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effect of dry seasons is to contract the materials, which then get shifted by the superincumbent weight, and sometimes choke the watercourse below. For the purpose of protecting the water-way of drains, turf is occasionally placed over the stones, as shown in fig. 58,

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where the watercourse is formed with three flat stones, or otherwise tiles, arranged as the sides of a triangle, and leaving an open duct between them. This duct is covered with a layer of loose stones, by which the stones forming the duct are kept in their places, and upon these stones a layer of turf is placed before filling the drain up with the soil. Fig. 59 represents a compound drain, having two clear watercourses and a layer of loose stones for intersticial drainage. The two courses are formed with two semi-cylindrical tiles, and a flat tile or sole between them. In all drains formed with soles and tiles, these are laid so that the joints in one break with those in the other; by which the joints are rendered less liable to be dislocated or disturbed than they would be if the joints in the soles and the tiles were laid coincident with each other.

109. The most complete and undoubtedly permanent form of drain is that which consists of an open channel formed entirely of single pieces of tile-work or piping.

These are now generally acknowledged to form the most superior drains, and in nearly all places in this country their cost will not much exceed that of the imperfect drains formed with loose stones. A drain of this construction is shown in fig. 60, where the earthen pipe is represented of an egg-shaped section, and a layer of loose stones placed above it. If drains be thus formed, the joints accurately laid, and the whole work carefully done, the drainage will remain in a perfect and unimpaired condition for a very long period.

110. Drains are liable to injury by vermin, as well as vegetation, the roots of trees, &c., acting in a very injurious manner when their progress is interrupted by underground constructions for drainage. Drains should, therefore, be laid apart from trees, or these cleared away before constructing the drains. The liability to injury by vermin is one feature in which pipe drains are superior to all others constructed of several parts, or depending partly upon the permanent position of the soil in which the drain is formed.

111. The form of construction being determined, the size of the drains is the next object of consideration. Formerly drains were commonly made of small depth. But deeper ones having been subsequently constructed, and considerable efficiency in the effect obtained, a great desire has arisen for deep drains. In arable districts one imperative condition as to the depth of drains is, that the lower and constructed part of the drain shall be below the action of the plough and other agricultural implements. The structure, depth, and position of the strata are also circumstances that will deserve regard in fixing the depth, as already explained at length in describing the several varieties of sections; and, besides these, another consideration which must be kept in mind

is the rate of fall which can be obtained, according to the levels of the surface of the district, to assist the discharge of the contents of the drain. As a general principle, if it were impossible to allow all these circumstances their due weight in arriving at a decision as to the depth of the drains, deep drains are doubtless more safe and likely to be efficient than shallow drains; but while all the facts exist, and may be ascertained by which the depth should be regulated, it is mere blind prejudice which advocates deep drains in all cases and under all circumstances. On the score of first cost, shallow drains have palpably the recommendation of economy in the less quantity of digging which they require.

112. As an advocate of deep draining, Mr. Elkington must be named as connected with some very successful experiments in treating land, which astonished the good farmers of the last century, who had been accustomed to pay very little attention to the improvement of their lands in this manner, and had been satisfied to trust the aqueous condition of their broad fields to the hedgeditch and ridge-furrow. Mr. Elkington, having a farm called Princethorp, in the parish of Stretton-upon-Dunsmore, county of Warwick, of which the soil was very poor, and so wet that the sheep rotted by hundreds, turned his attention to the best means of draining it. For this purpose he began operations in a field of wet clay soil, made nearly a swamp, and in some parts a shaking bog by the springs of water which issued from an adjoining bank of gravel and sand. Mr. Johnstone, who published an account of Mr. Elkington's "system," thus describes his proceedings :-" In order to drain this field, he cut a trench about four or five feet deep a little below the upper side of the bog, or where the wet

ness began to make its appearance; and after proceeding with it so far in this direction, and at this depth, he found it did not reach the main body of subjacent water, from whence the evil proceeded. On discovering this, Mr. Elkington was at a loss how to proceed. At this time, while he was considering what was next to be done, one of his servants accidentally came to the field where the drain was making, with an iron crow or bar, which the farmers in that country use in making holes for fixing their sheep hurdles. Mr. Elkington, having a suspicion that his drain was not deep enough, and a desire to know what kind of strata lay under the bottom of it, took the iron bar from the servant, and, after having forced it down about four feet below the bottom of the trench, in pulling it out, to his astonishment, a great quantity of water burst up through the hole he had thus made, and ran down the drain. This at once led him to the knowledge of wetness being often produced by water confined further below the surface of the ground than it was possible for the usual depth of drains to reach, and induced him to think of employing an auger, as a proper instrument in such cases."

113. These proceedings took place in the year 1764, and it is very evident from Mr. Johnstone's account of Mr. Elkington's discoveries, and the principles upon which he conducted his draining operations, as distinguished from the methods then in common use, that these methods were adopted without any reference whatever to the leading circumstances which properly regulate the steps to be taken. Thus the three leading points observed by Mr. Elkington, were, "1st, finding out the main spring, or cause of the mischief;" "2nd, taking the level of that spring, and ascertaining its

subterraneous bearings;" a measure never practised by any, till Mr. Elkington discovered the advantage to be derived from it; "and, 3rd, making use of the auger to reach or tap the spring, when the depth of the drain is not sufficient for that purpose."

114. The process of tapping is evidently available only when the spring is fed from a higher level, so that the pressure shall suffice to force the water upward through the auger-hole. Another method is sometimes adopted as a substitute for the auger-hole or vertical bore, namely, digging a well of depth proportioned to the pressure, and filling this well with loose stones, through which the water will rise, and thence pass away along the drain, with the bed of which the well communicates. Similar auger-holes, or wells, may be adopted to effect the precisely opposite object, viz., to make a downward passage of the drainage water from the drains which intersect an upper and clay stratum only, into a more porous bed beneath, in the body of which the water will become dispersed.

115. The cheapest method of forming open drains in grass land is by turning a furrow-slice over with the plough, and afterwards trimming it with the spade, the lines for the drains being previously marked with poles. The cost of these drains will not exceed one halfpenny per rood of six yards, which is the measure we shall adopt in all cases where the quantity is stated in roods. This mode of operating is inadvisable if the grass be rough and long, so that the plough is apt to become choked, or if swampy places occur. In such cases, it is far better to do all the work with the spade, by which the cost will be increased to 2d. per rood, if the drain be formed about 9 in. wide in the bed, 18 or

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