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of Crawford County, and Mammoth Care 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 

 eroding 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 suiiieient 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- 

 carbonate (CaH 2 (C0 3 ) 2 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 2 (C0 3 ), = C0 2 + H 2 + 

 CaC0 3 . 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 ealeareoms 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. AVhere 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. 



[13—21363] 



