146 



powers, which produce their effect almost in- 

 sensibly by progressive action. It would be in 

 contradiction to the design of this work, which 

 treats of the laws of nature, to discuss the origin 

 of things, and abandon the small number of 

 facts hitherto well observed, to wander amid 

 vague conjectures. We will only recommend 

 to those natural philosophers, who like to in- 

 dulge in geological hypotheses, not to forget the 

 horizontality, which is so often remarked in the 

 bosom of gypseous and calcareous mountains to 

 a vast extent, in the position of grottoes that 

 communicate with each other by passages. This 

 almost perfect horizontality, this gentle and 

 uniform slope, appear to be the result of a long 

 abode of the waters, which enlarge by erosion 

 clefts already existing, and carry off the softer 

 parts* so much the more easily, as clay or mu- 

 riat of soda is found mixed with the gypsum 

 and fetid limestone -f*. These effects are the 

 same, whether the caverns form one long and 

 continued range, or several of these ranges ly- 

 ing one over another, as happens almost exclu- 

 sively in gypseous mountains. 



* Saussure, Voyages, § 465, Freiesleben, Kupferschiefer, 

 T. ii, p. 172. 



i Stifikstein. According to an hypothesis of Mr. Wer- 

 ner, the caverns in the ancient gypsum of Thuringia are 

 owing to the abstraction of enormous masses of muriat of 

 soda. 



i 



