292 SKETCHES OF CREATION. 



Genesee shale. This bed of gravel is the reservoir, and 

 becomes charged with a supply of thick petroleum called 

 "surface oil." Some wells have yielded thousands of bar- 

 rels of surface oil. It may be necessary to add that in 

 some portions of Enniskillen the Genesee shale has been 

 removed, and the surface wells are evidently supplied from 

 the lower Marcellus shale, which also stocks the crevices 

 of the Hamilton limestones. In Venango County, Pennsyl- 

 vania, and Trumbull, and Knox, and contiguous counties in 

 Ohio, the Genesee shale is overlaid by porous sandstones 

 which serve as reservoirs of the oil. In the Glasgow re- 

 gion of Southern Kentucky, the formation overlying the 

 Genesee shale is the Mountain limestone; but this is in 

 places arenaceous, and in others vesicular and cavernous, 

 and thus furnishes the requisite conditions of oil-accumula- 

 tion. In one instance at least, in that region, the Genesee 

 shale itself affords the reservoir for the storage of its pro- 

 ductions. In West Virginia the oil seems to accumulate 

 in the conglomerate at the base of the Coal-measures. The 

 same is the case in Southwestern Pennsylvania, Southeast- 

 ern Ohio, and Northeastern Kentucky. The reservoir in 

 the Burkesville region of Southern Kentucky is found in 

 the shattered shaly limestones of the Cincinnati group. 

 These are reproduced in physical characters in the shat- 

 tered shaly limestones of the Hamilton group, which serve 

 as the place of deposit of the oils of Ontario. 



I close this sketch of the geological phenomena of petro- 

 leum by presenting a synopsis of oil regions and the for- 

 mations tributary to their supplies. 



I. The black shales of the Cincinnati group afford oil which 

 accumulates (l) in the fissured shaly limestones of the same 

 group, and supplies (A) the Burkesville region of Southern 

 Kentucky, and (B) Manitoulin Island in Lake Huron. 



H. The Marcellus shale affords most of the petroleum 



