When you gaze
at some line of cliffs that is being eaten away by the waves, or
reflect on the material carried out to sea by the flooded river,
you are--paradoxical as it may seem--beholding a material process
that has had a profound influence on the development of life. The
Archaean continent that we described was being reduced constantly
by the wash of rain, the scouring of rivers, and the fretting of
the waves on the coast. It is generally thought that these
wearing agencies were more violent in early times, but that is
disputed, and we will not build on it. In any case, in the course
of time millions of tons of matter were scraped off the Archaean
continent and laid on the floor of the sea by its rivers. This
meant a very serious alteration of pressure or weight on the
surface of the globe, and was bound to entail a reaction or
restoration of the balance.
The rise of the land and formation of mountains used to be
ascribed mainly to the cooling and shrinking of the globe of the
earth. The skin (crust), it was thought, would become too large
for the globe as it shrank, and would wrinkle outwards, or pucker
up into mountain-chains.
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