524 
NATURE 
[SEPTEMBER 28, 1899 
to recognise in these deposits an accumulation of materials 
analogous to many of the marine stratified rocks of the con- 
tinents, such as sandstones, quartzites, shales, marls, greensands, 
chalks, limestones, conglomerates, and volcanic grits. 
With increasing depth and distance from the continents the 
deposits gradually lose their terrigenous character, the particles 
derived directly from the emerged land decrease in size and in 
number, the evidences of mechanical action disappear, and the 
deposits pass slowly into what have been called Pelagic De- 
posits at anaverage distance of about 200 miles from continental 
coast-lines. The materials composing Pelagic Deposits are not 
directly derived from the disintegration of the continents and 
other land-surfaces. They are largely made up of the shells and 
skeletons of marine organisms secreted in the surface waters of 
the ocean, consisting either of carbonate of lime, such as Pelagic 
Molluses, Pelagic Foraminifera, and Pelagic Algze, or of silica, 
such as Diatoms and Radiolarians. The inorganic constituents 
of the Pelagic Deposits are for the most part derived from the 
attrition of floating pumice, from the disintegration of water- 
logged pumice, from showers of volcanic ashes, and from the 
débris ejected from submarine volcanoes, together with the pro- 
ducts of their decomposition. Quartz particles, which play so 
important a 7é/e in the Terrigenous Deposits, are almost wholly 
absent, except where the surface waters of the ocean are affected 
by floating ice, or where the prevailing winds have driven the 
desert sands far into the oceanic areas. Glauconite is likewise 
absent from these abysmal regions. The various kinds of 
Pelagic Deposits are named according to their characteristic 
constituents, Pteropod Oozes, Globigerina Oozes, Diatom 
Oozes, Radiolarian Oozes, and Red Clay. 
The distribution of the deep-sea deposits over the floor of the 
ocean is shown on the map here exhibited, but it must be re- 
membered that there is no sharp line of demarcation between 
them ; the Terrigenous pass gradually into the Pelagic Deposits, 
and the varieties of each of these great divisions also pass in- 
sensibly the one into the other, so that it is often difficult to fix 
the name of a given sample. 
On another map here exhibited the percentage distribution of 
carbonate of lime in the deposits over the floor of the ocean has 
been represented, the results being founded on an extremely 
large number of analyses. The results are also shown in the 
following table :— 
Sq. Geo. Miles. Percentage. 
Over 75% CaCO, 6,000,000 58 
5o\to 75% 5; 24,000,000 23°2 
Pic) “Coys 14,000,000 13°5 
Wnder 25/405, 59,000,000 575 
103,000,000 100 
The carbonate of lime shells derived from the surface play 
a great and puzzling vé/e in all deep-sea deposits, varying in 
abundance according to the depth of the ocean and the temper- 
ature of the surface waters. In tropical regions removed from 
land, where the depths are less than 600 fathoms, the carbonate 
of lime due to the remains of these organisms from the surface 
may rise to 80 or 90 per cent. ; with increase of depth, and 
under the same surface conditions, the percentage of carbonate 
of lime slowly diminishes, till, at depths of about 2000 fathoms, 
the average percentage falls to about 60, at 2400 fathoms to 
about 30, and at about 2600 fathoms to about 10, beyond which 
depth there may be only traces of carbonate of lime due to the 
presence of surface shells. The thin and more delicate surface 
shells first disappear from the deposits, the thicker and denser 
ones alone persist to greater depths. A careful examination of 
a large number of observations shows that the percentage of 
carbonate of lime in the deposits falls off much more rapidly 
at depths between 2200 and 2500 fathoms than at other depths. 
The Red Clay, which occurs in all the deeper stretches of the 
ocean far from land, and covers nearly half of the whole sea- 
floor, contains—in addition to volcanic débris, clayey matter, 
the oxides of iron and manganese—numerous remains of whales, 
sharks and other fishes, together with zeolitic crystals, man- 
ganese nodules, and minute magnetic spherules, which are be- 
lieved to have a cosmic origin. One hawl of a small trawl in 
the Central Pacific brought to the surface on one occasion, from 
a depth of about two and a half miles, many bushels of man- 
ganese nodules, along with fifteen hundred sharks’ teeth, over 
fifty fragments of earbones and other bones of whales. Some of 
these organic remains, such as the Carcharodon and Lamna 
NO. 1561, VOL. 60] 
teeth and the bones of the Ziphioid whales, belong apparently 
to extinct species. One or two of these sharks’ teeth, ear- 
bones, or cosmic spherules, may be occasionally found in a 
Globigerina Ooze, but their occurrence in this or any deposits 
other than Red Clay is extremely rare. 
