Vol. XI] DICKERSON— FAUNA OF THE VIGO GROUP 23 



south near the outer border of the continental shelf of the Phil- 

 ippines unbroken by straits like the San Bernardino of the 

 present. Diorites, schists, serpentines and associated meta- 

 morphic and igneous rocks composed this land mass and the 

 mud-laden, westerly-flowing streams deposited their loads in 

 the Philippine inland sea of Miocene age. Judging from the 

 coarse agglomeratic character of the basal Vigo beds in Leyte, 

 high grade, torrential streams descended to a semi-arid lowland 

 from a high, mountainous terrane to the east. The absence of 

 many reef building corals from the Vigo fauna is probably due 

 to the presence of muddy waters and the lack of strong cur- 

 rents, because the waters were quite warm enough for coralline 

 growth, judging from the presence of many tropical species. 

 From the character of both the sediments and fauna, the waters 

 of the Vigo sea were not too deep for the existence of reef- 

 building corals. During Malumbang time marine life condi- 

 tions were very similar to those prevailing in the Philippines 

 today, but the continental shelf was apparently far wider and 

 the islands much smaller, since coralline limestone covered more 

 extensive areas during the Pliocene than now. During the 

 Pleistocene, the islands were outlined about as at present but 

 many local changes took place during this time. Cebu for 

 example was probably greatly restricted during the Pleistocene 

 as well as during the Pliocene, and it was probably represented 

 by several small islets then. Recent and Pleistocene faulting on 

 a great scale seems to have largely controlled the physiography 

 of this island. The northwestern peninsula of Leyte, 40 miles 

 east, has not only a clear cut record in its terraced sides regis- 

 tering a series of uplifts, but an equally clear record of Recent 

 or Pleistocene submergence on its west side. This last event 

 is evidenced by a series of beautiful small bays, drowned valleys 

 of small westward flowing antecedent streams. Such local 

 movements did not seem to affect the species very materially on 

 the whole. It is quite possible that some forms had to seek 

 other quarters, but with such a great variety of neighborhoods 

 from which to choose, every clam could find its proper mud flat 

 and each snail its own dugout. The possible tendency of a 

 species to have within itself the power to evolve into a higher 

 form, or a form still better suited to its environment, is not 



