16 GEOLOGY OP OHIO. 



large and hitherto unknown Placoderms have been procured from the 

 Huron shale within the last year. These are too imperfect for descrip- 

 tion, but they indicate the existence of a varied ichthyic fauna in the 

 Huron epoch, and afford reason for expecting that J;he Huron shale will 

 yet contribute largely to our knowledge of the life of the Devonian age. 



It will be remembered by those who have read the first volume of this 

 report, that the Huron shale is regarded by the writer as the most impor- 

 tant source of supply of petroleum in this country, and also that the 

 greater part of the ^as-wells of Ohio and Pennsylvania derive their flow 

 of carburetted hydrogen from this formation. The arguments in favor 

 of this view are briefly stated in Volume I, Geology, (page 158, et seq.,} and 

 inost geologists have accepted them as affording a rational and satisfac- 

 tory explanation of the problem of the origin of petroleum. There are 

 some, however, who still cling to the theory that the petroleum and gas 

 which fill the cavities and interstices of the sandstones and conglom- 

 erates in the Oil Creek region, are indigenous in these rocks. This 

 hypothesis is certainly untenable. Sandstones and conglomerates are 

 made up almost altogether of comminuted quartz, which could contribute 

 nothing to the formation of hydrocarbons. All chemists agree that these 

 are of organic origin, and must have emanated from some source foreign 

 to the sandstones, and that these latter can only act as reservoirs to hold 

 them, or as channels through which they flow. 



That the hydrocarbons have not descended to saturate the sandstones is 

 certain, as they are always thrown upward by hydrostatic pressure, and 

 are, in fact, found working to the surface everywhere. They must, there- 

 fore, have risen from some source beneath to fill the reservoirs that hold 

 them. The organic sediments which underlie the oil-bearing sandstones 

 in Ohio and Pennsylvania are bituminous shales and limestones. In 

 making a choice between these, as the possible source of oil and gas, the 

 following facts deserve consideration, some of which have been already 

 noticed : 



1. No rock can furnish that which it does not contain, and none of 

 the limestones that underlie the oil regions of Ohio and Pennsylvania 

 hold more than one or two per cent, of organic matter. They are, there- 

 fore, entirely inadequate to supply the enormous flow of hydrocarbons 

 which has continued through ages past and will continue through ages 

 to come. In the argillaceous shales, sandstones, and conglomerates, the 

 amount of organic matter is even less than in the limestones ; hence the 

 theory that they can furnish petroleum or carburetted hydrogen in any 

 quantity is untenable. 



