THE MAMMOTH CAVE. Sli 
current sets in the opposite direction. When 
Green River is neither rising nor falling, the 
water of Echo River runs slowly in the direc- 
tion of Silliman’s Avenue, and is supplied from 
springs in the Cave. At such times its tempera- 
ture is fifty-nine degrees, the same as the uni- 
form temperature of the atmosphere of the Cave. 
When the water of Green River flows into Echo 
River at a temperature higher than that of the 
Cave, a fog is produced, which in point of den- 
sity, it is said, is not inferior to that off the 
banks of Newfoundland. Inexperienced persons 
have been lost in the fog on Echo River. 
At the time of our voyage across this river 
there was no fog, and the water, though not 
transparent, was beautifully clear. After pro- 
ceeding a short distance, the guide, who stood 
in the bow of the boat, silently propelling it by 
means of his hands, when within reach, and, at 
other times, by a staff applied to the ceiling 
and side-walls, struck up, at short intervals, a 
plaintive note of song. From the far distance, 
as from another world,—we had almost said 
from the spirit-world,—came answering melo- 
dies, as though a thousand tongues, attuned to 
different chords, had taken up the refrain, 
repeating it again and again, fainter and 
