THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 161 
ground of the ocean. Large numbers of Holothurians and other marine 
creatures here eat the mud to obtain the organic matter associated with it ; 
indeed, it is more than probable that all marine deposits are in this way 
passed through the intestines of organisms. Very many Crustaceans fre- 
quent this area to pick up the little particles of organic matter which are 
just settling on the bottom, and some of them—like Myctiphunes — are 
provided with phosphorescent organs to enable them to do this more effec- 
tively. All these mud-eating creatures are in turn the prey of carnivorous 
animals, both vertebrate and invertebrate. 
The continental slope extends from the mud-line (100 fathoms) down to 
the mean sphere level, 1450 fathoms. The continental slope, and similar 
areas around oceanic islands, present a greater variety of conditions than is 
found elsewhere on the ocean-bed beyond the continental shelf. At the 
upper limit the sun’s rays may produce twilight, but elsewhere there must 
be total darkness, except where this is relieved by the phosphorescent light 
of organisms. The temperature conditions are likewise widely different at 
the upper and lower limits of the region. At some points the descent from 
the 100-fathoms line is known to be almost perpendicular; at other points 
outcrops of stratified and volcanic rocks are indicated; generally, however, 
the slope is by no means pronounced, though much steeper than between the 
deeper contour-lines. 
The deposits now being laid down over the continental slope vary 
greatly according to position: off large rivers they are chiefly made up 
of detritus from the land; at other places, especially where cold and warm 
currents alternately occupy the surface, pelagic conditions are more or less 
approached, and Green Sand and phosphatic deposits are being laid down; 
quartz and other continental minerals predominate. Generally it may be 
said that in enclosed seas, and along the continental shelf and slope, de- 
posits are now forming which are chiefly made up of continental detritus, 
and are quite similar to those which have made up the stratified rocks of 
past ages. Indeed, it seems as if inland seas and the borders of conti- 
nental masses had again and again been pushed up into dry land, and again 
and again been torn down and transported to the ocean by the same denud- 
ing and disintegrating agents, the final result being that quartz particles 
1]f all the elevated portion of the earth’s crust were cut away and filled into the hollows till the 
whole surface were uniform, then the whole earth would be covered by an ocean 1450 fathoms in 
depth — the mean sphere level. 
i 
