144 



such as the cavern of Rosen muller, in Franco- 

 nia, Elden-hole, in the peak of Derbyshire, and 

 the Sumideroes of Charaacasapa * in Mexico. 

 Other caverns are open to the light at both 

 ends. These are rocks really pierced through ; 

 natural galleries, which traverse a solitary 

 mountain. Such are the Hole-Berg of Mug- 

 gendorf, and the famous cavern called Dantoe 

 by the Ottomite Indians, and the Bridge of the 

 Mother of God, by the Mexican Spaniards. It 

 is difficult to decide respecting the origin of 

 these channels, which sometimes serve as a bed 

 for subterraneous rivers. Are these pierced 

 rocks hollowed out by the impulse of a current ? 

 or should we rather admit, that one of the open- 

 ings of the cavern is owing to a falling down of 

 the earth subsequent to it's original formation, 

 to a change in the external form of the moun- 

 tain, for instance, to a new valley opened on it's 

 flank ? A third form of caverns, and the most 

 common of the whole, exhibits a succession of 

 cavities, placed nearly on the same level, in the 

 same direction, and communicating with each 

 other by passages of greater or less breadth. 



To these differences of general form are add- 

 ed other circumstances not less remarkable. It 

 often happens, that to grottoes of little space the 

 openings are extremely wide ; while we have 

 to creep under very low vaults, in order to pe- 



1 



* Near Tasco, and Tehuilotepec. 



V 



