power 
 of movement escape many dangers, such as frost, fire and 
 floods, that destroy plant life. 
 
 A rabbit may nip off the plant, which has no way of 
 escape or redress ; but when the wolf attempts to eat the 
 rabbit, the latter may escape by flight, and the former may 
 move to another locality and seek other food. However, 
 there are more or less well defined boundaries beyond which 
 neither the rabbit nor the wolf is likely to go. The area 
 over which an aggregate of associated animals wander and 
 struggle for existence is called a zoological province. All 
 the varieties of animals which characterize a zoological 
 province constitute its fauna. 
 
 The boundaries limiting these provinces are not always 
 sharply drawn. There is usually a mingling of the faunas 
 of adjoining provinces except where separated by some 
 natural feature producing an abrupt change of environ- 
 ment. This obstacle to the spread of life is called a bar- 
 rier. 
 
 The boundaries or barriers that restrain the animals to 
 certain provinces or areas are similar in many ways to those 
 which control the spread of plants. All barriers are rela- 
 tive and not insurmountable. Mountains, deserts, the 
 ocean, changes of temperature, the relative abundance of 
 other life in the form of food, shelter, or enemies are all 
 barriers of much importance in the study of the distribu- 
 tion of animals as well as plants. 
 
 As with the plants, so with the animals, the ocean forms one 
 of the most important of all barriers to land forms and is the 
 chief one in the following broad classification of the surface of 
 the earth into zoological regions: 
 
 1. North America — including North America as far south as 
 the Isthmus of Tehuantepec. Its fauna is very similar to that 
 of the Eurasian region, and they have more species in common 
 
432 
 
 PHYSICAL GEOGRAPHY 
 
GEOGRAPHY OF LIFE 433 
 
 than any of the other provinces. Among the forms peculiar to 
 it are the American bison, the musk ox, the Rocky Mountain 
 goat. The monkeys, horses, and swine do not exist here as in- 
 digenous forms. 
 
 2. Eurasian, including Europe, Africa, as far south as the 
 Sahara, and Asia north of the Himalayas. Here are large num- 
 bers of carnivorous animals, such as the wolf and wildcat, to- 
 gether with the reindeer, camel, and many varieties of wild sheep 
 and goats. The monkey tribe is entirely absent. 
 
 3. South American, including South America, the West Indies, 
 Central America, and southern Mexico. The characteristic forms 
 are the tapir, ant-eater, sloth, llama, monkey, and the condor and 
 rhea among the birds. Equally characteristic is the absence of 
 such representative families as oxen, horses, elephants, anthro- 
 poid apes, and moles. 
 
 4. African, including Africa south of the Sahara, southern 
 Arabia, and Madagascar. It has the greatest number of species 
 of all the provinces, and here the ungulates (hoofed mammals) 
 reach their greatest development, over 150 species of this group 
 being known. Well-known African animals are the giraffe, hip- 
 popotamus, gorilla, zebra, ostrich, and lion. The two latter are 
 characteristic but not really endemic, that is, limited to this 
 province. The most notable absences are the bear and deer. 
 
 5. Oriental, southern Asia and the islands of the East Indies 
 east to the Australian region. The province has many types con- 
 necting it to both the African and Eurasian regions. Species 
 peculiar to it are the tiger (also in Eurasian), orang-outang, 
 jungle bear, tapir and several species of antelopes. 
 
 6. Australian, including Australia, New Zealand (sometimes 
 made a sub province), New Guinea, and other smaller islands. 
 It is characterized by the extreme abundance of marsupials, 
 typified by the kangaroo, animals which carry the young in a 
 pouch, the very peculiar duckbill, and the almost complete ab- 
 sence of all five higher orders of terrestrial mammals from the 
 apes to the ant-eaters. The emu, cassowary, and lyre-birds char- 
 acterize the bird life. 
 
 347. Fresh Water Life.— While some animals are able 
 to exist in both fresh and salt water, yet the faunas are so 
 distinct as to warrant the separate consideration of fresh- 
 water forms. 
 
 28 
 
434 PHYSICAL GEOGRAPHY 
 
 The fresh water animals, especially those inhabiting the 
 larger lakes are divided into faunas, much as in the ocean. 
 The forms of the surface, the shores and the bottom are 
 usually here quite distinct. In the rivers the distinction 
 is less sharply marked, while in the ponds and brooks it 
 cannot be drawn. 
 
 These fauna include amphibians, larval and adult, many 
 varieties of fish, the larvae of many types of insects, and 
 some in the adult stages, many Crustacea, many worms, 
 one variety of fresh-water sponge, and other lower forms 
 of life. There is great variation in these species, for the 
 conditions of a fresh water existence vary greatly from 
 the turbulent brook to the majestic lake. 
 
 The transition belt at the mouths of rivers emptying 
 into the ocean, where the water is brackish, is hostile to 
 most forms of life, both of salt and fresh water, and has a 
 fauna peculiar to itself. 
 
 348. Oceanic Life.— The animal life of the ocean is 
 wonderfully varied and, to the interested observer, full of 
 beauty. As exposed on the shores between tides, brought 
 to the surface by the dredge and seine, or revealed by the 
 water telescope, the myriad forms entrance the beholder 
 with their profusion and tempt him to farther study. 
 
 The distribution of oceanic faunas, while governed by 
 the general principles previously outlined, is dependent 
 upon special conditions which must be noticed. 
 
 The temperature of the water is the most important 
 factor in the distribution of marine animals. It is de- 
 pendent upon three conditions, latitude, ocean currents 
 and depth. 
 
 In general the temperature of the surface oceanic waters is 
 higher at the equator and progressively diminishes toward the 
 poles. This is, however, modified by the ocean currents which 
 carry immense volumes of warm water into regions where the 
 
GEOGKAPHY OF LIFE 435 
 
 waters bordering the current are considerably colder. The 
 abrupt change thus produced is one of the important barriers 
 existing in the ocean. Species may be able to extend their range 
 widely where the change in temperature is gradual, but these 
 same species often cannot, endure the abrupt change of passing 
 from warm to cool water or the contrary. This is especially true 
 of the eggs of many of the molluscs. Hence, ocean currents often 
 form important boundaries to oceanic provinces. Similarly depth 
 is an important condition, for it directly affects temperature, as 
 the farther from the surface the cooler the water. It is closely 
 related to the effect of altitude upon the land, a few thousand 
 feet vertically causing greater changes in the faunas than many 
 hundreds of miles of latitude. So important is its effect that it 
 is used as the basis upon which oceanic life is classified, and the 
 following four great life zones are marked off by it. 
 
 Littoral Life, that of the shore, is the best known to 
 the ordinary observer of any of the oceanic zones. On 
 the beach at low tide among the seaweed are found many 
 interesting forms, the shore birds, many varieties of mol- 
 luscs .with their oddly shaped and often brightly colored 
 shells, sand worms, starfish, sea urchins, in fact, represen- 
 tatives of almost every known class of animals. It is 
 small wonder that men, from the ancient Greeks to the 
 modern scientist, have strongly believed that where land 
 and sea meet, life originated. 
 
 The conditions of life here are greatly varied. With 
 the ebb and flow of the tide, the dashing of the waves, the 
 winds, the sunlight, what more invigorating environment 
 can be conceived? 
 
 Intermediate Life, (sometimes included in Littoral) in- 
 cludes the life at moderate depths, ranging from low 
 water level to a depth approximating 500 fathoms. It is 
 not sharply separated from the Littoral and is sometimes 
 included in it. It is the zone of seaweeds and corals, and 
 here marine life reaches its maximum both in number and 
 variety of forms. Here flourish molluscs of many types, 
 
436 
 
 PHYSICAL GEOGRAPHY 
 
 including the common clam and oyster, corals, sea anem- 
 ones, sea cucumbers, crinoids or sea lilies, sponges and 
 
 Fig. 290. Skate, one of the odd but rather abundant forms of fish in the 
 intermediate zone of marine life. Cape Flattery Bank, Washington. 
 (U. S. Fish Commission.) 
 
GEOGRAPHY OF LIFE 
 
 437 
 
 many lower forms, along with lobsters, crabs, and the vast 
 multitude of fishes. Here life conditions, while more uni- 
 form than those of the Littoral zone, have not reached the 
 unvarying monotony of the great deeps. Food is abun- 
 dant, the depth is not too great for sunlight to penetrate, 
 and the waters are comparatively warm and undisturbed. 
 
 Abyssal life. The boundary between the preceding 
 zone and the abyssal, or deep sea, is not sharply defined, 
 many species passing far to each side of the arbitrary 
 
 Fig. 291. One of the deep sea fishes. They live in perpetual darkness in the 
 cold waters on the floor of the ocean basins. Taken from a depth of 
 several thousand feet. (Smith. Inst.) 
 
