434 



REPOKT OF NATIONAL MUSEUM, 1899. 



I, Fostoria, Ohio; II, Findlay, Ohio; III, St. Marys, Ohio; IV, Muncie, Indiana; V, Anderson, 

 Indiana; VI, Kokomo, Indiana; VII, Marion, Indiana. 



Natural gas in quantities to be of economic importance is necessarily 

 limited to rocks of no particular horizon. It is not, however, indige- 

 nous to the rocks in which it is now found, but occurs in an overlying 

 more or less porous sand or lime rock into which it has been forced by 

 hydrostatic pressure. The first necessaiy condition for the presence 

 of gas in any locality may indeed be said to depend upon the existence 

 of such a porous rock as may serve as a reservoir to hold it, and also 

 the presence of an impervious overlying strata to prevent its escape. 

 In Pennsylvania the reservoir rock is a sandstone of Carboniferous or 

 Devonian age; in Ohio and Indiana a cavernous dolomitic limestone of 

 Silurian (Trenton) age. 



PETROLEUM. This is the name given to a complex hydrocarbon com- 

 pound, liquid at ordinary temperatures, though varying greatly in vis- 

 cosity, of a black, brown, greenish, or more rarely red or yellow color, 

 and of extremely disagreeable odor. Its specific gravity varies from 

 0.6 to 0.9. Through becoming more and more viscous the material 

 passes into the solid and semisolid forms asphalt and maltha. Chem- 

 ically it is considered as a mixture of the various hydrocarbons included 

 in the marsh gas, ethyline and paraffin series. 



An ultimate analysis of several samples, as given by the reports of 

 the Tenth Census of the United States (1880), showed the following 

 percentages of the three essential constituents: 



Petroleum is limited to no particular geological horizon, but is found 

 in rocks of all ages, from the Lower Silurian to the most recent, its 

 existence in quantities sufficient for economic purposes being depend- 

 ent upon local conditions for its generation and subsequent preserva- 

 tion. Inasmuch as its accumulation in large quantities necessitates a 



