344 The Philippine Journal of Science mz 



gentle anticline which is defined along it becomes evident a short 

 distance south of Matataha River and persists over a length of 

 10 kilometers to a point east of Bondoc. Sandstones, about 300 

 meters in thickness, are exposed in the western limb at Ayoni, 

 dipping from 35° to 40° west-southwest and overlain conform- 

 ably by limestone. The sandstones probably represent the Can- 

 guinsa and part of the Vigo formation, and the limestone, the 

 lower stage of the Malumbang series. East of the axis in the 

 west slope of the Cudiapi Range, a similar section culminating 

 in limestone and calcareous sandstone is revealed. The inclina- 

 tion of the strata in the eastern limb is generally less than 15°. 



Between the northern end of the Ayoni anticline and the cross 

 fold at Mulanay, an area in which the strata are horizontal in- 

 tervenes. Mount Cancalao, left by erosion in the Matataha Val- 

 ley, affords a section of horizontal strata in which bluish black 

 shale at the base is covered by beds of sandstone, sandy micaceous 

 shales, and sandstone conglomerate with a total thickness of 

 nearly 200 meters. On the coast west of Mount Cancalao, the 

 strata dip seaward as they do at Ayoni, and precise measure- 

 ments would probably reveal a slight anticlinal fold between 

 the mountain and the coast. 



South of the Ayoni anticline as far as Silonguin (Canguinsa) 

 River, the structural relations are uncertain. The identity of 

 the smaller fold is lost in a general slight dip to the southwest, 

 which probably marks the western limb of the Central anticline. 



Cudiapi syncline. — The Cudiapi syncline is a shallow struc- 

 tural basin lying between the Central and Ayoni anticlines. The 

 rocks have been preserved from erosion within this zone and 

 form the rather flat-topped Cudiapi Range extending southeast 

 from the headwaters of Sibuyanin River to Silonguin River. 

 The Canguinsa sandstone and the Lower limestone of the Malum- 

 bang series are exposed over most of the surface, but remnants 

 of the Cudiapi sandstone occur locally. 



Maglihi anticline. — The Maglihi anticline — marked by Mount 

 Maglihi, a conspicuous peak formed by the almost vertical strata 

 in its crest — is an acute upward flexure in the eastern part of the 

 monocline which persists with a gentle eastward dip across the 

 southern end of the peninsula. The anticline is most clearly re- 

 vealed in the vicinity of Mount Maglihi, where the axis strikes 

 north 5° east, and the eastern limb is much steeper than the 

 western. South of the mountain, the axis plunges so that the 

 fold is barely perceptible in the strata near the southern coast. 

 Northward, it can be traced with some difficulty for several kilo- 

 meters and probably continues to Bahay where a similar fold 



