924 
THE VOYAGE OF H.M.S. CHALLENGER. 
action of the solvent than the thicker though smaller, Globigerina shells, this apparent 
anomaly will be explained. The agent concerned in the removal of these calcareous 
shells is believed to be sea water itself, and the carbonic acid dissolved in it. This 
question is discussed in Chapter XXII. (see p. 981). 
“ The action which suffices to dissolve the calcareous matter has little or no effect 
upon the silica, and so the siliceous shells accumulate and form a Radiolarian ooze in the 
central portions of the Pacific. A Diatom ooze has been found only in the Southern 
Ocean south of lat. 45° S. 
“ Red clay may be found anywhere within lats. 45° N. and S., and at depths greater 
than 2200 fathoms. It passes at its margins into the organic calcareous or siliceous 
oozes, found in the lesser depths of the abysmal regions, or into the terrigenous 
deposits. In its typical form the red clay occupies a larger area than any of the other 
true deep-sea deposits, covering the bottom in vast regions of the North and South 
Pacific, Atlantic, and Indian Oceans. As above remarked, this clay may be said to be 
universally distributed over the floor of the oceanic basins; but it only appears as a 
characteristic deposit at points where the siliceous and calcareous organisms do not 
conceal its proper characters. 
“ The abysmal region in which occur the organic oozes and red clay consists of vast- 
undulating plains from two to five miles beneath the surface of the sea, the average 
being about three miles, here and there interrupted by huge volcanic cones (the oceanic 
islands). No sunlight ever reaches these deep cold tracts ; the range of temperature over 
them is not more than 7°, viz., from 31° to 38°, and is apparently constant through- 
out the whole year in each locality. Plant life is absent, and although animals 
belonging to all the great invertebrate types are present, there is no great variety of 
form nor abundance of individuals. Change of any kind is exceedingly slow. 
“The abysmal region occupied by the organic oozes and red clay is estimated to 
occupy about three-eighths of the earth’s surface, or an area equal to that of the 
continents, while the region between the abysmal areas and the continents, — that covered 
by the terrigenous deposits, is estimated to occupy the remaining two-eighths of the 
surface of the globe. 
“ The terrigenous deposits of lakes, shallow seas, enclosed seas, and the shores of the 
continents, reveal the equivalents of chalks, green sands, sandstones, conglomerates, 
shales, marls, and other sedimentary formations. Such formations as certain Tertiary 
deposits of Italy, Radiolarian earth from Barbados, and portions of the Chalk where 
pelagic conditions are indicated, must be regarded as having been laid down rather along 
the border of a continent than in a true oceanic area. The argillaceous and calcareous 
rocks, recently discovered by Dr. Guppy, in the upraised coral islands in the Solomon 
group, are nearly identical with the volcanic muds, the Pteropod and Globigerina oozes 
of the Pacific are, however, also represented. 
