68o The Joitrnal of Forestry. 



6. Upon drained lands,wben the bottom is well stirred or subsoiled,the 

 descending water removes many substances injurious to vegetation, such 

 as the protoxide of iron, which forms in wet land, below the depth of 

 cultivation, a hard pan impenetrable to air, water, or the roots of plants. 



7. Moderately deep drainage renders deep cultivation both easy and 

 necessary; for as more soil is rendered available, roots penetrate 

 deeper and are less affected by drought. 



8. By the free admission of air more carbonic acid is generated in 

 the soil, and all vegetable substances contained in it are decomposed 

 more rapidly ; hence naked fallows become unnecessary, and the 

 rotation of crops may be enlarged. 



9. On pasture lands the inferior grasses die out, and are succeeded 

 by others of better quality ; the result is sounder sheep, a larger clip 

 of wool, and better hay. 



Though there are few districts in which land is not greatly improved 

 by judicious drainage, its beneficial results are more marked upon the 

 argillaceous soils, where infertility is caused mainly by the properties 

 those soils possess of resisting for a long time the penetrability of 

 air and water, and by their retaining water once admitted so long as 

 to cause it to become injurious. When undrained, the siliceous or 

 sandy soils also often remain infertile, in consequence of their retain- 

 ing so little moisture that the sun's heat injures the roots of plants. 

 The breaking up of the subsoil by drainage and deep cultivation 

 places the roots beyond the reach of excessive heat. 



Among the limestone formations, chalk, which is an earthy 

 carbonate of lime, generally requires drainage. From its whiteness it 

 reflects instead of absorbing the solar rays. Most of the calcareous 

 soils, however, are rich in vegetable matter, or humus, which is 

 completely insoluble in water, and is only obtainable by plants when 

 it becomes mixed with the oxygen of the air. 



A healthy state of siliceous, aluminous, or calcareous soils is 

 that in which, while their pores are charged with water, the interstitial 

 canals, or spaces between the clods, are free, in which condition they 

 will crumble to pieces in the hand. 



Much difference of opinion exists as to the general depth of 

 drainage ; and while many theorists advocate a uniformity of 4 feet, 

 there are excellent authorities who recommend a variation of from 

 2 feet 6 inches to 4 feet 6 inches, according to the texture of tlie soil. 

 It is but seldom that the error is on the side of excessive depth. As 

 long ago as the time of the Commonwealth, Captain Walter Blythe 

 wrote, "And for thy drayning trench it must be made so deepe that 

 it go to the bottom of the cold spewing moyst water that feeds the 

 flagg and rush, a yard or 4 feet deep if ever thou wilt drain to any 

 purpose, and one spade's graft beneath." 



