MAMMOTH CAVE.



mosphere, will account for the fact that individuals
are enabled to undergo such an unusual amount of
physical exertion in it. It is not an uncommon
occurrence for a person in delicate health to accom-
plish a journey of twenty miles in the Cave, without
suffering from fatigue. who could not be prevailed
upon to walk a distance of three miles on the surface
of the earth.
  HOW THE MAMMOTH CAVE WAS FORMED.
  The agencies concelned ill the tormation of the
Mammoth Cave, may be divided into Chemical and
Mechau ical.
            CHEMICAL AGENCIES.
  There can. be no doubt but that the solvent action
of water holdingf carbonic acid in solution, was the
primary agency concerned in the formation of the
Cave. Thus, the limestone, or carbonate of lime,
which constitutes the strata of rock through which
the Cave runs, is not soluble in water until it com-
hines with an additional proportion of carbonic acid,
by which it is transformed into the bicarbonate of
lime. Ia this way the process of excavation was
conducted, until communications were established
with running water, by which the mechanical agency
of that fluid was made to assist the chemical. The
little niches and recesses which are observed in
various parts of the Cave, and which seem to have
been chiseled out and polished by artificial means,
were formed in this manner; for when these points
are closely examined, a crevice will be observed at
the top or back of them, through which water issued
at the time of their formation, but which has been
partially closed by crystals of carbonate of lime, or
gypsum. At the time these niches were forming,
water flowed through the avenues in which they are
found. Examples of the action we have been de-
scribing, may be seen in Spark's Avenue, leading to
the Mammoth Dome.



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