CHAP, v.] Soil and Situation 113 



temperature of soils, and on the amount of moisture retained 

 in them. Southern and south-western aspects, owing to their 

 greater warmth and to the stimulation of evaporation, both 

 through the foliage and direct from the surface-soil, are usually 

 much drier and more apt to get heated than northern and 

 north-eastern exposures, which are cooler and damper, and 

 whose soil is usually less active both in awakening vegetation 

 in spring, in stimulating to assimilative processes, and in 

 decomposing the dead foliage on the ground so as to form 

 humus. On high ranges of mountains, however, trees will still 

 be found on the warmer aspects at levels above those limiting 

 their growth on the northern slopes. Eastern exposures are 

 most liable to danger from late frosts; whilst western and 

 south-western aspects are most exposed to damage from wind- 

 fall and breakage, as the heavy storms coming from these 

 directions are usually accompanied by rain, and often occur 

 at times when the soil is still sodden from recent downpours. 



The Slope or Gradient of any soil is necessarily of influ- 

 ence ; for the opportunities which rainwater has of percolating 

 down to the lower layers decreases as the angle formed with 

 the horizontal by the surface of the soil increases. According 

 to Grebe, soils with a slope of from 5 to 30 form the true 

 home of woodland growth; hence much land which is too 

 steep for agricultural cultivation is well adapted for sylvi- 

 cultural occupation. Grebe's classification of gradients, now 

 adopted at the experimental stations throughout Germany, is 

 as follows : 



gentle 5-io steep 21-30 



medium 11-20 very steep 31-45 



precipitous over 45 ; this is, however, incapable of sustaining tree- 

 growth. 



The Configuration of the Soil and of the surrounding 

 Country exerts a considerable amount of influence on the 

 woodlands. The soil near the base of hills is generally deeper, 

 richer, and more productive than on the slopes or ridges ; but 



I 



