SEPTEMBER 28, 1899] 
NATURE 
3000 fathoms have been called ‘‘ Deeps,” and distinctive names 
have been conferred upon them. Forty-three such depressions 
are now known, and the positions of these are shown on the map 
here exhibited ; twenty-four are situated in the Pacific Ocean, 
three in the Indian Ocean, fifteen in the Atlantic Ocean, and 
one in the Southern and Antarctic Oceans. The area occupied 
by these thirty-nine deeps is estimated at 7,152,000 square 
geographical miles, or about 7 per cent. of the total water-surface 
of the globe. Within these deeps over 250 soundings have 
been recorded, of which twenty-four exceed 4000 fathoms, 
including three exceeding 5000 fathoms. 
Depths exceeding 4000 fathoms (or four geographical miles) 
have been recorded within eight of the deeps, viz. in the North 
Atlantic within the Nares Deep; in the Antarctic within the 
Ross Deep ; in the Banda Sea within the Weber Deep; in the 
North Pacific within the Challenger, Tuscarora, and Supau 
Deeps ; and in the South Pacific within the Aldrich and Richards 
Deeps. Depths exceeding 5000 fathoms have been hitherto re- 
corded only within the Aldrich Deep of the South Pacific, to the 
east of the Kermadecs and Friendly Islands, where the greatest 
depth is 5155 fathoms, or 530 feet more than five geographical 
miles, being about 2000 feet more below the level of the sea than 
the summit of Mount Everest in the Himalayas is above it. 
The levels on the surface of the lithosphere thus oscillate between 
the limits of about ten geographical miles (more than eighteen 
kilometres). 
Temperature of the Ocean-floor. 
Our knowledge of the temperature on the floor of the ocean 
is derived from observations in the layers of water immediately 
above the bottom by means of deep-sea thermometers, from 
the electric resistance of telegraph cables resting on the bed of 
the great ocean-basins, and from the temperature of large masses 
of mud and ooze brought up by the dredge from great depths. 
These observations are now sufficiently numerous to permit of 
some general statements as to the distribution of temperature 
over the bottom of the great oceans. 
All the temperatures recorded up to the present time in the 
sub-surface waters of the open ocean indicate that at a depth 
of about 100 fathoms seasonal variation of temperature disappears. 
Beyond that depth there is a constant, or nearly constant, tem- 
perature at any one place throughout the year. In some special 
positions, and under some peculiar conditions, a lateral shift- 
ing of large bodies of water takes place on the floor of the ocean 
at depths greater than 100 fathoms. This phenomenon has 
been well illustrated by Prof. Libbey off the east coast of North 
America, where the Gulf Stream and Labrador Current run 
side by side in opposite directions. This lateral shifting can- 
not, however, be called seasonal, for it appears to be effected 
by violent storms, or strong off-shore winds bringing up colder 
water from considerable depths to supply the place of the sur- 
face drift, so that the colder water covers stretches of the ocean’s 
bed which under normal conditions are overlaid by warmer 
strata of water. Sudden changes of temperature like these 
cause the destruction of innumerable marine animals, and pro- 
duce very marked peculiarities in the deposits over the areas 
thus affected. 
It is estimated that 92 per cent. of the entire sea-floor has a 
temperature lower than 40° F. This is in striking contrast to 
the temperature prevailing at the surface of the ocean, only 16 
per cent. of which has a mean temperature under 40° F. The 
temperature over nearly the whole of the floor of the Indian 
Ocean in deep water is under 35° F. A similar temperature 
occurs over a large part of the South Atlantic and certain parts 
of the Pacific, but at-the bottom of the North Atlantic basin 
and over a very large portion of the Pacific the temperature is 
higher than 35° F. In depths beyond. 2000 fathoms, the 
average temperature over the floor of the North Atlantic is 
about 2° F, above the average temperature at the bottom of 
the Indian Ocean and South Atlantic, while the average tem- 
perature of the bed of the Pacific is intermediate between 
these. 
It is admitted that the low temperature of the deep sea has 
been acquired at the surface in Polar and sub-Polar regions, 
chiefly within the higher latitudes of the southern hemisphere, 
where the cooled surface water sinks to the bottom and spreads 
slowly over the floor of the ocean into equatorial regions. These 
cold waters carry with them into the deep sea the gases of the 
atmosphere, which are everywhere taken up. at ithe surface 
according to the known laws of gas absorption. In this way 
myriads of living animals are enabled to carry on their existence 
NO. 1561, VOL. 60] 
523 
at all depths in the open ocean. The nitrogen remains more or 
less constant at all times and places, but the proportion of 
oxygen is frequently much reduced in deep water, owing to the 
processes of oxidation and respiration which are there going on. 
