34 ON THE REVOLUTION'S OK 



globe ; let us analyse the causes which still affect its surface, and let 

 us determine the possible extent of their effects. It is a portion of 

 the history of the earth, so much the more important, as we have long 

 thought we could explain anterior revolutions by existing causes ; as 

 in political history we easily unfold past events, when we are well ac- 

 quainted with the systems and intrigues of our own times. But un- 

 fortunately j\ve shall find that this is not the case with physical his. 

 tory ; the thread of the operations is broken ; the march of nature is 

 changed ; and not one of her agents now at work would have sufficed 

 to have effected her ancient works. 



There are now existing four active causes which contribute to alter 

 the surface of our continents : the rains and thaws which lower our 

 lofty mountains, and cast their relics at their feet ; the flowing waters, 

 which carry away their remains, and leave them in places where they 

 retard their currents ; the sea, which sups the base of the lofty coasts, 

 and which forms the beach on which it casts the sand hills ; and 

 finally, the volcanoes, which perforate the solid layers, and elevate or 

 scatter on the surface the masses which they vomit forth.* 

 The falling away of portions of the Masses. 



Everywhere, where the broken layers . present their edge on the 

 rugged fronts, there falls at their base every spring, and even at every 

 storm, fragments of their component parts, which become round by 

 rolling one on the other, and which, in a mass, assumes a determined 

 inclination, conformably with] the laws of cohesion, thus forming, at 

 the foot of the height, a ridge more or less elevated, according as the 

 fall of materials be more or less abundant ; these ridges form the 

 sides of the valleys in all the high mountains, and are covered with 

 rich vegetation when the falling away of the upper parts becomes less 

 frequent ; but their want of solidity renders them liable to slip them- 

 selves, when they are undermined by streams ; and it is then that 

 cities, rich and thickly-populated districts, are overwhelmed by the 

 slipping of a mountain ; that the course of rivers is interrupted ; and 

 that lakes are formed on spots once fertile and luxuriant. But fortu- 

 nately these stips occur but seldom, and the principal influence of 

 these accumulated hills is to supply materials for the ravages of the 

 torrents, 



Alluvial Deposites. 



The waters which fall on the peaks and summits of mountains, the 

 condensed vapours, s or the liquefied snows, descend along their declivi- 



* See, on the changes of the earth's surface, known from history or tradition, 

 and consequently attributable to known causes, the German work of M. de Hof, in 

 2 vols. Svo. The collection of facts is gathered with as much care as learning. 



