causewaying may be seen in Edinburgh (Ratho, Dalmahoy Crags, and Corstorphine Hills), in Glasgow (Croy and Kilpatrick Hills), in Newcastle (Christon Bank and Wall), in Leeds (Richmond), and, indeed, in most of our large towns where the rock can be obtained at a cheaper rate than granite. In some instances quartzites and hard silicious sandstones are employed: they stand well, but, from their tendency to wear smooth and slippery, require to be laid, like the Moorfoot porphyry, in narrow courses.

For the footpaths of our towns flagstones are in great request, and some of them held in high estimation. Those from the lower old red sandstone of Caithness are extremely hard and durable, and can be obtained of great size, and from one to nine or ten inches in thickness. Being very hard and close in texture they are apt to become too smooth; some contain nodules of iron sulphide which resist wear, and render the surface irregular and somewhat dangerous, and many of the harder and thinner sorts are apt to crack unless carefully bedded, as all of them require to be. They are, however, impervious, or nearly so, to water, and make a clean and easily kept footpath. About 10,000 tons are annually exported from the county, at a value of between £4000 and £5000. Those procured from the lower old red of Forfarshire and Perthshire enjoy also a high reputation; but from their softer, more laminated, and absorbent nature, are better fitted for inside than for outside pavements. Local supplies of flagstones are also obtained from the coal-formation in several counties (Fife, Edinburgh, and Lanark); but those from the millstone grit and Gannister beds of Yorkshire and Derbyshire are perhaps the best and most durable, and capable of being raised of great size and of any thickness. Supplies are also obtained from the new red sandstone of Dumfriesshire and Cumberland, which are of fine even grain, and though rather soft, wear well and equably. Flags of fair quality are also raised from the middle oolite, and from the Wealden in Sussex, but they want the largeness, smoothness of surface, and compactness of texture which characterise those from the old and new red sandstones. What is wanted in a good flagstone is variety in thickness and size, a straight and even surface or bedding, and a non-absorbent and compact texture-laminated varieties being apt to split or peel off under the influence of frost and moisture. In some country towns the footpaths are neatly laid with pebble-stones; and in the suburbs of Edinburgh the larger chips obtained in dressing the causeway-blocks are closely

set on edge and beaten down to a smooth surface, thereby making a firm and durable material under the name of 66 Hornising," after a burgh surveyor of the name of Horne.

For kerb-stones, granite, greenstone, and some of the harder sandstones and limestones have long been used.

The granites of Aberdeen, Kirkcudbright, Wigtown, and Wicklow, make excellent material; some of the hornblendic greenstones, as those of Queensferry on the Forth, and of Corstorphine and Ratho near Edinburgh, are equally suitable, and more cheaply tooled; while many of the harder limestones (Derby, York, Westmoreland, and Devon) square well, and are extensively employed in their respective areas. In some towns sandstones on edge are employed; but these, unless hard and uniform in texture, are apt to split up under the weather, and wear irregularly. A straight, durable, and well-set kerbstone is indispensable to a good street, not only in retaining the flagstones and maintaining the gutters, but in imparting an appearance of finish and stability to all the lines and turnings.

II. RAILWAY CONSTRUCTION.

Many of the remarks on road-making are equally applicable to railway construction. The choice of route and study of gradients are determined in a great measure by the requirements of the district, though an engineer well acquainted with its geology and mineral resources may, with a little modification, not unfrequently add materially to the success of the undertaking. Where excavations and tunnellings are imperative, he will not only know better how to conduct these operations, but will be enabled to see how far the material excavated, or any portion of it, may be utilised on other portions of the line, either in walling, embanking, or building of bridges. From a study of the geological structure of the country passed through, he will also make provision for the development of its mineral resources, be these coals, metallic veins, building-stones, limestones, clays, or sands. The main line may not pass through all of these repositories, and yet it may be so planned that sidings and branch-lines can be conveniently attached in the event of subsequent requirement.

Cuttings and Tunnels.

