Later the earth wrinkled again in various
ways and places so that new ridges and mountains were formed with new
systems of lakes and oceans and rivers; and again the elements continued
to erode and partially destroy the higher masses and to lay down new and
later series of sedimentary rocks upon the old.
It seems scarcely credible that the apparently weak forces of nature like
those we have mentioned are sufficiently powerful to work over the massive
crust of the earth as geology says they have. Our attention is caught, as
a rule, only by the greater things, like the earthquakes at San Francisco
and Valparaiso, and the tidal waves and cyclones of the South Seas; but
the results of these sporadic and local cataclysms are far less than the
effects of the persistent everyday forces of erosion, each one of which
seems so small and futile. When we look at the Rocky Mountains with their
high and rugged peaks, it seems almost impossible that rain and frost and
snow could ever break them up and wear them down so that they would become
like the rounded hills of the Appalachian Mountain chain, yet this is what
will happen unless nature's ways suddenly change to something which they
are not now. A visitor to the Grand Canon of the Colorado sees a
magnificent chasm over a mile in depth and two hundred miles long which
has actually been carved through layer after layer of solid rock by the
rushing torrents of the river.
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