The practice of hollow draining was known by the Roman writers on agricul ture, and is particularly mentioned by them. In stilt clays it is of little service, and it is practised with desired effect only where the soil is of that porous sub stance, which easily admits the passage of the water through it Opinions differ with regard to the season for carrying these works into execution; some, with plausible reason, preferring the summer, and others, having nearly as much to state in recommendation °its-inter for the purpose. The depth of the drain. from the surface of the land, should generally be from twenty-six inches to thirty-two ; and the principal rule for their depth is, that they should be secured from receiv ing injury from the feet of horses or cat tle ploughing on the spot under which they are made. It is desirable to consti tute the drain in such a manner that the stones may lean towards each other, so as to form a triangle, of which the bottom of the drain forms the base in which case, the width of a foot may be regarded as sufficient for them. The ditches con structed for these drains must be execut ed with great neatness and care ; and with respect to filling them up, which they should be about ten inches deep, if stones are plentlfully at hand, they should be applied for this purpose But in many places, faggot-wood, horns, bones, straw. fern, and even turf, laid in like a wedge, are all used in different situations ; and drains constructed of these materials, thirty years ago, are found in several places effectually to answertheir purse still. By many persons, straw, twisted into a very large rope, has been success fully laid in the bottom of the ditch ; and by others, after twenty years experience. the white thorn has been recommended as answering better than all other mate rials.
Injurious moisture in land arises often from springs in the bowels of the earth. The person who first published the me thod of draining land, in these circum stances, was Dr John Anderson, of Aber deen, while Mr. &lkington was actually practising upon the same principle, in va rious parts of' England, with complete success ; and at leng,th obtained from the British parliament a thousand pounds, as the discoverer of so valuable an improve ment. In Italy and Germany, however, it is stated, upon respectable authority., that the art has been long known and practised. Soine of the strata of which the earth is composed will admit the free pas Sa.p of water through them, while others cfleettially resist it. Gravel is obviously characterised by the former quality, and clay by the latter. The upper part of mountains is frequently composed of gra vel, which extends far into their depth, and conveys with it the water received -upon their surface from the clouds. Meeting with layers of clay or rock, how ever, the water is tillable to permeate them, and flows upon the upper part of them obliquely-, according to that general direction of' the layers or laminx, which form the earth towards the plain or val ley. After descending for some way, the layer of gravel along which the water had passed, and from which it could not penetrate the clay, flowing only on its surfitce, often passes, in consequence of the obliquity just mentioned, under new strata of materials, consisting of clay, or some substance equally difficult to be pc netrated by moisture. The water is thus
confined between impervious bed.s. If the layer of gravel suddenly stops, in such 'circumstances, as it often does, the water which it had conveyed between these two beds, deriving fresh accumulation perpe tually from its original source, will at length permeate the superior layer, as cending through its weaker parts, and arriving at last at the surfitce, will there stagnate. The art of draining lands in this situation (the principle of which, in 1.vhatever research or casualty its disco very originated, is of such happy applica tion) consists merely of digging or boring with an augerinto the earth, so as to reach the layer of grarel ; the water in which, finding an easy and rapid access upwards by this vent, no longer pressesi n its former diffused manner, to the injury of the su perior clay, which will consequently cease to nourish moss and weeds through re dundant moisture, and be fitted for the purposes of useful cultivation. The ap. plication of this principle to the purposes of improved husbandry may be consider ed at present as in its infancy. It may be presumed that, in future periods, it may be carried to an extent of incalculable utility, and be connected with the supply of navigable canals, and the movement of machinery adapted to various objects of art and commerce. The manner in which the various strata are intermingled with each other must, it is obvious, as nearly as possible, be ascertained, before this practice can be applied with certainty of success ; a.nd the surest way of discover ing their direction consists in examining the beds of' the nearest rivers, and the ap pearance of their steep and broken banks. The examination of pits, wells, and quar ries, in the vicinity, will also contribute information on the subject. Rushes and other plants, which grow only in moisture injurious to other vegetables, will likewise often indicate where a collection of water is impeded in its course below, and con sequently presses upward, to the destruc tion of useful vegetation. In draining a large bog, it will be generally proper to dig a trench from one end of it to the other, with cross trenches at considerable distances, to allow the water a free clis charg-e, by frequently piercing the bottom, at which the springs are to be found, with an auger. A single perforation will fre quently, indeed, complete the object In stances have occurred, in which water thus raised has been made to ascend, by erect. ing round the perforation a building of brick, lined both sides with clay, above the level of the bog, applicable to a va riety of purposes, and conveyed by pipes, or otherwise, to a considerable distance. I) etailed regulations for the application of this important principle, so productive a source of improved cultivation, are pre cluded by the assigned limits of this ar ticle.