310 The Philippine Journal of Science ms 



affluents of nearly equal importance which unite in one stream 

 as they approach the western coast. The Ajus, farther north, 

 is like the Vigo in the orientation of its branches. Guinhalinan 

 River, which is one of the largest rivers on Bondoc Peninsula, 

 consists of two principal tributaries coming together from almost 

 exactly opposite directions. Its south fork heads in the north- 

 eastern part of the area mapped, and flows north-northwest for 

 a distance of 15 kilometers where it meets the north fork, which 

 comes an equal distance from the north-northwest. From the 

 point of confluence the merged streams flow eastward into Ragay 

 Gulf, a distance of 5 kilometers. Thus, the main drainage of 

 Guinhalinan River is at right angles to the course of, and about 

 six times as long as, the principal stream. 



TOPOGRAPHIC CONTROL 



The general alignment of the water courses parallel to the 

 trend of the peninsula and the relatively short stream lines at 

 right angles to this trend — an extreme example of which has 

 been cited in the case of Guinhalinan River — are obviously due to 

 the control exercised by the prevailing strike of the rock strata. 

 Not only has the strike of the inclined beds affected in this 

 manner the alignment of the rivers, but the structure has in- 

 fluenced the relative positions of the main valleys and uplands. 

 Thus, the valleys find their greatest development in, or near, the 

 crests of anticlines ; while the higher elevations occur in synclinal 

 troughs, on the limbs of the anticlines, or in regions where the 

 folding has not been severe (see geologic sections). 



The upper courses of Vigo, Matataha, and Canguinsa Rivers 

 all lie in the crest portion of the Central anticline. The lower 

 part of Vigo River has cut through the ridge bordering the east 

 coast along the axis of a small anticline, and Silonguin River 

 has followed a similar line of cross structure. At the mouth 

 of Mulanay River, likewise, the beds strike east-northeast and 

 are steeply inclined, although only the southern limb of this 

 possible cross anticline has been proved. The high areas in 

 Cudiapi Range and in Bondoc Head represent synclines, while 

 the plateau to the south and southeast of Canguinsa River oc- 

 cupies a region which has not been greatly disturbed in the 

 process of folding. The ridge on each of the lateral coasts 

 consists of strata lying well down in the limbs of the general 

 arch of the peninsula, with Mount Maclayao near the western 

 coast, marking also the southern limb of the cross flexure at the 

 mouth of Mulanay River. 



It is believed that the processes which resulted in the folded 

 condition of the strata were initiated prior to the emergence of 



