'fntiLICbllEr~ ~ 'ic i~Y-]i5$; "i4 rt~aE1:::.1.....: i-Trr"g TPE:~lrfi.y v-~ ~~:*::;?:iI('~'ln~i(' I- ~~ro: ~~I 2~; i P;,$';; r I.1~1 ihijJ': yb~t. 7:5;~I:,~9ixa: i:. ".~~~ ~ ~ t-"sr - i~_~: ~d~t\; i I - "Yt::h:hr C\t' i 1.1.:. -tr; ": ~~" _-'-' ,X? ':-Ir ~t*::~'-:.Ci T1*i ~~' I YJ b: -I"r:d ~ 1- Lij i:I:6-F" "c, -:~ i~ —I-.~~ s~ 2~:'I,-\i~:. ~~ I:i U3~~r;~k I-i I jS 1 - ~~f:;'.:I:'r ::::iiIcrm,~::~: ~ I ~r~~:~ ~ 6! d;i;:~ cI` i I i.~":~; ~,g ~t ~:?;*R.i;.'i.-.i.i I;-: i ~I~ ~'- -~::i~ ;;~- ' j r: r.. I.....; IF, ~;~i':/h w.;.; ~. ( S -:. - %~:' i ' 13(lR' Ciii~~' r.i~.1.:.h;;~ Y if: j )" I r I.I- i '!~ ' 'I —.1' t i:..~ ~r ~z I, lic ::,~.~, i?~~: `i i-,nEPbamIjarr-eP I1PrEll;roi-rr,:BiabOCtI[fLZ.;OOI::;: i i t cattt;u. yvtcoz' k-grR scr(ort i ~ i 5*1 ,, I )~ '9 'j I i P~ i~..~ ~'i ~: II i t i.~!; i~:~~ ~,~,:~ i ~; r I ~:. i. j. m::;, —:"r:t*,"~.lg:~~: ~: j i.-.': —~ ~ ~:- ~':i (; t ~,.1..r L I~; BRIEF MEMORANDUM '; I ON THEl I J i,~ -~... Ii.4... i.. -1 1... c j 1- I." " I,I j,, F --.:G:GEOLOGY OF THE I1HILIPPINE ISLANDS r:, ~:~ i:~,::~ *'_"r::~i.Ld I; :IY~.:,,,-,,;u\,~~\ c~,.;i3cZ.: : _ t;.~~1 ~~Z1 xf!~ ~ri; ii II - i.'' II..5; ~.,,,e r.4 ~'' -K' TiS.u:..B-(,~: ~t.i;' a: r i :r -1.J Z ~~:~.: ;f'~; 'r:~ i ~LT'.::j.: i ii~i " ~ ~; i' ~IJ:t p;.:J~ I c ) r. i~ ~ '; ir: Cj Z ..,~;~ "- i 4-:1 ii. ~: i~ ~~ii~ A ~~: —:..i. 11 4 P,. -. - 11 c.-ERG P. 1BIJCORTf iI -EXTRACT FROM THE TWENTIETI ANNUAL REPORT OF THE SURVEY, 1898-99 PART I[-GENERAL GEOLOGY. AND PALFEONTOLOGY:: -~~ ~ il~,' ~~ v ~~~ r.I i~ -;. 1, I: ~ ~~ i ~ r;~~ ~, `'9-; ' - I~ ~.* i. . ':-. ~v~ P ~.. ~ ~ ~.z i ~ ~, ~, 1 It: i *-~~r i r c *-i i r' r rr ~ i ~ ~ I r. s ~i ~! ~' ~9;i:: tL. j-I.I t-I ~~ 4, ~r.;C~zi_; r ii:Y; T; i:;,~~,, 1~::-~~. zi,~~ ~e~~i: I: *- t i, i " I.I \~~ ik: ~:~. ~~ ~ cLtl4;Nqt C ':ift *f? r;:.;~ii~~ i m " ~'; L ).:: i`` r~ i.: `1 —ii3 c ~r ~IY~I 1' 7. -Y: ~-r j/j :.~5 .rir;C i d:IE;i-Fu' rX~~:~, ~i r_ i J '; "''~'-~ b;. u ~- ~r A~ \ i. r 1:; 3 r s ~~'~~ ur:LT! ~.I:tf~~ r,: ~ ilr- i, i.i~ %:: ~ t,^YII.i) C u.?L,3~: r ~ ~~ ~ i, ^~r3 r.I~il:~?~.lr i \ L t-~: u 1. tit;ra::;?~ " 'd ~.....-1 \I i'tl ` ~;' ~"F ~I 1:;~1 ~.:-it i, ~.i:~sr. ~:;"7'~::;t;l~lj.,I i'.r"?~;tJ y:,.~a. 1~Q' ;,uLj...r i. ~-; i 'I.: -..i I i', r ~\c;i: e i." ":.~~I~~ '44 . 44 14 '4 4. fiG tw _-r-. a_ A= II BRIEF MEMORANDUM ON THE GEOLOGY OF THE PHILIPPINE ISLANDS BY GEORGE F. BECKER 20 GEOL, PT 2 ---- 1 I I BRIEF MEMORANDUM ON THE GEOLOGY OF THE PHILIPPINE ISLANDS.1 By GEORGE F. BECKER. Much office work must be done on the specimens collected and much literature abstracted before all of the information at my command on the geology of the Philippine Islands can be systematically presented. So far as my observation or my information goes, the geological history of the whole group is similar. I have seen that the postTertiary gradual upheaval, presently to be described, is common to Jolo, Mindanao, Luzon, and the intermediate islands; and descriptions leave little doubt that the Philippines belong, and have long belonged, to a single geological and biological province. Prior to the Tertiary epoch the Philippines consisted of slates and igneous masses, the age of which is as yet unknown, no fossils having been detected in these ancient rocks. They are now to be found chiefly in the northern and eastern ranges of Luzon, but appear to be represented also by some limited occurrences in Cebu, and seem to form the walls of the gold-bearing quartz veins of the province of Surigao, in the northeastern portion of Mindanao. They are doubtless in reality widely distributed, but in most localities are buried beneath more recent formations. During the Eocene, or earliest Tertiary, the archipelago must have consisted largely of swamps and shallow seas, perhaps not very different from those now existing in the same region. Limestones were formed at some distance from the coasts, shales and sandstones were laid down near the shores, and accumulations of vegetable matter grew in the swamps. These last were covered by mud, and, in the almost total absence of free oxygen, they were gradually converted into lignite, probably the most valuable mineral asset of American India. At the close of the Eocene a great crumpling and upheaval took place, which was felt from Switzerland to the Philippines, and perhaps most of all in the Himalayas, where marine Eocene beds now stand at 1 Memorandum addressed to the Military Governor as a preliminary report, and an official copy transmitted by the author to the Director of the United States Geological Survey. 