Globigerinae of every size, from the smallest to the largest, are associated together in the Atlantic mud, and the chambers of many are filled by a soft animal matter.  This soft substance is, in fact, the remains of the creature to which the Globigerina shell, or rather skeleton, owes its existence—­and which is an animal of the simplest imaginable description.  It is, in fact, a mere particle of living jelly, without defined parts of any kind—­without a mouth, nerves, muscles, or distinct organs, and only manifesting its vitality to ordinary observation by thrusting out and retracting from all parts of its surface long filamentous processes, which serve for arms and legs.  Yet this amorphous particle, devoid of everything which, in the higher animals, we call organs, is capable of feeding, growing, and multiplying; of separating from the ocean the small proportion of carbonate of lime which is dissolved in sea-water; and of building up that substance into a skeleton for itself, according to a pattern which can be imitated by no other known agency.

The notion that animals can live and flourish in the sea, at the vast depths from which apparently living Giobigerinae have been brought up, does not agree very well with our usual conceptions respecting the conditions of animal life; and it is not so absolutely impossible as it might at first sight appear to be, that the Globigerinae of the Atlantic sea-bottom do not live and die where they are found.

[Illustration:  DIATOM OOZE DREDGED FROM A DEPTH OF 1950 FEET.

(Magnified nearly 300 diameters.)]

As I have mentioned, the soundings from the great Atlantic plain are almost entirely made up of Globigerinae, with the granules which have been mentioned, and some few other calcareous shells; but a small percentage of the chalky mud—­perhaps at most some five per cent of it—­is of a different nature, and consists of shells and skeletons composed of silex, or pure flint.  These siliceous bodies belong partly to the lowly vegetable organisms which are called Diatomaceae, and partly to the minute and extremely simple animals, termed Radiolaria.  It is quite certain that these creatures do not live at the bottom of the ocean, but at its surface—­where they may be obtained in prodigious numbers by the use of a properly constructed net.  Hence it follows that these siliceous organisms, though they are not heavier than the lightest dust, must have fallen, in some cases, through fifteen thousand feet of water, before they reached their final resting-place on the ocean floor.  And, considering how large a surface these bodies expose in proportion to their weight, it is probable that they occupy a great length of time in making their burial journey from the surface of the Atlantic to the bottom.

[Illustration:  RADIOLARIA. (a. Natural size. b. One-third natural size.)]