438 
 
 PHYSICAL GEOGRAPHY 
 
 depth taken as the dividing line. Conditions of life here 
 are extremely uniform, no light, a uniform temperature 
 approximating 34 degrees, great pressure, little motion of 
 water, and a high percentage of oxygen. Few plants live 
 here, and the animals are carnivorous, feeding upon each 
 other and animal remains, which slowly sink down from 
 the surface. 
 
 Fig. 292. 
 sea. 
 
 One of the odd-shaped forms of life from the bottom of the deep 
 (Smith. Inst.) 
 
 Abyssal animals are much the same the world over, and in 
 spite of the seeming adverse conditions under which they live, 
 the life is quite varied, including all the main types from the 
 fishes down. Many of the forms are extremely odd and curious. 
 Knowledge of deep-sea life has been greatly extended during the 
 recent years by the use of the dredge. (Figs. 291 and 292.) 
 
 Pelagic life includes those forms which habitually live 
 on the surface of the open sea or at moderate depths below 
 it. Here under the favorable condition of abundant sun- 
 light and moisture, and with many minute forms which 
 furnish food to the larger animals, a rich and varied life 
 is found. Whales, many forms of fish, pteropods and 
 
GEOGRAPHY OF LIFE 439 
 
 cephalopods among molluscs, crustaceans, and vast num- 
 bers of lower forms such as the Portuguese man-of-war, 
 jelly-fish, infusoria and radiolaria are all pelagic in their 
 habits. 
 
 Between the surface zone with its rich fauna and the ocean 
 bottom with its scanty fauna is the great body of oceanic waters 
 which, so far as our present knowledge shows, is almost devoid 
 of life. 
 
 THE GEOGEAPHY OP MAN 
 
 349. Distribution of Mankind.— At the World's Fair 
 in St. Louis one could see men from all the continents and 
 many of the larger islands of the world. There was a 
 great diversity in color, size, and other physical features. 
 Are these people all from one parent family, and if so, 
 where was the home of that family, and how came this 
 great diversity in racial characteristics? 
 
 The original habitat of man is thought to be in western 
 Asia, from whence descendants migrated in different direc- 
 tions. Probably the principal factor in the variations in 
 color, size, facial features, and mental development was 
 geographical environment. After a long period of time 
 the slow changes finally resulted in a great many races 
 and tribes which are sometimes grouped in the following 
 four races,: 
 
 1. The Ethiopian or black race Number— 173,000,000 
 
 2. The Mongolian or yellow race " 540,000,000 
 
 3. The American or red race " 22,170,000 
 
 4. The Caucasian or white race " 770,000,000 
 
 Total 1,505,170,000 
 
 The original habitat of the Ethiopian race was Africa 
 south of the Sahara, Madagascar, and many of the East 
 
440 PHYSICAL GEOGRAPHY 
 
 Indies. The second probably started from the Tibetan 
 table-land. The third occupied the new world, America. 
 The fourth race probably started in North Africa. From 
 the original habitat these races have spread over the world 
 and are now mingled on all the continents. 
 
 For many centuries, the Red man held undisputed 
 sway in what is now the United States. About four cen- 
 turies ago the white man first came in small numbers, then 
 in larger numbers, and later he brought the Black man 
 first as a slave. The yellow man found his way across the 
 Pacific Ocean and entered our western border. We now 
 have all four races in large numbers. So on all the con- 
 tinents there is a commingling of different races. 
 
 It must be remembered that the above classification is an 
 arbitrary one, and only one of many attempts to classify the 
 human family. Bach of the divisions contains many classes and 
 tribes, each with its own characteristics of physical and mental 
 traits. There are distinctions in size and shape of the skull, 
 color and texture of the hair, language, and above all, mental 
 development. A much more elaborate classification is given in 
 the Standard Dictionary under Man. 
 
 The Mongolians have probably an older fairly authentic his- 
 tory than any of the others, but as far back as their history ox- 
 tends, the Chinese and the Japanese branches are separate. 
 They have retained their present national characteristics through 
 a longer period of time with less changes than any of the other 
 nations. 
 
 The peoples that have passed through the greatest changes 
 and most rapid development in civilization are some of the 
 branches of the Caucasian race. In none of the nations, how- 
 ever, does authentic history extend back to the beginning of the 
 race. That the different races are branches of one common fam- 
 ily is an inference or deduction based on a study of the whole 
 human family in their physical and mental characteristics, and 
 relations to each other and the other animal forms. The origin 
 of the human family is involved in obscurity. 
 
 350. Influence of Geography on Man.— While man by 
 
GEOGRAPHY OF LIFE 441 
 
 his ingenuity has prevailed over the forces of Nature in 
 many ways, yet it still remains true that he is greatly in- 
 fluenced by his geographic surroundings. The climate, 
 topography, proximity to the sea, all wield a wonderful 
 influence over man. 
 
 351. Climate.— All the great nations of the world have 
 had their rise and growth in the temperate climate. This 
 is not a coincidence. Man may carry civilization into cold 
 and hot climates and may foster it for a time, but the fact 
 remains that the development of the great civilized nations 
 has been in the temperate zone. 
 
 The continued heat of the tropics tends to make one 
 languid and lacking in enterprise. The warm climate re- 
 quires little clothing or shelter to protect one from the ele- 
 ments. The great abundance of tropical fruit makes the 
 food supply an easy problem. Thus the great incentive 
 to provide food, clothing, and shelter which arouses man to 
 his best efforts in a cooler climate is lacking in the warm 
 tropics. 
 
 In the polar regions the cold is so intense and long con- 
 tinued that it is a perpetual struggle for existence ; hence, 
 one does not find the opportunity to cultivate the mind 
 and surround himself with the luxuries and comforts of 
 modern civilization. 
 
 In the temperate region the cold winters rouse man to 
 exertion to provide food, clothing and shelter, and yet the 
 cold is not so severe as to dwarf his energies or prevent the 
 development of his mental and physical powers. 
 
 352. Influence of Topographic Forms.— As already 
 stated the surface features greatly influence the distribu- 
 tion of the population, as well as the occupations of the 
 people and many of their customs and habits. 
 
 The most densely populated areas are generally on the 
 plains because facilities for travel and transportation are 
 
442 
 
 PHYSICAL GEOGRAPHY 
 
 there superior and favor the commercial and manufactur- 
 ing industries. Such conditions also favor agriculture 
 and hence abundant food supply. 
 
 Life in the high mountains tends toward the isolation 
 of groups of people and the development and perpetuation 
 of local customs. There is little communication and in- 
 tercourse with outside people. In the absence of mineral 
 
 Fig. 293. Farm house m the Boston Mountains. In many mountainous 
 districts farming is not a profitable industry. 
 
 products or large forests the mountain people are liable to 
 be poor and live a very simple life with few luxuries. In 
 the primitive and pioneer stages the people in the moun- 
 tains depend largely for support upon hunting and fishing. 
 The charm and the freedom of such a life overcomes in 
 large measure any desire for so-called luxuries, and, hence, 
 any incentive or opportunity for wealth. When the moun- 
 
GEOGRAPHY OF LIFE 443 
 
 tain people are dependent upon agriculture, the barren 
 soil and rough surface prevents any profit more than mere 
 subsistence ; and, hence, the hard struggle for food and 
 shelter hinders, if it does not prevent advancement in cul- 
 ture, learning and conveniences of civilization. (Fig. 293.) 
 353. Proximity to the sea generally favors easy com- 
 munication with other nations and countries, and hence 
 fosters the commercial spirit which results in wealth and 
 cosmopolitan ideas. In past centuries many of the sea- 
 faring nations were war-faring as well and conquered by 
 might where at the present day the battles are fought 
 more on manufacturing and commercial lines. 
 
 A few examples will best illustrate the influence of geo- 
 graphic conditions on man. 
 
 The Eskimo gives all his time and energy to the chase. 
 He has no chance to raise vegetables, even if he desired. Hav- 
 ing but a limited supply of fuel he learns to depend largely on 
 the conservation of his own bodily heat for warmth, so he 
 dresses in furs, eats fat and lives in ice houses. His life is not 
 devoid of adventure, but there is little incentive to advancement, 
 and the Eskimos to-day are probably no better off than their 
 ancestors were centuries ago. 
 
 The Pigmies of the African forest live in a rude shelter of 
 bushes quickly constructed and, hence, it is no great hardship 
 to leave it and migrate to a distant part of the forest. They have 
 no agriculture and live on nuts and wild animals which they cap- 
 ture in snares and pits. Having no reserve supply of food they 
 are frequently subject to hunger and sometimes starvation. 
 There is no development of the mental faculties, and they remain 
 but little superior intellectually to the animals which they pursue. 
 
