SLOPE AND ASPECT. 19 



very badly. The washing- away then is due to the humus 

 having- become used up and there being- nothing- left to bind 

 the soil particles together. In such cases the application of 

 organic matter will help very materially. For this purpose 

 manure, straw or other material may be applied or crops like 

 clover and the grasses, which leave considerable organicmat- 

 ter, may be grown on the land. Crops that leave very little 

 humuo in the ground, such asnursury stock, which is dug out 

 by the roots, are most harmful in exhausting- the humus in the 

 soil, and land used for this purpose needs heavy manuring 

 with stable manure and an occasional seeding down to grass 

 or clover. 



Alkali Soils. In the prairie portions and occasionally else- 

 where in this section, we have a kind of soil in which there is 

 a superabundance of carbonate and sulphate of soda. This 

 kind of soil seldom extends over larg-e areas and generally 

 occurs in places lower than the surrounding- land. In some 

 places the alkali occurs in such abundance as to coat the 

 surface of the soil with a white crust. On such land very few 

 agricultural crops or trees grow well. The leaves of the trees 

 growing there generally take on a yellowish color and the 

 wood does not mature well in the autumn. Such land should 

 be drained so that the surface water at least can run off. In 

 this way the alkali can g-enerally be washed out in a few 

 years. It is seldom advisable to plant trees on these places, 

 but if this seems desirable, as is sometimes the case on prairies, 

 the best trees to plant are probably the Cottonwood and White 

 Willow. 



EFFECT OF SLOPE AND ASPECT ON TREE GROWTH. 



The slope of the land affords drainag-e and so affects the 

 growth of trees, but trees will grow on any slope, even on 

 pricipices if they can find room for their roots and the soil is 

 somewhat moist. The direction of the slope usually has a 

 very marked effect on the growth of vegetation. This is 

 especially the case where high ranges of hills and other local 

 conditions modify the climate. 



A Northern Slope receives no full sun light, the sun's rays 

 fall obliquely in the morning or toward evening according to 

 the angle of elevation. The winds it receives in winter are 



