The embankments are formed simultaneously with the cuttings, and the materials obtained from the latter are transported by barrows, carts, or waggons, to the former, according to the distance; barrow work ceasing to be economical when the distance to be traversed ex ceeds 100 yards, carts are then used ; and when the length of transport attains a quarter of a mile it is decidedly cheaper to use waggons upon temporary roadways, made in railway works of the metals, or rails, to be afterwards used for the permanent way. As embankments can thus only be commenced from their two ends at a time, it follows that when they are of considerable dimensions they may even regulate the duration of the works upon a railway, because bridges or tunnels can be commenced at once in several places. Time may occasionally be saved by the use of temporary wooden staging, and by =lying on the work in several layers or strata; but if the length of lead (or the dis tance traversed) be great, it is very rarely indeed that more than from 2000 to 2500 yards cube can be tipped at one end of a bank in a day. The earth in small banks is often rammed to ensure its uniform com pression, and even in the very rough and ready manner in which railway works are effected, especially in Enghind, the precaution of punning the earth at the back of culverts, or bridges, is generally adopted. For largo embankments it would be practically impossible to attempt to secure this theoretical perfection, and the earth is in them simply cast, or tipped, from a waggon, and is allowed to settle by its own weight, and by the effect of time. It is important, therefore, to observe that the earth taken from a cutting will, in the beginning, occupy a space about 4 greater in the back than it did in its natural position ; and that even after they have settled during three or four years the ma terials in a bank will still occupy a volume Ath greater than they did originally. The subsidence of new-made banks is indeed a source of danger and of expense on all railways, and it must be guarded against in the most careful manner; allowance should be made for such sub sidence, by keeping the crowns of the banks above the intended finished level.
In executing heavy embankments care must also be taken to ensure that the ground upon which they are to be founded should not be exposed to lateral displacement, or to any serious amount of vertical compression; although the latter objection ultimately resolves itself simply into a question of money. Accidents of this description fre quently occur upon the banks of rivers, or in alluvial districts; and the most efficient mode of dealing with them is to isolate the seat of the bank from the surrounding grciand, in such a manner as to cause the whole compression to take place vertically. In marshy and boggy grounds judicious drainage may do much good ; but the system adopted in carrying the Liverpool and Manchester Railway over the Chat Moss, of supporting the earth to be deposited upon a stratum of hurdles, or the one used by the Dutch engineers of forming as it were a floor of fascines, or of bundles of reeds, must in many instances be resorted to in addition to the introduction of lateral drains. On the Munich and Augsburg line an efficient method of carrying the rail way embankment over a peat-bog about 16 feet deep was used, which it may perhaps be desirable to mention here; it consisted in sinking a series of square holes, "en echiquier," about 2 ft. 10 in. apart, and measuring 1 ft. 9 in. square at the bottom, and 2 ft. 10 in. square at the top ; these holes were then filled with impermeable earth, and the embankment was laid on them ; the seating of the bank was first properly drained and a good outfall provided. Another class of posi tions in which it is necessary to take especial precautions in forming embankments, is when their feet are exposed to the action of large bodies of water, whether tidal, flowing, or comparatively still, as in lakes. The materials used below the water-line should be of the greatest possible specific gravity, the seat of the bank should be cleared, by dredging, of all loose or compressible mud, and the sides exposed to the wash of the water should be protected by beds of fascines, or by atone pitching in ordinary cases ; in sea water, or in open bays, it may even be necessary to carry the foot of the embankment upon solid masonry ; RIVER ; WEIN.
The earth-works upon most of the principal lines in England have been very heavy, and they seem in some exceptional cases even to have cost 20,000/. or 30,000/. per mile; nor has it been by any means rare for the average cubical quantity of earth so moved to average from 100,000 to 150,000 yards per mile. In other countries this portion of the cost of railways has been diminished; first, by reason of the lower price of labour ; but secondly and principally, by reason of the facili ties afforded by the steeper gradients now tolerated.
There are some minor works usually included in the description of the excavator's department in the construction of a railway, which are of sufficient importance to require notice. These are the fencing in of the land ; the formation of the cop mound, and of the ditch; the planting of the quickset hedge ; and the soiling and planting of the elopers Insignificant as thus° works may seem to be in themselves, much of the security from accidents of the railway depends upon their being well executed and well maintained ; and it is especially on account of habitual disregard the American engineers display to the ado enclosure of their lines, that the accidents from strayed animals occur so frequently with them. The planting of the slopes of em bankments, it may also be added, is an easy and profitable mode of protecting them.
Bridges are required on railways for the purpose of carrying them across the various watercourses; for maintaining the existing road communications either above or below the level of the rails; or for carrying the roadway above the surface of the ground in deep narrow gorges when for local reasons it is found that the construction of viaducts is preferable to the execution of heavy embankments. The choice of the materials used for the construction of railway bridges must mainly be influeuced by economical considerations, always bear ing in mind the fact that in under-bridges the materials used should he of a permanent description ; because the repairs of the substratum, so to speak, of a roadway are always attended with difficulty; for ore/. bridges wood, brick, stone, or iron may be used as may be found advisable. The reader is referred to the articles BRIDGE and Vianrcr for a detailed notice of the principles of construction required to bo followed in this class of works, and under SKEW Amen and 'rums:a Barnes will be found notices of peculiar forms of bridges frequently employed on railways. It seems that upon the average there are about 2i over or under road bridges per mile forward of railway in England, even when a considerable number of level crossings are allowed ; in England there is at least one crossing per mile. As was before said, the latter should be avoided as much as possible, for they are a fre quent source of accidents, and the cost of the guardian represents; the interest of a larger sum than an ordinary bridge would cost. It is not often, in fact, that an ordinary over or under bridge costs more than 10001. to 2000/. ; or perhaps, taking into account the approach reads, the latter figure may be taken as an average; this has to be set against the cost of the cottage, gates, and crossing, and the keeper's wages, in case a level crossing should be resorted to. It is usual to estimate that the cost of culverts, surface, or underground drains of a railway amounts to 20 per cent. of the cost of the under-bridges; the cutting of the lateral ditches being carried to the earthworks account. The masonry for lining tunnels, or for retaining walls, forms part of those special items in railway estimates.