There are none of these objections to the use of under-drains, as these are completely covered, and do not at all interfere with the cultivation of the surface. [With what materials may under-drains be constructed? Describe the tile.] Under drains may be made with brush, stones, or tiles. Brush is a very poor material, and its use is hardly to be recommended. Small stones are better, and if these be placed in the bottoms of the trenches, to a depth of eight or ten inches, and covered with sods turned upside down, having the earth packed well down on to them, they make very good drains. TILE DRAINING. The best under-drains are those made with tiles, or burnt clay pipes. The first form of these used was that called the _horse-shoe tile_, which was in two distinct pieces; this was superseded by a round pipe, and we have now what is called the _sole tile_, which is much better than either of the others. [Illustration: Fig. 4--Sole Tile.] [Why is the sole tile superior to those of previous construction? How are these tiles laid? How may the trenches be dug?] This tile is made (like the horse-shoe and pipe tile) of common brick clay, and is burned the same as bricks. It is about one half or three quarters of an inch thick, and is so porous that water passes directly through it. It has a flat bottom on which to stand, and this enables it to retain its position, while making the drain, better than would be done by the round pipe. The orifice through which the water passes is egg-shaped, having its smallest curve at the bottom. This shape is the one most easily kept clear, as any particles of dirt which get into the drain must fall immediately to the point where even the smallest stream of water runs, and are thus removed. An orifice of about two inches is sufficient for the smaller drains, while the main drains require larger tiles. These tiles are laid, so that their ends will touch each other, on the bottoms of the trenches, and are kept in position by having the earth tightly packed around them. Care must be taken that no space is left between the ends of the tiles, as dirt would be liable to get in and choke the drain. It is advisable to place a sod--grass side down--over each joint, before filling the trench, as this more effectually protects them against the entrance of dirt. There is no danger of keeping the water out by this operation, as it will readily pass through any part of the tiles. In _digging the trenches_ it is not necessary (except in very stony ground) to dig out a place wide enough for a man to stand in, as there are tools made expressly for the purpose, by which a trench may be dug six or seven inches wide, and to any required depth. One set of these implements consists of a long narrow spade and a hoe to correspond, such as are represented in the accompanying figure. [Illustration: Fig. 5. Upton tool. Spade and hoe.]