GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



335 



OBSERVATIONS ON A PORTION OF THE ATLANTIC TERTI- 

 ARY REGION. By T. A. Conrad. 



During a recent excursion through the Atlantic ter- 

 tiary region, I obtained two species of shells which ap- 

 pear to be new, and some beautiful zoophytes, one of 

 which I have herein described and figured. 



At the village of Upper Marlborough, in Prince 

 Georges county, Maryland, I found a very interesting 

 deposit of the age of the eocene formation of London and 

 Paris, and although the shells are mostly mere casts in 

 the indurated stratum, and almost entirely decomposed 

 in the green sands beneath, yet an attentive study of the 

 rocks of various localities from New Jersey to Alabama 

 inclusive, has removed all doubts from my mind relative 

 to the age of the deposit in question. Casts of those 

 most characteristic shells, Crassatella alia, and Cardita 

 planicmta are abundant, and not a single specimen of 

 either species has ever yet been found higher or lower in 

 the scale of formations than the eocene strata. The same 

 may be said of other species occurring abundantly in 

 the rocks of this locality. The bank of the small stream 

 at Upper Marlborough is high and precipitous, composed 

 of sand and clay, with an occasional mixture of eocene 

 green sand and indurated calcareous masses replete 

 with fossils, the whole consisting of what has been gene- 

 rally termed diluvium. To the west of the village is a 

 range of considerable hills, and on their steep acclivi- 

 ties are scattered abundance of the Ostrea compressi- 

 rostra of Say, and fragments of silicious rock which is 

 a mere aggregate of casts of bivalve shells. Perhaps 

 the summit of the tertiary here, does not exceed 30 



