362 The Philippine Journal of Science 1913 



of all the strata above the Vigo shale. The lower part of this 

 formation and the beds which underlie it are not exposed any- 

 where within the field, and their character is unknown. There 

 is a possibility also that some members of the Vigo shale above 

 the Bacau stage are concealed by the overlap of the uncon- 

 formable Canguinsa sandstone and, therefore, have escaped 

 examination. 



7. The petroleum is of low specific gravity, and contains a 

 large proportion of light oils. It has been suggested that its 

 properties are those of a clarified, or partly refined, oil. The 

 lighter fractions are weakly levorotatory in their effect on po- 

 larized light. 



Considering the field relations alone, the logical conclusion 

 would be that the petroleum in Tayabas is of organic origin 

 and is in no way connected with volcanic activity or other 

 inorganic processes. By some authorities, 20 the property of 

 rotating the plane of polarized light which Tayabas petroleum 

 exhibits would be accepted as conclusive evidence of organic 

 origin. 



If a definite organic source is sought, the presence of Globige- 

 rina and vegetable remains in the Vigo shale at once attracts 

 attention. Most of the oil observed occurs in the shale which 

 contains organic matter of this nature, and it is well known that 

 the decomposition, under certain conditions, of animal matter 

 similar to the soft parts of Globigerina does give rise to petroleum. 



The decomposition of organic matter, both Globigerina and 

 vegetable remains, in the Bacau stage of the Vigo shale may 

 have yielded the petroleum which is found in these beds. 

 However, neither Globigerina nor the vegetable remains are 

 especially abundant in the petroliferous beds, and it may be 

 questioned whether the quantity of organic matter which was 

 contained in the Bacau stage was adequate to have supplied 

 a large quantity of petroleum, or even the quantity of petroleum 

 which is to be observed. 



Some of the properties of the Tayabas petroleum suggest that 

 the oil may have migrated to its present position. Most oils 

 obtained directly from the rocks in which it is certain that they 

 have originated are high in specific gravity, and consist largely 

 of heavy oils, with a very small gasoline content. On the other 

 hand, oils which are believed to have migrated from a distant 

 source, to the natural reservoirs in which they have accumulated, 

 are of low specific gravity and are rich in volatile constituents. 



"Engler, C, Chem. Zentralbl. (1908), 2, 376. 



