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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.
Thomson's expectation has been, to some extent, already verified. Thus besides Globigerina, there are eighteen species of deep-sea Foraminifera identical with species found in the chalk.
The bottom in these two soundings might have been called 'grey ooze, for although its nature has altered entirely from the Globigerina ooze, the red clay into which it is rapidly passing still contains a considerable admixture of carbonate of lime.
Your laughter would be justified by the fact that all experience tends to show that oyster-shells are formed by the agency of oysters, and in no other way. And if there were no better reasons, we should be justified, on like grounds, in believing that Globigerina is not the product of anything but vital activity.
It therefore seems to be hardly doubtful that these wonderful creatures live and die at the depths in which they are found. Dr. Wallich ascertained that the sea-bottom at this point consisted of the ordinary Globigerina ooze, and that the stomachs of the star-fishes were full of Globigerinæ.
In a word, it is certain that these animals have lived and died when the place which they now occupy was the surface of as much of the chalk as had then been deposited; and that each has been covered up by the layer of Globigerina mud, upon which the creatures imbedded a little higher up have, in like manner, lived and died.
One of the commonest is something like a badly grown raspberry, being formed of a number of nearly globular chambers of different sizes congregated together. It is called Globigerina, and some specimens of chalk consist of little else than Globigerina and granules. Let us fix our attention upon the Globigerina. It is the spoor of the game we are tracking.
"Again, the were gradually becoming more and more convinced that all the important elements of the Globigerina ooze lived on the surface, and it seemed evident that, so long as the condition on the surface remained the same, no alteration of contour at the bottom could possibly prevent its accumulation; and the surface conditions in the Mid-Atlantic were very uniform, a moderate current of a very equal temperature passing continuously over elevations and depressions, and everywhere yielding to the tow-net the ooze-forming Foraminifera in the same proportion.
Professor Thomson gives the following account of this capital discovery: "According to our present experience, the deposit of Globigerina ooze is limited to water of a certain depth, the extreme limit of the pure characteristic formation being placed at a depth of somewhere about 2,250 fathoms.
"We conclude, therefore, that the 'red clay' is not an additional substance introduced from without, and occupying certain depressed regions on account of some law regulating its deposition, but that it is produced by the removal, by some means or other, over these areas, of the carbonate of lime, which forms probably about 98 per cent. of the material of the Globigerina ooze.
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