width for roads near the largest towns and cities, and that ten or twenty feet of this may in some cases be paved. The London Commercial Road, constructed by the last-named engineer, is of this width and character, and there are fifteen feet of gravel road at each side for light carriages or horses. It has been executed for sixteen years, and has given the greatest satisfaction; but Mr. Walker thinks that considerable improvement would be found from paving the sides of a road, upon which the heavy traffic is great, in both directions, and leaving the middle for light carriages; the carmen or drivers, walking upon the foot-paths or sides of the road, would then be close to their horses, without interrupting or being in danger of accidents from light carriages, which is the case when they are driving upon the middle of the road; and the unpaved part, being in the middle or highest part of the road, would be more easily kept in good repair. But unless the heavy traffic in both directions is great, one width, say ten or twelve feet, in the middle of the road, well paved, will be found sufficient for all ordinary wear. The width of many of the present roads is, besides, such, that ten or twelve feet can be spared for paving, while twice that width would leave too little for the gravelled part. Although the first cost of paving is great he does not think that any other plan can be adopted so good and so cheap in those places where the materials got in the neighbourhood are not sufficient for supporting the roads. A coating of whinstone is, for instance, more durable than the gravel with which the roads round London are made and repaired; but much less so than paving; although the freight and carriage of the whinstone, and of the paving-stones, which form the principal items of the expense, are nearly the same.

Proportioning the breadth of roads to the traffic for which they may be employed, has, perhaps, not been sufficiently attended to. In remote places, where there is but little traffic, the waste of ground occasioned by superfluous width of roads, is an error: there being many places where roads of twenty feet breadth would suit the public convenience, as well as if they were twice as broad; and it is clear that, if a road is one pole or perch wider than is necessary, there is a waste of 320 perches in a mile, equal to two acres of ground, which, at the rate of £3 per acre, would, if the road had been once well made, keep half a mile of such road as is here alluded to in good repair. According to Paterson, the breadth of the road and the width of the metals, or paved part, should depend on circumstances different from the former. For a few miles in the vicinity of such cities as London or Edinburgh, the most proper breadth at which a road should be formed, he thinks, is from sixty to seventy feet, and the metals from twenty-five to thirty-five feet; while, in the neighbourhood of such towns as Newcastle and Perth, it will be sufficient that it be formed forty feet broad, and that the width of the metals be about eighteen or twenty feet. These are the breadths presumed to be the most eligible in such situations. But rules cannot be given to suit every situation: the breadth ought to be regulated according to the

extent of the run of commerce, or traffic, upon the road. As a general rule however, for public roads over the different counties of Great Britain, I should suppose, he says, the following might in most cases be adopted. Take for instance the road betwixt Edinburgh and Glasgow or betwixt Edinburgh and Aberdeen, by the way of Dundee. These roads are formed a general from thirty-five to forty feet wide; and the breadth of the metals is from fourteen to sixteen feet for the most part. Such roads as these would be found to answer very well, in general, over the kingdom. A breadth sufficient for the general purposes of country travelling, according to M'Adam, is sixteen feet of solid materials, with six feet on each side formed of slighter materials. The Bristol roads, he says, are made with stone about the width of sixteen feet.

