AMERICAN GEOLOGY DECADE OF 1830-1839. 325 



land to the west of the Potomac mainly by primary granites, gneiss, 

 and slate, with a narrow band of transition limestone; Virginia by 

 transition limestone overlaid in part by graywacke; Tennessee by 

 graywacke overlaid at the Cumberland Mountains by Carboniferous 

 limestone; Kentucky. Indiana, and Illinois by Carboniferous limestone; 

 Missouri and Arkansas by Carboniferous limestone capped by calcareo- 

 siliceous hills, and Arkansas, from a point about midway between 

 the Fourche and Arkansas rivers, by graywacke capped by Old Red 

 sandstone and occasional Tertiary deposits, with sub-Cretaceous beds 

 beginning again at the Caddo River and extending nearly to the Red 

 River in Texas, w here they were covered by a ferruginous sandstone. 

 It was a reprint of this section in the Transactions of the Geological 

 Society of Pennsylvania that Lesley referred to in his Historical Sketch 

 of Geological Explorations as "a rambling description and a worth- 

 less geological section across the continent from New York to Texas." 

 In L835 Featherstonhaugh, again under instructions from Lieutenant- 

 Colonel Abert, made a geological reconnaissance of the region lying- 

 bet ween the seat of government and the Coteau des Prairies, by way of 

 Green Bay and the Wisconsin Territory. His report, issued in 1836, 

 formed Senate Document No. 333, comprising 168 pages, with -1 plates 

 of sections and diagrams. In this, as in his first, there is a large 

 amount of preliminary matter of a very general nature. He noted 

 that Washington and Georgetown were underlaid by gneiss, in which 

 were perceived evidences of an "extensive anticlinal movement by 

 which all the rocks along the entire length of the Potomac,' 1 as high 

 up as the great bituminous Held, had been affected, and that the true 

 dip of the rocks was often "contradicted by the cleavage." This was 

 a by no means unimportant observation. The erosive action of the 

 river, as manifested by potholes in the schists at Great Falls, was 

 dwelt upon and the Seneca sandstone and Potomac breccia described, 

 the former noted as often carrying anthracite and casts of calamites, 

 but no suggestion as to the geological age of the beds w r as given. The 

 Catoctin Mountains were described as "composed of primary slates, 

 sandstones, and quartz having a northeast direction. " Referring to 

 the relationship existing between the Potomac breccia and the lime- 

 stones, slates, and shales, he wrote: 



We thus have all the proofs that the Atlantic primary chain has come up from 

 below through the limestone, triturating and breaking it up into fragments of every 

 size, which wen- subsequently transported to the east of the chain by a current from 

 the west, and deposited there, intermixed with the decomposed red shale. 



He concluded, therefore, that the Atlantic primary chain was ele- 

 vated posterior to the deposition of the limestone, "which may be 

 considered the equivalent of the lowest beds of Mr. Murchison's 

 Silurian rocks." The unsymmetrical character of the folded sand- 

 stones and grits at Wills Creek, in Maryland, he described as affording 



