ria 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,[1] 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 Globi-
- ↑ The following passages, in Ehrenberg's memoir on "The Organisms in the Chalk which are still living" (1839), are conclusive: "7. The dawning period of the existing living organic creation, if such a period is distinguishable (which is doubtful), can only be supposed to have existed on the other side of, and below, the chalk formation; and thus, either the chalk, with its wide-spread and thick beds, must enter into the series of newer formations, or some of the accepted four great geological periods—the quaternary, tertiary, and secondary formations—contain organisms which still live. It is more probable, in the proportion of three to one, that the transition or primary period is not different, but that it is only more difficult to examine and understand, by reason of the gradual and prolonged chemical decomposition and metamorphosis of many of its organic constituents." "10. By the mass-forming Infusoria and Polythalamia, secondary are not distinguishable from tertiary formations; and, from what has been said, it is possible that, at this very day, rock-masses are forming in the sea, and being raised by volcanic agencies, the constitution of which, on the whole, is altogether similar to that of the chalk. The chalk remains distinguishable by its organic remains as a formation, but not as a kind of rock."
