RECLAMATION OF THE SOIL. 131 



(/>.) Trenching. 



{(■.) Raising the surface level. 



If the lowest part of the pan is not deeper than 18 inches 

 below the surface and not too hard, ploughing may be adopted ; 

 the pan, being brought to the surface and exposed to the 

 atmosphere, soon disintegrates. Pans situated at a greater 

 depth than 18 inches must be broken through by trenching 

 with spade, hoe, pick, or crowbar. In either case the operation 

 is expensive, hence it is usual to treat only part of the area, 

 in strips, patches, or holes. Strips may be 2 to 3 feet 

 broad, separated by unbroken ground 4 to 6 feet in ])readth, 

 so that the actual work is restricted to about one-third of the 

 area. Patches may be of various sizes, down to holes about 

 12 inches square. 



If the pan is very thick and goes to a greater depth than 

 3 feet, it may be cheaper to raise a portion of the land by 

 cutting ditches at intervals and placing the excavated earth 

 on the intermediate strips, thus providing the latter with 

 a depth of soil sufficient for the production of trees. 



The treatment of impermeable strata is always an expensive 

 matter, so much so in many cases that the utilisation of the 

 area becomes altogether unprofitable. In some cases the 

 expense may be avoided by planting a shallow rooted species 

 and being satisfied with moderate returns, 



2. Treatment of Swampy Ground generally. 



Each species thrives best with a definite degree of moisture 

 in the soil at all times of the year. That degree differs con- 

 siderably in the case of the several forest trees ; while some 

 like moist and even wet soil, others will not flourish in such 

 localities, and none of them in stagnant water. It follows 

 that an excess of moisture, over and above what is suitable 

 for a given species, must be removed before a wood is started. 

 The method of doing this depends on the cause of the excess 

 of moisture. 



A locality becomes swampy if it receives more water than 



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