drain has a fall of three inches, the next hundred feet should not have less than three inches, lest the diminished velocity cause silt, which required the speed which that fall gives for its removal, to be deposited and to choke the tile. This defect of grade is shown in Fig. 17. If the second hundred feet has an inclination of more than three inches, (Fig. 18,) the removal of silt will be even better secured than if the fall continued at the original rate. Some silt will enter newly made drains, in spite of our utmost care, but the amount should be very slight, and if it is evenly deposited throughout the whole length of the drain, it will do no especial harm; but it becomes dangerous when it is accumulated within a short distance, by a decreasing fall, or by a single badly laid tile, or imperfect joint, which, by arresting the flow, may cause as much mischief as a defective grade. The use of muslin bands practically prevents the entrance of silt.

Owing to the general conformation of the ground, it is sometimes absolutely necessary to adopt such a grade as is shown in Fig. 19,-even to the extent of bringing the drain down a rapid slope, and continuing it with the least possible fall through level ground. When such changes must be made, they should be effected by angles, and not by curves. In increasing the fall, curves in the grade are always advisable, in decreasing it they are always objec tionable, except when the decreased fall is still considerable,—say, at least 2 feet in 100 feet. The reason for making an absolute angle at the point of depression is, that it enables us to catch the silt at that point in a silt basin, from which it may be removed as occasion requires.

A Silt Basin is a chamber, below the grade of the drain, into which the water flows, becomes comparatively quiet, and deposits its silt, instead of carrying it into the tile beyond. It may be large or small, in proportion to the amount of drain above, which it has to accommodate. For a few hundred feet of the smallest tile, it may be only a

6-inch tile placed on end and discharge the water at its top.

sunk so as to receive and For a large main, it may

be a brick reservoir with a capacity of 2 or 3 cubic feet. The position of a silt basin is shown in Fig. 19.

The quantity of silt which enters the drain depends very much on the soil. Compact clays yield very little, and wet, running sands, (quicksands,) a great deal. In a soil of the latter sort, or one having a layer of running sand at the level of the drain, the ditch should be excavated a litle below the grade of the drain, and then filled to that level with a retentive clay, and rammed hard. In all cases when the tile is well laid, (especially if the collars, or, better, muslin bands are used,) and a stiff earth is well packed around the tile, silt will not enter the drain to an injurious extent, after a few months' operation shall have removed the loose particles about the joints, and especially after a few very heavy rains, which, if the tiles are small, will sometimes wash them perfectly clean, although they may have been half filled with dirt.

Vermin,-field mice, moles, etc.,--sometimes make their nests in the tile and thus choke them, or, dying in them, stop them up with their carcasses. Their entrance should be prevented by placing a coarse wire cloth or grating in front of the outlets, which afford the only openings for their entrance.

Roots. The roots of water-loving trees-willows, elms and swamp-maples-will often force their entrance into the joints of the tile and fill the whole bore with masses of fibre which entirely prevent the flow of water. Collars make it more difficult for them to enter, but even these are not a sure preventive. Gisborne says:

"My 'own experience as to roots, in connection with "deep pipe draining, is as follows: I have never known "roots to obstruct a pipe through which there was not a "perennial stream. The flow of water in summer and "early autumn appears to furnish the attraction. I have

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66 never discovered that the roots of any esculent vegetable "have obstructed a pipe. The trees which, by my own "personal observation, I have found to be most danger. "ous, have been red willow, black Italian poplar, alder "ash, and broad-leaved elm. I have many alders in close "contiguity with important drains, and, though I have 66 never convicted one, I cannot doubt that they are dan gerous. Oak, and black and white thorns, I have not “detected, nor do I suspect them. The guilty trees have "in every instance been young and free growing; I have "never convicted an adult. These remarks apply solely "to my own observation, and may of course be much "extended by that of other agriculturists. I know an in“stance in which a perennial spring of very pure and (I believe) soft water is conveyed in socket pipes to a 46 paper mill. Every junction of two pipes is carefully "fortified with cement. The only object of cover being "protection from superficial injury and from frost, the "pipes are laid not far below the sod. Year by year these "pipes are stopped by roots. Trees are very capricious in "this matter. I was told by the late Sir R. Peel that he "sacrificed two young elm trees in the park at Drayton "Manor to a drain which had been repeatedly stopped by "roots. The stoppage was nevertheless repeated, and 66 was then traced to an elm tree far more distant than "those which had been sacrificed. Early in the autumn "of 1850 I completed the drainage of the upper part of a boggy valley, lying, with ramifications, at the foot of marly banks. The main drains converge to a commor outlet, to which are brought one 3-inch pipe and three of 4 "inches each. They lie side by side, and water flows pe rennially through each of them. Near to this outlet did grow a red willow. In February, 1852, I found the 66 water breaking out to the surface of the ground about "10 yards above the outlet, and was at no loss for the cause, as the roots of the red willow showed themselves

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"at the orifice of the 3-inch and of two of the 4-inch pipes. "On examination I found that a root had entered a joint "between two 3-inch pipes, and had traveled 5 yards to "the mouth of the drain, and 9 yards up the stream, ❝forming a continuous length of 14 yards. The root which "first entered had attained about the size of a lady's little "finger; and its ramifications consisted of very fine and "almost silky fibres, and would have cut up into half a "dozen comfortable boas. The drain was completely "stopped. The pipes were not in any degree displaced "Roots from the same willow had passed over the 3-inch "pipes, and had entered and entirely stopped the first "4-inch drain, and had partially stopped the second. At "a distance of about 50 yards a black Italian poplar, "which stood on a bank over a 4-inch drain, had completely stopped it with a bunch of roots. The whole of "this had been the work of less than 18 months, including "the depth of two winters. A 3-inch branch of the same "system runs through a little group of black poplars. "This drain conveys a full stream in plashes of wet, and some water generally through the winter months, but "has not a perennial flow. I have perceived no indica"tion that roots have interfered with this drain. I draw "no general conclusions from these few facts, but they "may assist those who have more extensive experience in drawing some, which may be of use to drainers."

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Having considered some of the principles on which our work should be based, let us now return to the map of the field, and apply those principles in planning the work to be done to make it dry.

The Outlet should evidently be placed at the present point of exit of the brook which runs from the springs, cclects the water of the open ditches, and spreads over the flat in the southwest corner of the tract, converting it into a swamp. Suppose that, by going some distance into the next field, we can secure an outlet of 3 feet and