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 per- 

 fectly dry, differing 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 



