24 



mingled with it, as at York ; the fragments, however, are not ce- 

 mented together but form a loose friable mass. A rock, consisting 

 of cemented fragments of shells, occurs also at various other points 

 on the eastern portion of the Miocene district ; and a fragmentary 

 deposite, like that above described, is found near the extremity of 

 all the peninsulas formed by our great rivers. 



A very interesting feature in the structure of the cliff at York 

 remains to be described. Though the general direction of the fossil 

 beds is nearly horizontal, several of the strata of rock are composed 

 of transverse layers parallel to each other, generally dipping to- 

 wards the north, and making an angle of fifteen or twenty degrees 

 with the horizon. The course of these laminae sometimes differs in 

 adjoining strata, and in some places the obliquity diminishes gradually 

 until the laminae become horizontal ; thus presenting a remarkable 

 resemblance to the appearances described by Lyell and others, as 

 existing in the Crag of England. The phenomenon here described, 

 viewed in connexion with the fragmentary structure of the rock, and 

 the general distribution of broken shells over the lower extremity 

 of the peninsula, would seem to indicate the former agency in this 

 district of coast currents and an ocean surf. The beds of shelly 

 matter comminuted by these means, and subsequently elevated 

 above the level of the tide, would be gradually cemented into a 

 rocky mass by the crystallization between the particles of such 

 portions of the calcareous matter, as the rain when just fallen was 

 capable of dissolving. The solvent power of rain, being chiefly due 

 to a portion of carbonic acid with which it becomes united in its 

 descent through the air, would be lost, as the liquid percolated 

 through the shelly strata, and thus the calcareous matter which it 

 had seized, would be gradually deposited in the crystalline form. 



Besides shells and Zoophytes, the bones of cetaceous animals 

 and the teeth of sharks, are of very frequent occurrence in the 

 fossiliferous beds, but no remains of fresh water or land animals 

 have as yet been discovered. The total number of species of shells 

 from these points which have yet been identified, is about ninety-^jx, 

 to which may now be added several new species recently dis- 

 covered,*and described in a joint paper by Professor H. D. Rogers 

 and myself. 



The structure of the interesting portion of the state lying on the 

 eastern side of the Chesapeake is, so far as hitherto explored, ex- 

 tremely simple; but as yet only the surface strata have been 



