34 FOURTH REPORT — 1834. 



merous, and each individual remains in the position in which the 

 living shell is usually buried in the sand or mud ; that is, ver- 

 tical, with the short side pointing downwards : they are so fra- 

 gile, that they can rarely be taken entire from the matrix. Upon 

 this stratum of clay, in a matrix of sand, lies a bed of the Ostrea 

 virginica, in some places a foot in thickness. It is nearly 

 horizontal ; in some places at least eight or ten, and in others 

 not more than four feet above high- water mark. The diluvium 

 above exhibits a vein of small pebbles, traversing it horizontally, 

 and at a distance resembling a stratum of shells. Not only are 

 the fossils of this locality the same as existing species, but in 

 some instances they retain their colour ; a circumstance com- 

 mon to the later deposits of Europe. The distance fi*om the 

 nearest point on the Atlantic Ocean is about forty-five miles, 

 but it is at least one hundred by the course of the bay. It will 

 be observed, that nearly all the shells are known to inhabit 

 the shores of the United States at the present time : those of 

 them which are now only known in the fossil state are extremely 

 rare, or of minute dimensions." 



Mr. Conrad also mentions to me as an indication of the great 

 tranquillity which has attended the deposition of these beds, that 

 the miderlying blue clay is everywhere penetrated by the Pholas 

 costata in its natural position. The upper bed contains Ostrea 

 associated with Mytilus, a fragile shell, in a very entire and un- 

 disturbed condition. It is not a little curious that the same fel- 

 lowship of Ostrea virginica and Mytilus recurvus {hamatus. 

 Say,) should subsist at the present day in the Gulf of Mexico, 

 though the latter shell has never been seen in the more northern 

 latitudes of our coast. The Rangia, likewise a gulf shell exclu- 

 sively, occurs also in the same newer pleiocene, so that we seem 

 to have indications of a higher temperature even so late as the 

 newest of our tertiary periods. Several of the species, however, 

 in the foregoing table were long supposed by our conchologists 

 to inhabit, in the present day, only the most southern portions 

 of our Atlantic coast, but the same have been since found as far 

 north as the shores of Rhode Island. 



The bed of Ostrea virginica reposing upon the fossiliferous 

 blue clay, has already been referred to a somewhat newer date, 

 from the circumstance of its entire identity with the very recent 

 beds of fossil oyster seen on the margins of some of our rivers 

 and bays, in circumstances which prove them to be among the 

 very newest of aU the upheaved accumulations of the waters of 

 the coast. Considering these upper remains, therefore, as not 

 quite contemporary with the subjacent and more diversified 

 assemblage of marine shells, we may regard the latter as having 



