744 ABSTRACTS OF PAPERS 



Discussion of the Preceding Three Papers 



Dr. J. M. Clarke referred to the contiiiiioiis presence of Devono-Carbonifer- 

 ous continental deposits on all the eastern frontage of the Appalachians, espe- 

 cially to the delta work presumably of the Saint Lawrence River, represented 

 by the Bonaventure formations of the Gulf of Saint Lawrence. 



Dr. David White : The Pocono formation is essentially a unit though 

 erosionally disconnected in its extension from southwest Virginia to the 

 Mauch Chunk region of Pennsylvania. Along its easternmost belt it consists 

 of well washed and comparatively regular gray grits and sandstones, with 

 interbedded shales and coals. The character and extent of the sandstones 

 suggest coastwise distribution and differentiation of the material. The pres- 

 ence of coals, which throughout the greater part of the eastern border of the 

 existing Pocono zone are nearly if not quite of workable thickness, and the 

 occurrence, at many points at least, of roots in their place of growth in the 

 underclays, demonstrate extreme shallowness of water cover at the time of 

 deposition of the coals. The relative narrowness of the longitudinal zone of 

 typical Pocono sandstones and coals points either to the existence of an 

 estuary extending from the Tennessee region northward along the Appa- 

 lachian trough at this stage of the earliest Mississippian or to the presence of 

 barriers separating and essentially isolating narrow and shallow eastern 

 basins from the broader marine expansion on the west. In the former case 

 the narrow estuary, which seems more probable, was the starting point for 

 an extensive northwestward transgression, with the early development of 

 marine conditions. The rapid thickening of the beds toward the east (shore- 

 ward) and the increase of coarse detrital matter in the same direction har- 

 monize with the recognized existence of drainage from the eastern land out 

 into the basin. The latter, as sho^^^l by the coal deposition, included a broad 

 filled zone standing at times at or above sealevel. It is probable, however, 

 that the areas of actual Pocono "delta"' are now obliterated by erosion. 



Throughout most of the region or zone of tji^ical Pocono sedimentation 

 marine fossils have not been found. An exception is the Broad Top field, 

 where brachiopods and other marine mollusks occur in the lower part of the 

 formation, which there maintains a thickness of over 1,000 feet, though the 

 formation is very much reduced at the Allegheny front 



There is no evidence that the Mississippian sea was at any time deep in 

 the Appalachian trough, a feature already pointed out by Ulrich. The pres- 

 ence of conglomerates, of old soils, breccias, and land plant remains at various 

 horizons in different areas of the post-Pocono Mississippian, indicates a num- 

 ber of intervals and regions of exposure of portions, at least, of the trough. 

 These episodes will no doubt eventually be fitted into a somewhat complicated, 

 though very interesting, history of the Appalachian trough during Mississip- 

 pian time. 



Dr. G. W. Stosp : In discussing Mr. Branson's paper, I wish to refer to the 

 occurrence of the Price sandstone in the Abingdon quadrangle, Virginia, some 

 30 miles to the southwest. There the Price has a rather uniform thickness 

 of al>out ()00 feet for 50 miles along the strike, showing no thickening due to 

 deltas. There is a marine Mississippian fauna in the upi>er half of the for- 



