Another consideration appears to me to be in favour of the view that the _Globigerinoe_ 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 anything 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 Faroe Islands and Iceland, and between Iceland and East Greenland--or, in other words, in a region of the sea-bottom which lies altogether north of the parallel of 60° N.; while in the southern seas, the _Globigerinoe_ become dwarfed and almost disappear between 50° and 55° S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_ have vanished in 56° N., so that the persistence of the _Globigerina_ ooze in high latitudes, in the North Atlantic, would seem to depend on the northward curve of the isothermals 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 two thousand fathoms, is established. But it is not the only extensive deposit which is now taking place. In 1853, Count Pourtalès, an officer of the United States Coast Survey, which has done so much for scientific hydrography, observed, that the mud forming the sea-bottom at depths of one hundred and fifty fathoms, in 31° 32' N., 79° 35' W., off the Coast of Florida, was "a mixture, in about equal proportions, of _Globigerinoe_ and black sand, probably greensand, as it makes a green mark when crushed on paper." Professor Bailey, examining 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 Foraminifer were sornetilnes reproduced in solid counterparts of the glassy mineral, while the calcareous original had been entirely dissolved away. Contemporaneously with these observations, the indefatigable Ehrenberg had discovered that the "greensands" of the geologist were largely made up of casts of a similar character, and proved the existence of _Foraminifera_ at a very ancient geological epoch, by discovering such casts in a greensand of Lower Silurian age, which occurs near St. Petersburg.