reckhani.] 446 [Scpteinl)erlS. 



Other varieties derived from it will be found susceptible of the 

 following classification. 



f Lower DERivATiVESj-I^aptha.?, and gaseous carbides of )iydrogen 

 (by distiUation). 



^Malthas. 



.Asphalts. 



■ PjTo-aspbalts. 



ITigber Derivatives. <j 



(by inspissation | \ Asphaltic-Scbists. 



or decoiiipositiou ) L 



Pjjtroleum < 



Pyro-Scliists. 



The exceptional forms before mentioned, do not perhaps admit 

 of any classification in relation to petroleum, having been formed 

 probably under peculiar circumstances, Avhich were local in their 

 action. 



I shall assume, without asserting it to be a fact, that petro- 

 leum is the normal or primar}^ product of the decomposition of 

 marine animal or vegetable organisms, chiefly the former, and 

 that nearly all other varieties of bitumen are products of a sub- 

 sequent decomposition of petroleum, diff'ering both in kind and 

 degree. 



Various opinions have been expressed concerning the origin 

 of petroleum. Until quite recently, all of these theories were 

 based upon the assumption that it has been derived from vege- 

 tal)le or animal organisms. It has been supposed to be the pro- 

 duct of the decomposition of woody fibre by which more of 

 the carbon and less of the hydrogen has been evolved than by 

 the decomposition which has produced coal. Again, it has .been 

 supposed to be the product of the natural distillation of p^-robi- 

 tuminous shales and coals. M. Lesquereux attributes its origin 

 to the partial decomposition of low forms of marine vegetation. 

 Yet, again M. Berthelot has advanced the theory that by com- 

 plex chemical changes at present taking place in the interior of 

 the earth, petroleum is being continually set free. The follow- 

 ing extract translated from his paper, Avill serve to give an idea 

 of his views upon this subject. 



" If in accordance with an hypothesis recently" announced by 

 M. Daubre, it be admitted that the terrestrial mass contains free 

 alkali metals in its interior, this hypothesis alone, together with 

 experiments that I have lately published, furnishes almost of 

 necessity a method of explaining the formation of carbides of 

 h^'drogen. According to my experiments, when carbonic acid, 



