290 DENUDATION OF THE LAND. Chap. VL 



will never be removed as long as the wood 

 lasts; and mould will here tend to accumulate 

 to the depth at which worms can work. I 

 tried to procure evidence as to how much 

 mould is blown, whilst in the state of cast- 

 ings, by our wet southern gales to the north- 

 east, over open and flat land, by looking to 

 the level of the surface on opposite sides of 

 old trees and hedge-rows ; but 1 failed owing 

 to the unequal growth of the roots of trees 

 and to most pasture-land having been formerly 

 ploughed. 



On an open plain near Stonehenge, there 

 exist shallow circular trenches, with a low 

 embankment outside, surrounding level spaces 

 50 yards in diameter. These rings appear 

 very ancient, and are believed to be contem- 

 poraneous with the Druidical stones. Castings 

 ejected within these circular spaces, if blown 

 to the north-east by south-west winds would 

 form a layer of mould within the trench, 

 thicker on the north-eastern than on any other 

 side. But the site was not favourable for the 

 action of worms, for the mould over the 

 surrounding Chalk formation with flints, was 

 only 3*37 inches in thickness, from a mean of 



