200 



or causes of the decomposition of rocks ; and the ex- 

 tent to which we are to admit the term ; for it seems 

 not unfrequently misapplied. 



The destruction of mountains or rocks, does not vir- 

 tually imply the decomposition of either. 



Mountains and rocks may be broken down sudden- 

 ly, or gradually by the following causes : First, by 

 repeated shocks of an earthquake. In this instance, 

 they are generally displaced in large masses, and often 

 removed to a considerable distance from their original 

 gisement, particularly so, on the sides of mountains. 

 Secondly, rocks of a columniform structure, fissuratetl 

 or stratified, are often displaced and thrown down, by 

 the slow and imperceptible growth of vegetables, 

 which annually shoot the fibres of their roots further 

 and further into the open crevices, and by gradual ex- 

 pansion, force, little by little, the ponderous mass from 

 its balance, until it falls, frequently from an awful 

 height, and with a tremendous crash. This is a pow- 

 erful agent, not only in the disruption of rocks, but in 

 the demolition of old towers and other buildings. 

 Scarcely will it be believed that effects so astonishing 

 could be produced by causes, in themselves so unim- 

 portant and seemingly trifling. But numerous are the 

 instances in which the ponderous materials of lofty tow- 

 ers, antiquated abbeys, and splendid palaces, have, by 

 slow and imperceptible gradations, been lifted, piece by 

 piece, from the adhesive cement of their moss-grown 

 walls, and tumbled, in promiscuous ruin, at their 



