,8^. DEEP-SEA DEPOSITS. 23 



manganese has been obtained in some way from the sea water. 

 May not the presence of manganese in the deep-sea deposits be due 

 to the action described by Dieulafait — precipitation from a solution 

 of the carbonate, in consequence of oxidation— and its local accumu- 

 lation as nodules to some of the little known chemical processes 

 going on upon the sea-bed ? The wide distribution of manganese, 

 in a finely divided state, in the red clay areas of the Pacific, is 

 shown by their chocolate-brown colour, and also by microscopic 

 examination of the deposits themselves. 



Another chemical product of great geological interest in course 

 of formation in existing seas is glauconite. It forms an appreciable 

 part of the green sands and muds, and is found as isolated grains in 

 most of the blue muds. The grains rarely, if ever, exceed i mm. 

 in diameter. The typical grains are always rounded, often mammil- 

 lated, and of a black or dark green colour. Their forms often 

 suggest in a vague manner those of foraminifera. Mixed with the 

 typical grains are others, of a pale green colour, which are clearly the 

 casts of those organisms. Foraminifera wholly or partially filled 

 with glauconite, or allied substances, were very commonly observed, 

 and the appearances often suggested the conclusion that the growth 

 of the glauconite in the interior had broken off portions of the shells. 

 We may therefore suppose that the typical grains, of vague form, 

 are produced by growth after the shell has disappeared. The 

 chemical and microscopic characters of the recent glauconite are 

 identical with those of the same substance occurring in our green- 

 sands, as may be seen by comparing the description and analysis 

 given in the Survey Memoir on the Geology of the Isle of Wight with 

 those of this Report. The minerals associated with glauconite are 

 those of the terrigenous deposits. All the facts point to the conclusion 

 that glauconite is formed in the first instance in the hollow spaces of 

 calcareous organic remains, and especially in the interior of the shells 

 of the foraminifera. 



A few phosphatic nodules were dredged by the " Challenger," 

 and those from the outer edge of the Agulhas bank and from a station 

 in deep water to the south of the Cape of Good Hope are described 

 in detail. They vary in diameter from i to 3 cm., as a rule, but may 

 occasionally measure as much as 6 cm. across. The phosphate of lime 

 is amorphous, and merely acts as a cement to the other constituents 

 which are accumulating at the spot where the nodule was obtained. 

 Thus, in the concretions from the station on the Agulhas bank, the 

 phosphate of lime encloses grains of glauconite and quartz ; while in 

 those from the deep-water station, the shells of foraminifera filled 

 with and more or less pseudomorphosed by phosphate of lime are to 

 be found. 



The only chemical deposits which remain to be described are 

 crystals of phillipsite. These were especially noted in the red clay 

 areas of the central Pacific, where they occasionally make up 20 or 



