340 
THE VOYAGE OF H.M.S. CHALLENGER. 
operating upon very large samples of sea-water carefully collected from the central regions 
of the Atlantic, Mediterranean, and Indian Ocean, they have shown that a small quantity 
of mechanically-suspended hydrated silicate of alumina is always present in the water of 
these regions.* 
If these observations be confirmed by further investigations, it must be admitted that 
a small quantity of clay can be transported to the central regions of the great ocean 
basins, and, falling to the bottom, may there make up a part of Eed Clays and of the 
clayey matter in pelagic deposits. The amount of clay thus transported must, however, 
be very small, for otherwise it would mask the minute fragments of pumice, or the 
organic remains, which there make uj) so large a part of the deposits. 
In the deep-sea regions far from land the clay on the floor of the ocean appears, for 
the most part, to arise from the decomposition in situ of water-borne pumice and other 
volcanic rocks and minerals, which make up the principal inorganic constituents of the 
deposits of these regions. The vitreous and vesicular nature, as well as the small dimen- 
sions, of these volcanic fragments render them in a special manner liable to disintegration 
and decomposition, with the production of clay ; especially is this the case with the basic 
volcanic glasses. All the deep-sea clays contain a large number of minute glassy and 
other mineral particles, and hence they fuse readily before the blowpipe into a black 
magnetic bead. The amorphous material observed in these deposits is regarded as the 
argillaceous matter; it presents essentially vague characters, resembles a colloid substance, 
has no definite contours, is perfectly isotropic, is generally colourless, and forms a 
gelatinous-like mass that connects and agglutinates the other materials in the clay or 
mud. With these indefinite physical characters it becomes very difficult to estimate 
even approximately the amount of pure amorphous argillaceous matter in the samples 
of a marine deposit. A very small quantity of this slimy-like matter, however, may 
give a distinctly clayey character to a calcareous or siliceous mud or ooze, especially when 
the mineral particles in the deposit are of small dimensions. 
The clayey matter of marine deposits must then be regarded as a chemical product 
arising from the decomposition of the aluminous silicates composing the crust of the 
earth, cxj)osed to the action of water, either on the dry land or at the bottom of the sea. 
It may be formed in situ on the sea-bottom, and this is especially the case in pelagic 
deposits, or the clayey matter may be transported from the land surfaces and coasts to 
the ocean basins, and this is what especially takes place in terrigenous deposits. The 
amount of clay varies according to the abundance of other substances in deposits, being 
lejust in calcareous deposits like Coral lUuds and Pteropod and Globigerina Oozes, where 
it Iwcomes masked by the accumulation of carbonate of lime, and greatest in Red Clays 
• .Murray nn<l Ir\nne “On .Silica and the .Siliceoufl Remains of Organisms in Modern Seas,” Proc. Poy. Soc. Edin.^ 
vol. xviii. j»jt. 229-2.'iO, 1S91. Further experiments have shown that sea-water with a salinity of 1’02.5, after remaining 
for over thirty <lays al>wdutely at rest, holds up in suspension finely-divided clay in amount equal to 625 tons in one 
cuVdc mile of the water (J. M.). 
