GEOLOGICAL 



SOCIETY OF PENNSYLVANIA. 



port of mastodon remains having been found in these 

 clay deposits, nor has any well authenticated f^ct been 

 developed, which could authorize us to consider them of 

 more recent date than the period to which we have here 

 referred them. 



At Mr Ruffin's plantation, Shellbanks, I noticed some 

 marl pits in strata of the older pliocene, where a mark- 

 ed resemblance to the English crag was obvious, in a 

 ferruginous mixture of comminuted shells and silicious 

 sand. The upper stratum consists chiefly of finely com- 

 minuted shells, inclosing very small, generally young, 

 bivalves, and is about 4 feet thick. It is intersected by 

 numerous seams of clay, without organic remains. The 

 next stratum is of a grey colour, with fewer shells and 

 fragments of shells, and is about 3 feet thick ; and then 

 follows a marl full of large bivalves, in a state of decom- 

 position. 



Mr Ruffin pointed out to me the singularly broken 

 and irregular summit line of the tertiary, and remark- 

 ed, that if the sand and gravel were removed, the sur- 

 face would exhibit numerous deep funnel-shaped cavi- 

 ties. Have these been formed by eddies in the cur- 

 rents, which abraded the surface in the same manner 

 that the waters of rapid rivers hollow the rocks over 

 which they run? 



In most of the pliocene marl banks, the large Pecten 

 Madisoniiis, P. Jeffersonius, with Osty^ea compressiros- 

 ra^ and large Balani, form the mass of species at the 

 summit ; but they are not confined there exclusively, 

 occurring more rarely throughout every part of the de- 

 posits. 



DESCRIPTION OF NEW FOSSILS. 

 TESTACEA. 



Panopea elongata, PL 13, Jig. 1. Shell oblong, 



