ive feet, the amount of energy which they
transmit is very great. If it could be effectively applied to the
shores in the manner in which the energy of exploding gunpowder is
applied by cannon shot, it is doubtful whether the lands could have
maintained their position against the assaults of the sea. But there
are reasons stated below why the ocean waves can use only a very small
part of their energy in rending the rocks against which they strike on
the coast line.

In the first place, we should note that wind waves have very little
influence on the bottom of the deep sea. If an observer could stand on
the sea floor at the depth of a mile below a point over which the
greatest waves were rolling, he could not with his unaided senses
discern that the water was troubled. He would, indeed, require
instruments of some delicacy to find out that it moved at all. Making
the same observations at the depth of a thousand feet, it is possible
that he would note a slight swaying motion in the water, enough
sensibly to affect his body. At five hundred feet in depth the
movement would probably be sufficient to disturb fine mud. At two
hundred feet, the rasping of the surge on the bottom would doubtless
be sufficient to push particles of coarse sand to and fro. At one
hundred feet in depth, the passage of the surge would be strong enough
to urge considerable pebbles before it. Thence up the slope the
driving action would become more and more intense until we attained
the point where the wave broke. It should furthermore be noted that,
while the movement of the water on the floor of the deep sea as the
wave passes overhead would be to and fro, with every advance in the
shallowing and consequent increased friction on the bottom, the
forward element in the movement would rapidly increase. Near the coast
line the effect of the waves is continually to shove the detritus up
the slopes of the continental shelf. Here we should note the fact that
on this shelf the waves play a part exactly the opposite of that
effected by the tides. The tides, as we have noted, tend to drag the
particles down the slope, while the waves operate to roll them up the
declivity.

As the wave in advancing toward the shore ordinarily comes into
continually shallowing water, the friction on the bottom is
ever-increasing, and serves to diminish the energy the surge contains,
and therefore to reduce its proportions. If this action operated
alone, the subtraction which