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Parr II. Secr. ii. § 6.] MARINE DEPOSITS. 439 
fathoms they are often coloured green by glauconite. At greater 
depths they consist of blue or dark slate-coloured mud with a thin 
upper red or brown layer. ‘Throughout these land-derived sedi- 
ments particles of mica, quartz, and other minerals are distributed, 
the materials becoming coarser towards land. Pieces of wood, 
portions of fruits, and leaves of trees occur in them, and further 
indicate the reality of the transport of material from the land. Shells 
of pteropods, larval gasteropods, and lamellibranchs are tolerably 
abundant in these muds, with many infra-littoral species of Foramz- 
nifera, and diatoms. Below 1500 or 1700 fathoms pteropod shells 
seldom appear, while at 3000 fathoms hardly a foraminifer or any 
calcareous organism remains.’ Round volcanic islands the bottom is 
found to be covered with grey mud and sand derived from the 
degradation of volcanic rocks. ‘These deposits can be traced to great 
distances; from Hawaii they extend for 200 miles or more. Pieces 
of pumice, scorie, &c., occur in them, mingled with marine organisms, 
and more particularly with abundant grains, incrustations, and 
nodules of an earthy peroxide of manganese. Near coral-reefs the 
sea-floor is covered with a white calcareous mud derived from the 
abrasion of coral. The east coast of South America supplies a 
peculiar red mud which is spread over the Atlantic slope down to 
depths of more than 2000 fathoms. 
B. Abysmal.—Passing over at present the organic deposits which 
form so characteristic a feature on the floor of the deeper and more 
open parts of the ocean, we come to certain red and grey clays found 
at depths of more than 2000 fathoms down to the bottoms of the 
deepest abysses. These, by far the most wide-spread of oceanic 
deposits, consist of exceedingly fine clay, coloured sometimes red 
by iron-oxide, sometimes of a chocolate tint from manganese 
oxide, with grains of augite, felspar, and other volcanic minerals, 
pieces of palagonite and pumice, nodules of peroxide of manganese, 
and other mineral substances, together with Foraminifera, and in some 
regions a large proportion of siliceous Radiolaria. These clays seem 
to result from the decomposition of pumice and fine volcanic dust 
transported from volcanic islands into mid-ocean,? or from the 
accumulation of the detritus of submarine eruptions. The absence 
in them of obviously land-derived non-volcanic minerals seems to 
point to an abundance of submarine volcanic action, of which as yet 
no other evidence has been obtained. The extreme slowness of deposit 
is strikingly brought out in the tracts of sea-floor farthest removed from 
land. From these lovalities great numbers of sharks’ teeth, with ear- 
bones and other bonesof whales, were dredged up in the Challenger ex- 
pedition,—some of them quite fresh, others partially crusted with perox- 
ide of manganese, and some wholly and thickly surrounded with that 
substance. We cannot suppose that sharks and whales so abounded in 
the sea at one time as to cover the floor of the ocean with a continuous 
1 Murray, Proc. Roy. Soc. 1876, p. 519. 
? Murray, op. eit. and Proc. Roy Soc. Edin. ix. p. 247. 
