The key to this
beautiful harmony is the ancient glaciers; where they flowed the trees
followed, tracing their wavering courses along canons, over ridges, and
over high, rolling plateaus. The Cedars of Lebanon, says Hooker, are
growing upon one of the moraines of an ancient glacier. All the forests
of the Sierra are growing upon moraines. But moraines vanish like the
glaciers that make them. Every storm that falls upon them wastes them,
cutting gaps, disintegrating boulders, and carrying away their decaying
material into new formations, until at length they are no longer
recognizable by any save students, who trace their transitional forms
down from the fresh moraines still in process of formation, through
those that are more and more ancient, and more and more obscured by
vegetation and all kinds of post-glacial weathering.
Had the ice-sheet that once covered all the range been melted
simultaneously from the foot-hills to the summits, the flanks would, of
course, have been left almost bare of soil, and these noble forests
would be wanting. Many groves and thickets would undoubtedly have grown
up on lake and avalanche beds, and many a fair flower and shrub would
have found food and a dwelling-place in weathered nooks and crevices,
but the Sierra as a whole would have been a bare, rocky desert.
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