GENERAL IDEAS. 9 



cooler, and drier (generally at least), and winds are 

 more violent. This is equivalent to saying that 

 forest vegetation, which was vigorous enough in the 

 valleys, is less active on hill slopes, and "becomes 

 sluggish, and even disappears altogether, on high 

 unsheltered plateaux. The shape of the trees too 

 becomes deformed. But it is impossible to define 

 sharp] y the climate of valleys and of slopes, because 

 it depends entirely on the direction of the valleys, 

 and thus each case must be examined on its own 

 merits. 



INFLUENCE OF ASPECT. The influence exercised 

 by aspect on the climate and the necessity of study- 

 ing its action on the growth of trees, have already 

 been foreshadowed in what precedes. 



A northern aspect receives no sun ; on this aspect 

 therefore there is but little heat, and the light is 

 diffused ; the winds are cold, contain little moisture, 

 and are seldom strong. But on account of the low 

 temperature, the soil remains ever moist ; growth is 

 therefore rapid, the trees are regular in shape, but 

 the woody tissue is soft and not well lignified. 

 Timber grown on this aspect is unsuited for building 

 wood, but on the other hand well adapted for manu- 

 facturing purposes, especially for planking. 



On an eastern aspect the sun shines obliquely and 

 during the coolest hours of the day ; the temperature 

 and the light on this aspect are therefore moderate, 

 the wind is dry, and not violent. Under these 

 conditions the soil retains its moisture fairly well, 

 the growth is active, the trees are regular in shape, 

 and yield timber of average quality, useful for all 



