PRINCIPLES OF STRATIGEAPHIC CORRELATIONS 567 



Tennessee, central Virginia, and the Maryland basins, providing, of 

 course, that only the maximum development of the group in each basin 

 is compared. There are troughs in each basin, especially in the east half 

 of the valley between Staunton, Virginia, and Piedmont, Alabama, in 

 which the Stones Kiver is either entirely absent or but poorly developed. 

 Southwest of Piedmont, as at Pelham, a stronger representation of the 

 group is found. At and to the south of Pelham it is underlain by 500 

 feet to 1,000 feet of Canadian limestone, while over it are several hundred 

 feet of more or less argillaceous limestone that reminds strongly of the 

 upper members of the Chambersburg limestone in southern Pennsylvania. 

 Incidentally it may be stated that the sequence at Pelham, Alabama, in- 

 cluding the Stones Kiver and the Canadian limestones, is in closer accord 

 with the corresponding sequence in the Chambersburg-Strasburg belt 

 (see page 321) than any section in the intermediate areas. 



Following the Stones Eiver, Blount (upper Chazyan), sedimentation set 

 in and doubtless continued through a longer time in the Knoxville and 

 Athens troughs in the Tennessee basin than anywhere else in the Appa- 

 lachian Valley. This was succeeded by the Black Eiver epoch, in which 

 the area of maximum deposition was shifted northward to the Newman 

 trough. Toward the close of the epoch, however, it was moved to the 

 Chambersburg trough in southern Pennsylvania. In the Trenton epoch 

 central Pennsylvania has perhaps as good a right to claim the area of max- 

 imum limestone deposition as east Tennessee. The best development ob- 

 served in the latter State occurs on the west slope of Clinch Mountain, 

 where it begins with the upper Moccasin. In Pennsylvania the equivalent 

 of the Moccasin, which is older than the base of the Trenton at Trenton 

 Falls, New York, is well developed at Eeedsville. Here, however, the 

 greater part of the succeeding Trenton consists of shale. The most com- 

 plete post-Moccasin Trenton section observed to date is found at Belle- 

 fonte. Between the Eeedsville and the Bellefonte sections the aggregate 

 of Trenton limestone deposition in central Pennsylvania rises to some- 

 thing like 1,000 feet, which is little if any inferior to the aggregate for 

 this epoch in east Tennessee. 



In the beginning of the Cincinnatian stage — that is, in the Utica age — 

 sedimentation took place in New York and probably also in the St. 

 Lawrence Valley. Whether any part of the Appalachian Valley was sub- 

 merged at this time can not be decided positively at this time. In my 

 opinion, the presence of deposits of Utica age in this valley is highly 

 probable only in the Maryland basin. Later Eden deposits, however, are 

 confidently recognized throughout the length of the valley. They seem 



