X. A, 4 Pratt: Petroleum and Residual Bitumens 251 



The commonest fossil in the Canguinsa in Leyte is a species of 

 Globigerina, a low form of animal life which builds a very small, 

 spherical shell of calcium carbonate. These fossils were noted 

 in the upper part of the Vigo shale in Tayabas, and the study 

 of that field brought forth the suggestion that the petroleum, 

 which undoubtedly comes from the Vigo, might have originated 

 through the decomposition of the organic matter which the shells 

 once contained. The Canguinsa in Leyte appears to contain 

 even more examples of Globigerina than the Vigo ; possibly 5 per 

 cent of the area on an average surface of a fragment of Can- 

 guinsa clay-tuff from Leyte is covered by these small spheres. 



No petroleum was detected in the Canguinsa in Tayabas, but 

 in Leyte a majority of the outcrops of bituminous residues from 

 petroleum occur in the Canguinsa, and at one place petroleum 

 itself seeps from a tuff-sandstone phase of the Canguinsa. 



The Canguinsa is the surface rock over the larger part of 

 the Leyte petroleum field. It outcrops in the lower parts of 

 the hills which are capped by the Malumbang series and is intact 

 above the Vigo shale, except to the east and south of Jinabuyan 

 and Villaba. The ridge which culminates in Mount Benao con- 

 sists principally of Canguinsa rocks — clay-tuffs and clayey, tuff- 

 sandstones. The western face of Mount Benao affords the best 

 section of the Canguinsa observed in Leyte. In this region its 

 thickness is at least 300 meters, a figure which is comparable 

 with the estimated thickness of the same division of the Tayabas 

 sedimentary column. 



VIGO SHALE 



The Vigo shale consists of alternating, thin, perfect beds of 

 shale, sandy shale, and sandstone. The strata are differently 

 colored — dark gray, brown, and yellow — and outcrops often pre- 

 sent a variegated appearance- Toward the top of the formation, 

 dark-colored fine-grained shale, in thicker and less perfectly de- 

 fined beds, is predominant. This upper shale was referred to 

 as the Bacau stage of the Vigo in the report on the Tayabas 

 field, having been differentiated there because it appears to be 

 more petroliferous than the underlying beds. The Vigo is like 

 the Canguinsa in that its beds, both shale and sandstone, appear 

 to contain considerable tuffaceous material. The sandstone beds, 

 for instance, are made up of sharp or slightly rounded fragments 

 of feldspar, ferromagnesian minerals, glass, and quartz. Un- 

 like the Canguinsa, on the other hand, the Vigo rocks are some- 

 what indurated and usually fissile, so that they split into thin 

 laminae on disintegration. The fine-grained shale at the top of 



