ASPI1ALTUM FOR A MODERN STREET. 



227 



earth has been converted by a process of partial decay into bitumen. 

 This is called the 'indigenous' theory. Others think that the natural 

 heat of the crust of the earth generated by pressure and, perhaps, other 

 causes, has distilled bitumens from pyrobituminous minerals, and, in 

 some instances, from coal, and they have penetrated the surround- 

 ing and overlying porous formations, often filling crevices and forming 

 veins, Avhen the pressure becomes sufficient to rupture the overlying 

 formations. I am inclined to think this latter theory, of 'distillation,' 

 will best account for all the varying conditions under which the various 

 forms of bitumen occur. 



Bitumens occur in all periods of the geological history of the earth's 

 crust, but are mainly confined to the formations anterior to the coal 

 period and to the later formations of the tertiary. While asphaltum 

 is found in some of the oldest formations, the greater number of the 

 deposits of solid bitumen and bituminous rocks occur in the more recent 

 formations. 



In order to show graphically the relations of the pyrobituminous 

 minerals to the various forms of bitumen, I have arranged the following 

 table, which represents the development of our present knowledge of 

 these substances from the time when M. Leon Malo first published a 

 similar table about forty years ago: 



[Anthracite, North America, "Wales, Belgium, France, etc. 



, * 



r => 

 o 



c 



o 



In 



o 





3 



S 

 % 



Splint, 



Cannel, 



Peat, 



Shales, 



Schists. 



Natural gas 



^2 



o .9 



\ 



i 



- 



Found all over the world ; yielding bituminous sub- 

 stances by destructive distillation, shales of 

 Autun and Mansfeld, Bog-head mineral, Wollon- 

 gonite, etc. 



In the United States, Indiana, Ohio, Pennsylvania, etc. 

 Russia, France, China, etc. 

 Natural naphtha. — Persia, Cuba and generally in petroleum regions. 

 Petroleum. — Central United States, California, Peru, Cuba, Russia, 



Borneo, Java, etc. 

 Maltha. — Persia, Albania, Texas, California, Peru, Trinidad, Mexico, 

 Cuba, etc 

 North America. — New Brunswick, West Virginia, Utah, Califor- 

 nia, Mexico. 

 Central America. — Cuba and other West Indies. 

 South America. — Trinidad, Peru, Venezuela. 

 Europe. — Caucasia, France, Dalmatia, Italy, Germany. 

 Asia. — Asia Minor, Persia, Euphrates Valley. 

 Africa. — Egypt and other localities. 



North America. — Kentucky, Indian Territory, California, Utah, 



Texas, Athabasca River. 

 Central America. — Mexico and Cuba. 

 South America. — Island of Trinidad, Venezuela. 

 Europe. — Germany, France, Italy, Russia, Austria, etc. 

 Asia. — Asia Minor, Palestine, Persia, China. 

 Africa. — Egypt and other localities. 



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