Narrow roads, it is well observed by Fry, are almost always in bad condition, which is to be accounted for from the circumstance of every carriage being obliged to go in the same ruts; and, as each rut is generally only six inches wide, one foot of the road only is worn by the wheels instead of the whole breadth of it; which would be the case if the road were of a proper width, and if it were well constructed. If a road be laid out from twenty to thirty feet wide, so flat as that a carriage may stand nearly upright on every part of it, and if moderate care be taken by the surveyor to prevent the first formation of ruts, such a road will be worn by the wheels nearly alike on every part of it: provided also that the ground on each side, for at least four or five feet, be moderately flat, so as not to excite fear in the drivers of carriages; but if there be deep ditches close to the sides of the road, or if the circumjacent land fall off very abruptly to the depth of two or three feet, whereby fear of approaching the edges would operate on the minds of the drivers, every driver will instinctively avoid the danger on either hand; and a road so circumstanced will, in spite of any care of the surveyor, inevitably be worn into ruts in the middle. There is a remarkable instance of this kind in a piece of road on Durdham Down, near Bristol. This road is a causeway over a piece of soft ground; and, although it is from twenty to twenty-five feet wide, yet, as the ground falls away abruptly on both sides of it, it has been found impossible, for more than twenty years past, to his knowledge, to prevent deep ruts being formed along the middle of it; notwithstanding the Down itself consists of hard limestone; and the other roads upon the Down are as fine and even as any roads in England. Were this piece of road widened out on each side, in an easy slope about five feet, by rubbish of any kind, and by the scrapings of the load itself, whereby the instinctive operation of fear of approaching the sides of the present road would be obviated, that piece of road would be found to wear as fairly as the other roads on the same Down.

When roads run through marshy ground, observes Mr. Edgeworth, the substratum must be laid dry by proper drainage; and where the road is liable, from the flatness of the country, to be at times under water, the expense of raising it above the water must be submitted to in the

first instance. All drains for carrying off water should be under the road, or at the field side of the fences, and these drains should be kept open by constant attention, and should be made wide at the outlet.' Telford and Walker recommend the side drains to be in every instance on the field side of the fence. In cases, Telford observes, where a road is made upon ground where there are many springs, it is absolutely necessary to make a number of under and cross drains to collect the water and conduct it into the side drains, which should always be made on the field side of the fences. The orifices of these cross drains should be neatly and substantially finished in masonry. Before the materials are put on, run a drain along the middle of the road, all the way, from two to three feet deep; then fill it with stones up to the surface, making those at bottom of a pretty good size, and those at the top full as small as the road materials. And, in order that the quantity of stones used for the said drain may be as little as possible, and every way to save expense, it may be made as narrow as it can possibly be dug. From this leading drain make a branch here and there to convey off the water to the canals on the sides of the road.'-Paterson. This mode of draining he has found from experience to be so beneficial that a road so drained would be better and more durable with eight inches, than it would otherwise be with twelve inches of materials. And not only so, but that on such a road there would be a saving on the incidental repairs, ever afterwards, of about one-half of the labor, and at least onethird of the material. All moisture from under the road materials should be carried off by such drains. Where such drains are wanting, the road, on the return of a thaw, throws up to the surface all the water it had imbibed; and in many places the materials, swelling up, become quite loose and open. This is a natural consequence, where the material is not thick, and where the soil under the road is not perfectly dry. But, where a road is dried in the way described, it will be uniformly seen that the water, instead of spewing out on the return of a thaw, is sucked in by the drains, so leaving the surface of the road quite dry. It may be observed, at such times, that the places of the road where a few roods of such drain had been introduced, presented to the eye, at a quarter of a mile distance, quite a contrast to the other parts of the road; the one opaque and dry, from the moisture being sucked in, the other all wet and glistering, from its being thrown out to the surface.'-Paterson's Letters, &c., 44, 48, 84.

Embankments and bridges of different degrees of magnitude, are required in most lines of road. Large bridges we must leave to engineers; no department of their art having attained higher perfection. We here confine ourselves entirely to such stone arches as may be designed by road-surveyors, and built by country masons. In many cases cast-iron might be substituted for stone with economy and advantage as to waterway; but, though the principle of constructing both cast and wrought iron bridges is perfectly simple, the execution, and especially the putting up, requires more skill, and is attended with