3 4 GEOLOGY OF THE PHILIPPINE ISLANDS. an elevation of 16,000 feet above the sea. In these islands the Eocene strata are frequently thrown into a nearly vertical position and sometimes are actually overturned. In the Visayas the axis of upheaval trended a little east of north, corresponding to the direction of greatest extension of the islands of Cebu and Negros. These disturbances were accompanied by much faulting and it is believed by some metamorphism. Intrusions and extrusions of igneous rocks seem to lhave accompanied this upheaval, but no satisfactory study has yet been made of the phenomena, good exposures being rare. During the remainder of the Tertiary the islands appear to have been above water. Miocene and Pliocene strata have not been detected with certainty, though some traces of such beds will probably be discovered in future investigations. Near Jolo I found strata which appeared to be younger than the Eocene and older than the Recent period. In the main the area of the Philippines was probably then continental, and there is zoological evidence of a land connection with the Asiatic continent, probably by way of Borneo, during the middle Tertiary. This connection did not persist to the close of the Tertiary, however, and to its rupture is ascribable the extraordinary peculiarities of animal life in these islands, evolution here having been left to take its own course undisturbed by invasions. The subsidence which cut off immigration of the lower animals continuedl, seemingly, till somewhere about the close of the Tertiary, and long after Homo sapiens had made his appearance in the Malay Archipelago. This group also was very probably already inhabited during the Pliocene, possibly by the ancestors of the Negritos. This is a matter which requires careful iivestigation, for in the opinion of my late famous colleague, 0. C. Marsh, this archipelago is likely to have been one of the earliest haunts of the human species. When the elevation was at its minimum the archipelago was reduced to a group of small, hilly islets, four of which existed within the area now occupied by the Island of Luzoi. Cebu was almost completely submerged. At or before the period of maximum subsidence, began a series of eruptions which has not yet closed. Mayon Volcano in southern Luzon, had a violent eruption in 1897. It is probably the most beautifully symmetrical volcanic cone in the world, and the truncation at the top, due to the crater, is scarcely sensible.1 The work done in fusing lavas and ejecting ash is probably a manifestation of the energy involved in the mighty earth throes which bring about regional upheavals with incidental subsidences. The earlier of the eruptions under discussion were largely submarine, and vast additions were made to the superficial material of the archipelago by these outflows, especially in the central and southern portions of Luzon. The ejecta include andesites, rhyolites, basalts, and probably other less-common rock species. I The radius of any horizontal section is the hyperbolic sine of the distance from this section to the summit. BECKKR.] PLEISTOCENE AND RECENT UPHEAVAL. 