336 ^ ie Philippine Journal of Science 1913 



represent a continuous formation. The fact that parts of the 

 formation are typical agglomerate with a tuff aceous matrix makes 

 it very improbable that these outcrops represent an intrusion. 

 The material appears to be clearly of volcanic origin and to 

 consist principally of fragmental ejecta. Whether each outcrop 

 represents a center of local effusion, or is the remnant of a 

 larger sheet of agglomerate which came from a distance and 

 was interbedded in the shale, cannot be decided without further 

 investigation. 



The importance of the igneous rocks relative to the accumula- 

 tion of petroleum is problematical. Traces of oil and gas are 

 found in the shale on Tangob Creek adjacent to the largest 

 outcrop of agglomerate. If the observed outcrops mark local 

 centers of extrusion, then the beds stratigraphically below them 

 must be pierced and more or less broken by the volcanic vents 

 from which the agglomerate was thrown out. In the light of 

 drilling experience in most large oil fields this condition prob- 

 ably would be looked upon with disfavor. However, it is well 

 known that large flows of oil have been obtained in Mexico near 

 volcanic rocks which have come up through sedimentary beds, 

 and it has been suggested 15 that the vulcanism has supplied the 

 conditions necessary for the accumulation of the petroleum. 

 Thus, even if the agglomerate in Tayabas has been extruded 

 locally, it should not condemn any part of the field, and may 

 have had a desirable effect. 



If the agglomerate has not been extruded locally but has been 

 thrown out from a distant center, its presence probably has little 

 bearing on the question of petroleum exploitation. It is con- 

 ceivable, of course, that an impervious sheet of interbedded 

 agglomerate might influence the accumulation of any petroleum 

 in the rocks below it, but the data available do not warrant any 

 procedure based on this possibility. 



On the whole, in view of their limited extent and of their 

 probable extrusive origin, it may be concluded that the igneous 

 rocks have no important bearing, either favorable or unfavorable, 

 on the possibilities of this oil field. 



STRUCTURE 



General. — Bondoc Peninsula occupies a geanticlinal zone in 

 the folded strata of southern Luzon and the adjacent islands. 

 Ragay Gulf, lying east of the peninsula and between it and the 

 larger peninsula of southeastern Luzon, probably occupies an 



"Garfias, V. R., Journ. Geol. (1912), 20, 2, 666. 



