When completed, a thin coat of gravel spread over the surface is useful in diminishing the effect of the jolting of carriages on the now pavement. In case of taking up any part of a pavement to attend to water.pipos, &c., great care is necessary in relaying the part, in doing which it is well to apply sonic fresh broken stone to the bed, and to lay the paving atones without mortar, until the foundation is settled.
The serious defects of the common stone pavements have led to a variety of experiments on other methods of forming carriage-ways for streets, of which the adoption of broken stone, or MSC acLunised roads, has been the most general. Opinions differ widely as to the propriety of this measure, but an idea seems to be gaining ground that the comparative quietness of such a road, and its superior ease to passengers, are insufficient to counterbalance the increased draught of carriages, the dust of summer, the mud rapidly formed in wet weather, and the great expense of keeping in repair a metalled road when subjected to the constant wear of a busy town.
The enormous expense of maintaining some of the metalled roads in London has led to attention being given to various plans of paving with wood. A very coarse kind of wooden road, consisting of rough logs laid close together across the track, is much used in North America, under the name of corduroy roads, but the wooden pavement, properly so called, seems to have been first used in Russia, and tried on a limited scale at Vienna, New York, and some other places, within a few years. One of the earliest kinds used consists of blocks of fir or other wood cut into hexagonal cylinders, of 6 or 8 inches diameter, and from 8 to 12 or 15 inches deep, and placed close together, with the grain verti cally. The blocks are sometimes tarred, or may be kyanised ; but even where no such precaution is used, the wear is very trifling, as the swelling of the wood from moisture makes the joints very tight and impervious to water. Such a pavement is very smooth when first laid, but unless the foundation be very carefully prepared, it is liable to Kink into hollows like the common stone pavement, owing to the want of cohesion between the individual blocks, a deficiency which it has been proposed to remedy by pegging or dowelling the pieces together, though their form is not very suitable for the purpose. Some speci mens have been laid on a flooring of planks, to avoid this inconvenience. Numerous other systems of wood pavements have been adopted, but in spite of the incidental advantages (as in the case of the suppression of noise, &c.) they have been found to be so danger ous to horses as to render it necessary to abandon the use of that material.
Another description of road that has lately attracted much attention is that consisting of on asphaltic composition. Many attempts have been made to form roads of gravel and other materials united by animal oleaginous or gelatinous substances, or coal-tar, into a kind of concrete ; but such attempts have seldom proved successful on a largo scale. Mineral substances of similar character have proved more advantageous, and the native tuiplialte procured near &pied, in the department of l'Ain, and some other places, has been found to produce, when mixed with a small portion of native bitumen, a substance admirably adapted for the formation of smooth roads, and a variety of other important purposes. Its application to carriage-ways has been in this country chiefly confined to court-yards, for which, as well as for terraces and footpaths, it is very suitable. The asphaltic mastic of Seyasel, as prepared for use, consists of ninety-three parts of native asphalte reduced to powder, and seven parts of bitumen ; the two ' being melted together, and a little fine gravel or sand stirred in with the mixture. The composition is ready for use when it simmers with
a consistency similar to that of treacle, and it is spread while hot so as to form a coating about an inch thick upon a levelled foundation of concrete. The thickness of the asphalts is regulated by slips of wood or iron, which are often so disposed as to divide the pavement into ornamental compartments, the asphalte being made of various colours by the admixture of different kinds of sand or other substances. \nen, the ornamental character of the pavement forms a distinguish ing feature, beautiful imitations of mosaic work may be executed with aaplialte.. The genuine natural asphalte possesses a degree of elasticity that renders it exceedingly durable; but artificial compounds in imitation of it generally require too much bitumen, and are injuriously affected by great changes of temperature. Some experiments have been made, but with very indifferent success, on the formation of carriageways with large blocks of asphaltic composition containing a considerable quantity of gravel or broken stone. [ASPH ALM) Foot-pavements of flag-stones require very little remark. The curb atones should be very hard, and firmly set in cement on a bed of gravel. They usually rise about 6 inches above the surface of the carriage-way, which may be made to abut immediately upon them, without the intervention of a gutter. Where gutters are introduced, those of cast iron are to be preferred. The flagstones, which should never be less than 21 or 3 inches thick, are commonly bedded in mortar on a layer of gravel ; but sometimes, when there are no cellars underneath, are laid dry. The appearance of many of the new streets of London is greatly improved by the use of flagstones of extraordinary dimensions, extending the whole width of the pavement; and a similar appearance at much less coat may be obtained by the use of asphalte. A slight degree of slope should be given to the pavement, to conduct water to the gutters, for which purpose a fall of 1 inch in 10 feet is sufficient, while a steeper inclination is objectionable from its danger in slippery weather.
Among the substitutes for common Yorkshire flagstones that have ' been recommended, may be mentioned slate, which appears to be very durable. Some pavements or floors of this material have been laid at the London Docks, where, among other advantages, it is found pre ferable to wood in point of cleanliness. Trackways of slate 2 inches thick are found strong enough to bear waggons or carts with 4 or 5 tons of goods ; and some are laid of only half that thickness on an old wooden floor.
A ' Treatise on Roads,' &c., by Sir Henry Parnell, of which a second edition was published in 1838, may be consulted with advantage by those desirous of obtaining further information on the theory and practice of road-making. The works of Bergeir, :McAdam, Edgeworth, Sgauzin, Schwilgud, Lehay, and several others; and the various Parliamentary Reports relating to roads from the commencement of the present century, as well as those of the Holyhead Road Com missioners, also contain much valuable matter on this subject. It may be interesting to add, as a means of forming an approximate idea of the importance of our ordinary roads, that the sum laid out in the repairs of the turnpike roads of England and Wales in 1857 was not less than 1,127,791/., including the interest on the debt, or a sum of 182,034/. ; and that the county roads cost 2,286,559!. There are no recent returns of the lengths of the different kinds of roadways, but the cost of maintaining a turnpike road may be taken at 501. per mile, and that of county roads at 11/. per mile.