Stephens gives a minute description of the mole plow figured above, in his Book of the Farm. Its general structure and principle of operation may be easily understood by what has been already said, and any person desirous of constructing one may find in that work exact directions.
WEDGE AND SHOULDER DRAINS.
These, like the last-mentioned kind of drains, are mere channels formed in the subsoil. They have, therefore, the same fault of want of durability, and are totally unfitted for land under the plow. In forming wedge-drains, the first spit, with the turf attached, is laid on one side, and the earth removed from the remainder of the trench is laid on the other. The last spade used is very narrow, and tapers rapidly, so as to form a narrow wedge-shaped cavity for the bottom of the trench. The turf first removed is then cut into a wedge, so much larger than the size of the lower part of the drain, that when rammed into it with the grassy side undermost, it leaves a vacant space in the bottom six or eight inches in depth, as in Fig. [14].
The shoulder-drain does not differ very materially from the wedge-drain. Instead of the whole trench forming a gradually tapering wedge, the upper portion of the shoulder-drain has the sides of the trench nearly perpendicular, and of considerable width, the last spit only being taken out with a narrow, tapering spade, by which means a shoulder is left on either side, from which it takes its name. After the trench has been finished, the first spit, having the grassy side undermost as in the former case, is placed in the trench, and pushed down till it rests upon the shoulders already mentioned; so that a narrow wedge-shaped channel is again left for the water, as shown in Fig. [15].
Fig. 14.
Wedge-Drain.
Fig. 15.
Shoulder-Drain.
These drains may be formed in almost any kind of land which is not a loose gravel or sand. They are a very cheap kind of drain; for neither the cost of cutting nor filling in, much exceeds that of the ordinary tile drain, while the expense of tiles or other materials is altogether saved. Still, such drains cannot be recommended, for they are very liable to injury, and, even under the most favorable circumstances, can only last a very limited time.