DEPOSITS OF THE ATLANTIC IN DEEP WATER, ETC. 
31 
rests as to the material. This will no doubt be removed before 
long by the assistance of the chemists. 
Assuming, as is certainly probable, that foraminiferous mud 
is generally a nearly pure calcareous substance mixed with a 
small proportion of silica and some trace of organic matter, 
there can hardly be a doubt that its colour, texture, general 
nature, and contents, do correspond singularly with those of 
white chalk, and render it not unlikely that all those parts of 
Europe and Asia where chalk is now found were, during the 
cretaceous period, at least 8,000 feet below the sea. As some of 
them form hills of considerable height, a rise of at least 10,000 
feet in places is required for the appearance of the rocks in 
their present position. There is nothing in this assumption in 
any way opposed to what is already known regarding the 
elevation of the earth’s surface, during the tertiary period in 
Europe, Asia, and Africa. On the contrary, a change of level 
to this extent is indicated by the great mountain chains, all of 
which are modern, and all of which have probably been higher 
rather than lower than they now are during the tertiary period. 
The necessity of a warm sea bottom during the accumulation 
of foraminiferous mud, and the fact that warm sea bottoms are 
quite independent of latitude and have nothing whatever to do 
with the climate of adjacent land, are perhaps among the most 
important of the recent investigations. The influence of depth 
on the nature and homogeneity of deposits is also remarkable. 
That animal life exists in all its activity and without any check 
in the deepest recesses of the ocean has now become more than 
probable, and that geologists must look to bathymetrical con- 
ditions and conditions of bottom temperature far more than 
they have hitherto done in considering the circumstances under 
which deposits have been made is perfectly clear. 
As limestone of all kinds is apparently due to a large and 
rapid growth of animal organisms, while arenaceous deposits are 
chiefly abundant where life, if present, exists under less favour- 
able conditions, and as heat appears to play an important part 
in rendering the sea bottom favourable or otherwise for rapid 
accumulations of calcareous matter, it becomes evident that the 
direction of marine currents is even more than has yet been 
recognised a prime agent in all geological causation. The 
diversion of the warm currents from their present course to- 
wards the north-east between Iceland and the Hebrides would 
at once check or cause to cease the accumulation of foraminife- 
rous mud throughout the temperate latitudes of the north 
Atlantic. The depression of central Europe to become the 
bottom of a deep sea with an outlet into the Pacific would 
convey the warm currents eastwards, and produce accumulations 
which might rival the chalk in magnitude. On the other hand, 
