The Front Wall Of The Muir Glacier Is About Two
And A Half Or Three Miles Wide.
Only the central portion about two
miles wide discharges icebergs.
The two wings advanced over the
washed and stratified moraine deposits have little or no motion,
melting and receding as fast, or perhaps faster, than it advances.
They have been advanced at least a mile over the old re-formed
moraines, as is shown by the overlying, angular, recent moraine
deposits, now being laid down, which are continuous with the medial
moraines of the glacier.
In the old stratified moraine banks, trunks and branches of trees
showing but little sign of decay occur at a height of about a hundred
feet above tide-water. I have not yet compared this fossil wood with
that of the opposite shore deposits. That the glacier was once
withdrawn considerably back of its present limit seems plain. Immense
torrents of water had filled in the inlet with stratified
moraine-material, and for centuries favorable climatic conditions
allowed forests to grow upon it. At length the glacier advanced,
probably three or four miles, uprooting and burying the trees which
had grown undisturbed for centuries. Then came a great thaw, which
produced the flood that deposited the uprooted trees. Also the trees
which grew around the shores above reach of floods were shed off,
perhaps by the thawing of the soil that was resting on the buried
margin of the glacier, left on its retreat and protected by a
covering of moraine-material from melting as fast as the exposed
surface of the glacier.
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