256 ^^^^ Philip-pine Journal of Science isis 



Mount Benao, with at least 250 meters' thickness of this forma- 

 tion stratigraphically above them. 



Outcrop A is in a creek which flows into Campocpoc River. 

 Several exposures have been found at the surface, but attempts 

 to follow them with excavations have failed. Evidently only 

 loose debris or surface float from the true deposit, whatever its 

 nature may be, has as yet been discovered. In all, perhaps one 

 ton of bitumen has been recovered. 



At B a small vertical fissure filled with solid bitumen has been 

 exposed by a shaft about 3 meters deep. There are other out- 

 crops of similar bitumen near by, but only the one has been 

 opened enough to reveal its form. This fissure has sharp, reg- 

 ular walls and widens downward from 30 centimeters at the 

 surface to 60 centimeters at the bottom of the opening. The 

 bitumen is closely jointed at right angles to the walls, so that 

 it is removed in roughly columnar fragments. A small lens of 

 the clay wall was observed in the fissure surrounded by bitumen, 

 and small seams of bitumen extend out from the fissure along 

 joint planes in the clay, although there is no general impregna- 

 tion of the surrounding walls. The fissure trends a little north 

 of east across the beds of the Canguinsa, which strike west- 

 northwest and dip about 20° north-northeast. 



Outcrop C is identical in character with outcrop A. Nothing 

 in place has been discovered, but pieces of black, shiny bitumen 

 are scattered over the surface on the side of a hill of Canguinsa 

 clay-tuff. Probably both at A and C fissures similar to the 

 one at B will be found. 



At D there are several outcrops of viscous, black bitumen along 

 the bed of a small stream. The material varies from a semi- 

 liquid, through a sticky, viscous stage, to a rubbery semisolid. 

 The largest outcrop is a dome of bitumen-cemented breccia about 

 1 meter in diameter, which protrudes nearly a meter from the 

 surface of the Canguinsa clay-tufl? in the creek floor. The bitu- 

 men binds together the rock ^fragments in the breccia and also 

 occupies pores and vesicles in the fragments themselves. There 

 are at least two other outcrops of the same character. A shallow 

 excavation around the base of the larger dome shows that it 

 continues downward through the clay-tuff beds. Apparently 

 these breccia domes or chimneys penetrate the strata, although 

 there is no evidence of disturbance in the clay-tuff surrounding 

 them. 



The outcrops are in the basal part of the Canguinsa, very 

 closely above the Vigo shale. The dip in the surrounding rocks 

 is about 30° to the south-southwest. A few hundred meters to 



