278 THREE CRUISES OF THE “ BLAKE.” 
in the Gulf of Mexico, and during my first dredging trip I was 
struck with the change of the light yellowish-gray ooze of the 
trough of the Gulf Stream into the darker shades as we ap- 
proached the coast of Cuba. 
While running the line parallel to the coast from off Charles- 
ton to Cape Hatteras, we came twice upon localities where 
the sounding-cup brought up nothing but clean globigerine, 
the bottom consisting entirely 
of the modern greensand! to 
which Bailey and Pourtalés had 
already called attention as form- 
ing off shore on the Atlantic coast 
of the United States. From the 
examination of a large number 
of bottom specimens, Pourtalés 
succeeded in determining the 
position of a belt off the coast of 
Georgia and of South Carolina 
where the modern greensand was 
well developed. "The patches of 
greensand occurred in depths 
varying from fifty to a hundred fathoms on the boundary line 
between the siliceous sand and calcareous bottoms on the inner 
edge of the Gulf Stream. Now and then this modern greensand 
(Fig. 190) is found also in deeper water under the Stream itself. 
Pourtalés gives the following description of the formation of 
our modern greensand : — 
Fig. 190, — Greensand. 142 fathoms. 
(Blake Station 314.) 1$. 
* Ehrenberg made, as 1s well known, the interesting discovery that 
the so-called greensand or glauconite consists of the casts of foramini- 
fera.? That this process is still going on at the bottom of the ocean, 
1 Murray says, that fifty per cent of ? Bailey confirmed the observations of 
carbonate of lime, mainly made up of Ehrenberg, on the greensand of the Zeu- 
pelagic and other foraminifera, and forty — glodon limestone of Alabama, and detected 
per cent of greensand residue, enter into the same structure in some of the ereta- 
the composition of one of the samples of ceous deposits of New Jersey and Texas, 
modern greensand he examined. The and in the eocene of South and North 
remainder consists of siliceous organisms Carolina. 
and argillaceous and green amorphous 
matter, 