In the matter of excavating, for example, whether in open cuttings or in tunnels, no proper estimate can be made of the expense without a knowledge of the nature of the rocks to be passed through. Homogeneous chalk rocks, limestones,

alternations of sandstones and shales, masses of hard pebbly conglomerate, of gneiss, of greenstone, or granite, are things altogether different, not only requiring different amounts of labour, but different appliances for their successful excavation. A cutting through tough diluvial clay thickly studded with blocks and boulders may be as expensive as a cutting through

Cutting through Boulder-Clay, Linlithgowshire.

sandstone; and while the latter may be utilised as a buildingstone, the former is only fit for the formation of an embankment. And even after excavation, one set of rocks-granites, greenstones, limestones, and compact sandstones-will resist the action of all weathers, and stand firm and secure, while another set-soft sandstones, shales, clays, and sands-will

begin to disintegrate in a few months, and require facings-up or the further excavation of long flat slopes to render them secure. In passing along many of our railways where the cuttings are through glacial drifts-alternations of sands and clays, or nests of sand and gravel in boulder-clays—we frequently see the vast expense that has been incurred by subsequent reductions of the slope-the original having been left too steep and undrained; hence the frequent source of slips causing obstruction to the traffic and occasional accidents.

Again, in tunnelling, the structure of the rock, the inclination if stratified, the occurrence of faults, of water-bearing beds, and the like, are matters of prime importance, and no engineer can either estimate aright or construct aright who is incapable of appreciating such peculiarities in the rock-formations through which he has to pass. How different the tunnelling through the schists and granites of Mont Cenis, the chalk downs of Surrey, the oolites of Bath, the sandstones and shales of Glasgow, and the old red sandstone of Moncrieff Hill near Perth ! Thick-bedded and homogeneous rocks may be cut through and left without any protection, while soft sandstones, clays, and shivery shales require archings of brick or stone at every step: horizontal or moderately inclined strata may be left without artificial protection, while highly inclined beds require underarching to secure stability. A tunnel through hard homogeneous rock, and expensive to excavate, may be cheaper in the long-run than one through soft and unequal strata, requiring to be cased with masonry; and a gain may often be made by a few hundred yards' deviation rather than force the way directly through rocks of difficult and dangerous removal. Where a survey has been made, a geological map may often afford the necessary information; where no map exists, the engineer must prospect the route for himself, or render his views securer by pittings and preliminary borings.

As tunnels are generally carried through hills and elevated grounds, there is always a greater risk of meeting in with dykes and necks, fissures and faults, than when cutting through lowland tracks. Unless on hills of denudation, where the rocks are of a hard and homogeneous character, tunnelled heights are for the most part of a broken nature; hence the necessity for extra precaution on the part of the engineer and contractor. A little outlay in feeling one's way at the outset is often trebly repaid by the prevention of unnecessary labour and expenditure in the long-run. And here it may be observed that tunnelling is now a very different operation from what it was twenty or five-and-twenty years ago. Then matters depended very much

H

upon manual labour; whereas at the present day, mechanically impelled rock-drills, excavating machines, and new explosives, render the work at once cheaper, more expeditious, and satisfactory.

Embankments and Bridges.

The precautions necessary in the case of roadway embankments and bridges are much more imperative in the case of railways, where the operations are usually more numerous and extensive. Foundations, angles of slope, durability of material, and the like, are things of prime importance. A little extra outlay on the original construction is a trifle compared with subsequent alterations and repairs, requiring relifting of rails, and obstruction to, or even a temporary cessation of traffic. Again, in the utilisation of materials raised from cuttings and tunnels, the engineer should be careful that these are of a durable and lasting nature. Many of the sandstones and limestones that were excavated and applied to the building of retaining-walls, conduits, and fences, during the railway excitement of the forties and fifties, have since crumbled down to sand and mud, and have had to be replaced at treble expense by more durable material. We need not invidiously point to any particular line; the observer has only to use his own eyes, and especially in carboniferous districts, to be convinced of the truth of this It is in vain to leave the choice of such materials to contractors: their main objects are expedition and profit, and not stability. The engineer should select the material and stipulate for its employment-seeing, through his inspectors, that the stipulations are honestly fulfilled.

statement.

Water-Supply.

As permanent water-supplies are required not only for locomotives but for station purposes, this requirement should be kept steadily in view by the railway engineer. This has been an expensive item on many lines, and one which, in several instances, might have been avoided by judicious foresight. In general, a fair supply may be obtained by sinking wells, by drawing it from adjacent streams and lakes, or by leading springs which have been struck in the cuttings and tunnels. Wherever it can be led along the line from higher grounds, even though somewhat distant, this mode should be adopted, the natural gravitation dispensing with all the expensive adjuncts of boring, sinking, and pumping. Pumping involves a continuous outlay; the purchase of water-right is often a heavy item; but the intercepting of a spring costs nothing beyond the original outlay of piping to conduct it.