THE MAMMOTH CAVE. oa 
It may be well in this place to refer to the 
interesting relation subsisting between Mam- . 
moth Cave and Green River. There can be no_ 
doubt that Green River has-cut out the bed ‘or 
channel through which. it runs; for on ascend- 
ing its banks on either side for a distance of not 
less than three hundred feet, a plain is reached, 
which is not succeeded by a valley ; establishing 
conclusively that it has worn its bed to its pres- 
ent level by the mechanical and chemical 
agency of water, and that the avenues of the 
Cave were cut through with nearly equal pace,— 
those near the surface of the earth being formed 
first, and the others in regular order from above 
downward; the avenues through which Echo 
and Roaring Rivers run being the lowest and 
last formed. Both of these rivers are on a level 
with Green River, with which there is, as before 
stated, a subterraneous communication. _As 
Green River continues to deepen the valley 
through which it passes, the avenues of the 
Cave will continue to descend, until the springs 
which supply Echo and Roaring Rivers cease to 
flow, when the avenues through which. they run 
will become as dry as Marion’s Avenue, which, 
at an early period in the history of the Cave, con- 
5* 
