142 Prof. Rogers on Fossil Infusoria. 



cently discovered by me, in time for your forthcoming number. 

 Ere long however, I hope to have that pleasure. In the mean 

 time it may not be uninteresting to your readers to learn that this 

 deposit spreads northwards beyond the Potomac, and is found in 

 Maryland, forming at some localities, an important member of 

 the tertiary series. The general aspect of the mass as seen near 

 Piscataway, is like that of the principal Virginia localities, and 

 its position is above but apparently near the base of the meiocene. 

 On some of the fragments in my possession, are well preserved 

 impressions of meiocene shells, among which I may mention As- 

 tarte undulata as particularly distinct. 



Prof. Bailey, our Ehrenberg, having applied his skillful obser- 

 vation to a small portion of the material which I sent to him by 

 letter, has confirmed my ruder determination as to the prevalence 

 of various species of Coscinodiscus in the mass, and has besides 

 recognized a variety of other interesting forms. Through his 

 kind sanction, I annex a list of some of these curious and beauti- 

 ful objects, referring to his own memoir and accompanying fig- 

 ures for a more detailed description. 



Coscinodiscus argus ; C. excentricus ; C. lineatus ; C. oculus- 

 iridis ; C. patina ; C. radiatus, &c. Actinocyclus senarius ; A. 

 bisenarius ; A. quindenarius, &c. Podiscus Rogersi, occurs 

 sparingly. Zygoceros Tuomeyi, is not rare. Gaillonella sul- 

 cata ? abundant. Dictyocha fibula ? extremely abundant, far 

 more so than at any other known locality. Dictyocha speculum, 

 abundant. Several large and new ? species of Dictyocha ; several 

 small species of Navicula, one of which is panduriform ; besides 

 many other new and interesting objects, of which Prof. B. will 

 give an account in the continuation of his valuable memoirs on 

 our infusorial fossils. 



The extent to which the infusorial beds of the tertiary have 

 thus far been traced, invests them with a far higher geological 

 importance, than in my first observations I anticipated ; and 

 should they be found, as I believe they will, stretching north- 

 wards to the Delaware, and southwards far beyond the Roanoke, 

 they will deserve to be regarded as a prominent portion of our 

 great Atlantic tertiary series, and as one of the most striking ob- 

 jects in the geology of our great Atlantic plain. 



Very truly your friend, 



Wm. B. Rogers. 



B. Silliman, Jr., Esq. 



