NOTES ON THE HISTORY OF PETROLEUM OR ROCK OIL. 



By T. S terry HUNT, M.A., F.R. S., 



OF THE GEOLOGICAL SUEVEY OF CANADA. 



(From the Canadian Naturalist and Geologist.) 



Public attention has lately been drawn to the petroleum furnished 

 by the oil wells in Canada and the United States, and we have there- 

 fore 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 sub- 

 stances are mixtures of oils differing in volatility, and by exposure to 

 the air become less fluid, and partly by evaporation, partlv by oxida- 

 tion from the air, eventually become solid and are changed into min- 

 eral pitch. These substances, which are doubtless of organic origin, 

 occur in rocks of all ages, from the lower silurian to the tertiary pe- 

 riod inclusive, and are generally found impregnating limestones, and 

 more rarely, sandstones and shales. Their presence in the lower 

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

 they have not been in all cases derived from terrestrial vegetation, 

 but may have been formed from marine plants or animals ; the latter 

 is not surprising when we consider that a considerable portion of the 

 tissues of the lower marine animals is destitute of nitrogen, and very 

 similar in chemical composition to the woody fibre of plants. Besides 

 the rocks which contain true bitumen, we have what are called bitu- 

 minous shales, which, when heated, burn with flame, and by distilla- 

 tion at a high temperature yield, besides inflammable gases, a portion 

 of oil not unlike in its characters to petroleum. These are, in fact, 

 argillaceous rocks intermixed with a portion of organic matter allied 

 to peat or lignite, which, by heat, is decomposed and gives rise to 

 oily hydrocarbons. These inflammable or lignitic shales, which may 

 be conveniently distinguished by the name of pyroschists, (the hrand- 

 schiefer of the Germans) are to be carefully distinguished from rocks 

 containing ready-formed bitumen ; this being easily soluble in benzole 

 or sulphuret of carbon can be readily dissolved from the rocks in which 

 it occurs, while the pyroschists in question yield, like coal and lignite, 

 little or nothing to these liquids. 



It is the more necessary to insist upon the distinction between lig- 

 nitic and bituminous rocks, inasmuch as some have been disposed to 

 regard the former as the source of the bitumen found in nature, which 

 they conceive to have originated from a slow distillation of these 

 matters. The result of a careful examination of the question has, 

 however, led us to the conclusion that the formation of the one ex- 



