1912.] STEVENSON— THE FORMATION OF COAL BEDS. 501 



state of knowledge. Where plant-bearing, this shale resembles the 

 ordinary roof shale, but where carrying remains of animals it is 

 black, somewhat sandy and occasionally somewhat fetid. It recalls 

 conditions described by A. Agassiz as existing in the Pacific ocean 

 between IMexico and the Galapagos islands. 



The Uffington shale was followed by the often coarse and 

 massive Mahoning sandstone, containing one or more coal beds of 

 considerable extent, and that in turn was succeeded by a coal bed 

 underlying the Brush Creek limestone of I. C. White, the Black 

 Fossiliferous limestone of the early Pennsylvania reports. This 

 dark, almost black rock, enclosed in black shales, is the first lime- 

 stone which crossed the bituminous region and reached the line of 

 the Allegheny Mountains — it is recognized without doubt in western 

 Maryland. The deposit is wanting along practically the whole 

 eastern outcrop in West Virginia and most probably throughout the 

 interior of that state, for it has not been found under the great 

 anticline in Wirt county and black shale, at this horizon, is not re- 

 corded by the drillers of oil wells. It is persistent in western 

 Pennsylvania, which it enters from Preston county of Virginia and 

 Garrett of Maryland. The area, narrow at first, widens to 15 or 

 20 miles farther north and retains that width to the Ohio line. 

 Thence it is present for 40 or 50 miles southwestward into Jefifer- 

 son county of Ohio, beyond which it seems to be wanting for about 

 30 miles. But it reappears and is followed easily into Muskingum 

 county, beyond which no trace exists, the horizon being exposed at 

 very many places. The gap beyond Jefferson county is evidently 

 due to erosion, but there is no reason to suppose that the limestone 

 ever existed south from Muskingum county. The limestone and 

 shales are crowded with a marine fauna and the conditions indicate 

 that it was deposited in an estuary opening at the east.^® 



The Cambridge limestone of E. B. Andrews is at a little distance 

 higher in the Conemaugh column. A marine limestone, very near 

 this horizon, is in western Maryland, but that locality is more than 

 75 miles east from the nearest outcrop of the Cambridge; its rela- 



^ For the observations by Martin, I. C. White, Newberry, Stevenson, 

 and Orton, see " Carboniferous," etc., as above, pp. 167-189. 



