592 



F. G. CLAPP CLASSIFICATION OF PETROLEUM AND GAS FIELDS 



4uopoiuoa^ 



nejifoqoi 



CLASS Vn— CREVICES OF IGNEOUS ROCKS 



Petroleum aud solid bitumen have been noticed by various observers in 



traps, basalts, and other igneous 

 rocks. An interesting instance was 

 mentioned by Logan^^ in a green- 

 stone dike at Tar Point, Gaspe, in 

 the Province of Quebec. Another 

 unpublished occurrence of oil in 

 igneous rock from Colorado, con- 

 tributed by Dr. David T. Day, refers 

 to a boulder of vesicular basalt in 

 which the vesicles were filled with 

 oil. In order to prove whether the 

 oil had filtered in from exterior 

 sources, a fragment was boiled with 

 benzol until no more oil could be ex- 

 tracted, and the basalt still contained 

 much oil. It was shown, however, 

 that the cavities had been sealed by 

 a secondary deposit of carbonate of 

 lime, and that by removing this the 

 oil could all be extracted and the 

 basalt left intact. Thus the external 

 origin of oil was deemed possible. 



In the vicinity of Binny Craig, 

 Scotland, a volcanic neck or pipe was 

 encountered in an oil-shale working. 

 This dike consists of trap and con- 

 tains cavities in which mineral wax, 

 pitch, or paraffine was found. '^^ These 

 instances are not, however, in the 

 opinion of the present writer, due to 

 igneous origin of the oil, but to the 

 intrusion of the volcanic rock from 

 below into the sedimentary forma- 

 tions which contained the oil, and 

 consequently the volcanic rock must 

 have absorbed large quantities of 



'2 Sir William Logan : Geology of Canada, 1863, pp. 400-789. 



'8 Henry M. Cadell : Oil-shale holdings of the Lothians. Trans, Inst. Min. Engrs., 

 vol. 22, pp. 347-353. 



