viii,a,5 Pratt and Smith: Petroleum Resources 347 



floor of the valley is great enough that the entire thickness of the 

 strata above the Vigo shale should be included in the section ex- 

 posed in the eastern wall of the valley, unless the upper forma- 

 tions are thicker here than they were found to be farther north. 



On Sili Creek, a few hundred meters south of Sili, the Bacau 

 stage of the Vigo shale is exposed, but only over a small area, and 

 west of Sili the upper formations reappear and are found in the 

 floor of the next valley to the westward, at an elevation as low as 

 that of Sili Creek. This condition suggests that the general north- 

 east dip of the strata is reversed to a westward dip for a short 

 distance west of Sili. Faulting might produce the same effect, 

 but there is no evidence of faulting in this vicinity. Neither were 

 the suggested westward dips detected at Sili proper, but north of 

 Sili, at Tala, dips to the west are found in the upper formations. 

 On the basis of this evidence, a small anticline is shown along this 

 line in the geologic section. It will be noted that this fold is ap- 

 proximately in the position which a southward continuation of 

 the Central anticline would occupy. 



West of Tumbaga River, the Vigo shale reappears, dipping 35° 

 east-northeast, and the exposure extends southwest to the sea- 

 coast. The dip of the beds increases regularly toward the south- 

 west, becoming almost vertical at the eastern base of the chain of 

 hills along the western and southwestern coast. On top of Bon- 

 doc Head the Canguinsa sandstone and part of the Malumbang 

 series occur, lying almost horizontal. West of Bondoc Head on 

 the seacoast, the Vigo shale, dipping 30° to the northeast, is 

 encountered again. In the summit of the ridge near the mouth of 

 Bataniog Creek are sandstone and sandy conglomerate, similar 

 to the strata in the upper part of the Vigo shale near Matataha. 

 These beds dip to the east at an angle of 70° and strike about 

 north. 



If the monoclinal structure persists to the southwestern coast, 

 Bondoc Head should consist of steeply inclined beds of Vigo shale. 

 Instead, the summit of this mountain is covered with younger 

 formations. At the mouth of Bataniog Creek, again, are the 

 sandstones and conglomerates which are found usually at the top 

 of the Vigo shale. If there is no reversal in the general mono- 

 cline, these beds are out of their usual stratigraphic position, and 

 the indicated thickness of the Vigo shale is at least 3,600 meters. 

 Both these conditions seem improbable, and a close fold recumbent 

 to the southwest, as shown in the geologic section, is a more 

 reasonable interpretation of the data in hand. The relations may 

 be complicated by faulting analogous to the suspected faulting in 

 the Maglihi anticline. 



