X, A, 4 



Pratt: Petroleum and Residual Bitumens 267 



leum and residual bitumens in Leyte there is none which could 

 not have originated through the infiltration of petroleum from 

 the Vigo shale. Samples of Glohigerina, which were found in 

 the Vigo shale in Tayabas and were rather doubtfully credited 

 with the origin of the Tayabas petroleum in the previously cited 

 report on that field, occur abundantly in the Canguinsa as well as 

 in the Vigo in Leyte. If these little animals are really the ul- 

 timate source of the petroleum, then the Canguinsa must have 

 yielded more petroleum than the Vigo. But the truth of this 

 theory is not established. Nowhere, as a matter of fact, has Glo- 

 higerina been observed in numbers sufficient to justify the idea 

 that it is the source of more than a very limited quantity of 

 petroleum. 



That petroleum is present in the Vigo shale in Leyte as well 

 as in Tayabas and in Cebu is a matter of common observation. 

 Evidence has been cited in the descriptions of several of the 

 occurrences in Leyte which indicates that the petroleum moved 

 through the Canguinsa clay-tuff" along fractures, bedding planes, 

 faults, brecciated zones, and open fissures, but nowhere is there 

 evidence that the petroleum permeates the clay-tuff itself. It 

 is certain that the Vigo shale is petroleum-bearing, and while 

 the Canguinsa sandstone may also be a source of petroleum, it 

 is not unreasonable to assume that most of the petroleum and 

 residual bitumens now found in the Canguinsa migrated into 

 that formation from the underlying Vigo shale. 



The possible relation of the intrusive rocks to the accumu- 

 lations of petroleum which gave rise to the deposits of natural 

 bitumen should be taken into consideration. Outcrops L and M 

 consist of breccias very like the breccia produced by the Mount 

 Tabeyta intrusion. At outcrop D there are breccias and concre- 

 tions which appear to be related to hidden intrusions. Intrusive 

 rocks are found below the outcrops at N in the neighborhood of 

 a probable fault plane. It is true that in the immediate vicinities 

 of the largest intrusions no petroleum nor bitumen is encountered 

 at the surface, but at distances of from 2 to 3 kilometers from 

 the center of Mount Tabeyta, which is itself something like 1 

 kilometer in diameter at its base and over 200 meters high, 

 are several important outcrops. The larger number of the 

 intrusions found are in the Vigo shale and do not reach the 

 overlying rocks, a fact which makes it probable that in territory 

 covered by the upper rocks, like the vicinities of most of the 

 bitumen outcrops, other intrusions exist beneath the surface. 

 The suggestion may be made, therefore, that the intrusions have 

 driven petroleum from the beds penetrated — Vigo shale and pos- 



