370 The Philippine Journal of Science 1913 



cline has no oil seep on its crest, and it is a broad gentle fold. 

 The fact that no petroleum escapes from it may be taken as an 

 unfavorable or a favorable indication, arguing either the absence 

 of petroleum or that the petroleum has been confined by the un- 

 broken strata, there having been no opportunity for it to reach 

 the surface here, such as is afforded by the cracked and fissured 

 axial portions of the sharper folds. A broad gentle anticline 

 is generally looked upon with more favor as a natural reservoir 

 for petroleum than an acute anticline. Judged by this standard, 

 the Ayoni anticline would be considered promising. It is readily 

 accessible, and there has been comparatively little erosion along 

 its crest. Wells on its crest and eastern limb should pierce the 

 upper part of the Vigo shale under favorable conditions. 



On the other hand, there is an apparent transition in the 

 character of the Vigo shale from east to west at this latitude by 

 which shale grades into sandstone. It is possible that the shales 

 which appear to be the principal oil-bearing rocks are less ex- 

 tensive in the vicinity of Ayoni than elsewhere. The absence of 

 seepage, however, which might be taken to indicate such a change 

 in the character of the formations, can be accounted for readily 

 enough on other grounds as suggested above. 



Wells should be drilled along Malipa Creek, in the southern 

 limb of the Malipa anticline, and also, probably, farther south 

 in the eastern limb of the Central anticline. The structure is 

 not unfavorable, and traces of oil and gas are in evidence. A 

 well near the axis of the Malipa anticline would reach the beds 

 in the lower part of the Vigo shale, and from a site farther up 

 the creek higher strata including the Bacau stage could be invest- 

 igated. This region could be reached with comparative ease by 

 coming up the valley of Vigo River from the coast. 



The Bato anticline is not easily accessible, and the structural 

 relations are not clearly enough defined to make it a favorable 

 site for the first drilling, although it appears to be relatively 

 good territory. The lower part of the western base of Camba- 

 gaco Ridge would be a favorable site for testing the beds in the 

 Vigo shale beneath the overlap of the Canguinsa sandstone. 

 Wells so located, if drilled deep enough, would also encoun- 

 ter the Bacau stage of the Vigo shale in fairly good structural 

 relations. 



To reach the base of the Vigo shale and determine the value 

 of this zone in connection with petroleum, wells should start at 

 the lowest possible stratigraphic horizon. The upper valley of 

 Sibuyanin River in the western limb near the axis of the Central 

 anticline is probably the best site for such wells. The beds at 



