346 The Philippine Journal of Science m3 



coast is a ridge in which the strata from the Canguinsa sandstone 

 to the Upper limestone are found dipping from 30° to 40° east- 

 northeast. The top of the Vigo shale, exposed at several places 

 along Bahay River and Milipilijuan Creek, is the lowest horizon 

 reached by erosion. Most of the outcrops are in the eastern limb 

 of the fold and dip 55° east-northeast. 



West of Bahay River, which marks the axis of the flexure, the 

 formations still dip to the eastward, but at very low angles. At 

 the mouth of Apad Creek, which flows into Bahay River from the 

 west, the Canguinsa sandstone dips slightly eastward. Farther 

 up the creek, the Cudiapi sandstone appears above the Canguinsa 

 and dips to the southeast from 15° to 30°. Several of the expo- 

 sures of Vigo shale in Milipilijuan Creek dip to the westward, and 

 it is probable that the Vigo shale forms a true anticline at Bahay 

 with dips to the east-northeast and to the west-southwest away 

 from the axis. The flexure in the upper, less easily folded, strata 

 is anticlinal in character in that the strata are differently inclined 

 on either side of its axis so as to form an arch, although the dips 

 are all in a single general direction (eastward). In these beds 

 there is only an abrupt increase in the eastward dip along a line 

 which becomes the axis of an anticline farther south. 



There is evidence of displacement at Bahay similar to that near 

 Mount Maglihi. Acute folding with erosion along the crest might 

 account for the observed relations, but an accompanying upward 

 thrust of the eastern limb along a fault plane is indicated. The 

 objection to the theory of an overthrust of the eastern limb at 

 Mount Maglihi, discussed on page 345, applies with equal force 

 to the conditions at Bahay. 



Banaba monocline. — An extensive monocline, the general north- 

 east dip of which is conspicuous in Mount Banaba, forms the 

 southern portion of the peninsula. Based on rather meager 

 evidence, a minor overturn in the region of Sili and Tala and a 

 close fold near the southwestern coast are shown in the geologic 

 section (Map I) as modifications of this structure. 



The strike of the beds varies in different parts of the area. On 

 Mount Banaba it is north 30° west, near Bondoc Head it is north 

 50° west, and in the western part of the monoclinal area it is 

 north 15° west, parallel to the adjacent coast line. From Mount 

 Banaba to Sili the average dip is probably 15°, and in the section 

 between these places only the strata in the Malumbang and Can- 

 guinsa formations come to the surface. It it surprising, in view 

 of the general northeast dip, that the upper part of the Vigo shale 

 is not exposed in the deep valley of Amoguis River. The differ- 

 ence in elevation between the summit of Mount Banaba and the 



