42 THE POPULAR SCIENCE MONTHLY. 



The bag contained examples, those with calcareous shells rather stunted, of most 

 of the characteristic grou])s of the Southern Sea, including Umhellularia, Eupleo- 

 telln, Pterocriniis, Brisinga, OpMoglyj^ha, Pourtalesia, and one or two Mollusca. 

 Tliis is, however, very rarely the case. Generally the red clay is barren, or con- 

 tains only a very small number of forms." 



It must be admitted tliat it is very difficult at present to frame any 

 satisfactory explanation of the mode of origin of this singular deposit 

 of red clay. 



I cannot say that the theory put forward tentatively, and with 

 much reservation by Prof Thomson, that the calcareous matter is 

 dissolved out by the relatively fresh water of the deep currents from 

 the antarctic regions, appears satisfactory to me. Xor do I see my 

 way to the acceptance of the suggestion of Dr. Carpenter, that the 

 red clay is the result of the decomposition of previously-formed green- 

 sand. At present there is no evidence that greensand casts are ever 

 formed at great depths ; nor lias it been proved that Glauconite is 

 decomposable by the agency of water and carbonic acid. 



I think it probable that we shall have to wait some time for a suffi- 

 cient explanation of the origin of the abyssal red clay, no less than 

 for that of the sublittoral greensand in the intermediate zone. But 

 the importance of the establishment of the fact that these various 

 deposits are being formed in the ocean, at the present day, remains 

 the same, whether its rationale be understood or not. 



For suppose the globe to be evenly covered with sea, to a depth 

 say of a thousand fathoms then, whatever might be the mineral mat- 

 ter composing the sea-bottom, little or no deposit would be formed 

 upon it, the abrading and denuding action of water, at such a depth, 

 being exceedingly slight. Next, imagine sponges, Radiolaria^ Fora- 

 minifera, and diatomaceous 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 

 Foraminiferd) covering the bottom, while other Foraniinifera, with 

 the MacUolaria and Diatomacem^ would increase and multiply in the 

 surface-waters. In accordance with the existing state of things, the 

 Radlolaria and diatoms would have a universal distribution, the lat- 

 ter gathering most thickly in the polar regions, while the Forami- 

 nifera would be largely, if not exclusively, confined to the intermediate 

 zone ; and, as a consequence of this distribution, a bed of " chalk " 

 would begin to form in the intermediate zone, while caps of silicious 

 rock would accumulate on the circurapolar regions. 



Suppose, further, that a part of the intermediate area were raised 

 to within 200 or 300 fathoms of the surface for any thing that we 

 know to the contrary, the change of level might determine the sub- 

 stitution of greensand for the "chalk;" while, on the other hand, if 

 part of the same area were depressed to 3,000 fathoms, that change 

 might determine the substitution of a different silicate of ahunina 



