EXPEDITION OF THE CHALLENGER. 33 



rla to diatoms is much greater than in the colder seas. Nevertheless 

 the composition of the deep-sea mud of this intermediate zone is en- 

 tirely 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 tlic 

 account which he published in the " Monatsberichte " of the Berlin 

 Academy for the year 1853, of the soundings obtained by Lieutenant 

 Berry man, of the United States Navy, in the Nortli Atlantic, between 

 Newfoundland and the Azores. 



Observations which confirm those of Ehrenberg in all essential 

 I'espects have been made by Prof. Bailey, myself. Dr. Wallich, Dr. 

 Carpenter, and Prof. Wyville Thomson, in their earlier cruises ; and 

 the continuation of the Glohigerlna 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 an.\ variety of the Foramimfera 

 diminish, and even the Glohigerince become dwarfed. And this re- 

 sult, 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, MacUolaria, and diatoms, is obscured and overpowered 

 bj^.the immensely greater amount of calcareous sediment, which arises 

 from the asist'es-ation of the skeletons of dead Foraminifera. The 

 similarity of the deposit, thus composed of a large percentage of car- 

 bonate 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 resouably doubted that 

 ordinary metamorphic agencies are competent to convert the " modern 

 chalk" into hard limestone, or even into crystalline marble. 



Ehrenberg aj^pears to have taken it for granted that the Glohi- 



' The following passages, in Ehrenberg's memoir on " The Organisms in the Chalk 

 which are still living" (18o9), 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 Poli/thalamla, secondary are not distinguish- 

 able 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." 



VOL. VII. 3 



