Banks of various kinds, between this and the first natural kind, may be invented, differing only in the degree of incli nation which they have towards the sea ; that which slopes in the highest degree, as Fig ure 1, having the snrface covered over with sand or gravel ; and that which has the least slope, as Figure 8, may be covered with pavement ; the different intermediate :dopes being protected by materials which have a quality between the two, such as coarse gravel, chalk-stones, brick, and sand. The embankment, shown in Figure 9, is constructed of a sandy deposited upon a soil of the same quality ; but as it would not, for some time after being formed, be sufficiently impervious to water, a column of clay is carried upright in the middle, from the clayey sub stratum of the soil underneath, as is shown at x x, in the sec tion. This is called Puddling.
In eases where the shores are of a very sandy nature, embankments may be made wholly of a sort of wicker-work. Thus three or four rows of paling are put down, of different heights, and the vacant spaces between them well filled, by forcing in furze, brush-wood, or even straw, as represented at Figure 10. These substances, by detaining the mud and sand, as the tide passes through them, or during high floods, soon forms a sort of embankment, such as that SilOW11 in the above representation. It should afterwards he covered with some plant, which is capable of binding and giving it solidity, such as the elyinus a•enorius. An embankment, so con structed, would continue, during extraordinary tides, to retain still larger quantities of the sandy materials, until, ultimately raised above the range of the highest floods, a safe hank would be formed. By banks formed in this way, large quan tities of land might be gained in a very few years, in differ ent parts of the rivers Severn, !lumber, Frith, &c.
In all cases of embankment, however they may be formed, tunnels and sluices of a proper kind, with valves towards the sea or rivers, must be occasionally placed, according to cir cumstances, so as to permit the water that may be collected within to pass that of the sea or rivers, to flow up, with different intentions in the view of improving the land.
The utility of projecting points is very considerable, in different cases, on the sea-coasts and rivers, in defending the bays and inlets of the former, as well as guarding the banks of the latter, by diverting their streams or currents to the opposite sides. Hence arises the formation of piers, which become highly beneficial in defending embankments, as well as the borders of rivers and brooks. In the first of these
cases, they may generally be constituted and coated over with the same sort of material as that of which the embankment is formed; while, in the latter, they should be formed of some sort of stony matter, being constructed in such a way as to decrease in every direction as they advance outwards, as represented in Figure 11. In each of these cases, they are, however, capable of being constituted of brush wood, secured by means of stakes, often with more perfect success. And it frequently happens, that a simple rude wicker-work fence, of not more than three or four yards in length, may be fulls' sufficient for the purpose. Embankments formed of stone, unless constructed in the manner represented at the above figure, are apt to cause eddies below them ; while those fbrmned of brush-wood cannot have this effect.
It is obvious, that considerable attention must he required in deciding the most proper situations for constructing this sort of projection in, and the distances to which they should extend into the rivers; as a too extended 'Injection may be highly dangerous to the opposite bank, and of course do harm, instead of being beneficial; while not carrying them out sufficiently far may prevent the which is wanted. In eases where piers are to be formed of stone, as in rivers where the bottoms are of a rocky nature, the plan represented at Figure 11, is a good one, as it will scarcely cause any eddy, and be nearly similar to that of the wicker- work, in the effect which it produce:. Different works of these several kinds have been constructed in the northern parts of the island with much success.
Proper .,11alerials for Enihankments.—It will be obvious, that different sorts of materials may be made use of in dif ferent situations and kinds of works of this nature, with more advantage than others, both in so far as duration and expense are concerned.
Those steep upright embankments, which are constructed with the view of protecting bold shores, or coasts, and the banks of particular rivers, may probably be best formed of good brick, rubble, or ashlar work, in the manner of a wall, as seen at Figure 6, in the Plate, the materials being laid in the strongest 'Mortar that can be made. But where this is not the case, they may he built in the common way, and pointed with puzzolana earth, or what is termed the Roman cement, prepared by Messrs. Parker and Co., London. Concrete has been used most successfully and extensively for the purpose of embankments, as we have shown under that article.