EXTENSION COURSE IN SOILS. 37 
level of the bottom of the ditch between the stakes which are 50 feet 
apart. 
The height of the bottom of the ditch or the grade line, above the 
outlet can now be determined for each grade stake. These heights 
should be written in a column opposite the elevations of the surface 
of the ground. By subtracting the elevation of the grade line from 
that of the surface of the ground, the depth of cut can be found at 
each stake. These depths can be written in proper order in a third 
column. 
The construction of the ditch may now be undertaken. (Kef. No. 
8, pp. 89-98.) This should be started at the lower end, or outlet. 
It is necessary now to have a method of determining exactly when 
the grade line or bottom of the ditch is reached. To do this, place 
strong stakes at each of the two lower stakes with a line between. 
This line is to be placed at a uniform height above the bottom of 
the finished ditch. A string may be adjusted at a convenient height 
of 5 or 6 feet above the bottom of the ditch by subtracting the depth 
of digging at each stake from the 5 or 6 feet decided on and measuring 
up from the 'surface of the ground this distance on the stake. Fas- 
tening the string at this point for each of the two stakes will bring 
the string exactly parallel with the bottom of the ditch and 5 or 6 feet 
above it. 
Digging the ditch and completing the drain. — The tools necessary 
include a ditching spade with a blade about 8 inches wide, slightly 
curved, and square at the cutting edge; a long-handled pointed 
shovel; a tile scoop; and, if much tile is to be laid, a tile hook. A 
strong string is first stretched along the edge of the ditch to keep it 
straight. Digging begins at the lower end and proceeds upgrade 
in sections, removing the dirt to a spade depth at a time. The 
width of the ditch will depend on the depth but should be no greater 
than is absolutely necessary. Care must be taken not to remove 
dirt below the grade fine. When the grade fine is nearly reached 
over a distance of 6 or 8 feet the last thin layer of dirt is removed 
with the tile scoop, which produces a straight, smooth bottom on 
which the tile may be placed. Tile may be placed by hand, though 
if the ditch is deep and much is to be laid the tile hook will permit 
much more rapid and easy work. The tile should be placed so that 
they fit closely together end to end, and care must be taken whenever 
work is left for the night to have the upper end protected by a flat 
stone or otherwise so that much soil may not be washed in in case of 
rain. The tile should be covered immediately after laying to a depth 
of 2 or 3 inches after heavy soil or other material has been used over 
joints to prevent sand or other loose material from working into the 
tile. (Ref. No. 8, p. 99.) This is called blinding. The remainder 
