GEOGEAPHICAL CHANGES DURING PENNSYLVANIAN 155 



well records of West Virginia, but comparisons show quickly that the 

 drillers^ identifications are too often made at haphazard. Away from 

 the southeastern border, pebbles are extremely rare, except along a nar- 

 row rudely east and west strip across Indiana, Armstrong, Butler, Law- 

 rence, and Beaver counties of Pennsylvania. This lies many miles south 

 from the northern outcrop and south frora the similar strip in the Beaver 

 formation ; its variations are such as one finds in the gravels of the upper 

 Ohio river. Many similar valleys filled with standstone during the long 

 subsidence are recognizable in various parts of the area, and occasionally 

 one is found along an anticlinal crest which seems to have been made 

 by subaerial erosion. The sandstones for the most part are indefinite 

 within Ohio, but in Tuscarawas coimty the Lower Mahoning interval is 

 filled with conglomerate and farther south the Buffalo interval is filled 

 with very coarse sandstone at many places. Similar conditions were 

 observed in the Allegheny here. 



While in a general way the conditions were similar to those of the 

 Allegheny, showing a gradually contracting area, yet the subsidence was 

 such as to admit seawater to a much greater space. At the very begin- 

 ning one finds at somewhat widely separated localities in West Virginia 

 a marine fauna in the Uffington shale which rests directly on the Upper 

 Preeport coal bed, while at most exposures the shale yields only impres- 

 sions of land plants. JSTot enough information is available to justify any 

 suggestion respecting the relations of the marine localities, which are 

 confined to the easterly side of the great basin. 



The Brush Creek limestone, separated from the UfSngton shale by the 

 Mahoning interval, is confined in its best development to the northeastern 

 part of the area. It occurs irregularly in northeastern Ohio and is con- 

 tinuous in a not very broad area eastwardly and southeastwardly across 

 Pennsylvania into western Maryland and northeastern part of the West 

 Virginia coal field. It is wanting along the northern border in Pennsyl- 

 vania as well as east from the Alleghenies. ISTo trace of it appears in 

 most of Ohio and it is wanting under the Cowrun anticline, in the central 

 part of the basin; but a limestone at its place is present in the extreme 

 southern part of the area in West Virginia. The fauna is distinctly 

 marine and the distribution of the deposit leads one to look toward the 

 east for its connection with the sea. The Cambridge limestone, on the 

 other hand, represents an invasion by the interior, or Mississippian, sea, 

 for as a marine limestone it prevails from Armstrong county of Pennsyl- 

 vania westward into Ohio and thence southwardly into Kentucky. It is 

 wanting in the interior area, but reaches the middle line of the basin 

 in the southern part of West Virginia, in Cabell and Wa3rne counties, as 



