18 The Philippine Journal of Science _ 1921 
evidenced by the absence of reef-building corals from the Vigo 
and by the argillaceous and sandy character of the sediments of 
this group. A study of Vigo sedimentation indicates that an 
extensive land area stretched from north to south near the outer 
border of the continental shelf of the Philippines, unbroken by 
straits like the San Bernardino of the present. Diorites, schists, 
serpentines, and associated metamorphic and igneous rocks 
composed this land mass and the mud-laden, westerly flow- 
ing streams deposited their loads in the Philippine inland 
sea of Miocene age. Judging from the coarse agglomer- 
atic 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 currents be- 
cause, judging from the presence of many tropical species, the 
waters were quite warm enough for coralline growth. From the 
character of both the sediments and the fauna, the waters of the 
Vigo sea were not too deep for the existence of reef-building 
corals. During Malumbang time marine life conditions were 
very similar to those prevailing in the Philippines to-day, but 
the continental shelf was apparently wider and the islands were 
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 ag well as during the 
Pliocene, and it was probably represented by several small islets 
then. Recent and Pleistocene faulting on a great scale seems 
largely to have controlled the physiography of that island. The 
northwestern peninsula of Leyte, 40 miles east, has not only a 
clear-cut record in its terraced sides, registering a series of up- 
lifts, but an equally clear record of Recent or Pleistocene sub- 
mergence 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 neighborhood 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 
