THE MAMMOTH CAVE. 81 



current sets in the opposite direction. When 

 Green River is neither rising nor falling, the 

 water of Echo Kiver 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 



