POTTS VILLE FORMATION 219 



found at the base of the Pottsville formation. It is considered to repre- 

 sent the Sharon conglomerate because of its position conformably below 

 the Sharon coal. 



Sharon coal (3). — Good exposures of the strata at the base of the Potts- 

 ville are found one mile below Westernport, Allegany county, and in 

 the gorge of the Youghiogheny river, below Swallow falls, Garrett county. 

 At each of these localities there are beds of coal in a series of shales which 

 lie between the sandstone above mentioned and a much thicker and 

 more massive overlying sandstone. Both from the stratigraphic posi- 

 tion and from the evidence* of the abundant fossil plants, these beds 

 are regarded as the equivalent of the Sharon Coal group. 



Loioer Connoquenessing sandstone (4). — Overlying the shales of the 

 Sharon group is a mass of very coarse, thick-bedded, white sandstone, 

 which from its position is evidently the equivalent of the Lower Conno- 

 quenessing sandstone of Lawrence county, Pennsylvania. 



Quakertoivn coal (5). — Near the top of the Lower Connoquenessing 

 sandstone and overlain by a similar thick-bedded sandstone is a coal 

 seam which corresponds in stratigraphic position to the Quakertown coal 

 of Quakertown, Pennsylvania. The seam named the Bloomington coal f 

 was assigned to a stratigraphic position corresponding to that of the 

 Quakertown coal ; but under this appellation were also included at a 

 few points coals that are now known to belong to the Mount Savage and 

 the Clarion seams. 



Upper Connoquenessing sandstone (6). — Overlying the Quakertown coal 

 is a coarse white sandstone about 75 feet in thickness, which corresponds 

 to the Upper Connoquenessing sandstone described by Dr I. C. White, 

 from Lawrence county, Pennsylvania. 



Lower Mercer coal (7). — A very short distance above the top of the 

 Upper Connoquenessing sandstone is a thin coal, which corresponds in its 

 position with reference to the underlying and overlying beds to the 

 Lower Mercer coal of western Pennsylvania. 



Mount Savage fire-clay (8). — Above the Lower Mercer coal, or on top of 

 the Connoquenessing sandstone when that coal is absent, is the Mount 

 Savage fire-clay, so named from its typical development near the town 

 of Mount Savage, Allegany county, Maryland. The bed consists of a 

 mass of soft gray shale from 5 to 12 feet in thickness, which softens 

 readily, on exposure to the weather, to a plastic, very refractory clay. 

 As nodules in this mass, or replacing part or all of it, is the flint-clay, 

 which differs from the plastic clay in not becoming plastic either by 



* Mr David White, after an examination of the fossils, has informed the authors that he con- 

 siders them to belong to the horizon of the Sharon coal. 

 fThe Physical Features of Allegany County, pp. 115, 170. 



