Page:Popular Science Monthly Volume 7.djvu/43

Rh to diatoms is much greater than in the colder seas. Nevertheless the composition of the deep-sea mud of this intermediate zone is entirely different from that of the circumpolar regions.

The first exact information respecting the nature of this mud at depths greater than 1,000 fathoms was given by Ehrenberg, in the account which he published in the "Monatsberichte" of the Berlin Academy for the year 1853, of the soundings obtained by Lieutenant Berryman, of the United States Navy, in the North Atlantic, between Newfoundland and the Azores.

Observations which confirm those of Ehrenberg in all essential respects have been made by Prof. Bailey, myself. Dr. Wallich, Dr. Carpenter, and Prof. Wyville Thomson, in their earlier cruises; and the continuation of the Globigerina ooze over the South Pacific has been proved by the recent work of the Challenger, by which it is also shown, for the first time, that, in passing from the equator to high southern latitudes, the number and variety of the Foramimfera diminish, and even the Glbhigerinæ become dwarfed. And this result, it will be observed, is in entire accordance with the fact already mentioned that, in the sea of Kamtchatka, the deep sea mud was found by Bailey to contain no calcareous organisms.

Thus, in the whole of the "intermediate zone," the silicious deposit which is being formed there, as elsewhere, by the accumulation of sponge-spicula, Radiolaria, and diatoms, is obscured and overpowered by the immensely greater amount of calcareous sediment, which arises from the aggregation of the skeletons of dead Foraminifera. The similarity of the deposit, thus composed of a large percentage of carbonate of lime, and a small percentage of silex, to chalk, regarded merely as a kind of rock, which was first pointed out by Ehrenberg, is now admitted on all hands; nor can it be reasonably doubted that ordinary metamorphic agencies are competent to convert the "modern chalk" into hard limestone, or even into crystalline marble.

Ehrenberg appears to have taken it for granted that the