350 The Philippine Journal of Science 1913 



the base of the Canguinsa sandstone. In the lowest exposed 

 portions of the Vigo shale but little oil is to be observed. 



The oil is associated with the shale, rather than with the 

 sandstone, where sandy layers are interbedded, and in several 

 cases it comes directly from the shale. The absence of oil in 

 the interbedded sandstone at the outcrop may be due in part 

 to the rapidity with which it volatilizes and thus escapes from 

 porous media. 



Petroleum seeps were encountered at Banco, at Bahay, and 

 on Milipilijuan Creek along the Maglihi anticline; on Sili Creek, 

 a branch of Pagsanhan River ; at Bacau on the Central anticline ; 

 on Malipa and Tangob Creeks in the vicinity of Cabongahan; 

 at Bato, north of Cabongahan; and on Ajus River in the north- 

 eastern part of the field. Traces of oil and inflammable gas 

 were detected at several other places, including the outcrops of 

 Vigo shale dipping steeply south-southwest on the upper part 

 of Sobo Creek, south of Mulanay. 



PETROLEUM AT BANCO 



Petroleum is found at Banco near the head of Canibo Creek 

 which flows to the south from the small valley in the crest of 

 the Maglihi anticline. The seep is at an elevation of about 

 200 meters. A strong odor of kerosene reveals the presence of 

 the oil, which on closer inspection may be seen to rise in globules 

 from the bottom of the small stream and to float away in films 

 on the surface of the water. The seepage is accelerated by 

 probing in the rocks and debris in the bed of the stream, and 

 a small quantity of petroleum can be collected by skimming the 

 globules and films from the water. The underlying rocks are 

 concealed at the immediate point of escape, but 20 meters down- 

 stream bedded petroliferous shale and sandstone, belonging to 

 the Bacau stage of the Vigo shale, are exposed. These beds dip 

 to the west at an angle of 45°, so that the seep is in the western 

 limb of the anticline. The wall of the valley rises steeply on 

 the west to an elevation of more than 300 meters, and is made 

 up of the rocks of the Canguinsa sandstone and Malumbang 

 series. 



About 200 meters south of the main seep, oil may be detected 

 in blue to black petroliferous shale on the floor of an arroyo in 

 the western wall of the valley. Maalat Creek, an adjacent 

 tributary of Canibo Creek, contains salt water, as the native 

 name, "Maalat," implies. 