5 The period of upheaval, once initiated, does not seem to have been interrupted by any era of subsidence, and the modern coral reefs give evidence that it is still in progress. It is said that uplifts accompanying earthquakes have actually been observed by the Spaniards, and the earthquakes themselves are spasmodic jars in the process of elevation. The elevation has not been, properly speaking, catastrophic, however, for the tremors which may wreck a cathedral are insignificant from a terrestrial standpoint. On the whole, the uplift has been very gradual, so that even the coral polyp has been able to adjust himself to the changing conditions, building outward into deeper water as his old home was raised too high for his welfare. In this way nearly the whole of Cebu, to a height of over 2,000 feet, has been covered with a nearly continuous sheet of coral which can be followed seaward into living reefs. Much of Negros hlas been clothed with a similar mantle. On a small scale, also, off the coasts of these islands, and particularly about Mactan, reefs can still be studied in every stage of upheaval, all those portions being dead which are exposed to the air even at the lowest tides. In southern Luzon and to the northward of Lingayen Bay similar phenomena can be observed. Although ul)pheaval does not appear at any time since the close of the Tertiary to have given way to subsidence, there have been repeated pauses in the uplifting process. On exposed coasts these pauses are nmarked by benches eaten into the land by the action of the waves. Thus the southern ends of Cebu and Bolhol are terraced from top to bottom, each terrace beilg an old beach cut out of the rock mass by stormy seas. Pauses in the uplifting process are also marked by a rude stratification of the corals. Even in the interior of the islands terraces indicative of uplifts are frequently visible. Some of them represent base-levels of erosion, others are ancient coral reefs which hlave been checked in their upward growth by reaching the surface of the water. In short, terraces constitute one of the most prominent topographical features of the archipelago. The slowness of the uplift is emphasized by the stupendous accumulation of coral in these islands. Coral is, of course, mainly composed of calcium carbonate, and this is formed by the coral polyp from the lime salts dissolved in the sea. Now, the sea contains a very minute proportion of lime salts (chiefly the sulphate, or gypsum), say a tenth of 1 per cent, and corals are necessarily of slow growth because of the scantiness of the material with which they build. Tlie sheets of coral on uplifted areas seem to have a tendency toward a nearly uniform thickness, approximating to 100 feet. This is explicable from the habits of the coral animal, whiclh does not grow at a greater depth than 15 or 20 fathoms. Unlike merely sedimentary strata, the coral follows the topography of the rising surface along a contour of which it grew. Where muddy waters or frequent eruptions befoul the sea there are no coral reefs. 6 GEOLOGY OF THE PHILIPPINE ISLANDS. When the uplift began, say ten or twelve thousand years ago, the island shores were steep and the sea about them was relatively deep, so that an upheaval of 100 feet added but little to the area of the islands. As the amount of uplift increased to something approaching the mean depth of the circumambient sea, the area of the land increased in a far greater ratio to the increment of upheaval. The last rise of 100 feet has rescued from the seas the most valuable part of the archipelago. Examination of the charts will show that a fresh rise of 100 feet would add a further area, which, though important, would be less important than the actual lowlands of the Philippines. The plateau on which the island stands is now mostly above sea level. Area has also been added to the land by the formation of deltas at the mouths of the rivers, a process which has been greatly assisted by the mangrove trees and the nipa palms. These grow in the water in all favorable situations, and hold back the solid contents of the streams, adding their own debris to the accumulation. Along the eastern shore of Manila Bay the so-called "estero" or "bayou" country consists of the confluent deltas of the various rivers flowing into the bay. To the eastward of the estero country the ground passed over by General MacArthur's army from Manila to San Fernando consists of low, base-leveled terraces, all more or less dissected by water courses. These almost always have somewhat high and steep banks. They are in fact engorged, as is characteristically the case in a country undergoing upheaval; for upheaval increases the potential energy of the flowing water and leads to erosion of the stream beds. In my published memorandum on the mineral resources of the Philippines,' I have briefly noted the distribution of valuable minerals. The distribution of gold deposits indicates that this metal, when in place, is associated with the older rocks, and it will probably be found that the last great addition to the auriferous deposits was an incident of the post-Eocene upheaval. In some parts of the world gold is found in neo-volcanic rocks, as at Bodie in California and elsewhere. I have learned of no such occurrence in these islands. Where streams in the Philippines cut into the older rocks they seem nearly always to carry a little gold, which the natives have been exploiting time out of mind. There is a very general impression that Mindanao is a rich auriferous region, though little definite information is current on the subject. The absence of information seems to add the attractions of the imagination to the tales of a few prospectors. It is a fact, to which attention should be called, that each of the two auriferous provinces of Mindanaoviz, Surigao and Misamis-has been reported upon by a competent expert and that neither expert found anything to excite his enthusiasm. There is gold there, beyond a doubt, and the natives have been extracting it on a modest scale, yet with no little skill, for centuries. The informa I Nineteenth Ann. Rept. U. S. Geol. Survey, Part VI Continued, 1898, pp. G87-693. BECKER.] MINERAL RESOURCES. 7 tion at hand points to very moderate auriferous resources, comparable with those of the Carolinas and Georgia rather than with those of Colorado or California. Luzon, so far as I can judge from reports, is as rich in gold as Mindanao. It is probable enough that a fair number of spots exist in which capital invested in gold mines will find reasonable remuneration, but I fear that any "rush" to the gold fields will involve great disappointment. The whole archipelago has an area almost the same as that of Arizona. There is nothing known which indicates that the islands contain more gold than this Territory. The copper deposits of Lepanto seem rich and extensive, but very expensive roads will be needed to render them available. The high quality of some of the iron ores of Luzon is beyond question, but the lignite of the islands is not adapted to iron smelting. A moderate industry could be based on charcoal smelting, while the pig could be converted into steel and manufactured by the use of furnaces burning lignite gas. The so-called coal is a good lignite.' Its heating effect is from twothirds to three-fourths that of the best steaming coal. There are great quantities of this fuel, and much of it could probably be delivered at a profit on vessels at $2.50 (Mexican) per ton. The lignite is at least as good as the Japanese "coal," which is also lignite. The Japanese fuel often brings $9 or $10 (Mexican) in Manila, and is now much dearer; so that unless the price of such coal were to fall enormously, great profits await the coal miner. The development of a coal industry is of great importance to the industries of the archipelago, and, though our naval vessels would prefer Cardiff or Pocahontas coal, they could use Philippine lignite in case of need. MANILA, P. I., September 28, 189). 1 Lignite differs from tlrue coal chiefly in the amoumit of combined water, which is insignificant in true coal and usually from 8 to 18 per cent in lignite.