50 THE MAMMOTH CAVE. ‘ 
holes’ in the Main Cave are cut out of the solid 
rock in the same manner. 
“Another agency which contributes in part to 
change the appearance of the Cave is the efflo- 
rescence of the sulphate of soda, or glauber-salts, 
and the crystallization of sulphate of lime, or 
plaster of Paris. | 
“'The sulphate of lime, which is known under 
the names of gypsum, plaster of Paris, selenite, 
alabaster, etc., exerts a much greater influence 
in disintegrating rock than the sulphate of soda. 
The avenues in which gypsum occurs are pet- 
fectly dry, differmg in that respect from those 
that contain stalactites. When rosettes of ala- 
baster are formed in the same avenue with sta- 
lactites, the water which formed the latter has 
for ages ceased to flow, or they are situated far 
apart, as the former cannot form in a damp at- 
mosphere. The force exerted by gypsum in the 
act of crystallizing is about equal to that of water 
when freezing, and when it crystallizes between 
ledges of rock, they are fractured in every direc- 
tion, as instanced in Pensacola Avenue and 
Rhoda’s Arcade. 
“The formation of nitre is due, in part, to the 
decomposition of bats and other animals; but it 
must not be forgotten that limestone rocks are 
