vin, a, 6 Pratt and Smith: Petroleum Resources 311 



Bondoc Peninsula above sea level. Probably the elevation is 

 due, in part at least, to the folding and the main folds were out- 

 lined in the original land surface. If this theory is correct, the 

 early water courses must have occupied the structural troughs 

 or synclines. As folding progressed the anticlines became very 

 acute, and their position must have been marked by extensive 

 local shattering of the nonyielding limestone and calcareous sand- 

 stone in the upper part of the stratigraphic column. The syn- 

 clines, on the other hand, were left in broad gentle folds not 

 sufficiently pronounced to break the strata. Obviously, these 

 conditions would tend to hasten the progress of erosion along 

 the anticlinal zones; valleys probably formed on the anticlines 

 and developed with greater rapidity than was possible in the 

 synclines. Consequently, the synclines were soon deprived of 

 their streams through the piracy of the anticlinal drainage, 

 and the translation of the main water courses from synclines to 

 erosional valleys on the anticlines was accomplished. 



There is a striking contrast between the low hills and wide 

 valleys, which are found in regions where the soft shale in the 

 lower part of the stratigraphic column has been exposed to ero- 

 sion over large areas, and the steep-walled valleys and the general 

 youthful appearance of the topography in parts of the field where 

 the upper formations have been preserved. Once these pro- 

 tecting rocks are removed, the shale yields readily to the cutting 

 action of the run-off and relatively mature land forms result. 



It is probable that rivers emptying into the sea upon the lateral 

 coasts and gradually working inland along the lines of cross 

 structure have captured drainage, which previously had followed 

 the general strike of the formations. An apparent example of 

 a stream so captured is Canguinsa River, which probably at one 

 time flowed south into Amoguis River. 



STRATIGRAPHY 



Table of stratigraphy. — Table I shows the stratigraphic and 

 age relations of the rocks in the area under discussion. Tables 

 II and III with similar data for the largest producing oil fields 

 near the Philippine Archipelago are inserted for comparison. 10 

 Table II represents the Echigo field in Japan, and Table III 11 

 the Moera Enim field in southern Sumatra. 



10 Iki, Tounenaka, Preliminary notes on the geology of the Echigo oil field, 

 Mem. Imp. Geol. Surv. Japan (1910), No. 2, 29. 



u Tobler, Aug., Topographische und Geologische Beschreibung der Pe- 

 troleum Gebiete bei Moera Enim (Siid Sumatra). Tidschrift van het 

 Kominklijk Nederlandsch Aardrijkskundig Genootschap. (1906) Tweede 

 Serie, 23, No. 2, 199. 



