THE 



CANADIAN 



MTURALIST AND &EOLO&IST. 



Vol. YI. AUGUST, 1861. No. 4. 



ARTICLE XV. — Notes on the History of Petroleum or Roch 

 Oil. By T. Sterry Hunt, M.A., F.R.S., of the Geological 

 Survey of Canada. 



Public attention has lately been drawn to the petroleum fur- 

 nished by the oil wells in Canada and the United States, and 

 we have therefore thought it well to bring together some few 

 facts which may serve to explain the origin of this and of similar 

 substances, including naphtha, petroleum or rock oil, and asphalt or 

 mineral pitch, all of which are forms of bitumen, the one being solid 

 and the others fluid at ordinary temperatures. These differences 

 are, in many cases at least, due to subsequent alterations ; the 

 more liquid of these substances are mixtures of oils differing in 

 volatility, and by exposure to the air become less fluid, and partly 

 by evaporation, partly by oxydation from the air, eventually be- 

 come solid and are changed into mineral pitch. These sub- 

 stances, which are doubtless of organic origin, occur in rocks of all 

 ages, from the Lower Silurian to the tertiary period inclusive, and 

 are generally found impregnating limestones, and more rarely, 

 sandstones and shales. Their presence in the lower palaeozoic 

 rocks, which contain no traces of land plants, shows that they 

 have not been in all case=^ derived from terrestrial vegetation, but 

 may have been formed from marine plants or animals : the latter 



Can. Nat. 1 Vol. VI. No. 4. 



