20, 3 Schenck: Physiography and Geology of Samar 257 
caused the confusing heterogeneity of sedimentation observed 
to-day in the Tropics. There is not a great variety of minerals 
making up the various sedimentary formations. Almost without 
exception, these rocks are calcareous and the sandstones are not 
made up of pure quartz grains; instead, feldspar predominates. 
Because of this, the grains vary in size and shape and lack the 
well-rounded appearance of true sandstone grains. This is what 
one would expect, considering that not one of the igneous rocks 
noted is definitely acidic in character, ‘and that the basement 
complex is probably dioritic in character. The reworked Vigo 
rocks indicate a period of erosion after the Miocene, 
Structure.—An insufficient amount of definite information was 
obtained by the reconnaissance party to work out, in any detail, 
the broad structural relationships of the land, and before any 
conclusions can be reached several very important points must 
be determined. Among the thing's that remain to be determined - 
or about which some doubt now exists are: The extent of the 
Miocene beds, the presence of unconformities, the distribution 
of igneous rocks, the time of earth movements, whether marine 
terraces are local or general in extent, the lines of major faulting 
and folding, and whether or not the island has been differentially 
tilted. The data now in hand are sufficient for economic pur- 
poses and show, among other things, that the island has an ig- 
neous core; that there are some monoclinal strata, minor folds, 
much faulting, and unconformity after the Vigo Miocene. The 
information also indicates other suspected unconformities, a 
definite topographic unconformity between the Pleistocene and 
Recent formations, and complex earth movements. — 
HISTORICAL GEOLOGY 
The ups and downs of Samar have been many. They began 
in pre-Miocene times and continue at the present day. To write 
a complete and accurate geologic history of the island is well- 
nigh impossible; but it is not impossible to recount a few of the 
Principal happenings and to show how the predominant and char- 
acteristic fossil life, as preserved, belongs to the Foraminifera. 
The geologic relationships herein set forth are tentative only. 
The existence of pre-Tertiary formations is inferred, but not 
certain. Evidence points to what may be metamorphosed sedi- 
ments, as well as basic igneous material, as the basement complex 
of Samar; and a great deal of evidence, both botanical and zo- 
ological, points to a former land connection of the Philippines 
with other islands. For instance, plant affinities of the outer arc 
