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of erosion may be reached and divert the downward moving water. Any 
or all of these causes may change the downward flow of water into lateral 
flow, although in time they may cease to have this function, owing to 
chemical or mechanical erosion. 
Locally other factors may enter into the stoppage of the downward 
flow. These may be greater hardness or impurities of the limestone, ete. 
The horizontal flow will naturally follow the line of least resistance, 
which will be along the line of one of the joint-planes. Thus young caves 
and many which are older, follow approximately straight north and south, 
and east and west lines and have right-angled turns. ‘The direction of the 
cave stream will be determined by local conditions, such as hardness, dip, 
solubility and nearness to surface streams. 
At first the erosion will be by solution, but in time the cave stream 
will come to be governed by much the same laws as surface streams and 
corrosion will do its share in enlarging the cave. The original downward 
opening will become larger and surface material with its hard, angular 
pieces of chert, and soil will be washed into the opening, and sinkholes 
such as are characteristic of the Mitchell area, will be formed. In time 
these become very large, occasionally containing many acres; however, it 
may be said that the very large sinkholes (and these only) are formed by 
collapse of caves. 
In the young cave there will be no evidence of any erosion except 
that by solution. The water is very clear and contains a minimum amount 
of solid matter; the cave will be bounded on all sides by solid rock walls 
and angular protuberances will be everywhere conspicuous. 
So much for the common type of a very young cave. A multitude of 
factors determine the size and shape of a cave as it grows older. Much 
depends on the level of the surface stream into which the cave stream 
flows. If the surface stream is much lower than the level on which the 
cave stream flows, the latter will cut down rapidly, other things being 
equal, thus forming a narrow and deep cave such as is seen at the entrance 
of Shawnee Cave in Lawrence County, or in Wyandotte Cave. If the level 
of the surface stream is near that on which the cave stream flows, the 
tendency will be toward lateral erosion, and the cave will cut downward 
only as rapidly as does the surface stream of which it is a tributary. 
Most of the surface streams and probably all of the cave streams of 
the area had their origin since the Tertiary peneplanation. The Mitchell 
area has been elevated since then, as was mentioned above, but owing to 
