250 ON THE DESTRUCTION OF ROCKS. 



native copies of those far greater movements which 

 have formerly involved whole countries ; producing 

 the dislocations of the strata, and presenting, at their 

 places of fracture, the models of mineral veins. 



The exact causes of these great revolutions have 

 not always been ascertained ; but they have been at- 

 tributed, in many cases, and apparently with justice, 

 to the action of water. In other instances, they 

 appear to have resulted merely from the effects of 

 gravity, acting through a long period, on masses, 

 of which the support was gradually becoming en- 

 feebled ; till, the powers of resistance yielding to 

 those of motion, the whole has given way. A few 

 of the instances recorded by authors may amuse the 

 reader, and diminish the dulness of continued geo- 

 logical discussion. 



In 1618, the town of Pleurs, near Chavennes, 

 containing 2000 inhabitants, was suddenly over- 

 whelmed, and the ground is now covered with houses 

 and cultivation. 



Near Passy, between Salenches and Servoz, a 

 mountain thus gave way in 1751, with such a tre- 

 mendous concussion, followed by clouds of dust, 

 that it was supposed to have been the effects of a 

 volcanic eruption. The examination made of it by 

 Donati, renders this example interesting, as the 

 cause was ascertained. It was found that the water 

 of some lakes which were situated above, had insinu- 

 ated itself between the strata of schist and limestone 

 of which the mass was composed ; and that its sup- 

 port having thus been removed, it had slidden and 

 fallen. The mass of matter thus displaced was esti- 

 mated at 3,000,000 of cubic fathoms, and was suffi- 

 cient to form a considerable hill. 



But the most recent occurrence of this nature was 



