72 



sides of the hills the slopes are much more gradual 

 than on those sheltered from the wind. 



In cultivated districts, where the valleys are 

 inhabited and tilled, the protected area of the whole 

 surface must gradually diminish ; for, as the valleys 

 widen, the quantity of tillage is increased. But in 

 wild districts, where nature still reigns, what is 

 taken from the protected summit has an equivalent 

 returned in the valleys ; for when the latter have 

 become wide enough, peat forms there also, which, 

 once it has established itself, rapidly grows not only 

 on the flat, but also creeps up the slopes ; so that 

 eventually there is only a small fringe round the 

 edge of the table-topped summit which can be acted 

 on by the denuding forces. 



In moist climates, not only on mountains, but also 

 on low lands (if uncultivated), unless drained 

 naturally or artificially, peat will grow and defy 

 denudation. Even in cultivated tracts, when the 

 land is under grass and not in tillage, denudation 

 cart have very little effect. This is well illustrated 

 when a section is opened down a hill-slope that has 

 been for a long time grass land, more especially if it 

 merges at the bottom into a boggy flat. In this 

 instance it will be found that there is scarcely any 

 difference between the thickness of the surface soil 

 at the summit and base of the hill ; while the peat 

 from the flat has been gradually encroaching on the 



