284 THREE CRUISES OF THE •' BLAKE." 



ooze, I took from the contents of the ti-awl drawn from 860 

 fathoms equal portions of mud as it came 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 Hkewise measured, when their bulk was found to 

 be somewhat more than half the bulk of the sifted mud from 

 which they came. 



Pourtales, 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 calcareous bottom : — 



" In great depths, as, for instance, in the Straits of Florida, at the 

 outward limit of the rocky bottom (Pourtales Plateau), and, where 

 this does not exist, even in less depths, the bottom is covered 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 GiiK of Mexico, in the deep 

 channels which intersect the Bahama Banks, and then up the Atlantic 

 coast from about the hundred-fathom curve outward, or from the inner 

 Hmit 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 f oraminif ei-a 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 Textulariae, Marginulinae, 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 



^ The extent to which pteropod shells of the Tortugas. While examining the 



enter into the composition of the ooze of specimens of foraminifera collected by 



the Caribbean and Gulf of Mexico had Coast Survey expeditions, Pourtales made 



not then been noticed. the interesting discovery that many spe- 



2 As far back as 1850, Pourtales stated cimens of Orbulina contained a young 

 that at depths of 257 fathoms globige- Globigerina, more or less developed, and 

 rinae are still living in immense nam- 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. 

 swarmingf on the surface to the westward 



