16 KOUKTH REPORT — 1834. 



luvial mass deposited in front of the ancient rocky coast, than a 

 portion of the detritus left by diluvial action. 



Proceeding now from the Atlantic plain towards the moun- 

 tains, the diluvial matter is more irregularly distributed, in con- 

 sequence of the undulations of the surface. It may be seen in 

 greatest quantity in the valleys of the rivers, the boulders which 

 cover their beds and sides being almost invariably traceable to 

 formations which lie at some miles' distance to the north-west 

 mid north. This distribution of the diluvium from the north 

 and north-west is not confined to the rivers whose valleys run 

 in those directions, but belongs, it is believed, to at least all the 

 middle and northern latitudes of the continent. It is seen west 

 of the Alleghanies, throughout the i-egion of the Ohio and Mis- 

 sissippi, as well as extensively over the Atlantic slope and the 

 tertiary Atlantic plain. Bigsby and the travellers to the north 

 have already shown it to prevail in the latitudes north of the 

 United States. 



The very extensive valley which crosses Pennsylvania, Mary- 

 land and Virginia, lying immediately east of the blue ridge, though 

 it consists principally of transition limestone and greywacke slate, 

 is strewed also with innumerable blocks and boulders of the same 

 sandstone which composes most of the blue ridge, and appears, 

 so far as yet examined, to be newei', together with fragments 

 from the hills between the valley and the Atlantic. Opposite to 

 the passes or breaks in this first range of mountains, the quantity 

 of such -transported matter on the south-east of them is particu- 

 larly great ; and many of the first ridges of the chain are covered 

 to an unknown depth upon their flanks and even their summits 

 by the diluvial matter in a comminuted state. As an instance, the 

 mountain which bounds this valley in Pennsylvania, running 

 west from the Susquehannah through Cumberland county, and 

 called there the North Mountain, is covered with a mass of little 

 else than sand, such as could not be derived from the limestone 

 tract to the south-east, but just such as would be formed from 

 the disintegration of the sandstones of the Alleghanies. 



It is stated by Hayden, in his Geological Essays, that in 

 Washington city itself, which is south of the first primary ridge, 

 and about fifty miles south-east of the mountains, there is a 

 small area covered with rolled masses of sandstone, some of 

 which would weigh from 200 to 500 pounds, and containing 

 perfect impressions of shells resembling Terebratula. Now, no 

 fossiliferous formations occur until we pass beyond the blue 

 ridge, and the blocks must have come from the north-east or 

 north, at least sixty miles. I have myself seen fragments of 



