181 
of Crawford County, and Mammoth Cave of Kentucky are of this type. <A 
shaft was sunk to the depth of sixty feet at the mouth of Wyandotte 
before the solid rock floor was reached. 
A cave stream may undermine the rock beneath a low place such as a 
sink-hole, causing the overlying strata to collapse. In this case there will 
be two entrances at the place where the cave-in occurred. Should atmos- 
pheric agencies weather back the two entrances the cave stream will flow 
above ground for a greater or less distance. This action has occurred 
twice in Shawnee Cave, Lawrence County, and the surface portions of 
Lost River, Orange County, have probably come about in an analogous 
manner. 
A fourth type of cave entrance is that produced by a surface stream 
erodipg its way into a cave; but this type is probably common only in re- 
gions of great relief, such as those bordering the Ohio, since surface 
streams of sufficient size to accomplish this are rather rare in the Mitchell 
belt. 
MATERIALS DEPOSITED IN CAVES AFTER FORMATION. 
It was stated in the second portion of this paper that calcium bi- 
earbonate (CaH.(CO,),. was formed by the action of atmospheric water 
on limestone. This substance will remain in solution until evaporation 
takes place, when it will split up as follows: CaH.(CO,),—=CO,+H,O + 
CaCO,. The carbon dioxide being 1.5 times as heavy as air sometimes 
settles in the lower portions of caves, rendering them dangerous, but this 
is not often the case in the caves of the Mitchell area owing to the pres- 
ence of air currents which remove the gas. The CaCO, will remain as 
stalactitic and stalagmitic deposits. Owing to the fact that in the lower 
and younger parts of the cave, which contain water, the air is generally 
saturated so that evaporation is at least not rapid, the calcareous deposits 
are found in greatest abundance in the higher and drier passages. 
In the deposition of calcareous material the joint-planes again play 
a prominent part, due to the fact that water is able to find its way down 
through them. Very often the vertical joint along which a cave was 
formed will be marked overhead by a row of stalactites and sometimes 
by a row of stalagmites on the floor beneath. Where two joints cross 
each other the deposition is apt to be greatest. In Wyandotte cave in 
two places where large piles of rock have fallen (Senate Chamber and 
Monument Hill) owing to cross joints, the piles of rock are crowned 
with large stalagmites directly beneath the crossing of the vertical joints. 
[18—21363] 
