Ill EXPEDITION OF THE "CHALLENGER" 101 



Next, imagine sponges, Radiolaria, Foraminifera, 

 and diatcmaceous plants, such as those which now 

 exist in the deep-sea, to be introduced : they 

 would be distributed according to the same laws 

 as at present, the sponges (and possibly some of 

 the Formninifera) covering the bottom, while other 

 Foraminifera, with the Radiolaria and Diatomacew, 

 would increase and multiply in the surface waters. 

 In accordance with the existing state of thino-s, 

 the Radiolaria and Diatoms would have a universal 

 distribution, the latter gathering most thickly in 

 the polar regions, while the Foraminifera would 

 be largely, if not exclusively, confined to the inter- 

 mediate zone ; and, as a consequence of this distri- 

 bution, a bed of " chalk " would begin to form in 

 the intermediate zone, while caps of silicious rock 

 would accumulate on the circumpolar regions. 



Suppose, further, that a part of the intermediate 

 area were raised to within two or three hundred 

 fathoms of the surface — for an3rthing that we know 

 to the contrary, the change of level might deter- 

 mine the substitution of greensand for the 

 " chalk " ; while, on the other hand, if part of 

 the same area were depressed to three thousand 

 fathoms, that change might determine the substi- 

 tution of a different silicate of alumina and iron — • 

 namely, clay — for the " chalk " that would other- 

 wise be formed. 



If the Challenger hypothesis, that the red 

 clay is the residue left by dissolved Foraminiferous 



