And Again, The Rim Of The General Basin, Where It Is Elevated, As For
Example On The Southwestern Portion, Instead
Of being a ridge
sculptured on the sides like a mountain range, is found to be composed
of many short
Ranges, parallel to one another, and to the interior
ranges, and so modeled as to resemble a row of convex lenses set on
edge and half buried beneath a general surface, without manifesting
any dependence upon synclinal or anticlinal axes - a series of forms
and relations that could have resulted only from the outflow of vast
basin glaciers on their courses to the ocean.
I cannot, however, present all the evidence here bearing upon these
interesting questions, much less discuss it in all its relations. I
will, therefore, close this letter with a few of the more important
generalizations that have grown up out of the facts that I have
observed. First, at the beginning of the glacial period the region
now known as the Great Basin was an elevated tableland, not furrowed
as at present with mountains and valleys, but comparatively bald and
featureless.
Second, this tableland, bounded on the east and west by lofty mountain
ranges, but comparatively open on the north and south, was loaded with
ice, which was discharged to the ocean northward and southward, and in
its flow brought most, if not all, the present interior ranges and
valleys into relief by erosion.
Third, as the glacial winter drew near its close the ice vanished from
the lower portions of the basin, which then became lakes, into which
separate glaciers descended from the mountains.
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