IN MAMMOTH CAVE 251 



Another very interesting feature to me was 

 the behavior of the cool air which welled up 

 out of the mouth of the cave. It simulated 

 exactly a fountain of water. It rose up to a 

 certain level, or until it filled the depression 

 immediately about the mouth of the cave, and 

 then flowing over at the lowest point, ran down 

 the hill towards Green Kiver, along a little 

 watercourse, exactly as if it had been a liquid. 

 I amused myself by wading down into it as into 

 a fountain. The air above was muggy and hot, 

 the thermometer standing at about eighty-six 

 degrees, and this cooler air of the cave, which 

 was at a temperature of about fifty-two degrees, 

 was separated in the little pool or lakelet which 

 is formed from the hotter air above it by a per- 

 fectly horizontal line. As I stepped down into 

 it I could feel it close over my feet, then it 

 was at my knees, then I was immersed to my 

 hips, then to my waist, then I stood neck deep 

 in it, my body almost chilled while my face 

 and head were bathed by a sultry, oppressive 

 air. Where the two bodies of air came into 

 contact, a slight film of vapor was formed by 

 condensation ; I waded in till I could look under 

 this as under a ceiling. It was as level, and 

 as well defined as a sheet of ice on a pond. 

 A few moments' immersion into this aerial 

 fountain made one turn to the warmer air again. 

 At the depression in the rim of the basin one 

 had but to put his hand down to feel the cold 

 air flowing over like water. Fifty yards below, 

 you could still wade into it as into a creek, and 



