DEPOSITION IN THE SEA 257 
there is a constant deposit of land-derived fragments of 
very fine grain, and over this area a fine-textured mud 
is slowly forming. The distance to which this may 
be carried varies greatly with the conditions, in some 
cases being but a few miles, in others more than one 
hundred from the shore; but everywhere there is 
a decrease in coarseness of grain as the distance from 
the shore increases. 
There is also a decrease in the rate of deposit, be- 
cause much less can be carried by a slowly moving 
current than is accumulated near the land, the source 
of the materials. Of course, the nature of the mechani- 
cal sediment deposited, depends greatly upon the nature 
of the shore. Near coral islands it is a fine-grained 
lime mud, near granite coasts it is made of fragments 
of granite, near volcanic cones it is composed of bits 
of pumice, etc. 
Globigerina Ooze. Beyond the zone of mechanical 
deposit, although some fragments are constantly drop- 
ping to the bottom, these are much less numerous than 
the shells of those animals which float in the sea water. 
Therefore, here in the deep parts of the ocean, covering 
an area greater than one-half of the earth, there is 
slowly gathering an accumulation of animal remains. 
Among these, the most abundant and prominent are 
the shells of minute floating species, which live in 
countless millions in the surface waters. Species of 
