of the Ohio Coal-measures. 



199 



Clarion (Parker) coal. 



Thin sandstones at top with drab 

 argillaceous shales below. In 

 some localities there is a coal 

 seam 1 8' above the Bluebaugh coal. 



Brookville (Bluebaugh) coal. In the 

 thickest deposit 16" of shale 

 occurs, 1' below the top of the 

 coal. 



Homewood sandstone.* 



The Maryland Geological Survey fully accepted the modern 

 ruling that the name of a formation should refer to some locality 

 at which the rocks are well exposed. For this reason the time- 

 honored names of Rogers as Lower Productive Measures, etc., 

 which referred to the presence or absence of workable seams of 

 coal, were abandoned, and the names Allegheny, Conemaugh, 

 Monongahela and Dunkard were adopted. With the excep- 

 tion of Dunkard these are the oldest names, derived from geo- 

 graphical terms, proposed for the formations. In regard to the 

 Upper Barren Measures it was thought better to consider them 

 as one formation, hence the name Dunkard of Dr. White, 

 dropping the words " Creek series " as he originally published 

 it, was used instead of the two earlier terms of Prof. Stevenson. 



The names proposed by Messrs Darton and Taff were not 

 used because it was considered that the Pogers-Platt classifica- 

 tion, which also had priority, was a more satisfactory one. 



In our review of the Coal-measure formations of Ohio we 

 have shown that in the final classification their limits corre- 

 spond to those of Pennsylvania, and, therefore, it is proposed 

 that the names recently adopted for them by the Maryland 

 Geological Survey be used for the same formations in Ohio. 

 This will involve the following changes in the nomenclature 

 of the Ohio formations : 



Proposed names. 

 Dunkard formation. 

 Monongahela formation. 

 Conemaugh formation. 

 Allegheny formation. 



Present names. 

 Upper Barren Coal Measures 

 Upper Productive Coal Measures 

 Lower Barren Coal Measures 

 Lower Productive Coal Measures 



Columbus, 0., December, 1900. 



* This section of the Georges Creek valley is published with the permission of 

 Dr. Wm. Bullock Clark, State Geologist of Maryland. 



Some information concerning the lower part of the formation was obtained 

 from Prof. James Hall's report regarding the north fork of Jenning's run as 

 abstracted in Macfarlane's Coal-regions of America, 3d ed., 1877, p. 256. 



