
Parr IL. Szcr. iii. § 3.) OCEANIC OOZE. 469 
the upper waters, whence it descends as a kind of organic rain into the 
depths; though it may be questioned how far such fine sediment 
would be allowed to accumulate to a sufficient height on account of 
the scour of the ground-swell (p. 423). Mr. Murray holds also that 
the dead coral, attacked by the solvent action of the carbonic acid in 
‘the sea water, is removed in solution both from the lagoon (which 
may thus be deepened) and from the dead part of the outer face of 
the reef, which may in this way acquire greater steepness." 
Foraminiferal Ooze-—Recent deep-sea soundings and dredgings 
have shown that the bed of the Atlantic and other oceans is covered 
with a remarkable calcareous ooze formed of the remains of Fora- 
minifera, and chiefly of species of the genus Globigerina. Among 
abysmal deposits it ranks next in abundance to the red and grey 
clays of the deep sea (p. 439). It is a pale-grey marl, sometimes 
red from peroxide of iron, or brown from peroxide of manganese; 
and it usually contains more or less clay, even with occasional 
fragments of pumice. It covers an area of the North Atlantic 
probably not less than 1300 miles from east to west, by several 
hundred miles from north to south. 
(2.) Siliceous deposits formed from animal exuvie are illus- 
trated by another of the deep-sea formations brought to light by the 
Challenger researches. In certain regions of the western and 
middle Pacific Ocean, the bottom was found to be covered with an 
ooze consisting almost entirely of SRadiolaria. These minute 
organisms occur, indeed, more or less abundantly in almost all deep 
oceanic deposits. From the deepest sounding taken by the Challenger 
(4575 fathoms, or more than 5 miles) a radiolarian ooze was obtained 
(Fig. 181). The spicules of sponges likewise furnish materials 
towards these siliceous accumulations. 
In connection with the organic deposits of the sea-floor, reference 
may be made here to the chemical processes in progress there, and 
to the probable part taken in these processes by decaying animal 
matter. The precipitation of manganic oxide and its segregation in 
concretions, often round organic centres (p. 440), presents a close 
analogy to the formation of concretionary bog-iron ore through the 
operation of the humus acids in stagnant water. The crystallization 
of silicates in patches, cementing the particles of deep-sea ooze, 
observed during the Challenger expedition, is possibly also to 
be connected with the action of organic compounds (pp. 441, 463). 
The formation of flint concretions has been for many years a vexed 
question in geology. The constant association of flints with traces, 
more or less marked, of former abundant siliceous organisms seems 
to make the inference irresistible, that the substance of the flint has 
been derived from these organisms. The silica has first been ab- 
stracted from sea-water by living organisms. It has then been re- 
dissolved and redeposited (probably through the agency of de- 
composing organic matter), sometimes in amorphous concretions, 
1 Proc, Roy. Soc. Edin. 1880, p. 505. 
