464 STEVENSON— THE FORMATION OF COAL BEDS, [^'ov. i, 



become less important in Ohio, where occasionally they contain some 

 small pebbles. 



The Pittsburgh sandstone of H. D. Rogers, the first great inor- 

 ganic deposit of the Monongahela, is separated from the underlying 

 Pittsburgh coal bed by a shale varying much in thickness — often 

 wanting. The distribution and characteristics of this sandstone 

 show that great changes had taken place since the close of the Beaver, 

 even since the close of the Allegheny. The area as it now exists is 

 restricted to the southwest corner of Pennsylvania, a narrow strip 

 of eastern Ohio and north central West ^^irginia. Outliers in syn- 

 clinals at the east as far as the Potomac area of Maryland and West 

 Virginia may be regarded as evidence that the eastern border of the 

 deposit was not more than 75 miles west from the Archcean of 

 Appalachia. 



The horizon is marked by shaly sandstone and sandy shale in the 

 outliers, but when one. going westward, reaches the continuous area 

 in Westmoreland and Fayette of Pennsylvania, he finds commonly a 

 hard massive sandstone, occasionally changing into shaly sandstone. 

 I. C. White has followed this in West Virginia to the Kanawha River 

 and thence along the southern outcrop into Ohio. There, as in Penn- 

 sylvania, the rock is often coarse, at times forms clififs, is feldspathic, 

 seldom pebbly, except at the southwest, and the pebbles are always 

 small. Within little more than a score of miles from the eastern 

 outcrop this rock disappears, permitting, in southern Pennsylvania 

 and adjacent part of West Virginia, the Redstone limestone to rest 

 on the shale overlying the Pittsburgh coal. The change is very 

 abrupt. At Morgantown, W^est A'irginia, this sandstone, 40 feet 

 thick on the east side of the Monongahela River, is absent on the 

 west side and its interval has disappeared from the section. In 

 Pennsylvania, this sandstone extends southwardly from the northern 

 outcrop 60 or 70 miles but it thins westwardly so that in the West 

 Virginia " Panhandle " it is absent. Its continuity along the northern 

 outcrop is broken and a gap of perhaps 25 miles is in the panhandle 

 and Jefferson county of Ohio, but the rock reappears in Harrison 

 county of the latter state, where it is 40 to 70 feet thick. Thence it 

 has 'been followed to southern Ohio, where it is continuous with the 

 southern border as determined by I. C. White in West Mrginia. 



