1880.] 



NATURAL SCIENCES OF PHILADELPHIA. 



23 



Anne Arundel and Calvert Counties, on the Patuxent River, near 

 Benedict, and on tlie St. Mar3''s River, St. Mary's Count}', tend 

 to show, moreover, that the series of deposits intermediate between 

 the Eocene of Fort Washington and the Pliocene of the south- 

 east extremit}' of the peninsula belong to two different periods of 

 formation, an older and a newer; those belonging to the latter 

 period being characterized by a fauna, the proportion of living 

 forms in which is far in excess of that in the former. Sections 

 of the newer deposits are exhibited in Calvert County, near Cove 

 I*oint, on the Patuxent River, below Benedict, at about water 

 level, on the same river, further north, in the deposits above the 

 Perna beds, and more especiall}' on the St. Mary's River, St. 

 Mary's County. The older deposits are best shown in the oyster 

 beds, rising a few feet above tide- water, at Fair Haven, Anne 

 Arundel County (which point was considered by Conrad as the 

 northern termination of the peninsular Miocene formation), in 

 similar beds, also only a few feet above water level, at a point 

 about twenty miles further south ('' Colonel Blake's," of Conrad), 

 in the sections exhibited by the Calvert Cliffs, and in the Perna 

 beds on both banks of the Patuxent River. There is, further, 

 strong, although not conclusive evidence, for considering the beds 

 containing Perna maxillata and Oatrea percrassa as the lowest 

 of the series. 



The following tables exhibit as nearh* as possible the distribu- 

 tion of Lamellibranchiata in the deposits of both periods, those 

 of the newer being for conA^enience of comparison divided into 

 the Patuxent and St. Mary's groups : 



OLDER PERIOD. 



1 Area dipleura, 



(= A. calilplenra ?), 



2 " Marylandica, 

 H " subrostrata, 

 4 " triquetra, 



.*> Artemis acetabulum, 

 H Astarte varians, 

 1 " exaltata, 



8 Cardium craticuloides, 



9 " leptopleura, 

 1 Corbula idonea, 



1 1 Corbula elevata, 



12 Crassatella melina, 



13 " turgidula, 



14 Cytherca subnasuta, 



15 Isocardia Markoei, 



16 Leda liciata, 

 n Lima papyria, 



18 Lucina Foremani, 



19 " subplana, 



20 " crenulata, 



21 Mytilus incurva, 



