191-'.] STEVENSON— THE FORMATION OF COAL BEDS. 457 



cases, sandstones, due to filling of valleys and occupying restricted 

 areas, may be misleading. Yet examination of broad areas proves 

 that many sandstones are of great geographical extent, though often 

 interrupted and sometimes assuming the form of immense lentils 

 embedded in shale. In a general way, one may consider the varia- 

 tions as alike in all ; at one locality, the mass may be fine, coarse or 

 even pebbly to conglomerate in its different layers ; at another, it may 

 be wholly fine, coarse or pebbly ; while at a third, it may be repre- 

 sented by more or less argillaceous shale. It may be massive, irregu- 

 larly bedded or shaly and the change in structure or composition 

 may be abrupt or almost imperceptible. There would appear to be 

 no system in these variations; yet it may prove worth the pains to 

 seek some explanation of the conditions, for though the quest may 

 fail of complete success, one is likely to gather suggestions by the 

 way, which may prove of service in other directions. Four sand- 

 stones have been selected for study: Bonair of the New River, 

 Homewood of the Beaver, Pittsburgh of the Monongahela and 

 Waynesburg of the Washington. But in considering these, one 

 must make comparison with others. 



The Bonair sandstone of M. R. Campbell, midway in the New 

 River formation, can be followed from its northern termination in 

 West Virginia, along the eastern outcrop, and from northern Ten- 

 nessee, on the western, almost continuously into the southeastern 

 basins of Alabama. The eastern and western prongs on the sides of 

 Alleghania unite across that old ridge in central Tennessee, whence 

 the rock spreads as a sheet throughout the coal area of southern 

 Tennessee and of Alabama. The northern limit on the western side, 

 in the Ohio basin of Schuchert, is very near the northern line of 

 Tennessee where it is without pebbles ; but within less than 20 miles 

 southward it becomes notably a pebble rock; at 12 miles east from 

 the latter place it is described as 55 feet of " conglomerate and sand 

 stone " and a similar description is given for a section at 25 miles 

 south from the last ; but at 25 miles south-southwest, the Bonair is 

 a mass of conglomerate with shale, and the rock is still coarser at 

 a few miles southeast, on the eastern outcrop near the Alabama line. 

 At a few places, the western outcrop swings several miles toward 

 the west, approaching the border of deposit, and shows another type 



