OPERATIONS.] AGR1CULTU R E 329 thus be regarded as the outlets of a natural underground drainage. This provision for disposing of the water that falls from the clouds is usually so irregular in its distribu tion, and so imperfect in its operation, that it leaves much to be accomplished by human labour and ingenuity. The art of the drainer accordingly consists 1st, In improving the natural outfalls by deepening, straightening, or embanking rivers; and by supplementing these, when necessary, by artificial canals and ditches : and, 2J, In freeing the soil and subsoil from stagnant water, by means of artificial underground channels. The firiit of these operations, called trunk drair*age, is the most needful ; for until it be accomplished there are exten sive tracts of land, and that usually of the most valuable kind, to which the secondary process either cannot be applied at all, or only with the most partial and inefficient results. Very many of our British rivers and streams flow with a sluggish and tortuous course through valleys of flat alluvial soil, which, as the coast is approached, expand into extensive plains, but little elevated above the level of the sea. Here the course of the river is obstructed by shifting shoals and sand-banks, and by the periodic influx of the tides. The consequence is, that immense tracts of valuable land are at all times in a water-logged and comparatively worthless state, and on every recurrence of a flood are laid entirely under water. In a subsequent chapter on " Waste Lands" some account shall be given of the extent of this evil, and of the efforts that have been successfully devoted to its remedy. Some of these fen-land and estuary drain age works have been accomplished in the face of natural obstacles of the most formidable character, and constitute trophies of engineering talent of which the country may well be proud. Great as the natural difficulties are which have to be encountered in such cases, there are others of a differ ent kind which have often proved more impracticable. It has been found easier to exclude the sea and restrain land- floods, than to overcome the prejudices and reconcile the conflicting interests of navigation companies, commissioners of sewers, owners of mills, and landed proprietors. Although all these classes suffer the most serious losses and incon veniences from the defective state of many of our rivers, it is found extremely difficult to reconcile their conflict ing claims, and to allocate to each his proper share of the cost of improvements by which all are to benefit. A most interesting and instructive illustration of the urgent necessity for improving the state of our rivers, of the difficulties to be encountered in doing so, and of the incalculable benefits thus to be obtained, has been given in an essay on Trunk Drainage, by John Algernon Clarke, Esq., published in vol. xv. (part first) of the Journal of the Royal Agricultural Society of England. Mr Clarke, after some most important observations on trunk drainage, describes in detail works projected under powers granted in an Act of Parlia ment, passed in 1852, "constituting commissioners for the improvement of the river None and the navigation thereof." There is not a district of the kingdom in which works similar in kind are not absolutely indispensable, before extensive tracts of valuable land can be rendered available for profitable cultivation by means of underground drainage. It is interestingto know that the necessity for trunk drainage, and the means of accomplishing it, were distinctly set before the public 200 years ago by a practical draining engineer, to whose writings the attention of the agricultural com munity has been frequently directed of late by Mr Parkes, Mr Gisborne, and others. From the third edition (1652) of The Improver Improved, by Walter Blithe, the author referred to, in which the true principles of land drainage are stated as distinctly, and urged as earnestly, as by any of our modern writers, we here quote the following remarks : "A strait water-course, cut a considerable depth, in a thousand parts of this nation, would be more advantageous than we are aware of, or I will task myself here to dispute further. And though many persons are interested therein, and some will agree, and others will oppose ; one creek lyeth on one side of the river, in one lord s manor, and another lyeth on the other side, and divers men own the same ; why may not one neighbour change with another, when both are gainers ? If not, why may they not be. compelled for their own good, and tfie commonwealth s advantage? I daresay thousands of acres of very rich land may hereby be gained, and possibly as many more much amended, that are almost destroyed ; but a law is want ing herein for the present, which I hope will be supplied if it may appear advancement to the public ; for to private interests it is not possible to be the least prejudice, when every man hath benefit, and each man may also have an equall allowance if the least prejudiced. But a word or two more, a7id so shall conclude this chapter and it is a little to further this improvement through a great destruction (as some may say) ; it is the removing or the destroying of all such mills, and none else, as drown and corrupt more lands than themselves are worth to the commonwealth, and they are such as are kept up or dammed so high as that they boggyfie all the lands that lye under their mill-head. Such mills as are of little worth, or are by constant great charges maintained, I advise to ba pulled down ; the advance of the land, when the water is let run his course, and not impounded, will be of far greater value many times. But in case the mills should be so necessary and profitable too, and far more than the lands they spoil, I shall then advise, that under thy mill-dam, so many yards wide from it as may prevent breaking through, thou make a very deep trench all along so far as thy lands are putrefied, and thereinto receive all the issuing, spew ing water, and thereby stop or cut off the feeding of it upon thy meadow, and carry it away back into thy back-water or false course, by as deep a trench, cut through the most low and convenient part of thy meads. But put case that thou shouldst have no convenient fall on that side thy mill-dam, then thou must make some course, or plant some trough under thy mill-dam, and so carry it under into some lower course that may preserve it from soaking thy meadows or pastures under it ; and by this means thou maist in a good measure reduce thy land to good soundness, and probably wholly cure it, and preserve thy mill also." It is painful to reflect that after the lapse of two cen turies, we should still see, as Blithe did, much "gallant land" ruined for want of those draining operations which he so happily describes. A clear outfall of sufficient depth being secured, the way Subsoil is open for the application of underground draining. And here it may be proper to state, that there is very little of the land of Great Britain naturally so dry as not to be susceptible of improvement by artificial draining ; for land is not in a perfect condition with respect to drainage, unless all the rain that falls upon it can sink down to the minimum depth required for the healthy development of the roots of cultivated crops, and thence find vent, either through a naturally porous subsoil or by artificial channels. Much controversy has taken place as to what this minimum depth is. Suffice it to say, that opinion is now decidedly in favour of a greater depth than was considered necessary even a few years ago, and that the best authorities concur in stating it at from three to four feet. There are persona who doubt whether the roots of our ordinary grain or green crops ever penetrate to such a depth as has now been specified. A careful examination will satisfy any one who makes it, that minute filamentary rootlets are sent down to extraordinary depths, wherever they are not arrested by stagnant water. It has also been questioned whether any benefit accrues to crops from this deep descent of their roots. Some persons have even asserted that it is only when they do not find food near at hand that they thus wander. But it must be borne in mind that plants obtain moisture as well as nourishment by means of their roots, and the fact is well known that plants growing in a deep soil resting on a porous subsoil seldom or never suffer from drought. It is instructive, too, on this point, to observe the practice of the most skilful gardeners, and see tho importance which they attach to trenching, the great depth
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