How Much Denudation And Degradation Has Been Effected We Have No Means
Of Determining, The Porous, Crumbling Rocks Being Ill Adapted For The
Reception And Preservation Of Glacial Inscriptions.
The summit is now a mass of ruins, and all the finer striations have
been effaced from the flanks
By post-glacial weathering, while the
irregularity of its lavas as regards susceptibility to erosion, and
the disturbance caused by inter- and post-glacial eruptions, have
obscured or obliterated those heavier characters of the glacial record
found so clearly inscribed upon the granite pages of the high Sierra
between latitude 36 degrees 30 minutes and 39 degrees. This much,
however, is plain: that the summit of the mountain was considerably
lowered, and the sides were deeply grooved and fluted while it was a
center of dispersal for the glaciers of the circumjacent region. And
when at length the glacial period began to draw near its close, the
ice mantle was gradually melted off around the base of the mountain,
and in receding and breaking up into its present fragmentary condition
the irregular heaps and rings of moraine matter were stored upon its
flanks on which the forests are growing. The glacial erosion of most
of the Shasta lavas gives rise to detritus composed of rough
subangular boulders of moderate size and porous gravel and sand, which
yields freely to the transporting power of running water. Several
centuries ago immense quantities of this lighter material were washed
down from the higher slopes by a flood of extraordinary magnitude,
caused probably by the sudden melting of the ice and snow during an
eruption, giving rise to the deposition of conspicuous delta-like beds
around the base.
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