OF MARYLAND. 51 



^0 disintegrated that they cannot be referred, and it is in the 

 vicinity of a fossiliferous deposite containing particles of green 

 sand, an abundance of Gryphoea vomer and other Gryphcea^ 

 what appears to be the cast of an Exogyra, a zoophytic pro- 

 duction beUeved to be referrible to a Scyfihea, and Ostrea com- 

 pressirostra. It is probable, therefore, that ii belongs here as 

 •elsewhere to a period older than the Eocene tertiary to which 

 it has been hitherto referred. In the valley of the Piscataway 

 •a similar deposite occurs to that at Upper Marlborough, com- 

 prising mostly, however, among the species that can be deter- 

 mined Ostrea cotnpressirostra ; at Fort Washington, Mr. Con- 

 rad found 'a solitary valve oi Exogyi'a^""* associated with Cucul- 

 loea gigantea. On the banks of the Potomac, near Indian 

 point, there is an analogous formation, and still farther down, 

 between the mouth of Port Tobacco river and Pope's creek, a 

 mixed green sand occurs, in which are found the Gryphcea 

 vomer^ Ostrea co7npressirosira, Lignites, Pyrites and Seleuiie. 

 All these deposites ditfer materially from those that are found 

 inland, at the head of the water-courses, constituting what has 

 been elsewhere termed by way of distinction the blue-marl of 

 Charles county, and it is remarkable of these, that the only 

 fossil shell observed in them, in the superficial examinations 

 that have been so far made is the Venericardia plamcosta.\ 

 The fossiliferous deposites on the Patuxent side again differ 

 from the preceding. They commence high up in Prince 

 George's county, are found at the heads of nearly all the water 

 courses, extending down to the extreme end of the peninsula 

 of which they seem to form the substratum. Similar deposites 

 occur in the lower portions of Anne Arundel, and form the mass 



♦ Morton's Synopsis of Organic Remains, p. 19. 



t In Mr. Deshaye's Tables of Fossil Shells, appended to Mr. Lyell's Principles 

 of Geology, fourth edition, the different species of venericardia and cardia are 

 assio-ned as occurring in six localities of the Pliocene jteriod, fourteen of the Mio- 

 cene, and ten of the Eocene. If the localities previously mentioned, namely, at 

 Upper Marlborough, Fort Washington, and the banks of the Potomac, in Charles 

 county, notwithstanding the occurrence of the Exogyra and Gryphaa vomer, 

 continue to be referred to the Eocene period, it is more than probable that the 

 blue-marls of Charles county, will have to be referred to the Miocene epoch— an 

 opinion originally entertained, but afterwards yielded up. It is thought prema- 

 ture, however, to decide upon a question in reference to which scarcely the 

 elements are possessed. 



