MA'MMO'H CAVA.



part of a reservoir, where a current of air, from any
direction, is speedily neutralized. If a current of
air blows from without, inward, and is below fifty-
nine degrees, it does not pass more than a quarter of
a mile before it is brought up to that point. Air
above the average temperature of the Cave never
blows into it.
  Thtis it will be observed that a change of seasons
is unknown in the Mammoth Cave; and day and
night, morning und evening, have no existence in
this subterranean world. In fact, there is an eternal
sameness here, the like of which has no parallel.
  In manv parts of the Cave, time itself is not an
element of change; for where there is no variation of
temnperature, no water, and no light, the three treat
forces of geological transformation cease to operate.
        ATMOSPHERE OF THE CAVE.
  The proportions of oxygen and nitrogen bear the
same relation to each other in the Mammoth Cave
that they do in the external air, The proportion of
carbonic acid gas is less than that observed in the
atmosphere of the surrounding country, upon an
average of many observations. In the dry parts of
the Cave the proportion is about 2 to 10,000 of air;
in the vicinity of the rivers, something less. Not a
trace of ammonia can be detected in those parts of
the cave not commonly visited. The amount of the
vapor of water varies. Thus, in those avenues at a
great distance from the rivers, upon the walls and
floors of which there is a deposit of nitrate of lime,
the air is almost entirely destitute of moisture, from
the hygroscopic properties of that salt. and animal
matter mummifles instead of suffering putrefactive
decomposition. And for the same reason, no matter
what state of division the disintegrated rock may
attain, dust never rises. In portions of the Cave
remote from the localities in which the bats hyber-
nate, no organic matters can be recognized by the