Marsh, signifies a tract of ground partly covered with water, yet so as to permit grass or other vegetables to rise above its surface: these, while gradually decaying, occasion putrid exhalations, which are extremely pernicious to the health of mankind.
Marsh-lands are chiefly employed for the grazing of cattle, which, in such pastures, fatten speedily: it is by some writers, though believe, erroneously asserted, that sheep feeding on them, are preserved from the rot. Without attempting to decide this question, we shall observe (hat it will be advisable to raise a bank, and plant it with trees, if possible, in the midst of the marsh, either crosswise, or in a semi-circle : they would afford a shelter for the cattle, and in a few years repay the expence of forming the plantation. If the soil be situated near the sea, it will also be requisite to form ponds or reservoirs for the reception of the vain, in order that the sheep, etc. may at all times be furnished with sweet water. Such fence or trees will, at the same time, serve to intercept the sea-breezes, which often snip the tops of the grass, if unsheltered from their influence. in order to convert a marsh into firm or arable land, it should first be drained, in the manner described in p. 162 and foll, of our 2d vol. Its various parts ought next to be wholly changed : 1. By frequent ploughing, harrowing, and burning ; 2. By the addition of marle, clay, gravel, or other heavy substances ; 3. By such matters as aft chemically upon the soil, and bring its latent principles into action; for instance, lime, chalk, alkaline salts, etc. ; 4. By spreading those manures which have a large proportion of fat, or mucilage; such as putrid fish, sea-weed, stable-dung, etc. , because marsh-lands rarely contain any animal substances,' which arc, in a great measure, the chief constituent parts of a rich soil. —Lastly, by Compression, either by the treading of cattle, or by the use of rolling-carts, and similar heavy implements.
In the Transactions of the " American Philosophical Society," we meet with an ingenious inquiry into the causes of the insalubrity of flat and marshy situations; together with directions for obviating or correcting their effects, by Mr. William CuRrie. His plan aims at introducing and increasing the proportion of oxygen gas in the super-incumbent atmosphere, and preventing its future obstruction, by cutting off or diminishing the sources of putrefaction. He proposes to effect this object, by carrying off the stagnant waters through drains, or trenches; and, where the soil will not admit of these, by the aid of wells. With the same intention, all dead weeds, grass, and wood, are to be burned; all flats, sinks, or hollows, filled up with sand, clay, or lime; and these should be adorned with vigorous plants and grasses, particularly such as flourish late in the season ; because vegetables, continually exposed to the rays of light, decompose the water imbibed from the earth, and thus replenish the atmosphere with oxygen, or pure vital air.
Where marshy situations are too extensive to render them completely dry, they ought to be constantly flooded, by means of dams and sluices, to prevent the effects of putrefaction.- Lastly, to obviate still farther the pernicious consequences of residing near marshes or mill-ponds, it will be useful to plant between those waters and the dwelling-house, rows of such trees as vegetate rapidly, and retain their verdure to a late period of the year, so that the humid vapours may be intercepted, while such vegetables furnish a constant supply of oxygen to the atmosphere.