 Emigrants from Europe, scarcely three centuries ago, entered 
 the present area of the United States. They have cut down the 
 forests, cultivated ; the soil, built cities and factories, extended 
 steam railways and electric lines far and wide over the land. 
 Many boats ply the inland waters and hundreds of vessels sail 
 to and from foreign lands. Telegraph lines extend to distant 
 parts of the earth. One may read in the evening papers an ac- 
 count of any. or all of the important events that have happened 
 
444 PHYSICAL GEOGRAPHY 
 
 anywhere in the world during the day. If one desires he may 
 without leaving his chair talk by telephone with any of his friends 
 within a radius of several hundred miles. He has in his service 
 many of the varied products of the world; fruits of the field, 
 garden, mine, and factory are at his command. What a contrast 
 is this life with that of the Eskimo or the African Pigmy! 
 
 The difference in habit, customs, civilization, and develop- 
 ment of these peoples is not entirely due directly to climate, but 
 partially to racial differences. The North American Indian that 
 was here before the European, was and is yet, in his natural state, 
 as far below the white in civilization as he is superior to the 
 Pigmy. How far these racial differences are due to climatic con- 
 ditions in past ages is a subject worthy of consideration. 
 
 The influence of geography on the migrations of man, in the 
 founding of cities, in the construction of highways, has been sug- 
 gested at different places in the preceding pages and will be con- 
 stantly suggested to the student of history and geography in all 
 his study and travel. 
 
 The migrations westward from the early settlement at Phil- 
 adelphia first spread out in the Chester — "the Little Valley" — 
 and later in the "Great Valley" because in these valleys was a 
 rich limestone soil more productive and more easily tilled than 
 that on the bordering hills. The further migrations were 
 through the water gaps into the other valleys of the Alleghany 
 Mountains, where the people lingered long before making the 
 difficult and dangerous journey up and over the rocky forested 
 plateau extending west to the Ohio region. Besides the great 
 difficulty and danger in traveling, the climate of the plateau is 
 more severe and the soil less fertile than in the sheltered valleys 
 and coves. Hence in the valleys they lingered until the French 
 were pouring into the Ohio Valley by ascending the St. Lawrence 
 and crossing the Great Lakes and descending the tributaries of 
 the Ohio. (See fig. 294.) 
 
 Pittsburg was a strategic point in the early colonial days and 
 as Fort Duquesne and Fort Pitt, it was the scene of bloody con- 
 flicts between the nations. The early settlers knew nothing of 
 the great coal beds and the deposits of oil and gas that have been 
 so instrumental in making this one of the great manufacturing 
 cities of the world, but they could see its great advantages as a 
 commercial center, and hence, the feverish haste of the French 
 to get possession, and of the English to dispossess them. 
 
GEOGRAPHY OF LIFE 
 
 445 
 
446 PHYSICAL GEOGRAPHY 
 
 It is only necessary to study the geographic location and 
 surroundings of New York, Boston, Chicago, Buffalo, and the 
 other great cities to see that their growth has been governed by 
 geographic features, which frequently were not perceived by the 
 people at the time, but which governed them, nevertheless. 
 The student from previous reading, study and observation should 
 put in writing the geographic reasons for the location and growth 
 of our great cities. These should be compared in the class-room 
 and supplemented by explanations from the teacher. 
 
 354. Influence of Man on Geography.— Man is not a 
 
 mere passive agent. While he has been influenced in 
 many ways by his geographic surroundings, he has had a 
 very marked influence on them in return. As evidence of 
 this one needs but to compare the United States of to-day 
 with its condition four centuries ago. 
 
 A large part of the dense forests has been destroyed. 
 The freshly plowed soil exposed to the rains has been 
 washed in large quantities into the streams and carried to 
 or toward the sea. In the construction of cities, highways, 
 and railways, hills have been cut through, sometimes cut 
 down, valleys and lakes have been filled or partly filled. 
 Streams have been diverted from their courses. Great 
 dams or lakes have been constructed in some places and 
 destroyed in others. Many of the wild animals have been 
 wholly or partly destroyed and domestic animals have 
 taken their place. Orchards have replaced the forest in 
 part, grains and vegetables have taken the place of the 
 wild plants over large areas. 
 
 Canals have been dug across divides connecting differ- 
 ent river basins. The Chicago Drainage Canal carries 
 water from Lake Michigan into the Mississippi River, 
 water that under natural conditions would drain through 
 the St. Lawrence River. "We are even attempting to con- 
 nect the Atlantic and Pacific Oceans by an artificial chan- 
 nel. 
 
GEOGRAPHY OF LIFE 447 
 
 The steel bands of the railway connect the oceans at 
 several points and a considerable portion of the intervening 
 territory is covered with a lacework of steel rails over 
 which millions of tons of material are being shifted from 
 one part of the country to another, and, in connection with 
 the steamboats, part of it even to -distant countries. 
 
 Great stone qnarries in many places have left holes in 
 place of hills. Clay, sand, gravel, marl, and ore pits are 
 in many places so numerous and extensive as to entirely 
 change the surface features of the area. 
 
 In many places the mountains and plateaus are bored 
 and tunnelled by numerous excavations to an extent al- 
 most beyond belief. Besides the large mine openings man 
 has bored thousands of deep holes through which have been 
 taken vast accumulations of oil, and gas. 
 
 Elsewhere through artesian wells he has brought the 
 ground water to the surface in arid areas and thus added 
 to the fertility of the country. In other localities where 
 there was too much water and the land was swampy, 
 malarial, and unproductive, he has by surface or sub-sur- 
 face draining made it dry, healthful, and productive. 
 
 REFERENCES 
 
 Coulter, J. M., Plant Relations, D. Appleton & Co. 
 
 Clements, Research Methods in Ecology, University Pub. Co., 
 Lincoln, Nebraska. 
 
 Schimper, Planzen Geographie, Jena, Gustav Fischer. 
 
 Cowles, The Physiographic Ecology of Chicago and Vicinity, 
 Bot. Gaz. 31, 73, 1901. 
 
 Wolle, Diatomaceae of N. America (Hid. with 2,300 figs.) 
 The Comenius Press, Bethlehem, Pa., 1894. 
 
 Bray, Distribution and Adaptation of the Vegetation of Texas, 
 Bull. 82, University of Texas. 
 
 Lamson, Scribner, Grasses as Sand and Soil Binders. Year- 
 book, U. S. Dept. of Agr., 1894. 
 
448 PHYSICAL GEOGRAPHY 
 
 Hill, Physical Geography of the Texas Region, U. S. Geol. 
 
 Surv. Topographic Atlas. 
 Hitchcock, Methods Used in Controlling and Reclaiming Sand 
 
 Dunes. U. S. Dept. of Agr., Bur. of Plant Industry, 
 
 Bull. No. 57. 
 Lloyd & Tracy, The Insular Flora of Miss, and La., Dept. of 
 
 Botany, Columbia University, No. 174. 
 Webber, The Water Hyacinth and its Relation to Navigation. 
 
 U. S. Dept. of Agr., Bull. No. 18. 
 Allen — 1. The Geological Distribution of Animals, Bull. 
 
 U. S. Geol. and Geog. Surv. of the Territories, Vol. 
 
 IV, pp. 313 to 377. 
 2 The Geological Dis. of N. American Mammals, Bull. 
 
 Am. Mus. Nat. His., Vol. V, pp. 199-243. 
 Heilprin, Angelo, The Geog. and Geol. Dist. of Animals. Int. 
 
 Sci. Ser., London and New York, 1897. 
 Osborne, The Rise of the Mammalia in N. America, N. Y., 
 
 1893. 
 Merriam — 1. The Geog. Dist. of Life in N. America, Proc. 
 
 Biol. Sur., Washington, Vol. VII, 1892. 
 
 2. Life-Zones and Crop-Zones of the U. S., Bull. No. 
 
 10, Dept. of Agr. Div. of Biol. Surv. 
 
CHAPTER XII 
 
 PHYSIOGRAPHIC REGIONS OF THE UNITED 
 STATES* 
 
 The area of the United States is so large and diversified 
 that it contains numerous examples of all the different 
 physiographic types previously described. 
 
 The entire area of the United States is conveniently 
 divided for study into: (1) the Eastern or Atlantic region; 
 (2) the Lake region; (3) the Central or Mississippi 
 region; (4) the Southern or Gulf region; (5) the Western 
 Interior region and (6) the Pacific region. 
 
