284 THREE CRUISES OF THE / BLAKE." 
ooze, | took from the contents of the trawl drawn from 860 
fathoms equal portions of mud as it eame up; one part was 
left undisturbed and roughly measured, and the other was care- 
fully sifted; the pteropod shells and their fragments were then 
collected, and likewise measured, when their bulk was found to 
be somewhat more than half the bulk of the sifted mud from 
which they came. 
Pourtalés, who first traced the extent of the region covered 
by globigerina ooze in some parts of the Gulf of Mexico and 
upon the Atlantic coast of the United States, thus speaks of 
the foraminiferous caleareous bottom : — 
“In great depths, as, for instance, in the Straits of Florida, at the 
outward limit of the rocky bottom (Pourtalés Plateau), and, where 
this does not exist, even in less depths, the bottom is eovered by a 
chalk-like layer, which resolves itself under the microscope into a mass 
of foraminifera,’ and their fragments more or less comminuted. This 
formation extends almost uninterruptedly in the whole bed of the Gulf 
Stream, in the greater depths of the Gulf of Mexico, in the deep 
channels which intersect the Bahama Banks, and then up the Atlantie 
coast from about the hundred-fathom curve outward, or from the inner 
limit of the Gulf Stream, which nearly coincides with it, and so over 
the greater part of the Atlantic basin. The discovery of this forma- 
tion belongs to the year 1853, when it was found almost simultaneously 
by Lieutenants Craven and Maffit, then in the Coast Survey, and ex- 
ploring the Gulf Stream. It became more extensively known some- 
what later, by the soundings made for the Atlantic telegraph. 
“ The genus of foraminifera most abundantly represented in this bot- 
tom is the Globigerina ; hence the term ‘ globigerina bottom" (ooze) is 
becoming generally used. "Then comes in order of frequency Rotalina 
cultrata ; then several Textulariw, Marginulins, etc. It is now pretty 
generally admitted that these rhizopods live and die in these great 
depths,” although formerly false ideas of the effects of pressure, of the 
1 The extent to which pteropod shells of the Tortugas. While examining the 
enter into the composition of the ooze of specimens of foraminifera collected 
the Caribbean 
not then been n 
ind Gulf of Mexico had Coast Survey expeditions, Pourtalds n 
the interesting discovery that many 
P xd  eimens 
ourtalés state of Orbulina contained a 
slobige- Globigerina, more or less developed, and 
rine are still living in immense mdum- that these two genera must be considered 
bers. As I have mentioned before, I as probably two stages of alternate gen- 
found an allied species of globigerina eration. 
swarming on the surface to the westward 
