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TRANSACTIONS OF TEE 



feet in elevation above the level of the river. The strata 

 are nearly horizontal. The upper portion is an indu- 

 rated arenaceous marl, about 4 feet thick, replete with 

 casts of shells which generally have a chalky coating, 

 but occasionally the shells have been replaced by silex. 

 I have specimens of the rock enclosing great numbers of 

 the Turritella vetusta, nobis, which are very perfect and 

 beautifully mineralized. Beneath this crust is a mixture 

 of chloritic, quartzose and micaceous sand, the former 

 greatly predominating; it is in mineral character strictly 

 analogous to a variety of the secondary marl of New Jer- 

 sey, but widely different in its geological relations, as - 

 will be seen at a glance by one who can rightly interpret 

 its fossils, which never for a moment bewiider or mislead 

 the inquirer who is versed in this neglected but import- 

 ant collateral branch of geology. Having traced the burr 

 stone of Georgia, the fossilliferous sands of Claiborne, Ala- 

 bama, and a calcareous clay near Orangeburg, South 

 Carolina, to a common or synchronous origin, I immedi- 

 ately perceived that the deposit at Upper Marlborough 

 was a link in the interesting chain of older tertiary beds. 



The only secondary species observed here, is the 

 Gryphsea vomer (Morton), but as the matrix is merely the 

 detritus of the secondary green sand, it may be entirely 

 accidental, or it may be that the species was preserved, 

 as the Plagiostorna dumosum (Morton) certainly was, 

 having been found attached to an Ostrea in a tertiary 

 stratum at Claiborne, 



In the vicinity of the village of Piscataway, also in 

 Prince Georges county, about 16 miles from Upper 

 Marlborough, the same geological features are finely 

 exhibited. The hard crust which overlies the friable 

 chlorltic sand, consists chiefly of casts of a fine bivalve 

 described in this paper under the name of Panopea elon- 

 gata. I was the first to publish an account of this inter- 

 esting locality, and to refer it to the period of the Lon- 