The deep sea is a region of darkness as well as of low tem- 
perature, for the direct rays of the sun are wholly absorbed in 
passing through the superficial layers of water. Plant-life is in 
consequence quite absent over 93 per cent. of the bottom of the 
ocean, or 66 per cent. of the whole surface of the lithosphere. 
The abundant deep-sea fauna, which covers the floor of the 
ocean, is therefore ultimately dependent for food upon organic 
matter assimilated by plants near its surface, in the shallower 
waters near the coast-lines, and on the surface of the dry land 
itself. 
As has been already stated, about 7,000,000 square geo- 
graphical miles of the sea-floor lies within the 1o0-fathom line, 
and this area is in consequence subject to seasonal variations of 
temperature, to strong currents, to the effects of sunlight, and 
presents a great variety of physical conditions. The planktonic 
plant-life is here reinforced by the littoral sea-weeds, and animal- 
life is very abundant. About 40 per cent. of the water over the 
bottom of this shallow-water area has a mean temperature under 
40° F., while 20 per cent. has a mean temperature between 40° 
and 60° F., and 40 per cent. a temperature of over 60° F. 
It follows from this that only 3 per cent. of the floor of the 
ocean presents conditions of temperature favourable for the 
vigorous growth of corals and those other benthonic organisms 
which make up coral reefs and require a temperature of over 
60° F. all the year round. On the other hand, more than half 
of the surface of the ocean has a temperature which never falls 
below 60° F. at any time of the year. In these surface-waters 
with a high temperature, the shells of Pelagic Molluscs, Foram- 
inifera, Algee, and other planktonic organisms are secreted in 
great abundance, and fall to the bottom after death. 
It thus happens that, at the present time, over nearly the 
whole floor of the ocean we have mingled in the deposits the 
remains of organisms which had lived under widely different 
physical conditions, since the remains of organisms which lived 
in tropical sunlight, and in water ata temperature above 80° F., 
all their lives, now lie buried in the same deposit on the sea- 
floor together with the remains of other organisms which lived 
all their lives in darkness and at a temperature near to the 
freezing point of fresh water. 
Marine Deposits on the Ocean-floor. 
The marine deposits now forming over the floor of the ocean 
present many interesting peculiarities according to their geo- 
graphical and bathymetrical position. On the continental 
shelf, within the 1oo-fathom line, sands and gravels pre- 
dominate, while on the continental slopes beyond the I0o- 
fathom line, Blue Muds, Green Muds, and Red Muds, together 
with Volcanic Muds and Coral Muds, prevail, the two latter 
kinds of deposits being, however, more characteristic of the 
shallow water around oceanic islands. The composition of all 
these Terrigenous Deposits depends on the structure of the 
adjoining land. Around continental shores, except where coral 
reefs, limestones, and volcanic rocks are present, the materials 
consist principally of fragments and minerals derived from the 
disintegration of the ancient rocks of the continents, the most 
characteristic and abundant mineral species being quartz. River 
detritus extends in many instances far from the land, while 
off high and bold coasts, where no large rivers enter the 
sea, pelagic conditions may be found in somewhat close prox- 
imity to the shore-line, Itis in these latter positions that Green 
Muds containing much glauconite, and other deposits containing 
many phosphatic nodules, have for the most part been found ; 
as, for instance, off the eastern coast of the United States, off 
the Cape of Good Hope, and off the eastern coasts of Australia 
and Japan. The presence of glauconitic grains and phosphatic 
nodules in the deposit at these places appears tc be very intimately 
associated with a great annual range of temperature in the surface 
and shallow waters, and the consequent destruction of myriads 
of marine animals. As an example of this phenomenon may be 
mentioned the destruction of the tile-fish in the spring of 1882 
off the eastern coast of North America, when a layer six feet in 
thickness of dead fish and other marine animals was believed to 
cover the océan floor for many square miles. 
Inall the Terrigenous Deposits the evidences of the mechanical 
action of tides, of currents, and of a great variety of physical 
conditions, may almost everywhere be detected, and it is possible 