 355. 1. The Eastern, or Atlantic Region.— Under 
 this heading is included the eastern part of the United 
 States next to the Atlantic Ocean but not confined to the 
 area that drains into it. The southern part of the moun- 
 tainous area drains westward into the Mississippi, yet 
 physiographically it belongs to the same province as the 
 northern part which drains eastward into the Atlantic. 
 
 A. The Atlantic coastal plain is the part bordering 
 the seashore and may be divided into three portions ; ( a ) 
 the submarine plain, corresponding to the part of the con- 
 tinental shelf on our eastern seaboard. It is now under 
 
 *The different regions may be studied by following the order of geo- 
 graphical position, that is, beginning at one side, as the east, and taking up 
 each region in turn across the country to the west side, or by studying all 
 the areas of the same feature at one time, as, for example, all the moun- 
 tains first, then the plateaus and plains. While there are advantages in each 
 method the author favors the first. However, any teacher preferring the 
 second method can readily use it with the map and data given. In either 
 case only a brief outline can be given in a general treatise of this kind, 
 and the student will find it advisable to take up a few of the areas more 
 thoroughly by utilizing some of the reference works cited. A small map 
 showing all the different regions should be made by the student. 
 29 449 
 
450 
 
 PHYSICAL GEOGRAPHY 
 
 Fig. 295. Photograph of Relief map of part of Eastern and Central United 
 States. (E. E. Howell.) Trace out on this the physiographic regions 
 mentioned in the text. 
 
THE PHYSIOGRAPHIC REGIONS 
 
 451 
 
 the sea but parts of it have been land area at times in the 
 past and probably will be in the future; (b) the tidal 
 flats and coastal marshes comprise the portions of the coastal 
 plain that are at least partly exposed during the low tide 
 and are largely covered with water during high tide. Tn 
 
 Fig. 296. View on the low plains of Central Florida. The alligator and 
 rattlesnake are abundant where not destroyed by man. The vegetation is 
 typical of the swamp areas. Pine forests where not destroyed occur on 
 the more elevated portions. (A. M. Reese.) 
 
 some places they are covered with salt water, in others 
 brackish water (a mixture of salt and fresh) and in others 
 by fresh water. Some of the fresh water swamp areas are 
 above high tide but intimately connected with the tidal 
 areas, (c) The emerged plains include portions of the 
 coastal plain elevated above high tide, extending back in 
 places many miles from the sea. They are now covered 
 
452 
 
 PHYSICAL GEOGRAPHY 
 
THE PHYSIOGRAPHIC REGIONS 453 
 
 with layers of sand, clay, and marl that were deposited 
 over the former sea-bottom, and contain a great deal of 
 valuable farm land. In places the tidal flats are absent 
 and the emerged plains are separated from the submarine 
 plain by the shore line. What is the relation of the Fall 
 Line to this area? (See sec. 116.) 
 
 B. The Piedmont-New England Plateau. Inland from 
 the sandy coastal plain and separating it from the moun- 
 tains is an area covered with hard, crystalline rocks and 
 having a hilly, irregular surface. (See fig. 297.) 
 
 Since it lies at the foot of the higher mountains further 
 west it is called pied- (foot) mont (mountain). Since it 
 is elevated above the more recent coastal plain so promi- 
 nently it is called a plateau. It varies in width through 
 the Middle and Southern states, reaching its greatest width 
 in New England. The greater part of the piedmont belt 
 was in early geological times covered or partly covered 
 with mountains which during long ages were worn down 
 nearly to a plain, that is, to a peneplain. The entire area 
 was elevated again and the streams cut many deep valleys 
 into the uplifted plain, dissecting it into a complexity of 
 hills and valleys. The Fall Line separates this from the 
 coastal plain. (Figs. 194 and 297.) 
 
 C. The Appalachian Mountain Area. The somewhat 
 complex mountainous area in the Eastern United States 
 is divided into four regions each of which in turn has 
 many complexities. (Fig. 295.) 
 
 (a) The first range of mountains bordering the Pied- 
 mont plateau on the west is called the South Mountain in 
 Pennsylvania and the Blue Ridge in Virginia and farther 
 south. It is a very irregular range, both in size and struc- 
 ture. It is composed in part of very old rocks, hard and 
 crystalline, in part of brown sandstones and shales of more 
 recent age. 
 
454 PHYSICAL GEOGRAPHY 
 
 (b) The Great Valley of the Appalachians is the great 
 depression that separates the South Mountain Blue Ridge 
 from the ridges of the Alleghany Mountains on the west. 
 It is a broken diversified area, quite hilly in places, and 
 very different from an ordinary river valley. It is only 
 when we consider it in its relation to the mountains on 
 each side that it appears as a valley. Part of the area is 
 underlain by limestone and the other part mostly by shale. 
 In the residual clay overlying the rocks are vast quantities 
 of iron ore and white clay. 
 
 The great Shenandoah Valley of Virginia, the Cumber- 
 land and Lebanon Valleys in Pennsylvania lie in and form 
 part of the Great Valley that extends from Lake Cham- 
 plam, New York, to Alabama. 
 
 (c) Bordering the Great Valley on the west are the 
 Alleghany ridges which have a general northeast-south- 
 westerly trend. The ridges have a somewhat uniform 
 height and are quite variable in length. Some extend only 
 a few miles, some a hundred miles or more. In places 
 they are like upturned canoes, the "Canoe Mountains," in 
 other places they twist and turn in different directions. 
 (See figs. 238 to 242.) 
 
 The ridges are almost all composed of sandstone which 
 on disintegration gives rise to a quite unproductive sandy 
 soil. The valleys separating the ridges have generally a 
 limestone soil which is quite fertile. The valleys are 
 decked with valuable farms and the ridges formerly 
 forest-clad are now covered only with rocks and bushes. 
 Their chief products at present are pure water, pure air, 
 huckleberries and rattlesnakes, of which the first and third 
 can be transported to the towns in the valleys but the other 
 two can be best enjoyed by a trip into the mountains. 
 
 (d) Immediately west of the Alleghany ridges is the 
 Appalachian plateau, including the Alleghany plateau on 
 
THE PHYSIOGRAPHIC REGIONS 
 
 455 
 
 the north and the Cumberland plateau on the south. It is 
 bounded on the east by a steep irregularly notched escarp- 
 ment facing the narrow valley that separates it from the 
 Alleghany ridges, and it slopes westward gradually merg- 
 
 FiG. 298. Typical view on the Alleghany Plateau. Potomac Valley, near 
 Chaffee, Md. (Md. Geol. Survey.) The plateau is covered with forests 
 (where not destroyed) and parts of it are underlaid by beds of coal, and 
 pools of petroleum and natural gas. It is dissected by many rivers which 
 flow in deep valleys. 
 
 ing into the Mississippi and Lake Plains. It is deeply 
 trenched by great numbers of streams so that in many 
 places it resembles an irregular mountain mass. (See 
 Charlestown, W. Va., topographic sheet.) There are a 
 few elevated mountain ridges in this plateau area, such as 
 Chestnut and Laurel Ridges in Western Pennsylvania. 
 
 The Catskill Mountains form the northeastern end of 
 the Alleghany plateau. Many of the more rugged portions 
 
456 
 
 PHYSICAL GEOGRAPHY 
 
THE PHYSIOGRAPHIC REGIONS 457 
 
 further south are locally known as mountains, but like the 
 Catskills they are mountains of circum-erosion. The Erie 
 Canal and New York Central Railway run just north of 
 the plateau escarpment from Albany to Rochester. (Fig. 
 299.) 
 
 From a good map make a list of the streams that drain 
 (a) into the Atlantic from this plateau, (b) into the Ohio, 
 (c) into the Great Lakes. 
 
 (e) The Adirondack Mountains lie north of the Alle- 
 ghany plateau and are separated from it by the Mohawk 
 
 Fig. 300. View of the Adirondack Mountains near Keeseville, N. Y. The 
 bordering plain in the foreground. 
 
 Valley. The rocks of the Adirondack^ ally them closely to 
 the New England plateau area from which they are sepa- 
 rated by the Champlain Valley. They are older than the 
 Alleghany, the Catskill, or the Green Mountains. (Fig. 
 300.) 
 
458 PHYSICAL GEOGRAPHY 
 
 356. II. The Lake Plains.— Lying west of the Adi- 
 rondacks and extending west along the border of the Great 
 Lakes is a strip of variable width forming the lake plains. 
 The Lake Ontario plain is sharply divided on the west 
 from the Erie plain by the escarpment at the mouth of the 
 Niagara river gorge, but further east in New York State 
 the two plains merge into one. In Michigan, Wisconsin, 
 and Minnesota in places the plains are rugged and diversi- 
 fied by many hills, the area in places resembling the Pied- 
 mont plateau of the Atlantic region. The Lake Plains are 
 sometimes divided for more detailed study into (1) the 
 Superior lowland, (2) the St. Paul-Madison upland, (3) 
 the Green Bay lowland, (4) the Michigan-Huron-Erie low- 
 land, (5) the Lansing upland, (6) the Niagara upland, 
 (7) the Ontario lowland. 
 
