86 BAILEY, ON GREENSAND. 



portions were dissolved out. All the above mentioned spe- 

 cimens contained well-preserved and perfect shells of Poly- 

 thalamia. It appears from the above, that the occurrence of 

 well-defined organic 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 speci- 

 mens of soundings obtained 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 M. 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 petrify- 

 ing material is found as in the fossil casts, some being well- 

 defined Greensand, others reddish, brownish, or almost white. 

 In some cases I have noticed a single cell, of a spiral Poly- 

 thalamian cast, to be composed of Greensand, while all the 

 others were red or white, or vice versa. 



The species of Polythalamia whose casts are thus preserved, 

 are easily recognisable as identical with those whose perfectly 

 preserved shells form the chief part of the soundings. That 

 these are of recent species is proved by the facts that some of 

 them still retain their brilliant red colouring, and that they 

 leave distinct remains of their soft parts when treated witli 

 dilute acids. It is not to be supposed, therefore, that these 

 casts are of extinct species washed out of ancient submarine 

 deposits. They are noAv forming in the muds as they are 

 deposited, and we have thus now going on in the present 

 seas a formation of Greensand by processes precisely analogous 

 to those which produced deposits of the same material as long 

 ago as the Silurian epoch. In this connection, it is im- 

 portant to observe that Ehrenberg's observations and my 

 own cstablisli tlu^ fact that ot/ter organic bodies than Poly- 

 thalamia produce casts of Greensand ; and it should also be 



