SUBMARINE DEPOSITS. 275 



most favorable conditions for their preservation, therefore, the 

 fossils would give very imperfect e^'idence in regard to the 

 variety of species which once constituted the fauna of any dis- 

 trict. 



I quote from Murray and Pourtales : — 



" Between Cape Hatteras and Lat. 31° 48' N., the deposits are green 

 muds or sands. They are with two exceptions under 1,000 fathoms, 

 and are mostly under the waters of the Gulf Stream, or along its inner 

 margin. The mineral particles are much the same as those in the de- 

 posits north of Cape Hatteras, but are all very much smaller, and have 

 evidently not been transported by ice. The mineral particles, with the 

 exception of the concretions formed at the bottom, seldom exceed 0.4 

 mm. in diameter, and consist of quartz, feldspars, augite, hornblende, 

 magnetite, and a few fragments of glassy rocks. Glauconitic grains 

 and casts are frequently very abundant, as are also gTains of manganese 

 peroxide. 



" The carbonate of lime makes up usually over fifty per cent of the 

 whole deposit, and consists chiefly of the dead shells of pelagic and other 

 f oraminif era, along with shells of pelagic mollusks, fragments of echino- 

 derms and polyzoa, ostracodes, and coccoliths. All the tropical species 

 of pelagic foraminifera are abundant in these deposits, while they 

 were relatively rare in the deposits along the coast to the north of Cape 

 Hatteras. 



" The remains of sihceous organisms, as diatoms, radiolarians, sponge 

 spicules, and glauconitic casts of foraminifera and other organisms, 

 make up usually ten or twelve per cent of the deposit. 



" The finer washings of these deposits are of a greenish color, which 

 seems to be chiefly due to the presence of some amorphous organic sub- 

 stance, the nature of which has not yet been determined. A similar 

 greenish matter was met with by the ' Challenger ' in deposits from 

 the same depths off the coasts of Africa, Australia, Japan, and China. 

 These are the modern greensands and muds to which attention was first 

 called by the late Professor Bailey. 



" Many of these deposits might equally well be called globigerina 

 ooze. 



" Phosphate of lime and manganese concretions are present in all 

 the deposits, and one remarkable concretion is described in detail, from 

 Station 317, in a depth of 333 fathoms, immediately under the waters 

 of the Gulf Stream. The ground from which the concretion was pro- 

 cured was hard, and it appears to have been formed in the position 

 from which it was dredged. Its form was irregular, — the greatest 

 diameter being about nine inches, — and of a mottled black and broAvn 