much more risk than the erection of other bridges. One low arch is thought by Mr. Loudon to be in general the most desirable description of common road-bridges. But most of the country bridges, as Clarke observes, consist of several small, high, semicircular arches: where there is a single arch, the stream passes without interruption; if there are two or three in the same situation, the space through which the water is to pass is necessarily contracted by the width of piers. Ice, and large bodies carried down by the floods, frequently stop up the small arches, and the accumulated water carries away the bridge; but, if such accidents should not happen, the constant currents rushing against those piers wash out the mortar, loosen the stones, and very soon undermine the work if it is not extremely well put together, which is seldom the case. Unless the river or stream is narrow, or the banks very high, a semicircle is an inconvenient shape for an arch; it has been adopted on account of the insufficiency of the abutments, and because the pressure is more perpendicular; but scientific engineers, in all countries, now construct their bridges with wide openings, and make the arches either semi-ellipses, or segments of large circles; so that the space above the highest floods is comparatively little, and the ascent over the bridge inconsiderable. In country bridges in Ireland, Clarke continues, the foundations are invariably, and often intentionally, defective: the mason considers himself an honest man if his bridge lasts seven years; whereas, from the durability of materials in that country, it ought to endure for ages. Whatever is under water is out of sight, and is generally composed of loose stones, thrown promiscuously together, on which the masonry is erected, and all the pains and expense are bestowed on the cutwaters and wings, when the heaviest stones, and those accurately jointed, ought to be laid in the foundations. The greatest attention should be paid to the quality of the materials: the stones should be large, and laid in level courses, in the best mortar, composed of sharp sand, free from loam, and quicklime, accurately mixed together; the coping of the parapet is generally so slight that it is broken down as soon as built, and the entire parapet quickly follows; it ought to be of large heavy stones, roughly hammered, and there should be substantial quoins at the ends of the parapets with an immovable stone over them. Arches not exceeding eight feet span may be semicircular; tunnels not exceeding eighteen inches wide may be covered with strong flags, and either flagged or paved under, and there ought to be across either end a deep long stone, sunk below the surface of the current, and under the walls, to prevent the water from undermining the work.

Fences along the sides of roads are essential in all enclosed conntries; and all engineers and road-makers agree that they should never be allowed to rise to a greater height than what is necessary for a fence. To give free admission to the sun and air, by keeping the fences low, Marshall considers as providing an expensive, yet most accurate method of cleaning roads, incomparably more so than washing or scraping. The

legislature, Edgeworth observes, has limited, in several instances, the height of hedges to five feet; but this limitation is neglected or evaded. Even were it strictly adhered to, it would not be sufficient for narrow roads; the hedges would be still too high, for it is the sweeping power of the wind which carries off dust in dry weather, and which takes up moisture in wet. In fact, roads become dry by evaporation; and, when they are exposed to the sun and wind, the effect of heat and ventilation are more powerful than any surface drainage that could be accomplished. Walker observes that the advantage of having the hedge next the road consists in its greater safety to the traveller, particularly if a ditch of any considerable depth is necessary, and in the hedge being supported in its growth from the ground under the road, without drawing upon the farmer's side of the ditch. The fences, Telford observes, form a very material and important subject, with regard to the perfection of roads; they should in no instance be more than five feet in height above the centre of the road, and all trees which stand within twenty yards from the centre of it ought to be removed. I am sure that twenty per cent, of the expense of improving and repairing roads is incurred by the improper state of the fences and trees along the sides of it, on the sunny side more particularly; this must be evident to any person who will notice the state of a road which is much shaded by high fences and trees, compared to the other parts of the road which are exposed to the sun and air. My observations, with regard to fences and trees, apply when the road is on the same level as the adjacent fields; but in many cases, on the most frequented roads of England, more stuff has been removed from time to time than was put on; the surface of the road is consequently sunk into a trough or channel from three to six feet below the surface of the fields on each side; here all attempts at drainage, or even common repairs, seem to be quite out of the question; and by far the most judicious and economical mode will be to remove the whole road into the field which is on the sunny side of it.-Examination before the House of Commons, &c.

