AMERICAN" GEOLOGY DECADE OF 1860-1869. 513 



Lakes was flooded with fresh water, forming- a vast inland sea, in 

 which the laminated blue clays, the "oldest of our drift deposits," 

 were precipitated. Subsequent to this deposit of blue clays "an 

 immense quantity of gravel and bowlders was transported from the 

 region north of the Great Lakes and scattered oyer a wide area south of 

 them." This was due to floating ice and icebergs. The lake ridges 

 (ancient beaches), described by Whittlesey, Newberry regarded as 

 evidence that the Avater of the lakes remained for considerable inter- 

 vals much higher than at present. These are practically the same 

 views announced before the New York Lyceum in 1870 (p. r>15). 



In May, 1862, J. P. Lesley read a paper before the American Philo- 

 sophical Society describing the structure of the Allegheny Mountains, 

 in which he assumed that the rocks of the Blue Ridge Range, on the 

 eastern side of the valley, were a prolongation of the 

 struauTe^S 3 ' 11 Green Mountains of Vermont, and consisted, theref ore. 

 of the Quebec group, or Taconic System. In this he 

 followed the Rogers Brothers, as he acknowledged. He accounted 

 for the change in the drainage, as exhibited by the New River, which 

 breaks into the Appalachians, as due to a structural change in the 

 geology, most of the mountain valleys north of this being unbroken 

 anticlines and synclines, while most of those south of it are monoclines 

 bounded by immense faults or downthrows. The Appalachians of 

 southern Virginia and eastern Tennessee are grouped in pairs by faults, 

 the fracturing being in parallel strips from 5 to 6 miles wide, each 

 strip being tilted easterly so that the upper edge of one strip, with its 

 Carboniferous rocks, abuts against the bottom or Lower Silurian edge 

 of the strip next to it. The Paleozoic zone, therefore, included 

 between the Great Valley and the backbone escarpment, is occupied 

 by as many pairs of parallel mountains as there are parallel faults, and 

 as these faults lie in straight lines at nearly equal distances from one 

 another the mountain ranges run with great uniformity side by side 

 for 100 or 200 miles until cut off by cross faults, or by change in the 

 courses of the principal faults. 



In a paper before the American Philosophical Societ}^ the year fol- 

 lowing on a "remarkable coal mine or asphalt vein in 

 ind'eVolion, ^ 1 ." 1 the CoaI Measures of Wood County, (West) Virginia," 

 Lesley was led into a discussion of uplift and erosion, 

 and expressed sundiy ideas Avorth} r of note. 



Assuming that the valley cutting through this mine was one of ero- 

 sion and had been carved out since the vein was filled, Lesley speculated 

 on the time and causes of erosion and incidentally on the character of 

 the original uplift. He rejected the idea of cataclysmic erosion dating 

 back to the time of the uplift, as he did also that of the secularists, 

 who regard the present face of the country as but the latest phase of 



NAT MUS 1904 33 



