354 The Philippine Journal of Science mz 



northwest and dipping steeply both to the northeast and south- 

 west. Farther downstream the Canguinsa sandstone — massive 

 and clayey — appears on top of the bedded shale. The oil comes, 

 therefore, from the usual petroliferous horizon in the Vigo shale, 

 immediately beneath the Canguinsa sandstone. The seepage is 

 sufficient to permit of the collection of a liter of oil without much 

 difficulty. 



PETROLEUM ON SILI CREEK 



A large exposure of petroliferous shale occurs on Sili Creek, 

 about 2 kilometers south of Tala. The outcrop is at the con- 

 fluence of two small streams which constitute the headwaters of 

 Sili Creek, and is at an elevation of 100 meters. The shale, which 

 probably represents the Bacau stage of the Vigo shale, is exposed 

 in banks about 12 meters high along either side of both branches 

 of the creek for a distance of 100 meters. Overlying the shale, 

 the Canguinsa and Malumbang formations are exposed in the 

 surrounding hills. The structure in this region is not clear, 

 but it appears that the exposure lies near the crest of a small 

 anticline, trending north. Faint bedding planes dipping to the 

 east-northeast at angles of from 30° to 40° may be discerned in 

 the shale. No actual seepage of petroleum was observed, but 

 the streams which flow across the shale are small and afford 

 little chance for detecting films or seepage. The odor of light 

 oils is very strong in the neighborhood, and traces of oil can be 

 obtained by macerating the shale in water. 



Part of the shale outcrop at Sili is always barren of vegetation, 

 a condition due, in part at least, to the instability of the surface 

 which is constantly crumbling and sliding down into the streams. 

 The natives attribute the absence of the generally present cogon 

 to the petroleum in the shale. They maintain that the shale 

 has been known "to burn." Two similar barren places occur in 

 the vicinity of Bondoc Head. The latter places are held by the 

 natives to mark the graves of asuan (spirits). The ground is 

 said always to be hot and to have "burned with flames" in the 

 past. The reports of prospectors who had heard this story from 

 the natives, but probably had not visited the site of the alleged 

 phenomena, undoubtedly gave rise to the widely circulated state- 

 ment that a vent, from which natural gas escaped and was con- 

 tinuously burning, existed near Bondoc Head. 



The "graves of the asuan" are on Lomboy Creek above a vil- 

 lage called Dyap, in a region covered with cogon. Unlike the 

 exposures on Sili Creek they are not steep slopes, but are on 



