706 
this area is in consequence subject to sea- 
sonal variations of temperature, to strong 
currents, to the effects of sunlight and pre- 
sents a great variety of physical conditions. 
The planktonic plant life is here reinforced 
by the littoral seaweeds 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 favorable 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 
year round. On the other hand, more than 
half of the surface of the ocean has a tem- 
perature 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, Foraminifera, Alge, 
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 re- 
mains of organisms which lived in tropical 
sunlight, and in water at a temperature 
above 80° F., all their lives, now lie buried 
on the same deposit on the sea-floor, to- 
gether 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 interest- 
ing peculiarities according to their geo- 
graphical and bathymetrical position. On 
SCIENCE. 
[N.S. Vou. X. No. 256. 
the continental shelf, within the 100-fathom 
line, sands and gravel predominate, while 
on the continental slopes beyond the 100- 
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 depend on the 
structure of the adjoining land. Around 
continental shores, except where coral reefs, 
limestones and volcanic rocks are present, 
the material consists 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 ex- 
tends 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 insomewhat closer proximity 
to the shore line. Itis in these latter po- 
sitions 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 east- 
ern coasts of Australia and Japan. The 
presence of glauconitic grains and phos- 
phatic nodules in the deposit at these places 
appears tobe very intimately associated with 
a great annual range of temperature in the 
surface and shallow waters, and the conse- 
quent destruction of myriads of marine 
animals. As an example of this phenome- 
non 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 ocean-floor for many square miles. 
In all the Terrigenous Deposits the evi- 
dences of the mechanical action of tides, of 
currents, and of a great variety of physical 
