X, A, 4 Pratt: Petroleum and Residual Bitumens 261 



limestone and porous sandstone belonging to the Malumbang 

 series have been saturated with a viscous, black bitumen. The 

 Malumbang series is at least 50 meters thick here, and the beds 

 dip gently to the south. The outcrop is a cliff 12 to 20 meters 

 high, forming one wall of a caiion. The impregnation extends 

 over a distance of at least 50 meters along the canon floor. No 

 exploration has been performed, and there is no evidence as to 

 how far at right angles to the exposed face the impregnation may 

 continue. The lower bituminous beds are sandstone made up of 

 fine fragments of limestone, feldspar, glass, and quartz. The up- 

 per beds consist of a granular limestone which does not disinte- 

 grate upon the removal of the bituminous impregnation. Blocks 

 of the bituminous material of many tons' weight have been 

 broken off and carried down the cafion. 



Across the canon from the bituminous beds in the Malumbang 

 series, exposures of Vigo shale were observed dipping at a high 

 angle in a direction opposite to that in which the Malumbang 

 dips. The relations suggest the presence of a fault in the vicin- 

 ity, on one side of which the Vigo shale has been thrust up 

 until it is in contact with the Malumbang on the opposite side. 



On going down the canon westward, Canguinsa clay-tuff is 

 encountered beneath the Malumbang series, and in the floor of 

 the cafion near the base of the Canguinsa one of the bitumen- 

 filled cylindrical concretions, like those noted at outcrop D, was 

 observed. At a distance of about 1 kilometer from the deposit, 

 and at an elevation about 100 meters lower, Vigo shale appears 

 beneath the Canguinsa. The Vigo in this position dips to the 

 south at an angle of about 30° and is thus in conformity with 

 the overlying rocks. A small outcrop of andesite occurs a few 

 meters farther down the canon toward Baliti; it is evidently an 

 intrusion in the Vigo shale. 



Near the barrio of Tabubunga, 10 kilometers south of Villaba 

 and outside the area included in fig. 2, I saw a small quantity of 

 a viscous, black oil seeping from joints in a thin bed of sand- 

 stone near the base of the Vigo shale. This seepage is somewhat 

 more than 1 kilometer inland from Tabubunga along Tabubunga 

 River, at an elevation of about 30 meters. In going to the 

 seepage from Tabubunga, I crossed successively the Malumbang 

 series, the Canguinsa clay-shale, and practically all of the Vigo 

 shale almost to the contact of the latter with the basal complex 

 upon which the sedimentaries lie. The dip is constantly seaward 

 (west) at an angle of about 30° throughout each of the forma- 

 tions. Thus the sedimentary formations are much thinner at 

 Tabubunga than they are at Villaba. The thickness of the Vigo 