 357. III. The Mississippi Valley Region.— If one in- 
 cludes in the Mississippi Valley all the area between the 
 Alleghany plateau and the Rocky Mountains it forms one 
 of the largest and most important of the physiographic 
 regions of the United States and one so diversified that it 
 can be readily subdivided into a number of minor areas. 
 As already stated there is no sharp line of separation be- 
 tween the eastern side of the valley and the Alleghany 
 plateau. 
 
 (a) The northern part of Indiana, nearly all of Illi- 
 nois, portions of Missouri, Iowa, Kansas, Nebraska, Min- 
 nesota, and the Dakotas are covered with great stretches 
 of treeless plains known as prairies, in some places rolling 
 in others remarkably level for long distances. In the wild 
 state these prairies were covered with tall grass and al- 
 most devoid of trees. Since it has been brought under 
 cultivation many orchards and groves have been planted. 
 
 (b) The western part of the valley, extending from the 
 prairies to the Rocky Mountains and covering portions of 
 
THE PHYSIOGRAPHIC REGIONS 459 
 
 Colorado, Kansas, Nebraska, Wyoming, Montana, and the 
 Dakotas is known as the Great Western Plains. A large 
 part of the area has a semi-arid climate, too dry for farm- 
 ing (other than grazing), without irrigation. Some por- 
 
 FiG. 301. View on tne Great Western Plains. Notice tne dwelling . 
 house on the horizon. (U. S. Geol. Survey.) 
 
 tions of the area are watered from artesian wells (see. 58). 
 Other portions are irrigated from water ponded in the 
 deep canyons of the Rocky Mountains. 
 
 (c) There are several mountain areas over the western 
 part of the Mississippi Valley. The Washita Mountains 
 south of the Arkansas river in the states of Arkansas and 
 Oklahoma are ridge mountains similar in structure and 
 age to the Alleghany ridges of the Atlantic area. 
 
 (d) The Boston Mountains lie north of the Arkansas 
 river in Arkansas and Oklahoma. They consist in part of 
 dissected plateaus but there has been some folding and 
 faulting in places. They belong in the same class with the 
 Catskill Mountains, but are somewhat more complex. 
 
460 
 
 PHYSICAL GEOGRAPHY 
 
 (e) Covering a considerable area north of the Boston 
 Mountains is an upland area known as the Ozark Plateau. 
 The Boston Mountains stand on and form a part of the 
 plateau. (See fig. 295.) 
 
 (f) The Black Hills in western Dakota and Eastern 
 Wyoming are dome mountains in the same class with the 
 Adirondacks but more recent in age and less complicated 
 in structure. In the area bordering the Black Hills, and 
 to a less degree elsewhere in the western plains, there is a 
 
 Fig. 302. "Granite Needles" near Harney Peak in the Black Hills. (U. S. 
 Geol. Survey.) Part of the area is very rugged. There are other forms 
 of hills and ridges in the Black Hills area. 
 
 type of topography known as the Bad Lands. It consists 
 of a very irregular surface with a maximum number of 
 deep gullies and narrow ridges with sometimes fantastic 
 shapes. (Figs. 303, 39, 40, 41, and 234.) 
 
 (g) The Delta of the Mississippi is a vast stretch of 
 lowland covering a large part of Louisiana. It is covered 
 
THE PHYSIOGRAPHIC REGIONS 461 
 
 with a network of streams, bayous, and lakes. The greater 
 part of the lowland area is very fertile as it is composed of 
 rich alluvium carried down by the Mississippi river. The 
 water table is so near the surface that the region never 
 
 Fig. 303. "Chapeau de Femme" in the Bad Lands of S. Dakota. (U. S. 
 Geol. Survey.) Columns 40 ft. high. Notice the effect of alternating 
 hard and soft layers. The erosion is partly by occasional heavy rains, 
 partly by winds. 
 
 suffers from drought but sometimes it does from floods. 
 It is placed in the Mississippi Valley region but it is just 
 as properly a portion of the Gulf region as it has all been 
 reclaimed from the Gulf. 
 
 (h) The flood plain of the Mississippi is the lowland 
 area bordering the river that is subject to periodical over- 
 flow from floods in the river. It varies in width from a 
 few miles to 100 miles or more. 
 
 358. IV. The Gulf Region is in part a continuation 
 
THE PHYSIOGRAPHIC REGIONS 
 
 463 
 
 of the Atlantic coastal plain, consisting like it of a sub- 
 marine plain, coastal marshes, and. emerged plain. The 
 latter extends .north into and partly forms the Alabama- 
 Georgia cuesta* in the east and the Texas cuesta in the west. 
 
 Fig. 305. View on the staked plain or cuesta of Texas. (W. L. Bray.) It 
 is an arid region with little vegetation or surface water. 
 
 The Texas cuesta is also known as the Llano ^Estacado or 
 staked plain. The staked plain is the southern extension 
 of the Great Western Plains and like them is too arid for 
 agriculture except when irrigated. It terminates on the 
 west at the Pecos Valley. The Trans-Pecos country be- 
 tween the Rio Grande and the Pecos Rivers contains the 
 San Francisco or Trans-Pecos Mountains. 
 
 *A cuesta is a low ridge with a steep descent on one side and a gentle 
 slope on the other. On most cuestas the gentle slope is towards the present or 
 former sea shore. 
 
464 
 
 PHYSICAL GEOGRAPHY 
 
 359. V. The Western Interior Area.— (a) Between 
 the Great Plains and the S4erra Nevada is a stretch of up- 
 land country composed of mountains, plateaus, plains, and 
 basins. The great range of mountains bordering the plains, 
 the highest and most massive in the United States is com- 
 
 Fig. 306. Outcrop of a great sandstone ledge at the end of the Freezeout 
 Mountains in Central Wyoming. One of the subsidiary mountains in the 
 Rocky Mountain system. 
 
 monly known as the Rocky Mountains. They form the 
 backbone of the continent and consist of great complexities 
 of mountains rather than a simple range. There is a de- 
 pression or break in these mountains through central 
 Wyoming followed by the Union Pacific railway, south of 
 which the mountains have been called the Park Mountains 
 and those north the Stony Mountains. In both areas there 
 
THE PHYSIOGRAPHIC REGIONS 
 
 465 
 
 are many portions to which more local names have been 
 given, some of which are the Gallatin, Laramie, Freezeont, 
 Elk, and San Juan Mountains. Pike's Peak at Manitou 
 is one of the best known of the many high peaks, and is 
 the highest mountain peak in the world which has a rail- 
 way extending to its summit. 
 
 Fig. 307. Western escarpment in the Freezeout Mountains. (U. G. Cornell). 
 A typical "Hog Back" Ridge, one of the common physiographic features 
 of the Rocky Mountain region. 
 
 The Hog Back ridges forming the foothills of the 
 Rocky Mountains are characteristic features of this region. 
 They are narrow, sharp-crested hills formed by the out- 
 cropping edges of hard layers of rock between softer layers 
 which were turned up nearly vertical in the uplift which 
 formed the mountains. They vary in height from 100 ft. 
 to 1,000 ft. or more. (See figs. 307, 308, and 35.) 
 
 Numerous rivers have cut wonderful canyons deep into 
 30 
 
466 
 
 PHYSICAL GEOGRAPHY 
 
 the rocky center of these great mountains, exposing to 
 view many valuable veins of gold, silver and other metals. 
 
 1«'IG. 308. "Cathedral Spires" in the Garden of the Gods. (U. S. Geol. 
 Survey.) Formed by irregular erosion on the outcrop of the vertical beds 
 of red sandstone. 
 
THE PHYSIOGRAPHIC REGIONS 
 
 467 
 
 (b) The Wahsatch and Uintah Mountains in Utah, the 
 Basin Ranges in Nevada, Idaho, California and Arizona 
 are other large and picturesque mountains in the interior 
 region. 
 
 
 
 
 
 
 
 
 
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 Fig. 309. Knight's Butte, Central Wyoming. Copyright, 1900, by U. G. 
 Cornell. A view on the dissected high plains in the midst of the 
 Stony Mountains. 
 
