Book II. 



FORM AND MATERIALS OF ROADS. 



b35 



3434. A covering from four to five inches thick, according to Fry, forms a bed or mass, 

 which is proof against the severe crush of heavy wheels, while in the case of a very thin 

 covering, the stones lying bare upon a hard road, and receiving in this unprotected 

 state the stroke of every wheel that passes over them, like the thin covering on a mill- 

 bed, they are quickly reduced to powder, and disappear. Stones in a thick bed are 

 protected from the immediate destructive grind ; while stones that are thinly laid on are 

 instantly reduced to powder, either by pressure 438 



or grinding. 



3435. Telford, in filling broken stones, and 

 also in scattering them on the road, makes 

 use of a pronged shovel, fourteen inches square, 

 which may be universally recommended for this 

 purpose (fig. 438 d).. His large hammer (a) , 

 small one (b), and gauge for the size of the broken 

 stone (c), are in very general use, as well as 

 the pronged shovel. Hammers may be made 

 of cast iron where the stones to be broke are 

 about their own weight ; the best shape is a 

 narrow oval ; the advantage of using cast iron 

 is its cheapness. (^Farm. Mag. xxii. 159.) 



3436. Telford's level for adjusting the declivity of roads from the middle to tlie 

 sides (fig, 439.), is also a very complete implement of the kind. 



U 



439 



3437. Tlie mode of depositing materials bij Paterson is as follow's: "Bottom 

 metals should be broken on the road. When they are thus broken, they are, by the 

 force of the hammer, firmly bedded into the bottom, and are so closely and compactly 

 beaten together, that they become like pavement. In this state they are not only 

 less liable to sink, but they form a much better bed for the top metals than when they 

 are thrown loosely on. And besides this, when they are put on in a loose manner, 

 as is frequently done, the mud more readily works up through the metals in time 

 of rains, and makes a disagreeable road : the top metals also are easily beaten down 

 by the horses' feet and the carriages, through the bottom stones, when loose and 

 open ; so that the small metals frequently get undermost, and the large ones make 

 their appearance at the surface, very much to the injury of the road. Taking all these 

 circumstances, therefore, into consideration,- it is of the greatest importance that the 

 bottom metals should not only be much larger in size, but that they also be broken on 

 the road." This may be considered as at variance with several parts of Paterson's second 

 publication. (Letters, c^c.) The road being drained and prepared for the materials, he 

 then directs (p. 80.) to put them on in the following manner: " M' Adam's mode of 

 putting them on in coats of three or four inches, though good in particular instances, 

 will not do as an universal rule. If the bottom is wet, and the weather rainy, the earth 

 will poach and work up through the materials, in spite of all the attention and care that 

 can be bestowed. I would, therefore, recommend in such cases to put on the first 

 course from five to six inches thick. But then to leave these materials to consolidate, or 

 rather to move and shift about by the wheels j and then to be levelled by the rakes, alter- 

 nately, according to M' Adam's plan, wears away the corners of the stones, by which 

 means they do not unite together and make such a firm road. There were upwards of two 

 miles of road made under my directions lately, on which I caused a course of about six 

 inches to be put. But before opening it to the public, I got a heavy stone roller to ply 

 upon it for four days. This beat and firmed the materials so much, that the wheels of 

 the carriages made little impression upon it. Of course the materials retained their an- 

 gular points more than in rolling and shifting by every carriage-wheel that passed ; and 

 there was less labor in raking and levelling the road. This plan, which carries reason in 

 the face of it, I would strongly recommend. As to M' Adam's plan of putting on the 

 materials in shovelsfull, it is certainly good. I used to prohibit putting tliem on with 

 carts (as in that case you never have the small and the great properly mixed together), 

 and generally put them on with wheel-barrows. But even this does not mix them quite 



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