Book II. M'ADAM'S ROADS. 577 



the kingdom may be made smooth and solid in an equal degree, and to continue so at 

 all seasons of the year." It is doubted by some, whether this would be the case in the 

 northern districts at the breaking up of frosts, and especially in the case of roads not 

 much in use, and consequently consisting of a stratum less consolidated, and more pene- 

 trable by water. M'Adam, probably, has much frequented public roads in view. The 

 durability of these," he says, " will, of course, depend on the strength of the materials of 

 which they may be composed ; but they will all be good while they last, and the only 

 question that can arise respecting the kind of materials is one of duration and expense, 

 but never of the immediate condition of the roads." (Remarks on Roads, ^c. p. 11.) 

 The following observation of Marshal is worthy of remark, as tending to confirm, to a 

 certain extent, the doctrine of M'Adam : " It may seem needless to repeat, that the 

 surface of a road which is formed of well broken stones, binding gravel, or other firmly 

 coliesive materials, and which is much used, presently becomes repellant of the water 

 which falls upon it ; no matter as to the basis on which they are deposited, provided it 

 is sound and firm enough to support them." 



3582. M^Adam^s theory of road-making may be comprised in the following quotation 

 from his Report to the Board of Agricidture (vol. vi. p. 46.) : " Roads can never be 

 rendered perfectly secure until the following principles be fully understood, admitted, 

 and acted upon : namely, that it is the native soil which really supports the weight of 

 traffic ; that while it is preserved in a dry state it will carry any weight without sinking, 

 and that it does, in fact, carry the road and the carriages also ; that this native soil must 

 previously be made quite dry, and a covering impenetrable to rain must then be placed 

 over it to preserve it in that dry state ; that the thickness of a road should only be regu- 

 lated by the quantity of material necessary to form such impervious covering, and never 

 by any reference to its own power of carrying weight. There are some exceptions to 

 this rule ; a road of good naturally binding gravel may be laid on a sub-bed of bog earth, 

 which, from its tenacity, will carry all kinds of carriages for many years." 



3583. The erroneous opinion so long acted upon, and so tenaciously adhered to, that by 

 placing a large quantity of stone under the roads, a remedy will be found for the sinking 

 into wet clay or other soft soils ; or, in other words, that a road may be made sufficiently 

 strong, artificially, to carry heavy carriages, though the subsoil be in a wet state, and by 

 such means to avert the inconveniences of the natural soil receiving water from rain or 

 other causes ; has produced most of the defects of the roads of Great Britain. At one 

 time M'Adam had formed the opinion that this practice was only a useless expense ; but 

 experience has convinced him that it is likewise positively injurious. 



3584. If strata of stone of various sizes be placed as a road, it is well known to every 

 skilful and observant road-maker, that the largest stones will constantly work up by the 

 shaking and pressure of the traffic ; and that the only mode of keeping the stones of a 

 road from motion is, to use materials of a uniform size from the bottom. In roads made 

 upon large stones as a foundation, the perpetual motion, or change of the position of the 

 materials, keeps open many apertures, through which the water passes. 



3585. Roads placed upon a hard bottom, it has also been found, wear away more 

 quickly than those which are placed upon a soft soil. This has been apparent upon 

 roads where motives of economy or other causes have prevented the road being lifted to 

 the bottom at once ; the wear has always been found to diminish, as soon as it was pos- 

 sible to remove the hard foundation. It is a known fact, that a road lasts much longer 

 over a morass than when made over rock. The evidence produced before the committee of 

 the House of Commons showed the comparison on the road between Bristol and Bridge- 

 water to be as five to seven in favour of the wearing on the morass, where the road is laid 

 on the naked surface of the soil, against a part of the same road made over rocky ground. 



3586. The common practice, on the formation of a new road, is, to dig a trench below 

 the surface of the ground adjoining, and in this trench to deposit a quantity of large 

 stones ; after this, a second quantity of stone, broken smaller, generally to about seven 

 or eight pounds' weight : these previous beds of stone are called the bottoming of the 

 road, and are of various thickness, according to the caprice of the maker, and generally 

 in proportion to the sum of money placed at his disposal. On some new roads, made 

 in Scotland in the summer of 1819, the thickness exceeded three feet. That which is 

 properly called the road is then placed on the bottoming, by putting large quantities of 

 broken stone or gravel, generally a foot or eighteen inches thick, at once upon it. Were 

 the materials of which the road itself is composed properly selected, prepared, and laid, 

 some of the inconveniences of this system might be avoided ; but in the careless way in 

 which this service is generally performed, the road is as open as a sieve to receive water, 

 which, penetrating through the whole mass, is received and retained in the trench, whence 

 the road is liable to give way in all changes of weather. A road formed on such prin- 

 ciples has never effectually answered the purpose which the road-maker should con- 

 stantly have in view ; namely, to make a secure level flooring, over wliich carriages may 

 pass with safety and equal expedition at all seasons of the year. 



Pp 



