EXPEDITION OF THE CHALLENGER. 37 



menta. Xor can the presenco of the soft parts of the body in the 

 shells which form the Globigerina ooze, and the fact, if it be one, that 

 animals living at the bottom use them as food, be considered as con- 

 clusive evidence that the Glohigerince live at the bottom. Such as die 

 at the surface, and even many of those which are swallowed up by 

 other animals, may retain much of their protoplasmic matter when they 

 reach the depths at Avhich the temperature sinks to 34 or 32 Fahr., 

 where decomposition must become exceedingly slow. 



Another consideration appears to me to be in favor of the view that 

 the Glohigerinm and their allies are essentially surface-animals. This 

 is the fact brought out by the Challenger's work, that they have a 

 southern limit of distribution, which can hardly depend upon any 

 thing but the temperature of the surface-water. And it is to be 

 remarked that this southern limit occurs at a lower latitude in the 

 antarctic seas than it does in the North Atlantic. According to Dr. 

 Wallich ("The North-Atlantic Sea-Bed," p. 157) Globigerina is the 

 prevailing form in the deposits between the Farce Islands and Iceland, 

 and between Iceland and East Greenland or, in other Avords, in a 

 region of the sea-bottom which lies altogether north of the parallel of 

 60*^ north ; while in the southern seas the (r/o5^^er^os become dwarfed 

 and almost disappear between 50 and 55 south. On the other hand, 

 in the sea of Kamtchatka, the Glohicjerinm have vanished in 56 north, 

 so that the persistence of the Globigerina ooze in high latitudes, in the 

 North Atlantic, Avould seem to depend on the northward curve of the 

 isotherm als peculiar to this region ; and it is difficult to understand 

 how the formation of Globigerina ooze can be affected by this climatal 

 peculiarity unless it be effected by surface animals. 



Whatever may be the mode of life of the Foraminifera, to which 

 the calcareous element of the deep-sea "chalk" owes its existence, 

 the fact that it is the chief and most widely-spread material of the 

 sea-bottom in the intermediate zone, throughout both the Atlantic 

 and Pacific Oceans, and the Indian Ocean, at depths from a few 

 hundred to over 2,000 fathoms, is established. But it is not the 

 only extensive deposit which is now taking place. In 1853 Count 

 Pourtales, an ofticer of the United States Coast Survey, which has 

 done so much for scientific hydrography, observed that the mud form- 

 ing the sea-bottom at depths of 150 fixthoms, in 31 32' north, and 

 79 35' west, off the coast of Florida, was "a mixture, in about equal 

 proportions, of Globigerinm and black sand, probably green sand, as 

 it makes a green mark when crushed on paper." Prof. Bailey, ex- 

 amining these grains microscopically, found that they were casts of 

 the interior cavities of Foraminifera, consisting of a mineral known 

 as Glauconite ^ which is a silicate of iron and alumina. In these casts 

 the minutest cavities and finest tubes in the Foraminifera were 

 sometimes reproduced in solid counterparts of the glassy mineral, 

 while the calcareous original had been entirely dissolved away. 



