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long and devious channels and by wells, some of which, like the Mammoth 
Dome. are 150 feet from top to bottom. The floor of the main caye is on 
the second level, while its roof is on a level with the roof of the fourth 
tier. We can easily imagine that when the Green River had cut through 
the sandstone overlying the limestone in which the cave has been formed, 
an outlet for water collecting in the crevices of the limestone was found 
near the present entrance of the cave. The main crevice developed into a 
large stream, cutting down and dissolving the rock much more quickly 
than its smaller tributaries. The tributaries fell into the main stream in 
little cascades and their floors, the present fourth level, remained per- 
manently above the main caye or second level. As Green River cut 
through its limestone bed a lower exit was opened for the waters of this 
primeval mammoth river, and later still, a lower. By the formation of 
the pits and winding channels the water finally permanently abandoned 
the upper channels and is found now only in the lowermost levels. When 
this process began only aquatic animals could enter the cave. Even after 
the cave had become quite large it probably became full to the top during 
fioods. This is still the case in many caves of Indiana. As a matter of 
course only aquatic animals were able permanently to establish theim- 
selves. But when the upper levels became permanently dry other animals 
could and did enter the caves and others are evidently still colonizing 
them. 
The scenic parts which make the most lasting impression are Echo 
River, the Mammoth Dome and the main cave. The main cave is simply 
a very large winding tunnel, not startling in any way, but by the time 
one has walked for an hour or two it begins to impress one very forcibly. 
The Star Chamber and Martba Washington Statue, in this part of the 
eave, are remarkable in their way. The echo of Echo River lasts but 
twelve or fifteen seconds. H is remarkable for the blending of simple 
sounds, not for the repetition of words or phrases. 
