of Edinburgh, Session 1883-84. 
503 
ground sometime met with in such positions. By observations off 
the coast of France, it has been shown that fine mud is at times 
disturbed at a depth of 150 fathoms; but, while admitting that 
this is the case on exposed coasts, the majority of observations 
indicate that beyond 100 fathoms it is an oscillation of the water, 
rather than a movement capable of exerting any geological action, 
which concerns us in this connection. 
Although the great oceanic currents have no direct influence upon 
the bottom, yet they have a very important indirect effect on 
deposits, because the organisms which live in the warm equatorial 
currents form a very large part of the sediment being deposited 
there, and this in consequence differs greatly from the deposits 
forming in regions where the surface-water is colder. In the 
same way a high or low specific gravity of the surface-water 
has an important bearing on the animal and vegetable life of the 
ocean, and this in its turn affects the character of the deposits. 
The thermometric observations of the “ Challenger ” show that a 
slow movement of cold water must take ]3lace in all the greater depths 
of the ocean from the poles, but particularly from the southern pole, 
towards the equator. It could be shown from many lines of argu- 
ment that this extremely slow massive movement of the water can 
have no direct influence on the distribution of marine sediments. 
Glaciers which eventually become icebergs, that are carried far 
out to sea by currents, transport detrital matter from the land to 
the ocean, and thus modify in the Arctic and Antarctic regions the 
deposits taking place in the regions affected by them. The detritus 
from icebergs in the Atlantic can be traced as far south as 
latitude 36° off the American coast, and in the southern hemisphere 
as far north as latitude 40°. 
The fact that sea water retains fine matter in suspension for a much 
shorter time than fresh water should be referred to here as having 
an important influence in limiting the distribution of fine argillaceous 
and other materials borne down to the sea by rivers, thus giving a 
distinctive character to deposits forming near land. 
We have pointed out the influence of temperature and salinity 
upon the distribution of the surface organisms whose skeletons form 
a large part of some oceanic deposits, and may state also that the 
bathymetrical distribution of calcareous organisms is influenced by 
