INTERPRETATION OF ENVIRONMENTAL CONDITIONS 205 



again much farther west than in the intervening counties. This sandstone 

 becomes more and more indefinite from all sides toward the interior of the basin. 

 The Sewickley sandstone, underlying the Upper Sewickley coal bed, is fairly 

 persistent on the east side, but is wholly insignificant in Ohio. There, however, 

 an important sandstone overlies the upper Sewickley, not pebbly at the north- 

 west, but coarse and often pebbly in southern Ohio. In Pennsylvania and 

 northern Ohio a more or less persistent sandstone, the Uniontown, overlies the 

 Uniontown coal bed, but ordinarily it is unimportant and many sections show 

 little aside from shale in the interval. In West Virginia, however, a strip of 

 coarse conglomerate, evidently at this horizon, crosses the State from east to 

 west, passing through Lewis, Gilmer, Doddridge, Tyler, and Pleasants Counties 

 and extending into Washington, Morgan, and Athens of Ohio, where it is the 200- 

 foot conglomerate of Professor Andrews. It is coarser in West Virginia than in 

 Ohio. The strip is very narrow in the former State and fine-grained rocks 

 replace the coarse material at a short distance north and south ; but in Ohio the 

 area is broader, as though additional material had been brought in from that side. 

 This east-and-west line of coarse rock recalls those of the Beaver and Conemaugh 

 in Pennsylvania and may be explained in the same way. The general distribu- 

 tion of coarse material indicates a rising borderland and for the southwest a 

 notable encroachment. 



"The limestone [varies] greatly in composition. The Redstone is an impure 

 limestone, yielding a fair lime when burned carefully; the Fishpot, when thin, 

 usually resembles the Redstone, but when thick it is apt to contain some layers 

 of cement rock; the Benwood has several beds of hydraulic limestone, even of 

 cement rock, among its most persistent members, while some of the beds are so 

 impure as to break into small angular fragments after continued exposure; the 

 Uniontown and Waynesburg are rarely more than slightly magnesian. 



"Of the numerous limestones, only the Uniontown can be regarded as really 

 persistent; it is present in western Pennsylvania and in Ohio at nearly every 

 locality where its place is shown. The others may be regarded as confined to 

 southwest Pennsylvania, the West Virginia Panhandle, and the immediately 

 adjacent part of Ohio. Their great development is between the Monongahela 

 River at the east and the Ohio River at the west, where in considerable areas 

 limestone and calcareous shale fill more than one-half of the interval between the 

 Redstone and Uniontown coal beds. In all directions from this small area the 

 limestone diminishes quickly and is replaced by shale and sandstone; toward the 

 southwest only some thin streaks remain in West Virginia, and in some portions 

 of that State those streaks seem to be replaced by red shale. 



"These limestones are spoken of commonly as merely calcareous muds, and 

 that explanation of their origin was accepted tentatively on a preceding page. 

 But it is insufficient" [Mr. Stevenson regards the origin of the limestones as an 

 unsolved problem.] 



"Toward the close of the Monongahela the condition marking the later portion 

 of the Conemaugh was reached once more. In by far the greater part of the 

 area the deposits are fine in grain, and at the end the Waynesburg coal bed was 

 formed, in the northern part of the basin, a bed of curiously multiple structure, 

 which is retained. Like the Pittsburgh, it is wanting in the interior region, but 

 it seems to have reached irregularly southward to a long distance on each side. 



"The Washington opens with a plant-bearing shale like that overlying the 

 Pittsburgh, succeeded by a great sandstone, recalling in some respects the sand- 



