254 The Philippine Journal of Science 1915 



seepages I and J, again, there is a west-northwest-trending 

 anticline in the Vigo shale, with Mount Camaro lying on its 

 crest. The seepage at I on the northern limb of this fold is 

 marked by igneous rocks which may be either intrusive or a 

 part of the basal complex which underlies the Vigo shale. The 

 outcrop N is on a fault trending west-northwest, along which 

 there is also a small intrusion and from which the strata dip 

 away on either side. 



The southern part of the petroleum region, therefore, appears 

 to contain a number of small folds, the majority of which have 

 not yet been delineated. There are probably also more faults 

 than have been detected. The intrusions, to judge from their 

 distribution, are related to the folds in origin. In the northern 

 part of the peninsula the folding processes have been less intense, 

 and low broad folds would be expected in this territory. 



Both in Tayabas and in Leyte there is a discordance between 

 the Vigo shale and the overlying Canguinsa. This discordance 

 is evidenced by an abrupt flattening in the angle of dip on 

 passing from the Vigo to the Canguinsa in sharply folded areas. 

 The dip is constantly in the same direction, but is less pronounced 

 in the upper rocks than it is in the Vigo. Where the folding 

 processes have not been intense, and the dips are consequently 

 not steep, there is apparent conformity between the two forma- 

 tions. The possibility of an unconformity between the Vigo 

 and the Canguinsa was discussed at length in the report on the 

 Tayabas region. The question is important if, as is suggested, 

 the Vigo shale is the petroleum-bearing formation. No con- 

 clusive evidence of an erosional unconformity was discovered, 

 and it is, therefore, suggested that the observed difference in 

 the angles of dip in the two formations might be explained as a 

 mechanical discordance. It is conceived that the perfectly and 

 closely laminated character of the Vigo shale would tend to cause 

 it to respond more readily and more completely to processes 

 of folding than would the heavily bedded or massive Canguinsa. 

 The result might be a crumpling or wrinkling of the Vigo shale, 

 which would be less plainly manifested in the more competent 

 arch of the overlying Canguinsa. 



Whether the unconformity between the Vigo and the Can- 

 guinsa is erosional or only a mechanical discordance is not con- 

 clusively determined. If it is erosional, there may, of course, be 

 structures in the Vigo shale where it is covered by the upper 

 rocks which are not reflected on the surface. Likewise there 

 would be an overlap of the upper rocks on the upturned edges 

 of the Vigo. If the discordance is only mechanical, there may 



