SUBMARINE DEPOSITS. 279 



near our coasts, was discovered by Bailey, from the , examination of our 

 bottom specimens. In some of them the whole process can be followed 

 in the most interesting way. Thus w'e find, side by side, the tests per- 

 fectly fresh, others still entire, but filled with a rusty-colored mass, 

 which permeates the finest canals of the shells like an injection.^ In 

 others, again, the shell is partly broken away, and the filling is turning- 

 greenish ; and finally we find the casts without trace of shell, sometimes 

 perfectly reproducing the internal form of the chambers ; sometimes, 

 particularly in the larger ones, cracks of the surface or conglomeration 

 with other grains obliterate all the characters. They even coalesce into 

 pebbles, in which the casts can only be recognized after grinding and 

 polishing. 



" Why this process of transformation should occur only in partic- 

 ular localities is as yet unexplained.^ It is easy to distinguish this 

 fresh formed greensand from the tertiary one off the coast of New 

 Jersey, by the greater number of perfect tests of foraminifera mixed 

 with it." 



As was pointed out by Pourtales, it is remarkable how closely 

 the limits of the siliceous sand bottom coincide with the bound- 

 aries o£ the cold current coming from the north, while the limits 

 of the calcareous deposits correspond with the course of the 

 warm waters of the Gulf Stream. We might almost trace its 

 course by a study of the bottom specimens. On each side, as 

 well as at the falls of the Gulf Stream south of Hatteras, ooze 

 of varying composition was invariably brought up. The distri- 

 bution of the foraminifera seems to throw considerable light on 

 the circulation, and to give additional support to Commander 

 Bartlett's view, based upon thermometric sections, that the bulk 

 of the Arctic current does not extend south of Hatteras along 

 our coast, but that the colder and heavier waters of the northern 

 current plunge beneath the Gulf Stream off Hatteras, and flow 

 slowly on the outside edge of the Blake Plateau towards the 

 equator. 



During the years 1875 and 1876, previous to my connection 



1 Many of the foraminifera dredged by due to foraminifera, but also in part to 

 Pourtal^s and myself in the Straits of other organisms, and he suggests that we 

 Florida were filled with a yellow mass, may safely infer that this matrix has in- 

 like that of the first stage of transforma- variably been formed in connection with 

 tion into greensand. decaying organic matter. 



2 Bailey shows that the casts are not all 



