18 TRANSACTIONS OF THE [1888 



the first, plant remains are most abundant ; but near the top of 

 this the marine shells, Gryphea, Exogyra, Ammonites, etc., begin 

 to appear and become more abundant towards the top. The 

 next higher ridge, farther inland, yields other marine shells, 

 such as Belemnitella, Baculites, Exogyra and Terebratula harlani, 

 while the third plane of elevation, composed of the gray-green- 

 sand, reveals types of Ostrea, Gryphea, and Modiola, the 

 species of which have not yet been identified. 



The Eocene formation now comes into view, and rests over 

 the latter series in the region extending from the Magothy to 

 the South river, where it lies spread out interruptedly in an 

 uneven stratum. Near Chesapeake Bay it rests in the summits 

 of the low hills in a region which has been denuded down to 

 Avithin twenty feet, or even less, of ordinary tide level. On 

 this greatly reduced plateau a few dome-like hills rise here and 

 there above the general surface. Most of these have had the 

 grains of greensand dissolved from the surface, and sometimes 

 to the depth of a few feet inwards, giving them the appearance 

 of incoherent piles of ferruginous sand. In these hills, and 

 especially where the sand has been reduced to a fine snufF-like 

 condition, the fossil shells are packed in countless numbers. 

 The slopes once connected with these hills, which have been 

 divided and ravined by the downward cutting of rapid flowing 

 rills, likewise expose multitudes of the same fossil shells along 

 their faces and in their sides. Still other prominences, more 

 widely eroded, disj)lay beds of siliceo-calcareous rock, varying 

 from less than one foot to nearly three feet in thickness, chiefly 

 made up of the remains of molluscous shells. In these aggre- 

 gations we observe the coarse greensand grains in their normal 

 appearance, but harder than usual, mixed in great abundance 

 all through the stony mass. These indurated layers rest some- 

 what evenly at a low level, while the beds of shells enveloped 

 by or adhering to the ferruginous sandrock appear in and near 

 the hill-tops. The former fossils are generally clean and not 

 penetrated by ferruginous stains, although siliceous alteration 

 has transformed a notable proportion of the shelly remains into 

 a mineral of glass-like density. This is more particularly the 

 case with shells of medium or small size, for the large Ostrea 