 (c) The great Colorado Plateau west of the Park Moun- 
 tains and the Columbian Plateau west of the Stony Moun- 
 tains are two of the largest and highest plateaus in Amer- 
 ica. The first is deeply trenched by the great Colorado 
 River and its tributaries and the second by the Columbia 
 and Snake rivers. In both of these are some of the deep- 
 est and most picturesque canyons in the world. 
 
 (d) The Interior Basin lying between the two plateaus 
 and the Pacific mountains really consists of a great number 
 of basins containing numerous lakes, fresh, salt, and alka- 
 
468 
 
 PHYSICAL GEOGRAPHY 
 
 FiG. 310. Photograph of relief- map of portion of the Colorado Plateau and 
 the Grand Canyon of the Colorado. (B. E. Howell.) 
 
 line. The entire basin region has an arid climate but ir- 
 rigation has made some portions of it quite fertile and 
 prosperous. Much of the area is covered with plains of 
 sand, alkali, or salt. (Figs. 312, 274, 275, 79, 80, and 84.) 
 Some portions of this area are the lowest on our con- 
 tinent. The Salton basin in southern California is 287 
 feet below sea level and Death Valley in eastern California 
 
THE PHYSIOGRAPHIC REGIONS 469 
 
 is 276 feet below. Both of these areas belong by position 
 to the Pacific region but the fact that they are interior 
 basins, places them physiographically in the Western In- 
 terior region. They contain large deposits of salt, borax, 
 soda, and other salts. A great many mountains of the 
 class known as block mountains occur in the Interior Basin. 
 (See fig. 312 and sec. 266.) 
 
 Fig. 311. View in the Grand Canyon of the Colorado, the deepest 
 and one of the most picturesque canyons in the world. (A. R. 
 Crook.) 
 
 360. VI. The Pacific Area.— In its broader features 
 the Pacific region consists of two mountain ranges with 
 the Great Valley of the Pacific separating them. The 
 eastern of the two ranges is known as the Sierra Nevada 
 at the south and the Cascade Mountains farther north. 
 The western range is called the Coast Mountains. The 
 central portion of the Great Valley is the Valley of Cali- 
 fornia, occupied in part by the Sacramento and San Joaquin 
 rivers, the southern extension is through the Salton Basin 
 
470 
 
 PHYSICAL GEOGRAPHY 
 
 into the Gulf of California. Northward it is continued 
 as the Sound Valley through Oregon and Washington. 
 This valley on the west side of the continent corresponds 
 to the Great Valley of the Appalachians on the east and 
 adds to the symmetry of the national area. 
 
 Fig. 312. One of the block mountain rid 
 (D. T. McDougal.) 
 
 in the Interior Basin region. 
 
 This great western valley is more distinctly divided 
 into sections than is its eastern prototype. The Klamath 
 Mountains in Oregon form a mountain mass connecting 
 the Sierra Nevada, Cascade, and Coast Mountains across 
 the valley. In southern California also the Sierra Nevada 
 and Coast Mountains join and cut off the Salton Valley 
 from the Valley of California. 
 
THE PHYSIOGRAPHIC REGIONS 471 
 
 The student should make a classified list of the physiographic 
 features of the United States, locating each by states as follows: 
 
 I. Plains. 
 
 1. The coastal plains. 
 
 2. The interior plains that were at one time coastal 
 plains. 
 
 3. The cuestas. 
 
 4. The prairies. 
 
 5. Lake plains. 
 
 6. Alluvial plains — deltas. 
 
 II. Plateaus. 
 
 1. Arid plateaus. 
 
 2. Forested and cultivated plateaus. 
 
 III. Mountains. 
 
 1. Folded ridge mountains. 
 
 2. Domed mountains. 
 
 3. Mountains of erosion. 
 . 4. Block mountains. 
 
 5. Volcanic mountains. 
 
 IV. Rivers. 
 
 1. Which drain into the Atlantic? the Pacific? Gulf of 
 Mexico ? 
 
 2. Which flow through deep canyons? 
 
 3. Which have high falls? 
 
 4. Which are valuable aids in navigation? 
 
 5. Which drain fertile farm land? 
 
 6. Which drain coal basins? 
 
 7. Which have large deltas? 
 
 8. Which have none? 
 
 9. Which have no flood plains of any size? 
 
 V. Name and locate the salt lakes. 
 
 On a blank map of the United States sketch in the boundaries 
 of Lakes Iroquois, Passaic, Agassiz, Bonneville, Lahontan and 
 any other fossil lakes known. See references in chapter on lakes. 
 
 REFERENCES 
 
 1. Powell, Physiographic Regions of the United States. 
 
 2. Davis, New England Plateau. 
 
 3. Willis and Hayes, Appalachian Mountains. 
 
472 PHYSICAL GEOGRAPHY 
 
 All of the above published by the American Book Co. 
 
 4. Russell, Rivers of North America, G. P. Putnam's Sons. 
 
 5. Russell, Volcanoes of North America, Ginn & Co. 
 
 6. Russell, North America, D. Appleton & Co. 
 
 7. Hall, Geography of Minnesota, The H. W. Wilson Co. 
 
 8. The American Deserts. National Geographic Magazine, 
 
 April, 1904. 
 
 9. Mill, The International Geography, D. Appleton & Co. 
 10. Simonds, Geography of Texas, Ginn & Co. 
 
APPENDIX I 
 
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APPENDIX II 
 
 SOME OF THE COMMON METHODS OF MAP 
 PROJECTION 
 
 The cylindrical projection supposes a cylinder of paper 
 around the globe touching the equator and hence parallel 
 to the axis of the globe. On this the meridians and paral- 
 lels are projected at right angles to each other, the mer- 
 idians forming vertical lines and the parallels horizontal 
 ones. The meridians are equally spaced and all points on 
 the equator are in their true proportion, but toward the 
 poles the areas are much out of proportion. If the pro- 
 
 Fig. 313. Cylindrical projection. 
 
 jection of the parallels is from the center of the globe, the 
 pole of the earth is at an infinite distance and cannot be 
 represented ; also the polar regions are greatly exaggerated 
 and not represented beyond 70 or 75 degrees. If the pro- 
 jection of the parallels is at right angles to the axis, the 
 polar regions are out of proportion in the opposite direc- 
 tion. (See fig. 313.) 
 
 M creator's projection is a modified form of the cylin- 
 
 474 
 
METHODS OF MAP PROJECTION 
 
 475 
 
 drical, in which the parallels are so spaced that the degrees 
 of latitude and longitude are in their proper proportions. 
 It is much used by navigators in plotting the course at 
 sea, because the directions are all true and the course can 
 be plotted in a straight line. (Fig. 18, p. 34, is on Mer- 
 cator's projection.) 
 
 In the stereograpkic projection, commonly used in map- 
 ping the hemispheres, a sheet of paper is placed without 
 curving parallel to the axis of the globe, touching the 
 equator at one point in the middle of the hemisphere to be 
 mapped. The lines are then projected on the paper from 
 the point at the opposite end of the diameter touched by 
 the paper. 
 
 The globular projection differs from the stereographic 
 in being projected from a point 1.707 times the radius of 
 the globe. 
 
 The orthographic projection differs from the preceding 
 in being projected from a point at infinity; that is, the 
 lines of projection pass through the globe parallel to each 
 other and normal to the paper. 
 
 Fig. 314. Conical projection. 
 
 The conical projection assumes a cone touching the 
 earth on the parallel passing through the middle of the 
 area to be mapped and the lines projected on the cone from 
 
476 
 
 PHYSICAL GEOGRAPHY 
 
 the center of the globe. The cone is then split open on a 
 meridian line and spread out flat. This is more accurate 
 than any of the preceding for small areas away from the 
 equator. In large areas the distortion becomes pronounced 
 away from the center of the map ; but where greater accu- 
 racy is required this defect is sometimes remedied in part 
 by using a polyconic projection. 
 
 Fig. 315. Polar projection. 
 
 In the polar projection, as shown in fig. 315, the paper 
 is placed tangent to the pole and from the center of the 
 globe, one point on each parallel is projected to the paper 
 as at P, Q, R. With N (the pole) as a center, circles are 
 
METHODS OF MAP PROJECTION 
 
 477 
 
 drawn through these points for the parallels. Radial lines 
 from the center (N) form the meridians. 
 
 Polar 
 
 Fig. 31C. Projections illustrated with 
 wire screen. 
 
 In none of the above projections is a globe used in 
 actual construction, but the lines are located by com- 
 putation. 
 
