592 AGRICULTURAL REPORT. 
er to sink the excavation five or six feet without incurring any danger from caving. 
By employing the level, Fig. 12, and grading the bottom of a section one rod in 
length of the correct inclination, and laying the tiles or other material, as soon as about 
twenty feet can be excavated, the earth can be returned at once, and the props be re- 
moved to plank another section of the ditch. When the banks are stayed for a long 
distance with planks and props, a large quantity of lumber will be required. Besides 
this, the injury done to clean planks, when employed for such a purpose, wouJd render 
them of little value for most building purposes. 
Finishing the bottom of a ditch—When tiles or stones are employed to fill a ditch, it is 
of little acconnt whether the sides, a few inches upward from the bottom, be dressed 
true or left as uneven as a rough rock; but when filling with pieces of plank, it will be 
easy to finish the sides and corners of the bottom so smoothly that the pieces 
will fit neatly by usinga gauge, represented by Fig. 15, which consists of a piece of 
hard-wood board ten inches long by four inches wide, having one end of a handle 
e nailed firmly across the middle, as shown. When finishing the bot- 
Fig. 15.  . tom of a ditch, the ditcher should be provided with such a gauge, 
and be instructed to have the bottom of the ditch dressed so trus 
that the gauge will barely pass through it endwise. 
The correct depth of drains.—Where the ground is to be cultivated 
by deep plowing, or by spading, whether the ditches are filled with 
tiles, stones, or wood in any form, the excavation should never be 
made less than thirty inches deep. No plowing or spading will ever 
disturb the tile in a ditch of this depth. Ifa ditch is stoned, so that 
the surface of the leveling stones is ten to twelve inches above the 
bottom of the ditch, a suitable plow might disturb some of the stones, 
and cause mellow earth to work down into the water-course, and 
thus obstruct the stream. So long as a drain has a free outlet, there 
is little danger of sinking a ditch too deep. 
The rule adopted by all intelligent ditchers is, to sink the ditch at 
the most shallow place, not less than thirty inches; then, if the ditch 
will draw all the water when graded to that uniform depth, thirty 
inches will subserve the purpose as well as if the drain were three or 
four feet deep. After a ditch has been sunk thirty inches, any farther 
depth should be determined by the distance required to cut off the water-veins. The only 
objection that can be urged against a greater depth than thirty inches is the expense 
of digging. When the earth is so firm that the lower part of a ditch must be dug up 
with a sharp-pointed pick, it is estimated by practical ditchers that the labor of mak- 
ing a ditch four feet deep is fully equal to cutting two ditches, in the same kind of 
soul, only three feet deep. This assumption will not always be found reliable. If aditch 
be excavated to the depth of three feet, while it is of sufficient width to enable the 
digger to sink it another foot without increasing the width, it is evident that the labor 
required to excavate the fourth foot will not equal the labor of sinking it threé feet. 
If the ditch is so narrow, after having been sunk three feet, that the digger cannoé 
work conveniently at a greater depth without increasing the width, the labor incident 
to excavating the fourth foot may equal the expense of digging the first three feet. 
Most writers on underdraining have fixed the minimum depth of drains at four feet 
for all ordinary underdraining, but none of them have assigned any plausible reason 
therefor, except that it brings the line of saturation farther below the surface of the 
soil than the same line would be in case the drains were only three feet deep, which is 
correct. Yet, if a system of draining thirty inches in depth draws all the superfiu- 
ous water, we are not warranted in assuming that the soil would be any more produc- 
tive if the drains were sunk four feet deep. The roots of growing plants will not 
strike more than thirty inches deep, on an average, even if the ditches were sunk six 
feet deep. Hence, we shall need the evidence of well-conducted experiments to prove 
that it will pay to sink ditches four feet deep, before recommending the adoption of so 
expensive a system. ‘ ee 
Grading the bottom of ditches—When there is considerable slope to a ditch, if is im- 
portant that the bottom should be of uniform descent from the sammit of the slope to. 
the lowest point of the outlet. This is particularly desirable if the ditch is to be filled 
with stones, planks, or horseshoe tiles, in which cases the water flows on the ground ; 
and if the earth should be soft and readily washed away in some places, and be com- 
pact in other places, the bottom of the channel would be liable to be gullied where 
the water runs most rapidly. The object in having the bottom of a true grade is 
to secure a uniform current of the stream. The subject may be elucidated by the 
accompanying diagram, (Fig. 16,) in which a b represents the uneven surface of the 
slope, where the drain is to be made. There may be, for example, a marsh a little 
above b, to be drained. Instead of making the bottom of the drain to correspond as 
nearly as may be with the uneven surface of the slope, as represented by the line ed, 
of numerous angles, the bottom should be graded as straight as a line from ¢ to f; then 
water will flow from one end to the other with a uniform rapidity. A horizontal base- 
