138 PRELIMINARY WORKS. 



channel, situated in the liighest part of the area, c, c, c 

 the leaders, and h, h, h the distributing trenches. The 

 watering of the land may be caused by overflow from the 

 trenches, or by percolation ; in the latter case the trenches 

 would only be just filled, and no more. 



"Where extensive areas are to be irrigated, the channels and 

 trenches must be carefully laid out, with a suitable fall, so as 

 to prevent the bursting of the channels and the silting up of 

 the trenches. 



4. Treatment of Excessive Accumulations of Vegetable 

 Matter. 



Cases occur in which accumulations of vegetable matter 

 have to be disposed of, before the formation of a wood can 

 be taken in hand. Such accumulations may be objectionable, 

 because they are so thick that the seedlings cannot reach the 

 mineral soil within'a reasonable space of time, and run the risk 

 of drying up ; or they may have become acid, or bituminous ; 

 again, they may be accompanied by swampiness, or be liable 

 to dry up too quickly. 



The following cases specially interest the forester : — 



a. Peal Bogs. 



To render a peat hog fit for the growth of timber trees, 

 one or all of the following operations must be carried out : — 



(1.) Draining. 



(2.) Removal of at least a portion of the peat. 



(3.) Mixing the peat with mineral soil. 



The draining is done in the manner described above ; it is, 

 however, desirable to do this gradually, so that the layers 

 of peat may dry by degrees, to prevent the formation of ex- 

 tensive cracks. The feeders should at first be of moderate 

 depth, and gradually deepened, until the mineral soil is 

 reached. 



AVhen the layer of peat is sliallow, it can, after draining, 

 be mixed with the mhieral soil below it, and thus rendered 



