DRAINAGE. 49 



and this preparatory work may, according to circumstances, 

 extend to the soil, the subsoil, and the surf ace -growth of weeds. 

 Sour, wet, marshy, or water-logged lands, peats or clays, must 

 first of all be drained to carry off the injurious excess of soil- 

 moisture, and to allow of a freer circulation of oxygen within 

 the soil ; for wet, undrained land remains cold and inert. Bog- 

 myrtle patches are always sour and acid, and need very thorough 

 drainage and aeration before becoming plantable with profit ; 

 and where plenty of more suitable land is available, such 

 patches should be excluded in the meantime. 



In a wet climate like the West of Scotland a considerable 

 amount of surface - draining will usually have to be done, 

 merely to carry off the heavy rain-water falling during about 

 nine months in every year. Throughout most of the extensive 

 waste-lands in Scotland and Ireland there are large tracts with 

 deep peaty and mossy soil resting on stiff clay or hard gravelly 

 pan, preventing water percolating downwards ; and to be effective 

 drains should pierce through this, though the width, depth, and 

 distance apart of the drains will depend on the wetness of the 

 soil and the stiffness and depth of the impervious layer or sub- 

 soil. Another effect of drainage is practically to increase the 

 depth to which tree -roots can descend for their food -supply. 

 The deeper the drainage, the greater will be the permeability of 

 the soil, and its capacity for being warmed by the sun and thus 

 stimulated to provide plant-food. 



When any extensive drainage system is necessary, as in 

 preparing big peat-mosses for planting, a system of main drains, 

 side-drains, and feeders should be dug, beginning at the lowest 

 point. The main drains are usually about 3 to 4 ft. wide and 

 2 J to 3 ft. deep, though often much wider and deeper on 

 peat-bogs, and the small feeders are usually about a foot broad 

 or more, and 10 to 12 inches deep, and the sides of all drains 

 should be cut with sloping edges to prevent the sides falling in 

 from top-pressure or scouring. The bottom of the drain should 



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