3. Of the foundation of roads.-Edgeworth, Marshall, and all the practical engineers before Mr. M'Adam differ with him as to the base of roads. The author of Landed Property in England would prepare the ground by striking off the protuberances, and filling up the hollow parts: the footpath and the higher side of the soft road being raised with the earth which is required to be taken off the bed of the hard road; whose base or foundation ought to be formed with peculiar care. Every part is required, as he says, to be firm and sound dry earth, or hard materials, being rammed into every hollow and yielding part. In a dry situation, as across a gravelly or stony height, little more, he says, is required than to remove the surface mould, and lay bare the rock, or bed of gravel beneath it: and, then, to give the indurate base a round or a shelving form, as the lying of the ground may require. In this way, a travelable road may be made, and kept up, at one-tenth of the expense incurred by the ordinary practice in this case;

stone.

which is to gather up the surface-soil into a ridge, and, on this soft spongy bed, to lay, coat after coat, some hard materials,-fetched perhaps from a distance. But M'Adam contends that a stratum of hard materials covering a morass will last longer than a similar stratum laid on rock; indeed, according to this able engineer, it may be questioned whether a properly made road on a bog, which yields by its elasticity, will not last longer than one on a firm surface. In Ireland this is said to be found actually the case: For the same cause,' as Fry observes, that a stone placed upon a wool-pack would bear a greater pressure before it would be broken, than it would if placed on an anvil.'-Essay on Wheel Carriages, &c. Edgeworth and many others have recommended covering the base of an unsound road with faggots, branches, furze, or heath. Flat stones, he adds, if they can be had, should then be laid over the faggots, and upon them stones of six or seven pounds' weight, and, lastly, a coat of eight or ten inches of pounded If the practicability of consolidating a mass of stones of six or eight ounces weight and under each, so as to act as one plate or flooring, be admitted, then the faggots and flat stones must at least be useless, and the stones of six or seven pounds' weight injurious; because, whenever the upper stratum has worn down a few inches, some of these stones, and eventually the greater number will be worked up to the surface, and the road destroyed or put in a state to require lifting, breaking, and relaying. A basement of trees, bavins, or bushes, was made use of by Walker when the ground was soft. They carry off the water previous to the materials of the road being so consolidated as to form a solid body, and to be impervious to water. Bushes are, however, not advisable to be used, unless they are so low as always to be completely moist. When they are dry and excluded from the air they decay in a few years, and produce a sinking in the road; a thickness of chalk is useful for the same purpose in cases where bushes are improper: the chalk mixing with the gravel or stones becomes concreted, and presents a larger surface to the pressure.

Mr. M'Adam would lay his metals' at once on the earth, provided it were even a bog, ‘if a man could walk over it.' In his examination before the house of commons he says, 'the Somersetshire morass is so extremely soft that when you ride in a carriage along the road you see the water tremble in the ditches on each side; and the vibration so great that it will break you in.' Yet here he would use no large foundation stones, nor faggots, nor any material larger than will weigh six ounces. If a road be made smooth and solid, it will be one mass, and the effect of the substrata, whether clay or sand, can never be felt in effect by carriages going over the road; because a road well made unites itself in a body like a piece of timber or a board.' And we may now introduce

4. Mr. M'Adam's system. This able and ingenious engineer agrees with many of his predecessors that a good road may be considered as an artificial flooring, forming a strong, solid, smooth-surfaced stratuin, sufficiently flat to

