This, it is true, must not be
taken too literally. Many a period of rapid change is probably
contained, and blurred out of recognition, in that long chronicle
of geological events. When a region sinks slowly below the waves,
no matter how insensible the subsidence may be, there will often
come a time of sudden and vast inundations, as the higher ridges
of the coast just dip below the water-level and the lower
interior is flooded. When two invading arms of the sea meet at
last in the interior of the sinking continent, or when a
land-barrier that has for millions of years separated two seas
and their populations is obliterated, we have a similar
occurrence of sudden and far-reaching change. The whole story of
the earth is punctuated with small cataclysms. But we now come to
a change so penetrating, so widespread, and so calamitous that,
in spite of its slowness, we may venture to call it a revolution.
Indeed, we may say of the remaining story of the earth that it is
characterised by three such revolutions, separated by millions of
years, which are very largely responsible for the appearance of
higher types of life. The facts are very well illustrated by an
analogy drawn from the recent and familiar history of Europe.
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