52*

HISTORY OF ENGINEERING.

Book T.

lower side of the road, the breadth of the foundation shall be 24 inches, and 18 inches atthe top, or level of the lower side of the road. If the height is 4 feet, the breadth of thefoundation is to be 30 inches, and at the top 24 inches. If the height is 6 feet, the breadthat the foundation is to be 3 feet, and 2 feet at the top. If the height is 8 feet, the breadthof the foundation is to be 4 feet, and at the top 2 feet, and so on in proportion to anygreater or lesser height. In forming these breastworks, the stones are to be laid in regularmanner, quite through the thickness here described ; the slope which is necessary to bringthe wall to its thickness at the top is all to be taken off the outside, and the stones are tobe laid mostly lengthwise into the wall; the space behind the breastwork and naturalground, up to the level of the top of the formed roadway, is to be filled up with coarsegravel or stones, (neither sand, sods, nor moss, to be used,) and if with stones they are to becovered and brought to the levels formerly described, with a layer of strong swarded turf,before the cleansed gravel is laid on.

“ At all times, when the nature of the cutting makes it possible, the resident overseershall have an opportunity of examining the breastwork when completed, before the innerside shall be filled up with stones or gravel as aforesaid, and also, where it shall be necessaryfor the due execution of the said road, to erect parapet walls above breastworks, or uponrock, they are to be built with stones laid in good lime mortar, agreeably to the ground report.

“ These parapets are to be 2 feet wide at the foundation, and 18 inches at the top. Theheight above the finished roadway is to be 2 feet 9 inches, including a coping of stones 9inches deep. These coping stones are to be chosen, so as to meet one another in closeregular beds or upright joints, to be firmly wedged together, and pointed with lime mortar.

“ At each extremity of the parapets the copings are to be well secured with the endsturned down under the roadway, and also where it shall be necessary in forming the road,to cut and remove earth from the higher side, to the depth of 2 feet or more, the road mustbe formed 21 feet 6 inches wide, and, to prevent the earth from falling into the drain on theupper side of the road, a wall of dry stones must be erected of a height according to thedepth of the cut. The foundation of those retaining walls is to be laid in all cases 6 inchesbelow the bottom of the drain, on the upper side of the road; there the thickness is to befrom 15 to 18 inches to the height of 4 feet; above that height they are to be ^ of thethickness. The stones with which they are constructed are to be laid in a regular andworkmanlike manner for the whole thickness of the wall; they are to be carried to such aheight, that the slope from them to the solid ground of the bank above is not to be lessthan two horizontal to one perpendicular, and that slope to be covered with turf laid flat.

“ And further, the contractors are to be bound to cut down all heights, fill up all hollows,and blast all rocks upon the said line of roads, as pointed out by the said reports, andwhich shall be requisite and necessary for the same : and further the said line of road shallbe formed and prepared for the gravel for one mile at least per advance to the satisfactionof the surveyor employed by the said commissioners before any of the cleansed gravel islaid on.”

Every necessary precaution was taken to render these roads efficient, and where thefoundations were of a soft nature, concrete was spread entirely over the surface, made withhard stone, or gravel mixed with lime in the proportion of one of the latter to four of theformer; and the greatest care was used, when the water was added, that the lime wasproperly slaked and saturated. The depth of the bed of concrete varied according to cir-cumstances : in some instances, 6 inches was found sufficient, in others more than doublethat depth was required; and before this became thoroughly set or hard, the broken stonewas laid on, in order that it might bed itself, and unite firmly with the upper surface; forit is very important that there should be a junction between the two bodies, otherwisethe stones would be in constant motion, and never form a firm and durable crust; bylaying the courses of broken stones on at intervals, the roadway is rendered perfectly solid,and in one mass from bottom to top.

Glasgow and Carlisle Road differs materially from those in the Highlands, as it wasnecessary to provide for the transit of the mail, and heavy coaches and carts carrying 3 or 4tons; it was made with the utmost care, all the ascents and descents set out with an easy

Fig. 533. SECTION OF HOAD.

and regular slope, never exceeding a rise of 1 in 30. These works were directed by Mr.Telford, after the act of parliament was passed in 1816.

The old road, which had become impassable, was in length 102 miles; the present is notmore than 93, and in order to gain this 9 miles, it was necessary to reconstruct 69 milesentirely, and to build fifteen new bridges ; exclusive of the bridges, the expense of the road-