Appalachian Geosyncline. 245 



miles northwest.* The delta in Maryland and southern Penn- 

 sylvania grew, therefore, from the southeast against and 

 past the zone of maximum depression. From the south- 

 east, consequently, the sediment was brought and in great 

 volume. The appearance of the subaerial conditions first in 

 eastern New York is adequately accounted for, first, by the 

 more rapid subsidence of the basin in Pennsylvania ; and 

 second, the subsequent erosion there of its whole southeastern 

 side, where terrestrial deposition must have prevailed before 

 it reached the middle of the basin. After the subaerial condi- 

 tions became established in eastern Pennsylvania as far as .the 

 region of greatest thickness the advance of the shore line was 

 northwestward, contrasting with the initial western advance in 

 New York. 



The gradation in the coarseness of the sediments agrees with 

 the indications of the shore lines. It is the eastern outlier 

 which shows the only striking conglomerates. In the main 

 areas the gray sandstones with fine-grained conglomerates dom- 

 inate on the eastern side of the southern anthracite basin, 

 far removed from the region of the Catskill Mountains. In 

 Maryland the eastern outcrops show a less arenaceous nature 

 than do the eastern outcrops in central Pennsylvania, but on 

 the strike of the later folding they correspond to a more 

 western part of the formation in Pennsylvania. A wider 

 eastern zone may therefore have been eroded in Maryland, 

 following the Permian folding. The sediment did not how- 

 ever come from the region of the present Southern Appa- 

 lachians, since marine conditions prevailed longest in the south, 

 the Catskill disappears in Virginia, and in Tennessee the Upper 

 Devonian is represented merely by a thin black shale. In 

 general the Paleozoic sediments of the Appalachian geosyn- 

 cline do not show transportation along its axis from the north 

 or south, but transference into it from a land parallel with it. 

 The axis of upwarp and that of downwarp seem in fact to have 

 been genetically related, as is so commonly the case in the 

 present mountain chains. 



The indications given by the directions of delta growth, 

 thickness of the Catskill beds, and the gradations in their 

 texture, are, therefore, that the sediment was brought in along 

 the whole front of the geosyncline by more than one river and 

 from the southeast as well as the east and possibly northeast. 

 The result was a confluent piedmont plain and delta front 

 building out a terrestrial coastal plain. More detailed study 

 may be able to locate the several centers of principal delta 

 growth. 



* Stose and Schwartz, U. S. Geol. Surv., Folio 179, pp. 12, 13, 1912. 