admit of carriages standing upright on any part of it, capable of carrying a great weight, and presenting no impediment to the animals or machines which pass along it. In forming this flooring, he has, however, gone one material step beyond his predecessors in breaking the stone to a smaller size, and in forming the entire stratum of this small-sized stone. It is in this point, of making use of one small size of stones throughout the stratum, that the originality of Mr. M'Adam's plan consists. It is doubted by some whether this would be durable in the northern districts at the breaking up of frosts, and especially in the case of roads not much in use, or consisting of a stratum less consolidated, and more penetrable by water. The durability of roads,' he says, 'will of course depend on the strength of the materials of which they may be composed, but they will all be good while they last, and the only question that can arise respecting the kind of materials is one of duration and expense, but never of the immediate condition of the roads.'-Remarks on Roads, &c. p. 11. Roads can never be rendered perfectly secure, according to this gentleman (see his report to the board of agriculture), until the following principles be fully understood, admitted, and acted upon namely, that it is the native soil which really supports the weight of traffic; that while it is preserved in a dry state it will carry any weight without sinking; and that it does, in fact, carry the road and the carriages also; that this native soil must previously be made quite dry, and a covering impenetrable to rain must then be placed over it to preserve it in that dry state; that the thickness of a road should only be regulated by the quantity of materials necessary to form such impervious covering, and never by any reference to its own power of carrying weight. The erroneous opinion, so long acted upon, that by placing a large quantity of stone under the roads, a remedy will be found for the sinking into wet clay, or other soft soils; or, in other words, that a road may be made sufficiently strong, artificially, to carry heavy carriages, though the sub-soil be in a wet state, and by such means to avert the inconveniences of the natural soil receiving water from rain, or other causes, seems to have produced most of the defects of the roads of Great Britain. At one time Mr. M'Adam had formed the opinion that this practice was only a useless expense; but experience has convinced him that it is likewise positively injurious.

In confirmation of this, if strata of stone of various sizes be placed as a road, it is well known to every observant road-maker that the largest stones will constantly work up by the shaking and pressure of the traffic; and that the only mode of keeping the stones of a road from motion is to use materials of a uniform size from the bottom. In roads made upon large stones, as a foundation, the perpetual motion, or change of the position of the materials, keeps open many apertures, through which the water passes. It has also been found that roads placed upon a hard bottom wear away more quickly than those which are placed upon a soft soil. This has been apparent upon roads where motives of eco

nomy, or other causes, have prevented the road being lifted to the bottom at once; the wear has always been found to diminish, as soon as it was possible to remove the hard foundation. As to the fact, already adverted to, that a road lasts much longer over a morass than when made over rock, the evidence produced before the committee of the house of commons showed the comparison, on the road between Bristol and Bridgewater, to be as five to seven in favor of the wearing on the morass, where the road is laid on the naked surface of the soil, against a part of the same road made over rocky ground.

Water, with alternate frost and thaw, are the great evils to be guarded against in the base of a road consequently nothing can be more erroneous than providing a reservoir for water under the road, and giving facility to the water to pass through the road into this trench, where it is acted upon by frost to the destruction of the road. As no artificial road can ever be made so good and so useful as the natural soil in a dry state, it is only necessary to procure and preserve, according to M'Adam, this dry state of so much ground as is intended to be occupied by a road. The first operation is to be the reverse of digging a trench. The road should not be sunk below, but rather raised above the ordinary level of the adjacent ground; care should at any rate be taken that there be a sufficient fall to take off the water, so that it should always be some inches below the level of the ground upon which the road is intended to be placed: this must be done, either by making drains to lower ground, or if that be not practicable, from the nature of the country, then the soil upon which the road is proposed to be laid must be raised by addition, so as to be some inches above the level of the water.

Having secured his soil from under-water, the road-maker is next to secure it from rain by a solid road made of clean dry stone or flint, so selected, prepared, and laid, as to be perfectly impervious to water; and this cannot be effected unless the greatest care be taken that no earth, clay, chalk, or other matter, that will hold or conduct water, be mixed with the broken stone; which must be so prepared and laid as to unite with its own angles into a firm, compact, impenetrable body. The thickness of this body is immaterial, as to its strength for carrying weight; this object is already obtained by providing a dry surface, over which the road is to be placed as a covering or roof, to preserve it in that state: experience having shown that if water passes through a road, and fill the native soil, the road, whatever may be its thickness, loses its support, and goes to pieces. In consequence of an alteration in the line of the turnpike-road, near Rownham-ferry, in the parish of Ashton, near Bristol, it was necessary to remove the old road. This road was lifted, and re-laid very skilfully in 1806; since which time it has been in contemplation to change the line, and consequently it has been suffered to wear very thin. At present it is not above three inches thick in most places, and in none more than four yet, on removing the road, it was found that no water had penetrated, nor had the frost affected it during