218 ^^'6 Philippine Journal of Science ism 



Sample 2313. — This sample is a much finer and more even- 

 grained grayish rock with much the same mineral composition 

 as sample 2312. The porosity of this specimen is greater. 



Sample 2314. — This sample is a still finer grained rock with 

 more of the characters of a shale than of a sandstone. 



In the same series of sediments with these sandstone l)eds 

 are several layers of conglomerate, conformable and of vary- 

 ing thickness. These conglomerates consist of many kinds of 

 pebbles in a firmly cemented, sandy matri.x. At one place I noted 

 pebbles and fragments of the following kinds of rocks : 



1. Limestone with coral remains. 



2. Andesite — 3 or 4 varieties. 



3. Amygdaloid. 



4. Shale. 



5. Rock resembling jasper, but which is probably rhyolite, as it 



appears to have quartz phenocrysts. 



6. Diorite — coarse-grained. 



7. Diorite — fine-grained. 



8. Picrite — a rock rich in olivine. 



9. Quartz. 



Occasionally fossil shells are found, one of which is pre- 

 sumably Vicarya callosa Jenk. Hence the age of these beds is 

 that of the Lower Miocene, or the same age as the Cebu coal 

 measures. Fuller descriptions of these sedimentaries are given 

 by Abella, 



The shales. — The shales exposed in the lower reaches of the 

 streams flowing from the cordillera are thin-bedded and gray- 

 ish to bluish, and resemble other Tertiary shales in many parts of 

 the Philippines, the type example of which is the Vigo series on 

 Bondoc Peninsula, Tayabas, Luzon. ^ These shales have prac- 

 tically the same mineral composition as the sandstone, the chief 

 difference being in grain size. In the upper part of Tigum 

 River the shales are yellowish, but lower down, where we first 

 discovered them, they are bluish. In the survey of Tigum River 

 we found that there are at least 5,000 meters of these shales 

 exposed from the point where the survey began to the first 

 considerable thickness of sandstone. Of course, there are oc- 

 casional thin beds of sandstone in this series, but they are 

 negligible. Several wells have been drilled by the Bureau of 

 Public Works in these shales in the hope of obtaining artesian 

 water, but they have been generally unsuccessful. 



♦ Cf. Pratt, W. E., and Smith, W. D., This Journal, Sec. A (1913), 8, 331. 



