88 J. J. STEVENSON — LOWER CARBONIFEROUS, APPALACHIAN BASIN 



vonian. The deposits are in contrast with those of the Chemung and 

 Catskill ; at the east they are for the most part sands, often very clean, 

 at times coarsely conglomerate. The lowest bed is conglomerate, most 

 markedly so along the easterly outcrops, but more or less so at localities 

 in western Pennsylvania and northern West Virginia. The transition 

 from the Catskill is abrupt but not absolute, for red beds occur at man}^ 

 localities in eastern Pennsylvania, while in the north central part of 

 that state green is the characteristic color of many sandstone beds. The 

 material grows finer westward, the thickness varying slightly beyond 

 the Alleghenies, and in northwestern Pennsylvania thin calcareous beds 

 make their appearance, one of which may have been persistent south- 

 ward in West Virginia. 



Throughout the Chemung and Catskill the land must have been sub- 

 siding at the east; the streams were approaching nearly to baselevel 

 and only fine material was brought down. Two interruptions occurred, 

 during which were formed the Chemung conglomerates. 



The extreme subsidence had been reached in New York as earl}^ 

 as the beginning of the Chemung, and the streams brought down mud 

 and fine sand, in great part containing so much iron as to be colored 

 red or green. As the subsidence of the mainland became marked 

 farther and farther south, the red and green beds covered a greater area, 

 and in the Catskill one finds those beds to the southern limit of the 

 formation. It is worth}^ of note that the Amnigenia catskillensis, which 

 in the Catskill Mountain region began its existence in the lower Che- 

 mung, graduall}' moved southward, so that before the close of the 

 Catskill it had reached the southern border of Pennsylvania. As the 

 change in Chemung rocks had become complete at the end of that 

 period, one may imagine that some relation may have existed between 

 the great sinking of the Appalachian land and the elevation of land on 

 the western side, by which the Catskill trough was narrowed. 



The Catskill was closed by an elevation in the Appalachian region, 

 rendering the streams more or less torrential, so that the last period of 

 the Devonian was opened by the deposit of coarse rocks. Answering to 

 the eastern elevation was the western depression, so that the subsidence 

 and amount of deposit was almost as great in Ohio and Kentucky as in 

 Pennsylvania and the most of Virginia. Southward the subsidence con- 

 tinued far beyond the limits of the Catskill and possibly beyond that of 

 the Chemung. 



As already stated, the Catskill may have been almost landlocked. 

 The absence of salt in the beds, which otherwise recall in many ways 

 the Salina of New York, and the almost total absence of marine life 

 seem to suggest that during the greater part of the Catskill sentimenta- 



