24:2 Notes on Fetroleum 



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 w^oody fibre of plants. 

 Besides the rocks which contain true bitumen we have what are 

 called bituminous shales, which when heated burnwath flame, and 

 by distillation 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 

 pyroschistSy (the brandschiefer of the Germans) are to be carefully 

 distinguished from rocks containing ready-formed bitumen; this 

 being easily soluble in benzole or sulphure 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 

 lignitic and bituminous rocks, inasmuch as some have been dis- 

 posed to regard the former as the source of the bitumen found in 

 nature, which they conceive to have originated from a slow distil- 

 lation of these matters. The result of a careful examination of 

 the question has however led us to the conclusion that the form- 

 ation of the one excludes more or less completely that of the 

 other, and that bitumen has been generated under conditions dif- 

 ferent from those which have transformed organic matters into 

 coal and lignite, and probably in deep water deposits, from which 

 atmospheric oxygen was excluded. Thus in the palaeozoic 

 strata of North America we find in the Utica and Hamilton 

 formations, highly inflammable pyroschists which contain no sol- 

 uble bitumen, and the same is true to a certain extent of some lime- 

 stones, while the Trenton and Corniferous limestones of the same se- 

 ries are impregated with petroleum or mineral pitch, and as we shall 

 show, give rise to petroleum springs. The fact that intermediate 

 porous strata of similar mineral characters are destitute of bitu- 

 men, shows that this material cannot have been derived from over- 

 lying or underlying beds, but has been generated by the transfor- 

 mation of organic matters in the strata in which it is met with. 

 This conclusion is accordance with that arrived at by Mr. S. P. 

 Wall in his recent investigations in Trinidad. He has shown that 

 the asphalt of that island and of Venezuela belongs to strata of the 



