Therefore a man should examine for himself the great
piles of superimposed strata, and watch the rivulets bringing down mud, and
the waves wearing away the sea-cliffs, in order to comprehend something
about the duration of past time, the monuments of which we see all around
us.
It is good to wander along the coast, when formed of moderately hard rocks,
and mark the process of degradation. The tides in most cases reach the
cliffs only for a short time twice a day, and the waves eat into them only
when they are charged with sand or pebbles; for there is good evidence that
pure water effects nothing in wearing away rock. At last the base of the
cliff is undermined, huge fragments fall down, and these remaining fixed,
have to be worn away atom by atom, until after being reduced in size they
can be rolled about by the waves, and then they are more quickly ground
into pebbles, sand, or mud. But how often do we see along the bases of
retreating cliffs rounded boulders, all thickly clothed by marine
productions, showing how little they are abraded and how seldom they are
rolled about! Moreover, if we follow for a few miles any line of rocky
cliff, which is undergoing degradation, we find that it is only here and
there, along a short length or round a promontory, that the cliffs are at
the present time suffering. The appearance of the surface and the
vegetation show that elsewhere years have elapsed since the waters washed
their base.
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