60 



roof of the cavern, and detaching fragments, it was found to consist 

 of a breccia of bones of animals long extinct, mixed with fragments 

 of flint or stone, bearing evident traces of human art. 



In order to explain these circumstances, it is only necessary to 

 admit the upheaval of the land and the occurrence of torrents. 



Fig. 1. 



1st Period. Let us suppose two caverns, a lower, A, and an 

 upper, B C, communicating with each other by a long rent or pipe 

 P. This pipe may be supposed of any height, sufficient when filled 

 with water to produce the required force. 



The lower cavern is supposed to be nearly at the level of the sea. 



Fig. 2. 



Pholades and other marine animals will perforate or attach them- 

 selves to the bottom and sides of the cavern, and if the sea entirely 



