viii, a, 5 Pratt and Smith: Petroleum Resources 345 



is indicated. At Bahay, however, the western limb is not clearly 

 defined in the younger formations and the axis has changed its 

 direction to the north-northwest, in conformity with the general 

 strike in the field. 



In the region of Mount Maglihi, the western limb of the fold 

 can be identified without difficulty. For several hundred meters 

 west of the axis, the Upper limestone and Cudiapi sandstone dip 

 from 15° to 20° to the westward, reversing the monoclinal slope 

 from the summit of Mount Banaba and forming the eastern limb 

 of a shallow syncline occupied by Malumbang Valley. The Vigo 

 shale, exposed at the oil seep near Banco, likewise dips to the 

 westward, but at a greater angle (45°). North of Banco, the 

 crest of the fold is less deeply eroded, and the base of the Can- 

 guinsa sandstone is not uncovered. On Mount Maglihi and 

 Mount Morabi, which are in the eastern limb close to the axis, 

 the Canguinsa sandstone dips generally about 55° to the east, 

 but locally it is vertical, or even overturned slightly to the west. 

 The Canguinsa sandstone is calcareous in this locality, and in 

 the summits of the hills just mentioned contains sandy limestone 

 a few meters thick (Table XI) . In the Malumbang series, lying 

 farther from the axis in the eastern flank of the fold, the angle 

 of dip decreases regularly to about 30°. 



The more highly inclined strata east of the anticlinal axis 

 are exposed in apparently greater thickness than is evident in 

 the western limb, and the lower part of the Canguinsa sandstone 

 in the eastern limb is brought into close association with the Ma- 

 lumbang series in the opposite limb. The relations suggest 

 faulting along the strike of the beds in the crest of the anticline 

 with an upward thrust of the eastern limb, but in the absence of 

 precise measurements actual movement along the suspected 

 fault plane cannot be established. 



A commonly stated law applying to asymmetric anticlines is 

 that the active thrust came from the side of gentler slope, that is, 

 in the case under discussion, from the west. If the force came 

 from the west, the eastern limb could scarcely have been thrust 

 up over the western. Since the evidence of the overthrust of 

 the eastern limb is not conclusive, and the law as to the direction 

 of the active forces — while not of universal application — is as- 

 sumed to hold true generally, the occurrence of actual displace- 

 ment along a fault plane in this fold must be questioned. 



At Bahay the relations are similar to those in the region just 

 described. Bahay River, flowing north, and Milipilijuan Creek, 

 flowing south, have cut out a deep valley along the axis of the 

 flexure and parallel to the coast line. Between this valley and the 



