307 



5th. A few good Greensand easts of Polytlialamin were found 

 in the residue left on dissolving a specimen of mail from tlie 

 Artesian Well at Charleston, S. C. ; depth 140 feet. 



6th. Abundance of organic casts, in Greensand, &c., of Poly- 

 thalamia, Tubuli, and of the cavities of Corals, were found in the 

 specimen of yellowish limestone, adhering to a specimen of Scu- 

 tella Lyellii from the Eocene of North Carolina. 



7th. Similar casts of Polythalamia, Tubuli, and of the cavities 

 of Corals, and species of Encrinites, were found abundantly in a 

 whitish limestone adhering to a specimen of Ostrea selloeformis 

 from the Eocene of South Carolina. 



The last two specimens scarcely gave any indications of the 

 presence of Greensand before they were treated with dilute 

 acid, but left an abundant deposit of it when the calcareous 

 portions were dissolved out. All the above-mentioned specimens 

 contained well-preserved and perfect shells of Polythalamia. It 

 appears from the above, that the occurrence of well-defined or- 

 ganic casts, composed of Greensand, is by no means rare in the 

 fossil state. 



I come now to the main object of this paper, which is to 

 announce that the formation of precisely similar Greensand and 

 other casts of Polythalamia, Mollusks, and Tubuli, is now going 

 on in the deposits of the present ocean. In an interesting report 

 by Count F. Pourtales, upon some specimens of soundings ob- 

 tained by the U. S. Coast Survey in the exploration of the Gulf 

 Stream, (See Report of U. S. Coast Survey, for 1853, Appendix, 

 p. 83,) the sounding, from Lat. 31" 32', Long. 79^ 35', depth 150 

 fathoms, is mentioned as " a mixture in about equal proportions of 

 Globigerina and black sand, probably greensand, as it makes a 

 green mark when crushed on paper." Having examined the 

 specimen alluded to by Mr. Pourtales, besides many others from 

 the Gulf Stream and Gulf of Mexico, for which I am indebted 

 to Prof. A. D. Bache, the Superintendent of the Coast Survey, 

 I have found that not only is Greensand present at the above 

 locality, but at many others, both in the Gulf Stream and Gulf 

 of Mexico, and that this Greensand is often in the form of well- 

 defined casts of Polythalamia, minute Mollusks, and branching 

 Tubuli, and that the same variety of the petrifying material is 

 found as in the fossil casts, some being well-defined Greensand, 

 others reddish, brownish, or almost white. In some cases I have 



