A curious, useful, and highly ingenious method of embank ing, and preventing the waters of the tides from soaking through the porous banks, made in the fen-lands, and low marshy grounds, was described by Mr. John Smith, in the 11)urth volume of " Communications to the Board of Agricul ture," who begins by " concisely observing, that the great land of the fens is divided into three large levels ; and that each of these levels is subdivided into numerous districts by hanks : but as these banks are made of fen-moor, and other light materials, whenever the rivers are swelled with water, or any other district is deluged either by rain, a breach of hanks, or any other cause, the waters speedily- pass through these light, moors, porous banks, and drown all the cireum jacent districts. The fens have thus sometimes sustained or £30,000 damages by a breach of the banks, though these accidents seldom happen in the same district twice in twenty years. The water, however, soaks through all fen banks every year, in every district ; and when the water mills have lifted the waters up out of the fens into the rivers in a windy day, a great part of the water soaks back through the porous banks, in the night, upon the same land again." And he adds, that "this water that soaks through the bank drowns the wheat in the winter, washes the manure into the ddies, destroys the best natural and artificial grasses, and pre vents the fens from being sown till too late in the season. This stagnant water lying on the surface, causes also fen agues, &e. Thus, says he, the waters that have soaked through the porous fen-banks have done the fertile fens more real injury than all the other floods that have ever come upon them." Haying been much concerned in fen-banking from his youth, he had some time since devised the plan which he now finds to answer so well ; but found it difficult to prevail with any gentleman, who had a proper extent of this sort of land, to give it a fair trial. However, during the last autumn, he prevailed with a person in the parish where he lives to try it, which showed it to be equal to his highest expectations.
The improved method of embanking proposed by this gentleman, consists chiefly in this : that "a gutter is cut eighteen inches wide, through the old bank down to the clay (the fen substratum being generally clay ;) the gutter is made near the centre, but a little on the land-side of the centre of the old bank. This gutter is afterwards tilled up in a vary solid manner with tempered clay ; and to make the clay resist the water, a man in boots always treads the clay as the gutter is filled up. As the fen-moor lies on clay, the whole expense of this cheap, improved, and durable mode of waterproof banking costs in the fens only sixpence per yard. This plait was tried on a convenient film, and a hundred acres of wheat were sown on the land. The wheat and grass lands on this farm were all dry, whilst the fens around were covered with water. This practice is, after all, nothing more than making a puddle-Lank, well known to all engineers, or those engaged in forming canals.
The term embankment in canal-making is applied to any large mound of earth, either for confining the \rater of the canal or reservoir, or tor carrying the former across a valley or low piece of ground. The method of constructing such embankments is nearly the same as in those for railways, except that in the former the sides have puddle-trenches formed near the canal, to prevent leakage.
The embankments on some of the great lines of railway in this country are of immense magnitude, on the London and Birmingham railway, for instance, the total of embankments amounted to about 11 millions of cubic yards. The follow ing extracts from specifications for works of this kind will show the usual mode of construction.
"The whole of the embankment in this contract shall have slopes of two to one (that is to say) where the base of the slope is two feet, its height shall be one foot only, and they shall be thirty-three feet wide at the level of the red line in the section, neither more nor less.
" Each of the embankments shall be uniformly- carried forward as nearly as the finished heights and width as the due allowance for shrinking of materials will admit of; and this allowance shall not exceed or fidl short of the quantity deemed necessary by the engineer. In all cases, this must be care fully and strictly attended to, in order to avoid the necessity of making any subsequent addition, either to heights, or the width of' the embankment, to bring them to their proper level and dimensions.
"The surface of the embankment shall be kept in such fur m or be intersected by such drains, as will always prevent the formation of pools of Nv ater upon them, and insure the embankment being kept as dry as possible.
"Whenever the material, teemed over the end of the embankment, shall not form the proper slope, it shall be care fully trimmed to its required form ; and this operation must proceed at the same time with the end of the embankment, so as to obviate the necessity of any future addition of material to the sides of' the embankment.
"As the embankments advance, and become consolidated, the slopes shall be carefully trimmed into planes having the proper slope, and be neatly covered with a uniform substance of turf; of not less than eight inches in thickness, and laid with the green sward outwards; the turf must be taken from the ground to be occupied by the base of the embankment, and cut square, so as to be laid on the slopes in the form of flags ; and where the land is arable, the slopes of the embankment shall be covered with soil. It must be uni formly laid on, of the thickness of six inches, and sown with rye-grass and clover-seed, as soon as the proper season will admit of its being done, not less than one pound and a half of clover-seed, and one pound and a half of rye-grass seed, to be sown to each acre.
" When the material, brought to the embankment, consists of large lumps, they shall be broken into pieces of not more than six inches in diameter." .Eepense aj forming embankments.—This must obviously be very ditrerent in different situations and circumstances, according to materials and the price of labour, but though in general pretty considerable, it is seldom so high as is com umonlv supposed. It is probable, that in cheap districts, and where the materials are plentiful, the expense of forming an •arth.bank, covered with sand or gravel, such as that shown at Figure 1, could not be less than from fourpence orsixpence, to tenpence or a shilling, the cubic yard. And such as have more steep and hold slopes, as from thirty-five to forty degrees, and are formed with pavement on the surfaces, cannot cost less than from ninepence to one shilling the cubic yard. One made on the plan of that shown at Figure could not be constructed for less than from twelve or fifteen to thirty pounds for every thirty-two yards. And one con structed of brushwood, in the same method, for soft ground, which will not admit of a wall, would not be lower than from sixpence or eightpence, to six or seven shillings fur each foot forward in a lineal manner. In many situations, the ezpenses would, however, in all sorts of embankments, stand a great deal higher than these.
In some districts, embankments are formed by the rod and the floor, the former being from four to five pounds, and the latter about four shillings and sixpence, the workmen finding all sorts of necessary things for the business.