GEOGEAPHICAL CHANGES DURING PENNSYLVANIAN 149 



any locality west from the Kanawha, but Doctor White discoTered an 

 abundant marine fauna in shales associated with the Eagle limestone. 



For the most part fresh-water conditions prevailed during the early 

 part of the Beaver, and one may regard the marine forms found near 

 the bottom of the formation on the east side as due to communication 

 there with the Atlantic. At a much later time, however, subsidence on 

 the westerly side admitted seawater to the broad valley on that side; so 

 that in Ohio one finds extending southwestwardly from Mercer county 

 of Pennsylvania to Perry county of Ohio the important Mercer lime- 

 stones, extending farther eastward than does the Sharon sandstone, but 

 apparently not so far west. As shown by Mr Eead's * descriptions and 

 as figured in one of his diagrams, the Ohio valleys were not filled l)y 

 deposits until after the Mercer limestones had been formed. As the 

 deep, broad valley in which the Eoclicastle beds and the Mercer lime- 

 stones were deposited was for the most part west from the present area 

 of Coal Measures, the limestones can not be traced beyond Perry county, 

 where the Lower Mercer is very thick at its western outcrop. These lime- 

 stones carry a typically marine fauna. 



The sandstones of the Beaver are the Connoquenessing and the Home- 

 wood. These can not be recognized farther south than northern Ten- 

 nessee. Along the eastern outcrop they are sandstones, with few pebbles 

 northward to northern West Virginia, beyond which into the Northern 

 Anthracite field they are pebbly and at times largely conglomerate. On 

 the western side they are sandstone, often shale, until near the last ex- 

 posures at the north, where they sometimes contain pebbles. The one 

 exception on the west side is in Knox county of Ohio, where one is on 

 the extreme western outcrop. In the deeply buried interior area more 

 or less sandstone is present at one or other of the intervals in nearly every 

 boring, though there is great variation and very many borings show little 

 aside from shale; but in an irregular east and west strip crossing Clear- 

 field, Jefferson, Clarion, and Mercer counties of Pennsylvania, at a con- 

 siderable distance south from the northern outcrop, one finds the Home- 

 wood sandstone coarse and at times coarsely conglomerate. The Home- 

 wood is pebbly also along a line extending from southern Payette of 

 Pennsylvania to the eastern outcrop in Maryland, as though a valley had 

 existed there. The strip farther north evidently marks a river valley, 

 but the source of the pebbles is difficult to determine. The distribution 

 of the sandstones shows that the elevation continued on the east side, 

 strongly at the north, but less and less strongly toward the south, while 

 the pebbly rocks of Knox as well as of Summit and Portage, on the 



* M. C. Read : Geology of Ohio, vol. iii, p. 544. 



