entire extent, but they gradually diminish in thickness as 

 they proceed upward. It is in some of the separating 

 seams of this division that the leaves and stems of plants 

 have been discovered. 



The inferior portion of this deposition of clay, where it 

 closely approximates to the supporting indurated rocks 

 below, when freshly exposed to view, assumes the appear- 

 ance of a compact cohesive mass, the particles of which it 

 is constructed being of an exceedingly fine nature ; but 

 when for a few days it becomes subject to the direct in- 

 fluences of the weather, it most generally exhibits a ten- 

 dency to separate vertically into a rudely columnar struct- 

 ure, much resembling in general aspect many of the 

 granites of our Eastern States. 



This formation of clay rests in an unconformable posi- 

 tion upon the Hudson river sandstones and shales beneath; 

 but in some instances a more ancient drift or boulder sys- 

 tem intervenes, the currents of which swept in a south- 

 erly direction over the principal portion of the State of 

 New- York, producing those numerous scratches which are 

 80 distinctly visible upon the surfaces of most of its rocks, 

 and giving evidence that a long period of time must have 

 necessarily elapsed of tranquil waters reposing over this 

 region of country, in order to leave so uniform a deposi- 

 tion of clay, amounting to about one hundred feet in 

 thickness. It was after the completion of this deposit, 

 that the violent action took place which tore up and dis- 

 located the upper portion of this formation. 



The numerous beds of gravel and hrovm sand which are 

 inclosed within this upper or drab-colored variety of the 

 marly clay,— and which, no doubt, were the agents em- 

 ployed in the opening and upturning of its strata,— are of 

 a different nature from the overlying formation of yellow 

 ferruginous sand. The materials which characterize these 

 deposits are for the most part of a greenish brown color, 

 and appear all to have been derived from the primary 



