The
present Arctic climate is itself a comparatively new and abnormal state
of things due to geographical modification. As to "epoch" and "period,"
I use them as synonyms to avoid repeating the same word.
3. Rate of deposit and geological time: there no doubt I may have gone
to an extreme, but my "twenty-eight million years" may be anything under
100 millions, as I state. There is an enormous difference between _mean_
and _maximum_ denudation and deposition. In the case of the great faults
the upheaval along a given line would itself facilitate the denudation
(whether subaerial or marine) of the upheaved portion at a rate perhaps
a hundred times faster than plains and plateaux. So, local subsidence
might itself lead to very rapid deposition. Suppose a portion of the
Gulf of Mexico near the mouth of the Mississippi were to subside for a
few thousand years, it might receive the greater part of the sediment
from the whole Mississippi valley, and thus form strata at a very rapid
rate.
4. You quote the Pampas thistles, etc., against my statement of the
importance of preoccupation.
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