NOVEMBER 24, 1899. ] 
depths. These observations are now suffi- 
ciently numerous to permit of some general 
statements as to the distribution of tem- 
perature 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 shifting 
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 Professor 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 cannot, 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 surface 
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 tem- 
perature like these cause the destruction of 
innumerable marine animals, and produce 
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 
@ 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 bot- 
tom of the North Atlantic basin and over a 
SCIENCE. 
755 
very large portion of the Pacific the tem- 
perature is higher than 35° F. In depths 
beyond 2,000 fathoms the average tempera- 
ture 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 tempera- 
ture 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 sur- 
face 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 the surface according to the known 
laws of gas absorption. In this way myriads 
of living animals are enabled to carry on 
their existence 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 pro- 
cesses of oxidation and respiration which 
are there going on. 
The deep sea is a region of darkness as 
well as of low temperature, 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 sur- 
face of the lithosphere. The abundant 
deep-sea fauna, which covers the floor of 
the ocean, is, therefore, ultimately depen- 
dent for food upon organic matter assimi- 
lated 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 geographical miles of the sea 
floor lies within the 100-fathom line, and 