Our knowledge of the marine deposits is limited to the super- 
ficial layers; as a rule, the sounding-tube does not penetrate 
more than six or eight inches, but in some positions the sound- 
ing-tube and dredge have been known to sink fully two feet 
into the deposit. Sometimes a Red Clay is overlaid by a 
Globigerina Ooze, more frequently a Red Clay overlies a Glob- 
igerina Ooze, the transition between the two layers being either 
abrupt or gradual. In some positions it is possible to account 
for these layers by referring them to changes in the condition 
of the surface waters, but in other situations it seems necessary 
to call in elevations and subsidences of the sea-floor. 
If the whole of the carbonate of lime shells be removed by 
dilute acid from a typical sample of Globigerina Ooze, the 
inorganic residue left behind is quite similar in composition to 
a typical Red Clay. This suggests that possibly, owing to some 
hypogene action, such as the escape of carbonic acid through 
the sea-floor, a deposit that once was a Globigerina Ooze 
might be slowly converted into a Red Clay. However, this is 
not the interpretation which commends itself after an ex- 
amination of all the data at present available ; a consideration 
of the rate of accumulation probably affords a more correct 
interpretation. It appears certain that the Terrigenous Deposits 
accumulate much more rapidly than the Pelagic Deposits. 
Among the Pelagic Deposits, the Pteropod and Globigerina 
Oozes of the tropical regions, being made up of the calcareous 
shells of a much larger number of tropical species, apparently 
accumulate at a greater rate than the Globigerina Oozes in 
extra-tropical areas. Diatom Ooze being composed of both 
calcareous and siliceous organisms, has again a more rapid rate 
of deposition than Radiolarian Ooze. In Red Clay the mini- 
mum rate of accumulation takes place. The number of sharks’ 
teeth, of earbones and other bones of Cetaceans and of cosmic 
spherules in a deposit may indeed be taken as a measure of the 
rate of deposition. These spherules, teeth and bones are 
probably more abundant in the Red Clays, because few other 
substances there fall to the bottom to cover them up, and they 
thus form an appreciable part of the whole deposit. The 
volcanic materials in a Red Clay having, because of the slow 
accumulation, been for a long time exposed to the action of sea~ 
water, have been profoundly altered. The massive manganese- 
iron nodules and zeolitic crystals present in the deposit are 
secondary products arising from the decomposition of these 
volcanic materials, just as the formation of glauconite, 
phosphatic, and calcareous and barytic nodules accompanies 
the decomposition of terrigenous rocks and minerals in deposits 
nearer continental shores. There is thus a striking difference 
between the average chemical and mineralogical composition of 
Terrigenous and Pelagic Deposits. 
It would be extremely interesting to have a detailed examin- 
ation of one of those deep holes where a typical Red Clay is 
present, and even to bore some depth into such a deposit if 
possible, for in these positions it is probable that not more than 
a few feet of deposit have accumulated since the close of the 
Tertiary period. One such area lies to the south-west of 
Australia, and its examination might possibly form part of the 
programme of the approaching Antarctic explorations. 
Life on the Ocean-floor. 
It has already been stated that plant-life is limited to the 
shallow waters, but fishes and members of all the invertebrate 
groups are distributed over the floor of the ocean at all depths. 
The majority of these deep-sea animals live by eating the mud, 
clay or ooze, or by catching the minute particles of organic 
matter which fall from the surface. It is probably not far from 
the truth to say that three-fourths of the deposits now covering 
the floor of the ocean have passed through the alimentary canals 
of marine animals. These mud-eating species, many of which 
are of gigantic size when compared with their allies living in the 
shallow coastal waters, become in turn the prey of numerous 
rapacious animals armed with peculiar prehensile and tactile 
organs. Some fishes are blind, while others have very large 
eyes. Phosphorescent light plays a most important 7é/e in the 
deep sea, and is correlated with the prevailing red and brown 
colours of deep-sea organisms. Phosphorescent organs appear 
sometimes to act asa bull’s-eye lantern to enable particles of 
