The breadth of roads should vary according to circumstances. In the vicinity of large towns, where the traffic is considerable, the road should be not less than 60 feet between the fences. Where here is less traffic, fifty feet will be sufficient. The whole breadth should, in these cases, be metalled, or laid with broken stones. Near London, and the capitals of Edinburgh and Dublin, perhaps 70 feet is not too great a width, and a footpath should be provided on each side. "The road," says Mr. Telford, in a specification for the Holyhead road, " is to be 30 feet wide, exclusive of footpaths, with a fall of 6 inches from the centre to the side channels." The bed of the new road being prepared for the reception of the materials, should, if of a wet or spongy nature, be well 'rammed' with chips of stone; in some situations it is advisable to lav a stratum of hand-laid stones, of from 5 to 7 inches in depth, with their broadest ends placed downwards, and the whole built compactly together. On this is to be laid the 'metal,' or broken stones, to the depth of at least 8 inches, broken of a uniform size, so as to form a solid and compact body.

To insure uniformity in the size of the broken stones, various tests have been suggested; perhaps the most simple is, that every piece shall pass through a ring of 2 1/2 inches diameter. On this body of metal, no binding or gravel should be used; the angular sides of the metal soon lock into each other, and form a smooth surface. In the selection of road-metal, we prefer the several varieties of greenstone. The best kinds of these are less friable than granite, when broken into small pieces. It is, however, often necessary, for want of better materials, to use sandstone, common limestone, and chalk, even in districts where there is a great deal of traffic; in some instances, where coal is abundant, sandstone is reduced to a vitreous mass in kilns erected by the road side.

"Well-made roads, formed of clean, hard, broken stone," observes Mr. Macneill, "placed on a solid foundation, are very little affected by changes of atmosphere; weak roads, or those that are imperfectly formed with gravel, flint, or round pebbles, without a bottoming, or foundation of stone pavement or concrete, are, on the contrary, much affected by changes of the weather. In the formation of such roads, and before they become bound or firm, a considerable portion of the sub-soil mixes with the stone or gravel, in consequence of the necessity of putting the gravel on in thin layers: this mixture of earth or clay, in dry, warm seasons, expands by the heat,.and makes the road loose and open; the consequence is, that the stones are thrown out, and many of them are crushed and ground into dust, producing considerable wear and diminution of the materials. In wet weather, also, the clay or earth mixed with the stones absorbs moisture, becomes soft, and allows the stones to move and rub against each other, when acted upon by the feet of horses or wheels of carriages.

This attrition of the stones against each other wears them out surprisingly fast, and produces large quantities of mud, which tend to keep the road damp, and by that means increases the injury."

The immense traffic in the streets of London, and other large cities, and the inconveniences resulting from a frequent derangement of the pavement, have long rendered the establishment of a firm, durable, and smooth city road, a great desideratum. The alternate dust and mud on broken stone roads have proved them unfit for crowded thoroughfares. They have been tried, but tailed. stone paving of various kinds, and even cast-iron plates, in the form of a causeway, have been suggested. Of the two kinds of stone pavement with which London, Dublin, and Edinburgh, are paved, the one is termed rubble causeway, the other aisler causeway. In the former the stones are very slightly hammer-dressed; in the latter they vary from 5 to 7 inches in thickness, from 8 to 12 in length, and about a foot in depth. The Commercial Road of London is a fine specimen of the aisler causeway. It leads from Whitechapel to the extensive establishments of the East and West India Docks, at Black wall and Poplar. It is 2 miles long, and 70 feet wide. The footpaths are laid with Yorkshire flags, and the stoneway of granite. The tramway is composed of large stone blocks, 18 inches wide by 12 inches deep, and from 2 1/2 to 10 feet long.

