[Footnote 7: The North Atlantic Sea-bed, p. 137.]
On the other hand, Müller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and other observers, found that Globigerinoe, with the allied genera Orbulina and Pulvinulina, sometimes occur abundantly at the surface of the sea, the shells of these pelagic forms being not unfrequently provided with the long spines noticed by Macdonald; and in 1865 and 1866, Major Owen more especially insisted on the importance of this fact. The recent work of the Challenger fully confirms Major Owen's statement. In the paper recently published in the proceedings of the Royal Society,[8] from which a quotation has already been made, Professor Wyville Thomson says:—
"I had formed and expressed a very strong opinion on the matter. It seemed to me that the evidence was conclusive that the Foraminifera which formed the Globigerina ooze lived on the bottom, and that the occurrence of individuals on the surface was accidental and exceptional; but after going into the thing carefully, and considering the mass of evidence which has been accumulated by Mr. Murray, I now admit that I was in error; and I agree with him that it may be taken as proved that all the materials of such deposits, with the exception, of course, of the remains of animals which we now know to live at the bottom at all depths, which occur in the deposit as foreign bodies, are derived from the surface.
[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured
by the soundings of H.M.S. Challenger during her cruise in the Southern
Seas, in the early part of the year 1874."—Proceedings of the Royal
Society, Nov. 26, 1874.]
"Mr. Murray has combined with a careful examination of the soundings a constant use of the tow-net, usually at the surface, but also at depths of from ten to one hundred fathoms; and he finds the closest relation to exist between the surface fauna of any particular locality and the deposit which is taking place at the bottom. In all seas, from the equator to the polar ice, the tow-net contains Globigerinoe. They are more abundant and of a larger size in warmer seas; several varieties, attaining a large size and presenting marked varietal characters, are found in the intertropical area of the Atlantic. In the latitude of Kerguelen they are less numerous and smaller, while further south they are still more dwarfed, and only one variety, the typical Globigerina bulloides, is represented. The living Globigerinoe from the tow-net are singularly different in appearance from the dead shells we find at the bottom. The shell is clear and transparent, and each of the pores which penetrate it is surrounded by a raised crest, the crest round adjacent pores coalescing into a roughly hexagonal network, so that the pores appear to lie at the bottom of a hexagonal pit. At each angle of this hexagon the crest gives off a delicate flexible calcareous spine, which is sometimes four or five times the diameter of the shell in length. The spines radiate symmetrically from the direction of the centre of each chamber of the shell, and the sheaves of long transparent needles crossing one another in different directions have a very beautiful effect. The smaller inner chambers of the shell are entirely filled with an orange-yellow granular sarcode; and the large terminal chamber usually contains only a small irregular mass, or two or three small masses run together, of the same yellow sarcode stuck against one side, the remainder of the chamber being empty. No definite arrangement and no approach to structure was observed in the sarcode, and no differentiation, with the exception of round bright-yellow oil-globules, very much like those found in some of the radiolarians, which are scattered, apparently irregularly, in the sarcode. We never have been able to detect, in any of the large number of Globigerinoe which we have examined, the least trace of pseudopodia, or any extension, in any form, of the sarcode beyond the shell.
* * * * *
"In specimens taken with the tow-net the spines are very usually absent; but that is probably on account of their extreme tenuity; they are broken off by the slightest touch. In fresh examples from the surface, the dots indicating the origin of the lost spines may almost always be made out with a high power. There are never spines on the Globigerinoe from the bottom, even in the shallowest water."
There can now be no doubt, therefore, that Globigerinoe live at the top of the sea; but the question may still be raised whether they do not also live at the bottom. In favour of this view, it has been urged that the shells of the Globigerinoe of the surface never possess such thick walls as those which are fouled at the bottom, but I confess that I doubt the accuracy of this statement. Again, the occurrence of minute Globigerinoe in all stages of development, at the greatest depths, is brought forward as evidence that they live in situ. But considering the extent to which the surface organisms are devoured, without discrimination of young and old, by Salpoe and the like, it is not wonderful that shells of all ages should be among the rejectamenta. Nor can the presence 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 conclusive evidence that the Globigerinoe live at the bottom. Such as die at the surface, and even many of those which are swallowed by other animals, may retain much of their protoplasmic matter when they reach the depths at which the temperature sinks to 34° or 32° Fahrenheit, where decomposition must become exceedingly slow.
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.