290 DENUDATION OP THE LAND. Chap. VL 



taiiied long ago, by Play fair, who, in 1802, 

 wrote, " in the permanence of a coat of 

 " vegetable mould on the surface of the earth, 

 " we have a demonstrative proof of the con- 

 " tinued destruction of the rocks."* 



Ancient encampments and tumuli. — E. de 

 Beaumont adduces the present state of many 

 ancient encampments and tumuli and of old 

 ploughed fields, as evidence that the surface 

 of the land undergoes hardly any degradation. 

 But it does not appear that he ever examined 

 the thickness of the mould over different 

 parts of such old remains. He relies chiefly 

 on indirect, but apparently trustworthy, evi- 

 dence that the slopes of the old embankments 

 are the same as they originally were ; and it 

 is obvious that he could know nothing about, 

 their original heights. In Knole Park a 

 mound had been thrown up behind the rifle- 

 largets, which appeared to have been formed, 

 of earth originally supported by square blocks 

 of turf. The sides sloped, as nearly as I could 

 estimate them, at an angle of 45° or 50° with 

 the horizon, and they were covered, especially 

 on the northern side, with long coarse grass, 



* ' Illustrations of the Huttonian Theory of the Earth,' p. 107, 