GENERAL REFERENCES 
 
 Special references are given at the end of each chapter. 
 The following general reference hooks contain valuable 
 data on different phases of the subject and should be con- 
 sulted as far as possible by both teacher and students : 
 
 1. Physiography by R. D. Salisbury, Henry Holt & Co. 
 
 2. Text Book on Geology, 3 Vols., by Chamberlin and Salis- 
 bury, Henry Holt & Co. 
 
 3. Other text books on Physical Geography and Geology. 
 
 4. The International Geography by 70 authors, D. Appleton 
 & Co. 
 
 5. Proceedings of the 8th International Geographical Con- 
 gress, Washington, 1904. 
 
 6'. Publications of the U. S. Geological Survey consisting of 
 Geologic and Topographic Atlas, Monographs, Bulletins, Profes- 
 sional Papers, Annual Reports, and Water Supply and Irrigation 
 Papers. 
 
 The contour maps of the Topographic Atlas are of special 
 importance. They can be obtained from the Director of the U. S. 
 Geological Survey, Washington, D. C, at five cents each or three 
 dollars per hundred. 
 
 PERIODICALS 
 
 The National Geographic Magazine, Washington, D. C. 
 
 The Journal of Geography, N. Y. 
 
 The Bulletin of the American Geographical Society, N. Y. 
 
 School Science and Mathematics, Chicago, 111. 
 
 The Journal of Geology, Chicago, 111. 
 
 478 
 
INDEX 
 
 i 
 
 Abyssal life, 437 
 
 Adirondack Mountains,457 
 
 Aggrading, 71 
 
 Aletsch Glacier, 139 
 
 Alkali plains, 317 
 
 Alkaline lakes, 113 
 
 Alleghany plateau, 93, 327, 454 
 
 Alluvial cone, 87 
 
 fan, 86 
 
 plain, 313 
 
 soil, 263, 269 
 Alpine glaciers, 141 
 Aluminium ores, 250 
 American Museum of Natural History, 
 
 11, 282, 283, 284 
 Andromeda nebula, 14 
 Anemometer, 379 
 Aneroid barometer, 353 
 Antecedent river, 94 
 Anticline, 337 
 Aphelion, 22 
 Aquifer, 42, 55, 56 
 Arid climate, 97, 98 
 Arroyo, 98, 330, 331 
 Artesian well, 55, 311 
 Atmosphere, 348 
 Atoll, 222 
 Augite, 244 
 Aurora borealis, 396 
 Ausable Chasm, 73, 322 
 
 Bad Lands, 65, 330, 461 
 
 Barnett Falls, 131 
 
 Barogram, 354 
 
 Barograph, 355 
 
 Barometer, 352 
 
 Barriers, 212, 344, 417, 431 
 
 Bars, 209 
 
 Base level, 71 
 
 Bates' Hole, 65 
 
 Beach, 208 
 
 Beaver lakes, 105 
 
 Biela's comet, 10 
 
 Big trees, 412, 429 
 
 Black Hills, 460 
 Blind fish, 43 
 
 Block mountains, 341, 470 
 Bogs, 124 
 Bore, tidal, 183 
 Boston Mountains, 459 
 Boulder clay, 148, 149 
 Boulders, 158, 160, 161 
 Breakers, 177 
 Breakwater, 233 
 Breccia, 257 
 Building stone, 346 
 Buttes, 323, 324, 462 
 
 Calcite, 244 
 
 Calderas, 295 
 
 Calendar, 29 
 
 Calories, 357 
 
 Canoe mountains, 339, 340, 454 
 
 Canyons, 322 
 
 Caroline Bridge, 48 
 
 Catskill Mountains, 455 
 
 Cave deposits, 50 
 
 Caves, 42 
 
 Chamberlin, T. C, 13 
 
 Charleston earthquake, 300 
 
 Chimney rocks, 204 
 
 Chinook, 377 
 
 Cirques, 140 
 
 Clay, 257 
 
 Cliff glaciers, 141 
 
 Climate, 288, 394, 400, 441 
 
 Cloudburst, 387 
 
 Clouds, 363, 382-385 
 
 Coal, 258 
 
 Coastal plain, 310, 312, 313, 355 
 
 Cold wave, 377 
 
 Colorado plateau, 467 
 
 Composition of earth's crust, 238 
 
 of atmosphere, 349 
 Continental glaciers, 141 
 
 shelf, 169 
 Continents, 236 
 Contour maps, 36 
 
 479 
 
480 
 
 INDEX 
 
 Copper ores, 249 
 Coral, 218 
 Coal Creek, 80 
 Coral reefs, 221 
 
 harbors, 232 
 Corrasion, 73, 152 
 Crater Lake, 103 
 Creep, 263, 264 
 Crevasse, river, 82 
 
 glacial, 145 
 Crouse Boulder, 158 
 Crystals, 241 
 Cuesta, 463 
 Cycle of erosion, 87 
 Cyclones, 370, 371, 386, 389 
 Cypress, 402 
 
 Daniel's comet, 10 
 
 Day, 30, 31 
 
 Deeps, 174 
 
 Deep sea deposits, 189, 190 
 
 life, 194, 436, 437 
 
 oozes, 190 
 Degrading by streams, 70 
 Deltas, 84, 101, 114, 460 
 Delta harbors, 230 
 Desert plants, 407 
 Deserts, 328-335, 419 
 Dew, 381 
 Dew poiiU R80 
 Diastrophism, 274 
 Diatoms, 117, 118, 119, 190 
 Dikes, 205, 297 
 Diorite, 260 
 Directions, 20 
 Disintegration of rock, 262 
 Distributaries, 84, 314 
 Divides, migration of, 95 
 Dolomite, 245 
 Domed mountains, 340 
 Dredges, 172, 173 
 Drift, glacial, 149 
 
 oceanic, 187 
 Drumlin, 150 
 Dust, 351 
 
 Earth, a magnet, 33 
 motions of, 19 
 origin of, 11 
 part of solar system, 2 
 revolution of, 21 
 
 rotation of, 20 
 
 shape of, 16, 17 
 
 size of, 17 
 
 structure of, 19 
 
 shine, 5 
 Earthquake waves, 178 
 Earthquakes, 104, 299-307 
 Eel grass, 218 
 Eclipses, 7 
 
 Economic features of coastal plains, 
 313 
 
 of glaciers, 167 
 
 of harbors, 232 
 
 of mountains, 345 
 
 of the ocean, 195 
 
 of plateaus, 325 
 
 of swamps and marshes, 125 
 Ellipse, 9 
 
 Engrafted rivers, 94 
 Epeirogenic movement, 275 
 Epiphytes, 403 
 Eratosthenes, 18 
 Esker, 150 
 Eskimo, 443 
 Eureka Springs, 59 
 
 Fall line, 135 
 
 Falls, 125 
 
 Faults, 322, 325 
 
 Feldspar, 242 
 
 Ferrel's law, 187 3 7 
 
 Fiord harbors, 231 
 
 Fissures, 296 
 
 Flood plains, 78, 123, 315, 461 
 
 Fluorite, 254 
 
 Forests, 423-430 
 
 Fossil, shore lines, 224 
 
 lakes, 116 
 
 reefs, 222 
 Foucault's pendulum, 20 
 Frost, 381 
 
 Gabbro, 260 
 
 Garden of the Gods, 160, 46C 
 
 Gegenshein, 398 
 
 Geographic cycle, 270 
 
 Geysers, 61 
 
 Glacial channels, 162, 163 
 
 plains, 317 
 
 soils, 269 
 Glaciers, 138-167 
 
INDEX 
 
 481 
 
 Glaciers, economic effects of, 167 
 movements of, 143-164 
 North American, 165 
 
 Cllauconite, 191 
 
 Graded streams, 71 
 
 Grand Canyon, 323, 468, 469 
 
 Granite, 259, 260 
 
 Graphite, 253 
 
 Gravitation, 17 
 
 Great Interior Basin, 112 
 
 Great Lakes, 111 
 
 Great Salt Lake, 108, 112, 214, 225 
 
 Great Valley, 248, 444, 454 
 
 Groundwater, 41, 53 
 
 Gulf Stream, 185 
 
 Gypsum, 252 
 
 Halite, 250 
 Halley's comet, 10 
 Hanging valleys, 156, 157 
 Harbors, 228-234 
 Hardness, scale of, 240 
 Hematite, 246 
 Hog Back Mountains, 465 
 Hook, 209 
 Hornblende, 244 
 Horse latitude, 370 
 Hot springs, 61 
 Humidity, 379 
 Hurricane, 297 
 Hygrodeik, 381 
 Hygrometer, 380-381 
 Hyperbola, 9 
 
