178 J. J. STEVENSON CAEBONIFEROUS OF APPALACHIAN BASIN 



that this arbitrary boundary does not coincide with the paleontologic 

 boundary, which is lower, 100 feet or more; he would include in the 

 Allegheny a small coal bed, 73 feet below the Buck Mountain at Potts- 

 ville, and would carry the boundary downward to a still undetermined 

 line between that coal bed and the plant horizon at 210 feet below the 

 Buck Mountain. The flora of the Twin or Buck Mountain coal bed is 

 comparable to that of the Clarion group in western Pennsylvania. 



Table oi? Foemations 



Later information, as well as better knowledge of the relations ob- 

 tained during the progress of this work, makes necessary some revision 

 of the nomenclature employed. 



No change is suggested for the Mississippian (A. Winchell, 1870). or 

 Lower Carboniferous, and the terms, Logan, Tuscumbia, Maxville, and 

 Shenango are retained ; but paleontological studies, of which preliminary 

 results have been published, seem to make clear that the writer has 

 included under the Logan some deposits which may be of earlier age. 

 The observations on which dependence was placed for connection around 

 the northwestern and western outcrop in Pennsylvania and Ohio appear 

 to be defective. There is apparently no room for doubt in the great 

 part of the basin, for the vast number of oil-well records in southwestern 

 Pennsylvania 'and in West Virginia make abundantly evident that the 

 great oil-bearing sandstone is essentially continuous throughout and the 

 same with that which both Andrews and Orton term Logan in south- 

 eastern Ohio. 



But a new grouping for the Pennsylvanian or Upper Carboniferous 

 seems to be required, in view of conditions described under the caption 

 of Geographical changes. It is presented in the following table : 



Pennsylvanian 

 (H. S. Williams) 



Pottsville (J. P. Lesley) 

 Athens (J. J. Stevenson) 



Wheeling (.J. J. Stevenson)^ 



Duukard (I. C. White, re- 

 stricted by J. J. Stevenson ) 



r Rockcastle ( A. R. Crandal 1 ) 

 Beaver (J. P. Lesley) 

 Allegheny (H. D. Rogers, 



restricted by F. Piatt) 

 Conemaugh (F. Piatt) 

 Mouongahela (H.D.Rogers, 

 restricted by I. C. White) 

 Washington ( J.J.Stevenson) 

 Greene (H. D. Rogers, re- 

 stricted by J . J. Stevenson ) 



The term "Athens" refers to the county of that name in Ohio, and 

 "Wheeling" to the stream which flows through the western portions of 

 Greene and Washington counties of Pennsylvania, Marshall and Ohio 

 counties of West Virginia, localities in which the respective columns 

 are shown in their full extent. 



