+d 
20, 1 Smith: Pidatan Oil Field, Cotabato, Mindanao 29 
very profoundly. In the region adjacent to the seep the forma- 
tions which might be counted upon to contain oil are so badly 
disturbed that no regular structures could be made out, and as this 
is the crux of the whole matter in an oil field, a favorable impres- 
sion of this locality cannot be entertained. This does not mean 
that oil does not exist there. It might even be there in fair 
quantity; but with other difficulties, already referred to and 
which must be considered, drilling for oil does not promise to be 
an economic venture. This is a feature which many would-be oil 
producers do not adequately consider. Both the location of 
the seep and the composition of the oil, which has none of the light 
fractions and very little residue either of paraffine or of asphalt, 
indicate very local and abnormal conditions. 
Description of formations.—The tentative stratigraphy of the 
Pidatan field is shown in Table 1. Beginning at the bottom 
the oldest rocks seen by the writer are the Vigo shales, with 
which are intercalated thin-bedded, sandstone layers. No deep- 
seated igneous rocks were noted, and it is probable that erosion 
has not proceeded far enough to reach them. The Vigo shales 
in this region are very much like the same formation in other 
parts of the Philippines, particularly in Bondoc Peninsula. A 
typical specimen is buff-colored with dark variations, exceedingly 
fine-grained, but not showing many microscopic forms such as 
Globigerina, as in the case of the Bondoc or Leyte shales. The 
shales and sandstones in this series are thin-bedded, and the 
shales break with a conchoidal fracture. Very few fossils were 
found in them. Structurally this formation is badly disturbed. 
Dips of 15° to 45° are common, and several outcrops show the 
shales and sandstones standing on end; that is, dipping 90°. 
Overlying the Vigo series and with a marked angular unconfor- 
mity is the Malumbang formation consisting of three members, as 
follows: The uppermost is limestone, fairly hard and white, and 
contains fragments of coral; below this is a soft, marly facies, 
quite fossiliferous; the principal genera found in this marl are 
Cardium, Arca, and Tellina. Below this marl comes a coarse, 
yellowish sandstone which contains a few fossils including some 
fragments of reef corals, and from the presence of these reef 
corals the writer concludes that this sandstone belongs with the 
-Malumbang rather than with the Canguinsa, which was not seen 
by him and may be missing. Detailed work here may cause 
him to change this opinion. 
Above the Malumbang come two or three formations, the exact 
positions of which are somewhat uncertain, particularly that of 
