The average depth of the ocean is about two and a half miles; therefore,
since many parts are relatively shallow, there must be enormous depths.
A few of these, technically called "deeps," are about six miles deep, in
which Mount Everest would be engulfed. There is enormous pressure in
such depths; even at 2,500 fathoms it is two and a half tons on the
square inch. The temperature is on and off the freezing-point of fresh
water (28°-34° Fahr.), due to the continual sinking down of cold water
from the Poles, especially from the South. Apart from the fitful gleams
of luminescent animals, there is utter darkness in the deep waters. The
rays of sunlight are practically extinguished at 250 fathoms, though
very sensitive bromogelatine plates exposed at 500 fathoms have shown
faint indications even at that depth. It is a world of absolute calm and
silence, and there is no scenery on the floor. A deep, cold, dark,
silent, monotonous world!