NOVEMBER 24, 1899. ] 
conditions, may almost everywhere be de- 
tected, and it is possible to recognize in 
these deposits an accumulation of materials 
analogous to many of the marine stratified 
rocks of the continents, 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 de- 
crease in size and in number, the evidences 
of mechanical action disappear, and the de- 
posits pass slowly into what have been called 
Pelagic Deposits at an average distance of 
about 200 miles from continental coast- 
lines. The materials composing Pelagic 
Deposits are nof directly derived from the 
disintegration of the continents and other 
land-surfaces. They are largely made up 
of the shells and skeletons of marine organ- 
isms secreted in the surface waters of the 
ocean, consisting either of carbonate of lime, 
such as pelagic Molluscs, pelagic Foramini- 
fera, 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 vol- 
canic ashes and from the débris ejected from 
submarine volcanoes, together with the 
products of their decomposition. Quartz 
particles which play so important a réle 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. 
SCIENCE. 757 
The distribution of the deep-sea deposits 
over the floor of the ocean is shown on the 
map here exhibited, but it must be remem- 
bered that there is no sharp line of de- 
marcation between them ; the Terrigenous 
pass gradually into the Pelagic Deposits, 
and the varieties of each of these great di- 
visions also pass insensibly 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 per- 
centage 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. Geog. Miles. Percentage. 
Over 75% CaCO,...... 6,000,000 58 
50 to 75% He Meeere 24,000, 000 23°2 
25 to 50% SNe ee 14,000,000 13°35 
Under 25% Paehercce 59,000,000 57-5 
103,000,000 100 
The carbonate of lime shells derived from 
the surface play a great and puzzling réle 
in all deep-sea deposits, varying in abund- 
ance according to the depth of the ocean 
and the temperature 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 di- 
minishes, till, at depths of about 2,000 
fathoms, the average percentage falls to 
about 60, at 2,400 fathoms to about 30, and 
at about 2,600 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 de- 
posits ; the thicker and denser ones alone 
persist to greater depths. A careful ex- 
amination of a large number of observations 
