630 M. L. FULLER APPALACHIAN OIL FIELD 



In northern West Virginia substantially the same series and intervals 

 are found as in Pennsylvania, but in southern West Virginia the thick- 

 nesses have changed considerably. The Pottsville sandstones and Green- 

 brier limestone have each tliickened to several hundred feet, while the 

 Pocono has largely disappeared and the Devonian shales have probably 

 decreased in thickness from 4,000 to about 2,000 feet. In Kentucky the 

 equivalent of the Pottsville has further increased in thickness, being about 

 1,000 feet thick, as compared to 150 feet in northern Pennsylvania, while 

 the Devonian has thinned down to an insignificant 150 feet. In Ten- 

 nessee there is a still further thickening of the higher Carboniferous beds, 

 while the Pocono disappears and the Devonian thins to 50 feet. In the 

 Warrior coal field of Alabama, lying west of the outermost strong fold, 

 the Pottsville is 2,500 feet thick, while the Pocono is always, and the De- 

 vonian commonly, missing. 



The foregoing statements of thicknesses apply to the beds of the basin 

 lying to the west of the strongly folded area of the Appalachians in which 

 the productive oil pools occur. The thicknesses in the mountains are 

 quite different, the formations usually being much more strongly devel- 

 oped in the latter area. 



The Devonian shales thin rapidly to the west as well as to the south. 

 In southeastern Ohio their thickness has decreased to 3,000 feet, while in 

 the central Ohio oil pools the Devonian representative, the Bedford shale, 

 is only about 2,000 feet thick. 



The accompanying table shows the comparative stratigraphic columns 

 of the Carboniferous and Devonian series in various States, as compiled 

 from publications of the • United States Geological Survey and other 

 sources.^^ The Silurian probably occurs at a depth of 8,000 to 8,500 feet 

 in southwestern Pennsylvania and northern West Virginia, with the 

 Trenton limestone of the Ordovician about 1,500 feet deeper. Neither 

 are within the present limits of drilling. In Kentucky and Tennessee 

 both are within reach of the drill in the western portion of the basin and 

 along the flanks of the Cincinnati anticline, where they reach a thickness 

 of several thousand feet. In Alabama the Silurian has largely disap- 

 peared, but the Ordovician still has a thickness of 1,000 feet. 



OIL HORIZONS 



General discussion. — In the Appalachian province the range of oil and 

 gas horizons is almost coextensive with the geological column. Oil occurs 



11 See Folios of U. S. Geol. Survey as follows: Rogersville (Pa.), No. 146; Buckhan- 

 non (W. Va.), No, 34; London (Ky.). No. 47; Briceville (Tenn.), No. 33, and Birming- 

 ham (Ala.), No. 175. 



