26 



which forms the winter torrent, carries down the 

 larger fragments, and, dashed against each other, 

 their angles are rounded off. The looser mate- 

 rials of the soil, through which these torrents 

 pass, are still more easily swept away ; and in this 

 manner, year after year, the surface of the 

 mountain is conveyed into the valley. As the 

 torrent reaches the level ground, its rapidity 

 lessens, the larger fragments proceed no farther, 

 and only the earth and sand reach the river, 

 where they subside to the bottom, and form allu- 

 vial flats, and push out the deltas which may be 

 seen at the mouths of almost every river. Some 

 of the prodigious deltas made by the great rivers 

 of the continent, I think I mentioned to you in 

 one of our earliest conversations, as well as the 

 great deposit of new land on the coast of Italy. 



" Fortunately, over a large part of the earth's 

 surface, these wasting causes have no influence ; 

 the green sward which clothes it is an effectual 

 protection. The barrows of the ancient Britons, 

 though above two thousand years old, retain their 

 original outline, and the fosse surrounding them 

 is still distinct. Even on the sides of mountains, 

 where the causes which I have described are 

 always more or less in operation, still there is a de- 

 gree at which further waste will be checked ; the 

 abrupt precipice may in time be broken down 

 into a slope ; but vegetation will creep up, and that 

 slope will then be defended by its grassy coat. 



