DRAINAGE. 615 



choked with soil, the larger the aperture of the tiles, and in 

 sandy soil it should be at least two inches. 



After laying the tiles, which should be done in dry weather, 

 and as rapidly as possible, the trenches are filled in with 

 earth, and the greatest care should be taken, especially when 

 the soil is stony, that the pipes are neither broken nor 

 displaced. 



iii. DURABILITY. 



The durability of the drains depends on the nature of the 

 soil, the quality of the tiles and the care taken in executing 

 the work. Well-burned tiles at depths of 3J to 4J feet should 

 last for 25 years and more ; for instance, draining-tiles laid in 

 1850, in the Prussian Crown Estates, were in good order in 

 1880. 



The cost of draining with tiles is about S per acre, and 

 this is, of course, prohibitive for purely forest work. 



d. Comparison of Draining -Tiles with Open Drains. 



Drainage improves soils by lowering the level of subsoil 

 water, and exposing a larger area of the soil to the influence 

 of atmospheric air, thus rendering it warmer and accelerating 

 the decomposition of humus. As compared with open drains, 

 draining-tiles waste no productive area, are less subject to 

 damage and drain the soil better, and their use is highly 

 advisable in agricultural lands, but in forests they are much 

 more costly to lay out than open drains, and they easily 

 become choked by the rootlets of trees and of weeds such as 

 Equisetum, Arundo, etc., and also by frogs' spawn. Deposits of 

 iron-ochre may also be formed in the pipes, and they may 

 become filled with sand. 



Experience has shown that in forests all the disadvantages 

 of draining-tiles occur more frequently than in agricultural 

 lands, and they can be profitably used only in forest nurseries, 

 or for bad forest meadows. The production of hay in meadows 

 may be increased 25 per cent, by good drainage, and the 

 quality of the hay is also improved, 



