Rogers.] 104 [May 19, 



marking, and gave to the whole deposit the distribution and strati- 

 fication which it now presents; or, on the other hand, it may be con- 

 ceived that the transporting force of the rivers themselves, swollen 

 and rapid as they must have been in the closing ages of the glacial 

 period, brought about the same results. But even, in this case, it is 

 highly probable that glacial action had much to do with the original 

 accumulation of the rocky debris en the flanks of the Blue Ridge, 

 and in the Appalachian valleys beyond. 



Jn the belt partially occupied by the surface deposit here referred 

 to, there is exposed another group of strata, with which, at first view, 

 the sandy and argillaceous layers of this formation might readily be 

 confounded. These are the silicious, argillaceous and pebbly beds, 

 which, underlying the tertiary in Virginia, and the well marked cre- 

 taceous formation further north, have, in the latter region, been 

 regarded as belonging to the base of the cretaceous series of the 

 Atlantic States. In Virginia the formation consists typically of a 

 rather coarse, and sometimes pebbly sandstone, in which the grains 

 of quartz and felspar are feebly cemented by kaolin, derived from the 

 decomposition of the latter, and of argillaceous and silicious clays 

 variously colored, and more or less charged with vegetable remains, 

 either silicified, or in the condition of lignite. These constitute the 

 group of beds designated in the Virginia geological reports as the 

 Upper Secondary Sandstone, and referred by me long since (1842) 

 to the upper part of the Jurassic series, corresponding probably to 

 the Purbeck beds of British geologists. From the Potomac north- 

 ward, this group of deposits, as exposed in the deep railroad cust 

 between Washington and Baltimore, and on to Wilmington, is made 

 up of variegated, soft, argillaceous and silicious beds, which, from 

 the preponderance of ferruginous coloring towards the Delaware, has 

 been called by Prof. Booth the red clay formation. At a few points 

 only towards the bottom of the deposit, it brings to view a bed of 

 the felspathic sand, or crumbling sandstone, above referred to. 

 Traced transversely, it is seen to dip beneath the cretaceous green- 

 sand at various points in New Jersey, Delaware and Maryland, 

 but in Virginia disappears in its eastward dip beneath the Eocene 

 tertiary. 



How far we may consider this group of sediments in Maryland, 

 Delaware and New Jersey, as merely a continuation of the Virginia 

 formation above described, can be determined only by further inves- 

 tigation. But the discovery in them at Baltimore, by Prof. Tyson, of 



