side rail, should not be greater than to compensate for the centrifugal force, at the slower rate of travelling with heavy trains.

The following Table will shew the elevation to be given to the outside rail, of different radii, above that of the inner rail of such curve; so that the whole amount of centrifugal force, is balanced by that of the gravity of the load, towards the inside of the curve.

§ 16.-Plan of crossing Streets, and Turnpike Roads.

Having thus described the mode of executing a railway on ordinary ground, the plan of drainage, and the coating and laying the railway; we shall now describe the plan of crossing streets and roads. Fig. 10 is a section, and Fig. 11, Plate V., a plan, of crossing a street, or public highway, near a town; a a a, &c. is masonry, forming the foundation whereon the railway is to be

laid, and the drains, bb, for carrying off the water, and acting, likewise, as a receptacle for the dirt. The blocks cc, are placed upon the masonry, and upon the blocks, and attached to the chair, is a frame of cast iron, inclosing the rails, as shewn in Fig. 11, rr being the rails, e e, e e, the cast-iron frame, with the cross ribs, lll, &c. Between the rails, rr, and the sides, e e, of the iron frame, there is just sufficient width for the flanch of the wheels of the carriages to pass along; and being open underneath to the drains bb, except where covered by the blocks cc, and chairs ff, Fig. 11, all the dirt falls down into the drains, and keeps the rails entirely free for the passage of the carriages.

The stones gg, gg, are penned close against the outer sides of the iron frame, and on a level with the top of it; so that, when carts, or other carriages, cross the rails, they are not subjected to any jolt. Between the stones gg, the road is paved in the ordinary way, and which, resting on the solid masonry, is kept very firm and level.

Fig. 12 shews the manner of passing common roads, where the passage is not very great. In this case, the masonry is not required, the blocks c c are set, as in the common way, upon the coating a a; a cast-iron frame, similar to that before described, and shewn in Fig. 11, is laid upon the blocks, for the purpose of protecting the rail, from the wheels of the carriages crossing the road; but in this case, there is no drain or receptacle for the water and dirt, as in the former cases, any dirt falling into the cavity, against the rails, being taken out by the attendants, when necessary. The road may be either paved on the surface, against the frame-work, or covered with broken stones, or with the common material of the road; in the latter case, however, the

iron frame-work, as shewn in the drawing, must be of larger dimensions, to prevent its being broken by the wheels of the carriages.

§ 17.-Mode of passing yielding Ground, or Mosses.

We have thus described the different modes of executing, and laying down railways upon ordinary ground. It would be going beyond the proper sphere of a work of this kind, to attempt to offer plans to meet difficulties in extraordinary cases, the intention being, rather to describe what has been done, than to devise plans for executing unforeseen difficulties. The modes of passing yielding ground, mosses, or bogs, adopted by some engineers, may, however, be described in this place; and the Chat Moss, on the Liverpool and Manchester railway, being the most extensive moss yet passed over, we shall give the plan adopted by Mr. Stephenson, for carrying the railway over this moss.

This moss is of considerable extent, comprehending an area of about twelve square miles, being of so soft and spongy a nature, that cattle cannot walk upon it, and an iron rod sinks with its own weight. The depth varies from ten to thirty-five feet, resting on clay and sand. The distance which the railway was to be carried over it, was upwards of four miles and a half, an undertaking which required some degree of nerve to contemplate. It is necessary to premise, that, in carrying the railway across the moss, the level required, that it should, in some places, be twelve feet above, in others, nine feet below, and to vary from these, to level with the original surface of the moss. We have, therefore, three distinct operations, viz., embanking the railway above; forming a cut below; and forming the road

There is

Embanking the railway above the moss. another moss, of considerably less extent than this, over which the railway passed, and which, at one end, was terminated by an extensive cutting of clay and gravel. As an embankment, of four feet in height, had to be formed over this moss, the materials from the excavation were used for this purpose. The moss was about

twenty feet deep, and it was soon found, that as the materials were successively laid upon the moss, the whole mass gradually sunk; and when the embankment was finished, although the actual level of the railway was only four or five feet above the original surface of the moss, the quantity of the metal deposited would have formed, on ordinary ground, an embankment twenty-four or twenty-five feet high; with such materials, therefore, (clay and gravel,) it would have been impossible to form an embankment over Chat Moss. The quantity required, and the consequent expense, would have been enormous. Mr. Stephenson had recourse, therefore, to the moss itself, for materials to form the embankment, which, by its inferior specific gravity, would not sink to such an extent as gravel and clay. In its natural state, the moss was unfit for this purpose, but drains were cut, five yards apart, which laid the moss between the drains dry, and rendered it excellent material for the purpose. With this material, embankments were formed upon part of the moss, and it was found to require only about four times the quantity of material, that would have sufficed for sound ground, and the road appears in quite as good order, as in any other part of the line.

Forming a cut below the level of the surface of the moss, was accomplished entirely by draining; the drain was cut along the line of the railway, eighteen inches to two feet deep, which laid dry that portion of the

moss between them. About twelve inches in thickness, thus dried, was excavated at a time; and it was, in that manner, successively drained and excavated, until the proper depth was obtained. The permanent road was then formed in the manner hereafter described.

Laying down the road upon the surface of the moss. Drains were first of all cut on each side of the line, and lateral ones, where necessary, to carry off the water. By this means, a certain depth of moss on the top was partially consolidated, and formed a layer or surface of dry moss, of considerable tenacity; upon this, hurdles, nine feet long, and four feet broad, wickered with heath, were laid down transversely. In many places, only one layer of hurdles was required; but when the moss was very soft, two layers were used. Upon this, was laid about two feet of ballast, or gravel, to form the permanent road; and wooden sleepers, stretching across each line of road, were used to lay the rails upon. The stability of the road, therefore, depends solely upon the tenacity of the materials, supported by the buoyancy of the moss. When we consider, however, the area of base thus firmly united and bound together, and the support which even so spongy a substance as the moss must give to so extensive a platform; it is natural to suppose, that the impression made upon so great an area, by the pressure of so inconsiderable a proportion of the whole weight as that of a train of carriages, must be slight indeed; and we find, that, since the opening of the railway, the passage of the traffic over the moss proves that the road is exceedingly stable. It may be necessary to remark, that the surface of the moss is higher than that of the country bordering its edge.

Figs. 13 and 14, Plate V., shew this mode of forming a railway over a moss; a a are the hurdles, or wickered foundation, which may either be single, or two or three