They are laid in rows four feet apart, on a hard gravel bottom, or a concrete foundation, and have their ends closely and firmly jointed to each other, so as to prevent movement, either lateral or longitudinal. On this tramway a waggon weighing, with its load, 10 tons, was drawn by one horse from the West India Docks, a distance of 2 miles, rising 1 in 274, at the rate of nearly 4 miles per hour. The works were executed under the direction of Mr. James Walker, the engineer, by whom the plans were furnished, and whose report to the trustees of the road contains much useful information.

Fig. 1. {Plan.)

Road Materials Etc 451

Mr. Stephenson, the engineer, describes in the Edinburgh Encyclopediaamode of constructing a smooth and durable city road, which is both economical and ingenious. - " A street or highway, supposed to measure about thirty feet in Fig. 2. (Section.) breadth, is laid out in five compartments, independently of foot-paths. Two of these are laid with the aisler causeway tracks, five feet apart, the horse-paths of rubble causeway, or broken stones, in the usual way. A B C D (Fig. 1) point out a compartment of the road, laid partly with broken stones, in which E E and F F are the aisler causeway tracks, A B being a paved open drain, on the side of the road. I N shows the limits of a road, also laid with tracks of aisler causeway, as marked at L L and M M; but here the compartments between and on each side are paved with rubble, or inferior causeway stones. Fig. 2 is a section of the plan described under Fig. 1, and shows the particular form of the aisler causeway tracks; a is a paved drain, b one of the sides, made with broken stones, c c two of the aisler causeway tracks, and d the horsepath between them.

Road Materials Etc 452

In the year 1825, Mr. Thomas Parkins obtained a patent for an improved mode of paving. The patentee proposed to lay on common roads continuous lines of granite blocks, on which the wheels of carriages are to run; the upper surfacesare to be level with the road, the under surface flat, and the stones are fitted together by "bird's-mouth joints." Each stone is thus supported by the stones on each side of it, and prevented from partial depression. Whatever merit may be due to Mr. Parkins for the methods he has suggested, so many and so various are the improvements in pavements since the date of his patent, that it is unnecessary to describe more minutely the several modes by which he proposes to connect the blocks of stone together.

Fig. 3.

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In the same year, a patent was granted to Mr. John Lindsay, of the Island of Herm, near Guernsey, for certain improvements in paving; it is described in Vol. XI. No. 64, of the London Journal. Fig. 3 is a cross section of the street; D D is a properly-prepared foundation; b and c c are blocks of smooth granite, placed longitudinally, and parallel to each other, for the carriage wheels; d d are also stone blocks, with trenches in their upper surfaces, to serve as drains for surface moisture or rain. The intermediate spaces e e e. e are filled up by common paving stones, with their broadest surfaces downwards, the interstices to be filled with granite chips or cement. The central line of granite blocks b is to be sufficiently broad to allow two carriages to pass; and the side blocks c c are only required to be wide enough for one wheel to run on. Upon the kerbs, carriages with heavy loads will pass with ease, and comparatively little labour to the horses. Mr. Lindsay's plan of preparing the foundation for the reception of the blocks, it is unnecessary to detail; and we believe the method of fastening the blocks by cramps or bars of iron, has been long known, and, in many cases, acted upon.

Though we conceive his invention to possess but little novelty, the patentee deserves credit for attempting to improve our street pavement; so valuable, as we have before observed, in a smooth and solid roadway, that every suggestion for its attainment is entitled to respect.

Mr. H. T. Cassell of Mill Wall, Poplar, has obtained a patent for a bituminous composition, called by him "lava stone." The patentee describes the merits of the invention to consist in the discovery of a mode of combining certain materials to form a species of stone uniting the advantages of metal with those of stone. The properties of this stone are durability and toughness. It does not absorb water, and is a non-conductor of heat. Each of these properties can, in the process of combination, be increased or diminished, to suit the purposes for which the stone is intended. In paving a street, the following method is pursued: - Instead of disturbing the bottom, it is to be consolidated by picking, raking, and rolling. A coating of bituminous lava is then run over, and the whole rendered impervious to water. This coating is then to be paved over with granite stones of the usual description, and the interstices are to be filled in with hot bituminous lava.