188 
THE VOYAGE OF H.M.S. CHALLENGER. 
forms of vegetable and animal life are very numerous, the former being especially so 
in the shallower water where there is abundant sunlight. Zoologists have divided this 
region into several sub-zones, such as Laminarian, Coralline, and Coral zones. 
Deep-Sea Deposits . — The deposits of this vast zone or region extend from the 100- 
fathom line down to the greatest depths of the ocean, and they cover considerably more 
than one-half of the earth’s surface. Gravels and sands, which prevail in shallow water, 
are only accidentally met with in the deep-sea areas. Muds, organic oozes, and clays are 
the characteristic deposits, and in their physical properties they present great uniformity. 
In special regions where the surface waters are aifected by floating ice a greater diversity 
is introduced from the varied nature of the transported materials. Tides, currents, and 
waves produce some mechanical eflFects at the upper limits of the deep-sea region, but on 
the whole there is an absence of the phenomena of erosion, and mechanical actions would 
appear to be absent except in the case of submarine eruptions. The depth is too great 
for sunlight to penetrate, and vegetable life, if present, is limited to the deposits near the 
100-fathom line. Animal life, on the other hand, appears to be present everywhere 
throughout the deep sea, being more abundant, however, in the shallower depths near 
continental shores. The temperature is below 40° F. throughout the larger part of the 
area, and if subject to variation with latitude or change of season, these changes affect 
only the depths immediately beyond the 100-fathom line. Throughout the whole 
region there is a very uniform set of conditions. In the shallow- water and littoral 
zones, owing to the rapid accumulation and the mechanical effects of transport and 
erosion, the effects of chemical modification are not apparent in the deposits, but in 
Deep-Sea Deposits, in consequence of the less rapid rate of accumulation, absence of 
transport, the nature and the small size of the particles, many evident chemical reactions 
have taken place, resulting in the formation in situ of glauconite, phosphatic and 
manganese nodules, zeolites, and other secondary products. As we descend from the 
100-fathom line into deeper water and approach the central regions of the great ocean 
ba.sins, tlie deposits undergo a change, arising from a diminution in the number and size 
of particles derived directly from the land, together with an increasing abundance of 
amorphous matter arising from the ultimate decomposition of minerals and rocks, and 
accompanied in all moderate depths by an increase of the remains of pelagic organisms. 
We thus pass insensibly from those Deep-Sea Deposits of a terrestrial origin, which 
we call “ Terrigenous,” to tho.se Deep-Sea Depo.sits denominated “ Pelagic,” in which 
the remains of calcareous and siliceous organisms, clays, and other substances of secondary 
origin, play the })rincipal role. 
With these introductory observations on Marine Deposits in general, we now proceed 
to consider the sj)ecial subjects of this Report, — the nature, composition, and distribution 
of Deep-Sea Deposits. 
