534 PRACTICE OF AGRICULTURE. Part III. 



3428. JFith resjject to the order and mode of laying out the materials, there is some dif- 

 ference of opinion. Some begin with the largest, and finish with the very smallest, or 

 with gravel ; some lay on the whole at once, and others in two or more stratums, and so on. 

 That such a mode of depositing materials could never make a good road, is evident, for the 

 reasons given by M'Adam and Clarke; the larger stones would soon rise to the surface, 

 and roll about loose on it ; the stratum being thus broken up, would admit and retain 

 water, which, by the traffick of the road, would render the substratum, in all such places, 

 a mass of mud, and the whole would become bad in proportion to the traffick, the sub- 

 soil, and the climate. Marshal is equally wrong in his directions for forming farm- 

 roads, by filling the wheel-tracks with hard materials. In depositing these, he says, the 

 largest and roughest are to be thrown to the bottoms of the wheel -trenches, as found- 

 ations for the hardest, which ought to receive the immediate pressure of the wheels, the 

 softest and finest being disposed of in the horse-track. It is evident the continual action 

 of the wheels in the same rut, aided by the water which must infallibly lodge there, 

 would soon work up the larger and rougher stones, and render the traction more oppres- 

 sive than if no metals had ever been laid there. 



3429. Telford^s mode of disposing of the materials of roads is as follows : Where a 

 road has no solid and dry foundation, it must be constructed anew. Upon the eighteen, 

 centre feet of it stones must be put, forming a layer seven inches deep. Soft stones will 

 answer, or cinders, particularly where sand is prevalent. These bottoming stones 

 must be carefully set by hand, with the broadest end down, in the form of a close, 

 neat pavement ; the cavities should be filled with stone chips, to make all level 

 and firm, and no stone should be more than five inches broad on its face. 

 Over its bottoming of stones or cinders, six inches of stones, of a proper quality, broken 

 of a size that will, in their largest dimensions, pass through a ring of two and a half 

 inches diameter, must be laid. The six feet of the road, on each side of the eighteen 

 centre feet (making thirty feet), when formed of a proper shape, may be covered with 

 six inches of good clean gravel, or small stone chips. 



3430. 1^0 covering or mixture irf any sort is added to the material by Edgeworth, ex- 

 cept clean angular gravel, that may insert itself between the interstices of the stones ; 

 but no more should be used than what will thus sink to a level with the surface. If 

 the whole were covered with gravel, it would be impossible to discover the defects of the 

 road, till it might be too late. No stones larger than an inch and a half diameter should 

 be suffered to remain on the road ; where much inaccuracy in this respect is suspected, 

 an iron ring may be employed as a gauge. In all cases, after the road has been covered 

 with stones, it should be carefully examined, and every stone that is too large should be 

 picked off, to be broken smaller. 



3431. The preference generally given to gravel, Paterson considers to be greater than 

 it deserves, and that the earth obtained from the sides of the road, free of expense, will 

 not only barely answer the purpose, but in most cases equally well ; and that on a per- 

 fectly dry bottom, it is questionable whether it should not even be preferred to gravel. 

 It is in winter only, and on wet ground, that I consider gravel entitled to any preference 

 whatever. (Treatise, ^c. 'p. 43.) 



3432. The mode of laying on gravel, according to Walker, " is to lay it on as it comes 

 from the pit, excepting the upper foot, or eighteen inches or so, which is screened ; 

 but in all cases, whether the material is gravel or hard stone, the interstices between the 

 pieces should be filled up solid with smaller pieces, and the finishing made by a thin 

 covering of very small pieces, or road-sand or rubbish, for those interstices must be filled 

 up before the road becomes solid, either in this way or by a portion of the materials of 

 the road being ground down, which last mode occasions a waste of the material, and 

 keeps the road unnecessarily heavy and loose. In the original making or effectually 

 repairing of a road, it is, I think, best that the whole of the proposed thickness be laid on 

 at once, for the sake of the road as well as of the traveller ; the materials of the road then 

 form a more solid compact mass then when they are laid in thin strata at different times, 

 for the same reason that a deep arch of uniform materials is preferable to a number of 

 separate rings." Laying on a stratum of unsifted gravel, under a sifted stratum, is 

 rather at variance with the doctrine of " a deep arch of uniform materials ;" and 

 it seems to us, that when a stratum of properly broken stones are to be powerfully 

 rolled, the previous filling up of their interstices with very small matters might 

 counteract the effect of rolling, in squeezing the angular stones into the angular 

 interstices. 



3433. The mode of laying on gravel by M'Adam, is that of scattering with a shovel, 

 and never emptying down cart or barrow-loads on the middle of the roadway, as is 

 generally practised. He completes the stratum by three separate layers, leaving the 

 first to be consolidated by wheels, and in some cases a heavy roller, before he lays on 

 the second ; and the second, in like manner, before he lays on the last. 



