We find by practical experience, as we argue from cause and effect, that no available rock-oil exists in the Eastern basins or the Devonian rocks east of the Allegheny escarp ment, for reasons before stated ; and we find, by the same processes, that but little available petroleum exists in the great regions west of the Ohio and the Mississippi, but less and less in a westward direction : first, because it was never so abundant in the West as in the East ; and second, because the petroleum of the Devonian rocks—its most abundant region, generally—lies too deep below the surface to exist in the state of oil, if it exists at all. The mountain limestone is over one thousand feet thick in the Great Central coal field ; and, therefore, through a great portion of this field the Devonian oil-formation must be from 1000 to 2000 feet below the surface, at which depth the hydro-carbon exists principally in a state of gas.
The Great Central coal-field of Indiana, Kentucky, Illinois, Missouri, Iowa, and other 'Western States, contains but a limited thickness of coal in a few thin seams on their northern and western border, proving that the amount of bitumen which existed on the waters along the borders of this great inland basin was extremely limited : conse quently, we cannot expect to find petroleum to any great extent in the rocks beneath those portions of that field.
In Eastern Kentucky a different result may be expected. There the basins are deep and the coal-seams are numerous and highly bituminous, while the shale is also highly charged with bitumen. The mountain or Carboniferous limestone is not in its usual Western thickness, and the Devonian rocks come nearer to the coal measures. It is also nearer to the volcanic regions of heat, since the coal of Eastern Kentucky is as near the Blue Ridge as that of Northwestern Pennsylvania : hence we may expect a great portion of the Central coal-field in Kentucky, and perhaps in Southern Illinois and Indiana, to be oil-producing territory. In Western Kentucky the same results may be obtained.