ings, and the filling
above these should consist of a strong clay, which will remain in place
after the shavings rot away.

*Amending the Map.*--When the tiles are laid, and before they are covered,
all deviations of the lines, as in passing around large stones and other
obstructions, which may have prevented the exact execution of the original
plan, and the location and kind of each underground silt-basin should also
be carefully noted, so that they may be transferred to the map, for future
reference, in the event of repairs becoming necessary. In a short time
after the work is finished, the surface of the field will show no trace of
the lines of drain, and it should be possible, in case of need, to find
any point of the drains with precision, so that no labor will be lost in
digging for it. It is much cheaper to measure over the surface than to dig
four feet trenches through the ground.

CHAPTER V. - HOW TO TAKE CARE OF DRAINS AND DRAINED LAND.

So far as tile drains are concerned, if they are once well laid, and if
the silt-basins have been emptied of silt until the water has ceased to
deposit it, they need no care nor attention, beyond an occasional cleaning
of the outlet brook. Now and then, from the proximity of willows, or
thrifty, young, water-loving trees, a drain will be obstructed by roots;
or, during the first few years after the work is finished, some weak
point,--a badly laid tile, a loosely fitted connection between the lateral
and a main, or an accumulation of silt coming from an undetected and
persistent vein of quicksand,--will be developed, and repairs will have to
be made. Except for the slight danger from roots, which must always be
guarded against to the extent of allowing no young trees of the dangerous
class to grow near a drain through which a _constant_ stream of water
flows, it may be fairly assumed that drains which have been kept in order
for four or five years have passed the danger of interruption from any
cause, and they may be considered entirely safe.

A drain will often, for some months after it is laid, run muddy water
after rains. Sometimes the early deposit of silt will nearly fill the
tile, and it will take the water of several storms to wash it out. If the
tiles have been laid in packed clay, they cannot long receive silt from
without, and that which makes the flow turbid, may be assumed to come from
the original deposit in the conduit. Examinations of newly laid drain