 Icebergs, 160 
 
 Ice tables and pinnacles, 146 
 
 Indus River, 85 
 
 Insolation, 6 
 
 International date line, 31 
 
 Iron ores, 246 
 
 Iroquois Lake, 116 
 
 Islands, 236 
 
 Isobars, 356 
 
 Isoclinal lines, 33 
 
 Isogonic lines, 33 
 
 Isostacy, 277 
 
 Isotherms, 364 
 
 Kame, 149 
 Kaolin, 245 
 Karsten, 46 
 
 Kettle holes, 149 
 
 Kingston earthquake, 305 • 
 
 Laccolites, 297, 341 
 Lacustrine plains, 316 
 Lakes, 100-137, 224 
 
 disappearance of, 114 
 
 function of, 119 
 
 in arid regions, 121 
 
 levels, 113 
 
 origin of, 100 
 
 shores, 224 
 Land, 235 
 Latitude, 24, 25 
 Lava, 289 
 Lead ores, 249 
 Levee, 82 
 Levee lakes, 84 
 Life history of lakes, 120 
 
 of a land area, 270 
 
 of mountains, 342 
 
 of a river, 87 
 
 of sedimentary rocks, 269 
 
 of a volcano, 296 
 Life in caves, 43 
 
 in lakes and rivers, 117 
 Life zones, 414 
 Lighter, 233 
 Lightning, 395 
 Limestone, 223, 258 
 Limonite, 246 
 Lisbon earthquake, 306 
 Longitude, 24, 27, 28 
 Lost River, 45 
 
 Magnesite, 254 
 
 Magnetism, 32 
 
 Magnetite, 248 
 
 Mammoth Cave, 44 
 
 Man, distribution of, 439 
 
 Mangrove, 217 
 
 Mantle rock, 264 
 
 Maps, 35, 36, 474 
 
 Marble, 258, 261 
 
 Marengo Cave, 51 
 
 Marl, 114 
 
 Marshes, 123 
 
 Maturity of topography, 271 
 
 Meanders, 79, 80 
 
 Mediterranean seas, 170 
 
 Mercator's projection, 474 
 
482 
 
 INDEX 
 
 Mesa, 323 
 
 Metamorphic rocks, 260 
 
 Meteorites, 10 
 
 Meteors, 10 
 
 Mica, 243 
 
 Minerals, 239 
 
 Mineral springs, 60 
 
 Mirage, 397 
 
 Mississippi River, 458, 81, 83, 84, 
 
 315 
 Mississippi valley earthquake, 299 
 Missouri River, 77 
 Monadnocks, 271, 272, 318 
 Monsoon, 377 
 Moraines, 147 
 Mount Pelee, 281 
 Mount Potosi, 67 
 Mount Vesuvius, 278, 279 
 Mountains, 262, 335, 346, 419, 442 
 Muck, 268 
 Muirs Butte, 292 
 
 Nadir, 21 
 
 Natural Bridge, 46, 206, 207 
 
 Nebula, 12, 13 
 
 Nebular hypothesis, 12 
 
 Neve, 140 
 
 Niagara Falls, 126, 127 
 
 Northeaster, 377 
 
 North Platte River, 88 
 
 Obsidian, 260 
 
 Ocean, 169 
 
 Ocean life in, 192, 194 
 
 currents, 185 
 Onyx marble, 51 
 Oozes, 190 
 Ores, 246 
 
 Orogenic movement, 275, 336 
 Ouray, Colo., 86, 142, 153, 154, 155 
 Overleaded stream, 76, 77 
 Ox-bow lakes, 81 
 Oxygen, 349 
 
 Parabola, 9 
 
 Peat, 115 
 
 Pelagic life, 194, 438 
 
 Peneplain, 271, 318 
 
 Perched boulders, 158 
 
 Perihelion, 22 
 
 Phases of moon, 5 
 
 Physical Geography, 1 
 Physiographic agencies, 274 
 
 features, 309 
 
 regions, 449 
 Piedmont glaciers, 141 
 
 plateau, 452 
 Pigmies, 443 
 Pilaster, 51 
 Pittsburg, 444, 445 
 Plains, 309, 419 
 Planetoids, 2, 3 
 Planets, 2 
 
 Planetesimal hypothesis, 13 
 Plant Geography, 402 
 Plateaus, 321 
 Playas, 98 
 Polar projection, 476 
 Pot-hole, 73, 155 
 Potomac River, 70 
 Prairies, 320, 411 
 Precipitation, 385 
 Projections, 35, 474 
 Pumice, 260 
 Pyrite, 248 
 
 Quaking bogs, 123 
 Quartz, 240 
 Quartzite, 261 
 
 Rainbow, 397 
 Rainfall, 40, 386 
 Rain gauge, 385 
 Rapids, 69 
 Reaches, 69, 134 
 Reelsfoot Lake, 104 
 References, 39, 99, 137, 167, 196, 
 234, 273, 307, 346, 398, 447, 471, 
 478 
 Residual soil, 267, 268 
 Reversed drainage, 93 
 
 rivers, 92 
 Revolution of the earth, 21 
 River deposits, 77 
 
 profile, 68, 69 
 
 piracy, 95 
 
 swamp, 83 
 
 valley, 64 
 Rivers, 40, 63, 67, 72 
 Rocking stones, 158 
 Rocks, 254 
 Rocky Mountains, 464 
 
INDEX 
 
 483 
 
 Saint Elmo's Are, 396 
 
 Salinas, 112 
 
 Salt, 250 
 
 Salt lakes, 111, 214 
 
 marshes, 124 
 
 plains, 317 
 Salts of the ocean, 171 
 Salton sink, 107, 108 
 Sand dunes, 226 
 Sandstone, 256 
 
 San Francisco earthquake, 302-305 
 Sargasso seas, 186 
 Sargassum, 407 
 Satellite, 4 
 Sea caves, 206 
 Sea water, composition of, 170 
 
 density of, 172 
 
 depth of, 174 
 
 temperature of, 175 
 Seasons, 22 
 
 Sedimentary rocks, 255 
 Seepage, 60 
 Seiche, 114 
 Shale, 257 
 Shooting stars, 10 
 Shore cliff, 203 
 
 lines, 197-234, 277 
 
 terraces, 213 
 Sink holes, 45, 106 
 Snow fields, 138 
 Soil, 262,- 402 
 Solar day, 30 
 
 system, 2, 3, 473 
 
 time, 30 
 Sounding and dredging, 172 
 Spit, 209 
 
 Spouting caves, 208 
 Springs, 51, 58 
 Stalactite, 50 
 Stalagmite, 50 
 Standard time, 3 1 
 Subsequent streams, 94 
 Sulphur, 252 
 Superimposed rivers, 92 
 Swamps, 123 
 Syenite, 260 
 Syncline, 337 
 
 Talc, 253 
 Talus cone, 87 
 Taughannock Creek, 78 
 
 Temperature, 357, 360, 413 
 
 Tent meteorite, 11 
 
 Terminator, 5 
 
 Terraced mountains, 338 
 
 Terraces, 92, 93, 123 
 
 Thermogram, 358 
 
 Thermograph, 359 
 
 Thermometer, 357 
 
 Thunderstorm, 387 
 
 Tides, 181, 184 
 
 Till, 149 
 
 Timber line, 410 
 
 Time, 29 
 
 Tinker's Falls, 134 
 
 Toad Stool Park, 66 
 
 Topographic atlas, 38, 478 
 
 Topography of ocean bottom, 188, 23£ 
 
 of shore lines, 197, 203 
 Tornado, 375, 376 
 Transportation by rivers, 74, 75 
 Trade wind, 368 
 Travertine, 5 1 
 Tripoli, 118 
 Tufa, 51, 290 
 Tundras, 321 
 
 Underloaded stream, 76 
 Undertow, 178 
 Uncompaghre Creek, 76 
 Universe, 3 
 
 Vegetation, 402 
 
 Vegetation on the shore line, 217 
 Veins, 48, 49 
 Volcanic harbor, 231 
 mountains, 341 
 Volcano, 279, 287, 295 
 
 Wadies, 97 
 
 Water, effect on life, 403 
 
 Water gaps, 94 
 
 plants, 404 
 
 table, 41, 54 
 
 zone, 41 
 Waterspout, 376 
 Watkins Glen, 73 
 Waves, 176, 179, 181, 199, 200 
 Weather, 388 
 Weather forecast, 393 
 
 map, 390 
 
484 
 
 INDEX 
 
 Wells, artesian, 55 
 
 common, 54 
 Whistling caves, 208 
 Williamette meteorite, 11 
 Wind, 366, 368-379 
 Wind gaps, 94 
 Work of rivers, 72 
 
 Wyandotte Cave, 52 
 
 Youth of 'a river, 87 
 
 Zinc ores, 259 
 
 Zodiacal light, 398 
 
 Zones, 366, 367, 393, 413 
 
 Zoological provinces, 430, 431, 432 
 
}M 1 1908