42 ON DRAINING GROUND FOR FLANTATIONS. 
often necessary to exercise caution, and not bring too much 
into any common discharge, along a great declivity, before 
reaching a well-swarded channel or stream, as an accumu- 
lation of water to one point of exit, particularly in ground 
not adhesive, has the effect during floods of cutting ravines, 
overlaying lower and more fertile grounds with débris, and 
shutting up and diverting the course of streams, and the like. 
To prevent such inroads it is sometimes necessary to cause- 
way, in a concave form, the course of a drain along a steep 
declivity. Stones for such a purpose are generally found 
abundantly on the ground, and even when carted loosely into 
the bottom of a ditch they have the effect of preventing the 
water from deepening the trench, although they are not built; 
but, if the descent is rapid, building is generally required. 
Where stones are scarce, well-swarded turf, closely built, 
by being set on edge, is found to suit the purpose, where the 
discharge of water is not constant; in such the herbage grows, 
and becomes quite fixed, and sufficient for the discharge of a 
flood, if only of afew days at a time. For such places a 
shodding of stone and turf alternately make the strongest 
fence of any against the inroads of water. The stones, if flat, 
should be set on edge, if boulders, on end; and although the 
stones are generally round, yet by introducing a fresh turf set 
on edge between each course of stones, the turf grows, and 
the roots, belonging commonly to a mixture of grasses, fill up 
all crevices underneath, and the wild native vegetation spreads 
above, and thus encases the stones securely. I have seen this 
description of work resist the inroads of streams in flood, 
where more costly mason-work was of less use. The more 
gentle the cavity in the bottom, or the slope on the sides, the 
greater the strength of the work. 
In forest planting, deep-rooted plants require a soil more 
elevated above the rise of water than the pines and other 
surface-rooted trees. Young plantations recently formed are 
more apt to suffer in the absence of drainage than plantations 
that are more advanced ; because, when trees (particularly 
the pine tribe) become so far advanced as to form a cover on 
