A B C D point out a compartment of a road laid partly with broken stones, in which E E and F F are the aisler-causeway tracks, A B being the sky or open drain upon the side of the road, which, if situated within, or. near a populous town, is supposed to be paved. In the same manner, G H I K show the limits of a road also laid with tracks of aisler causeway, as marked at I. L and M bI, but here the compartments between and on each side are paved with ruble or inferior causeway stones.
Fig. 2. is a section of the plan described under Fig. I, and shows the particular form of the aisles causeway tracks, and other parts of the road, 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 horse-path be tween them. In the same manner, e _if and g show the street laid with ruble causeway-stones on each side and between the tracks.
Fig. 3. includes a cross and longitudinal section of one of the track-stones, and from its simple form it will be seen that they may be prepared at the least possible expense, requiring only that the sides which come in contact should be squared, and made to form a joint touching throughout from the bottom to the top, the other sides being dressed as common aisler causeway. The diagram a b represents a section of one of these stones taken across, or at regular angles, to the direction of the track. It measures eighteen inches in breadth at the base, twelve inches at the upper surface, and four teen inches in depth. c d is another section of the same stone, taken in the longitudinal direction of the track, which is here supposed to be eight inches in thick ness, though in this dimension it may be varied to any range from six to nine inches to suit the quarry.
Fig. 4. is a semi-cross section or a common road. The letters A B C showing the metal or broken stones in strata of a uniform thickness in the central parts as between A B, but diminishing towards the side drain at C. The chief thing to be observed, is the
form given to the bottom, which takes the same curve as the upper surface of the road. By this means the drainage is assisted, and the road metal is saved, as there is not a greater depth of broken stones under the horse-track where it is less required than under the carriage-wheels.
Figs. 5, 6, and 7, represent a plan of stone-railways suggested by Mr. Matthews of Walworth, to the mittee of the House of Commons on highways. He proposes that the stones should be in pieces, measuring four feet two inches in length, eleven inches in breadth at the top, fourteen inches at the base, and ten inches in depth. The diagrams to which the figures refer, show three sets of tracks with various modes of forming the connecting joints. Fig. 5. is a kind of mortice and tenon joint, marked a b and a b, in which the stones are inserted into each other near the top, in a bevelled fashion, with a view to prevent the joint from sinking. Fig. 6. forms a plain bevelled joint, in which the ends of the two rails are made to rest upon a centre or intervening block of stone, as at c d and c d. In fig. 7, the letters f g and f g show the same description of joint, and its bearing, but with a joint somewhat more complicated in its outline or form.
Authors to be consulted. Bergier's Historie des Grandes Chemins de l'Empire. Philips' Dissertation concerning the High Roads. Homer's Enquiry into the State of Roads. Lambert on the best Ascent of Roads. Edgeworth on Roads and Carriages. Young's Natural Philosophy. Wilkes on Concave Roads. Wright on Watering Roads. Ellis on Washing Roads. Cumming on Broad Wheels, &c. Booth on Wheel Carriages. Erskine on Iron-roads. General Rules for Rood-mak ing, published by Taylor, London. Patterson's Practi cal Treatise. M'Adam's Remarks on the Present Sys tem of Road-Making. Communications to the Board of .1griculture. Parliamentary Reports.