20 INTRODUCTION. 



merits that are thus loosened, must ultimately be sepa- 

 rated, and fall by their own weight. In like manner, 

 the rain that falls upon lofty places must wash down 

 the softer and less compact soils ; and thus it may be 

 asserted, that, from the necessary action of the weather, 

 there is a continual tendency to flatten the general sur- 

 face of the earth. The process is, no doubt, a slow 

 one, but it is sure ; and there is no part of the world 

 without some traces of its effects. In the champaign 

 counties of England, the pavements, altars, and other 

 remains of the Romans, are invariably found below 

 ground. In the soft lands near the mouths of the large 

 rivers, and also under the peat-bogs, the ruins of former 

 forests and former animals are abundant, and diffused 

 over all parts of the country. It is true that some 

 of the surfaces (those of the peat-bogs in particular) 

 have the power of elevating themselves, as the mosses 

 with which they are covered decay at the root while 

 they are growing at the top ; and they powerfully retain 

 humidity, by the presence of which both operations are 

 so much facilitated, that a depth of many feet has been 

 found in the memory of one individual. Other in- 

 stances occur, however, where no such assistance could 

 be obtained. In cutting the Caledonian canal, from the 

 Moray Firth on the east side of Scotland, to Fort 

 William on the west, the implements and weapons of a 

 former people were found at the depth of more than 

 twelve feet, beneath a covering of loose stones, intermix- 

 ed with very little even of sand, and exhibiting hardly a 

 trace of vegetation, except the scanty covering upon 

 the surface. 



Another class of revolutions, of which there are traces 



