330 
DRAINAGE OF SOILS. 
ably increased, but the vvork is done in a less accurate manner. Par¬ 
ticular care must also be taken that the bottom of the drains are 
made with a regular descent, so that the water runs from the one end 
to the other without standing dead; and where bore-holes or wells 
are necessary, they must he made before the conduit is laid, in order 
that the sand may be removed which the water may throw up from 
the stratum below, and would otherwise be deposited in the bottom of 
the drain which would thereby be rendered useless. The dimen¬ 
sions of the conduit depends upon the quantity of water it has to 
carry; thus, in an outlet drain, it requires to be larger than in a 
cross drain, which has only the water collected in itself to discharge. 
In general cases, therefore, the conduit in an outlet should be made 
from nine to twelve inches square, and, in cross drains, from four to 
six inches square. When the bottom of the drain is very soft, it 
must be laid with flag stones, to prevent the materials from sink¬ 
ing ; and the stones forming the side walls of the conduit must all be 
laid on their flat beds, and covered with strong covers well joined to¬ 
gether and packed at their ends; the space above, in clayey soils, 
must be filled with stones, broken to the size of a man’s clenched 
hand, to within twelve inches of the surface of the ground, which re¬ 
maining space must be filled with porous earth. Before the earth is 
put into the drains, the stones must be covered with straw, rushes, 
or turf with the green side downwards, to prevent the loose particles 
from subsiding into the crevices among the stones. In cases where 
all the water comes from bore-holes, or rises in the bottom of the 
drain, eighteen inches of small stones above the covers is sufficient; 
but when it comes from the sides of the drain, it is necessary to fill 
the drain above the covers with some kind of porous substances, six 
inches higher than where the water breaks out; the neglect of this 
precaution is the reason why so many drains have so little effect in 
drying land. 
In making covered drains, particular attention must be paid that 
they are not carried into the outlet at right angles, as their ends 
should be turned down in the direction, the water is to run a short 
space before they join it, to prevent the water in the outlet depositing 
any sand or sludge in their mouths, which will be the case if this is 
not attended to ; indeed it often happens, on almost every estate that 
the drains are stopped and rendered useless from this precaution 
being neglected. The mouths of the drains ought also to be well 
built and secured with iron gratings, to prevent vermin from getting 
into them; and it must be examined from time to time, to see that 
it is in proper repair and the outlet kept a sufficient depth, so that 
