1875.1 103 [Rogers. 



wholly absent from the shorter valleys, and also to determine to what 

 extent the general deposit is continued from valley to valley over the 

 intermediate higher grounds. 



Although from the facts thus far observed, it would seem that the 

 transporting agency by which these deposits were accumulated was 

 chiefly or wholly operative in the lines of the river valleys, the great 

 height to which, as before stated, the deposit reaches, shows that the 

 relative level of the water, or probably ice, concerned in the trans- 

 portation, must have been much above the water level as it now 

 exists, and that the then actual river valleys were of correspondingly 

 greater width. The distances over which the fragments of Appala- 

 chian rocks found in these surface deposits have been carried, may 

 be judged from the following facts. 



The distance from Richmond, in a straight line to the nearest out- 

 crop of the Primal or Potsdam sandstone west of the Blue Ridge, is 

 about eighty miles; that following the course of the James River is 

 one hundred and sixty miles; the distance from Washington to the 

 western side of the Blue Ridge in a straight line is about forty miles; 

 that along the Potomac River between fifty and sixty miles. 



What relation this deposit bears to the drift of the more northern 

 regions as to the manner and time of its production, is a question of 

 great interest. The materials of the deposit are distinctly stratified, 

 and the fragments, instead of being angular, as so common in the 

 drift proper, are well rounded and smooth. Nor has there been thus 

 far observed, any case of that striation of surface which is so fre- 

 quently met with in the larger fragments of the northern drift- 

 Tracing the formation, however, as it shows itself successively at 

 Richmond, Washington, and other localities still further northward, 

 the stratification becomes less perfect, and the coarser materials are 

 more scattered through the mass, and after crossing the Delaware the 

 whole deposit cannot be distinguished from the material considered 

 in that region as a modified drift. 



Speculating on the causes by which these deposits have been 

 formed, it may, on the one hand, be imagined that during the glacial 

 period the icy covering of the north and west prolonged itself in the 

 valleys of the great rivers, as far south as the James, and even the 

 Roanoke River, bringing down to the belt of land now marking the 

 limit of tide water, debris from the Appalachian rocks, mingled with 

 materials derived from the intervening region, and that the grinding 

 and sorting action of the waters subsequently obliterated glacial 



