84 • BRITISH FOREST TREES. 



occupied, for several hundred feet of perpendicular 

 altitude up the slope, hy gravel, which covers the 

 primitive strata to considerable depth, especially in 

 the eddies of the salient angles of the hill. Every 

 description of tree grows more luxuriantly here than 

 in any other situation of the country ; the causes of 

 this are, 1^^, The open bottom allowing the roots to 

 penetrate deep, without being injured by stagnant 

 moistm-e ; 2d, The percolation of water down through 

 the gravel from the superior hill ; 3d, The dryness 

 of the surface not producing cold by evaporation, 

 thence the ground soon heating in the spring ; M/i, 

 The moist air of the hill refreshing and nourishing 

 the plant during the summer heats, and compensa- 

 ting for the dryness of the soil ; 5th, The reverbera- 

 ting of the sun's rays, between the sides of the nar- 

 row valley, thus rendering the soil comparatively 

 warmer than the incumbent air, which is cooled by 

 the oblique cm-rents of the higher strata of air, oc- 

 casioned by the unequal surface of the ground. 

 This comparatively greater warmth of the ground, 

 when aided by moistm-e, either in the soil or atmo- 

 sphere, is greatly conducive to the luxuriancy of 

 vegetation. 



J^irm dry clays and sound b?vw7i loam. — Soils 

 well adapted for wheat and red clover, not too rich, 



