The great extent of the Tertiary in this country, will supply 

 us with fossil shells not inferior in numbers and beauty to those 

 of 'Europe; for it extends from the State of Delaware coastwise 

 to the Gulf of Mexico. The inferior stratum is a lead-coloured 

 clay, and of such thickness, that no excavation appears to have 

 penetrated entirely through it. Above the clay is a bed of 

 sand, the thickness of which, where .it encloses organic remains, 

 is very inconsiderable; in some places it is extremely fria- 

 ble, and in others indurated and mixed with comminuted shells. 

 The fossils of both strata are equally abundant, and appear to 

 bo the same in both, although a few may perhaps occur more 

 frequently in one than in the other : thus the Panopea is most 

 abundant in the clay, and it is an interesting fact, that the in- 

 dividuals of this genus remain in the position assumed by the 

 burrowing bivalves, that is, vertical, with the anterior side 

 pointing downwards. This proves that they had actually bur- 

 rowed into the beds where they are now found, and that the 

 revolution which destroyed them has not affected the relative 

 position of the strata: indeed no g trace of violence nor action 

 .of an agitated sea or current, is perceptible in the strata as they 

 remained at the final recession of the sea ; but prior to this e- 

 poch, another period has been characterized by a violent agita- 

 tion of the ocean, as the matrix of the present race of fossils 

 is often, in great part, composed of comminuted shells. 



The fact that a long period elapsed from the commencement 

 to the termination of the revolution which exposed these sub- 

 marine bods, is particularly obvious along the north bank of the 

 Potomac river. At Fort Washington, fifteen miles below 

 Washington City, the fossils are more elevated and have a dif- 

 ferent character from any I have observed elsewhare : they 

 consist chiefly of casts of extinct species, and are character- 

 ized by a gigantic Ciicullcea, resembling an European species 

 and the Ostrea compressirostra, which is the analogue of the 

 European O.bellovacina. South of this locality, on St. Mary's 

 river, the fossils are very different and embrace many of the 

 common existing species of our coast. This is the most exten- 

 sive of either of the Tertiary beds. The last deposit of marine 

 reliquiae consists of shells now inhabiting the coast of the 

 middle and southern States: it occurs on the north bank, and 

 near the mouth of the Potomac. The greatest elevation of these 



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