1888] MARYLAND ACADEMY OF SCIENCES. 19 



compressirostra and overgrown specimens of Cardita planieosta 

 have not been found to undergo such a decided alteration. 

 Small examples, however, of both these species, as likewise of 

 TurrUella mortoni, Turritella Jmmerosa, Pectunculus stamineus, 

 CueuUea transversa, Dosiniopsis meehii, Crassatella alta, Nucu- 

 lana protexta, Axinea idonea, and various undetermined species, 

 have been found by myself partially or completely silicified. 

 The two conditions of the fossil molluscan shells characterize 

 the Eocene beds in most of their modifications on the Western 

 Shore. This, however, is true more especially of the country 

 which rises from the southern shore of the Magothy river, 

 crosses the Severn below the great highlands of Round Bay, 

 and keeping up to a short distance above Crownsville, bends 

 away towards the southwest until the vicinity of Upper 

 Marlboro is reached. East of this point the same conditions 

 reappear at intervals in most of the hydrated greensand hills, 

 across Prince George's and Anne Arundel counties to below 

 South river, and to within perhaps a mile from Chesapeake 

 Bay. A gradual slope rises and undulates from the lowlands 

 on the Chesapeake shores of Anne Arundel until it reaches a 

 summit of nearly one hundred and twenty feet in the country 

 stretching from Round Bay towards the Potomac river, and 

 before reaching the mouth of Piscataway Creek. 



A series of Cretaceous mounds rise high into the central part 

 of the region between the Severn and the Potomac, and give 

 extensive exposures in the deep cuts of the railroad below 

 Millersville. Next we find them in the hills around the head 

 of South river, and then across the Patuxent they form a heavy 

 backbone for all the highlands between that river and the 

 Potomac. This latter river has bayed out its precipitous shores 

 in many places (a notable example of this kind is seen below 

 Fort Washington), so that while leaving a high pile of marl 

 near and above the mouth of Piscataway Creek, it has deeply 

 denuded the country lower down, and produced an extensive 

 lowland in the direction of Mattawoman Creek. The high cliff 

 at the Fort is composed of dark marls, overlaid by the paler 

 grayish olive-colored marly clay of the Eocene formation (?) 

 which becomes more ferruginous and sandy as we approach the 



