THE VEGETATION OF WOODLANDS. 1 5 



For the same reason, the farmland of hilly countries is mainly 

 confined to the valleys. The contrast between the valley and 

 the higher plateau-country is frequently very marked, and 

 many readers must have seen the arrangement of vegetation 

 here described. On the plateau, heather moor extends for 

 miles, growing on a gritty, sandy soil and supplied only by 

 such water as falls from the atmosphere. The slow growth 

 of the heather and other plants shows that only such plants 

 can survive as require little food-material, yet here and there 

 numbers of Scots pine have grown up from seedlings where 

 moor-firing has not taken place. This vegetation extends to 

 the edge of the valleys, but there becomes mixed with bracken, 

 a plant indicating deeper soils. On the higher slopes trees 

 are met with, chiefly birch, rowan and thorn, with occasionally 

 a stunted oak ; here the soil is still shallow for trees, and 

 the water-supply is mainly aerial Lower down the slope 

 emerging springs indicate the supply of underground or telluric 

 water, and this, combined with deeper soil and more humus, 

 favours a better growth of trees and ground-vegetation, and 

 we get a typical wood. At the bottom of the slope the soil 

 is much deeper owing to the accumulation of fallen stones and 

 soil, and humus rapidly accumulates as the soil is shaded, and 

 well supplied with moisture from the springs emerging at 

 different levels on the higher slope. In the bottom of the 

 valley the water is conveyed away by the stream, or if not it 

 collects and renders the soil unsuitable for the more important 

 timber trees, but well adapted for swampy thickets of alder 

 and willow. 



Another feature in the soil-conditions and water-supply of 

 a valley wood may be added here. If one stands at any 

 point in a valley, it will generally be found that one bank is 

 steep, while the other slopes more gradually. On the gentler 

 slope, tree-growth is much better than on the steeper slope, 

 and sometimes this is so marked that while one slope is almost 

 treeless, the other is well wooded. The steep slope may be 

 due to river erosion, but it also generally indicates that the 

 strata of that side dip inwards, so that little or no water 

 flows out. On the other hand, the dip or gentler slope weathers 

 less rapidly, and soil accumulates and is supplied with water 

 from outflowing springs, all the conditions being thus favourable 

 to the growth of woods. 



