THE MAMMOTH CAVE. 41 



The opening surrounding the mouth of the 

 Cave is irregularly funnel-shaped ; the walls 

 being steep, and forty or fifty feet in height, 

 and between fifty and one hundred feet across 

 the top of the funnel. 



"Trees," says Taylor, "grow around the edges 

 of the pit, almost roofing it with shade ; ferns 

 and tangled vines fringe its sides; and a slender 

 stream of water falls from the rocks which arch 

 above the entrance, dropping like a silver veil 

 before the mysterious darkness beyond." 



At nearly all seasons a mist or fog may be 

 seen hanging over the mouth of the Cave. 



When the.external air is warmer than that of 

 the Cave, the mist is produced by the condensa- 

 tion of the moisture of the former by the 

 reduced temperature of the latter. On the 

 contrary, if the temperature of the external 

 atmosphere is lower than that of the Cave, the 

 moisture of the air of the latter is condensed in 

 a similar manner. 



When the temperature of the outer air is the 

 same as that of the Cave, no fog or cloud is 

 observable about its mouth. 



The entrance of the Mammoth Cave, at an 

 early period of its history, as has already been 

 stated by Mr. Gorin, was situated about half a 



4* 



