Had the glaciers that once covered the range been melted at once,
leaving the entire surface bare from top to bottom simultaneously, then
of course all the lakes would have come into existence at the same time,
and the highest, other circumstances being equal, would, as we have
seen, be the first to vanish. But because they melted gradually from the
foot of the range upward, the lower lakes were the first to see the
light and the first to be obliterated. Therefore, instead of finding the
lakes of the present day at the foot of the range, we find them at the
top. Most of the lower lakes vanished thousands of years before those
now brightening the alpine landscapes were born. And in general, owing
to the deliberation of the upward retreat of the glaciers, the lowest of
the existing lakes are also the oldest, a gradual transition being
apparent throughout the entire belt, from the older, forested,
meadow-rimmed and contracted forms all the way up to those that are new
born, lying bare and meadowless among the highest peaks.
[Illustration: THE DEATH OF A LAKE.]
A few small lakes unfortunately situated are extinguished suddenly by a
single swoop of an avalanche, carrying down immense numbers of trees,
together with the soil they were growing upon.
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