Book II. ROADS OF VARIOUS ENGINEERS. 581 



csonsolidated as to form a solid body, and to be impervious to water. Bushes, however, 

 the Down are as fine and even as any roads in England. Were this piece of road 

 widened out on each side, in an easy slope of about five feet, by rubbish of any kind, 

 and by the scrapings of the road itself, whereby the instinctive operation of fear of 

 approaching the sides of the present road would be obviated, that piece of road would be 

 found to wear as fairly as the other roads on the same Down. 



3602. In regard to the drainage of roads, Marshal directs to examine the site in every 

 part, to ascertain whether offensive waters lodge beneath it, or quicksands, and land springs, 

 which break out in a wet season. If defects of this kind be found, effectual drains are 

 to be run up to them, from the ditches or outer side drains of the site. 



3603. When roads run through viarshy ground, Edgeworth observes, " the substratum 

 must be laid dry by proper drainage ; and where the road is liable, from the flatness of 

 the country, to be at times under water, the expense of raising it above the water must 

 be submitted to in the first instance. All drains for carrying off water should be under 

 the road, or at the field-side of the fences, and these drains should be kept open by con- 

 stant attention, and should be made wide at the outlet." 



3604. The method of draining which Paterson has found the most effective is thus 

 de-scribed: " Before the materials are put on, run a drain along the middle of the road, 

 all the way, from two to three feet deep ; then fill it with stones up to the surface, mak- 

 ing those at bottom of a pretty good size, and those at the top fully as small as the road 

 materials. And, in order that the quantity of stones used for the said drain may be as 

 little as possible, and every way to save expense, it may be made as narrow as it can 

 possibly be dug. From this leading drain make a branch here and there, to convey off 

 the water to the canals on the sides of the road." This mode of draining he has found, 

 from experience, to be so beneficial, that a road so drained would be better and more 

 durable with eight inches, than it would otherwise be with twelve inches of materials ; 

 and not only so, but that on such a road there would be a saving on the incidental 

 repairs, ever afterwards, of about one half of the labour, and at least one third of the 

 material. 



3605- All moisture from under the road materials must be carried off by such drains. 

 Then, if the materials are properly broken, they will become so firm and solid that little 

 or no water will get through them ; and if it should, this drain would carry it away. 

 So that, under any view of it, tlie utility of these drains must be very apparent ; but when 

 we consider that, to have the ground under the road materials perfectly dry is to insure 

 a good road, these drains become indispensably necessary, and the expense is a mere trifle. 

 There are two miles of road, which were made on this plan under Paterson's directions, 

 which have stood all the winter rains without injury, and which promise to make one of 

 the finest roads in the kingdom. There is another road of ten miles, that he has lately 

 planned, for the greater part of which he has specified two such drains, running parallel 

 to each other, and five feet apart ; and he would even recommend three or four parallel 

 drains where there is a great breadth of metals, except where the road is formed over dry 

 sand or open gravel. Although the effect of such drains will be at all times beneficial 

 to the road ; in time of a thaw, after there have been a few weeks of frost, it will be 

 peculiarly so. In frost, the surface of the road, though wet before, becomes dry, the 

 water being absorbed by the road, or otherwise condensed by the frost ; but no sooner 

 is this succeeded by a thaw, than the absorbed or condensed water again makes its 

 appearance all over the surface of the road. This is the time that these drains are so 

 peculiarly beneficial. 



3606. Wliere such drains are wanting, the road, on the return of a thaw, throws up to 

 the surface all the water it had imbibed ; and in many places, the materials, swelling up, 

 become quite loose and open. This is a natural consequence, where the material is not 

 thick, and v^^here the soil under the road is not perfectly dry ; but where a road is dried 

 in the way described, it will be uniformly seen, that the water, instead of spewing out on 

 the return of ^ thaw, is sucked in by the drains, so leaving the surface of the road quite 

 dry. It may be observed, that at such times, the places of the road where a few roods 

 of such drain had been introduced, presented to the eye, at a quarter of a mile distant, 

 quite a contrast to the other parts of the road : the one opaque and dry, from the moisture 

 being sucked in ; the other all wet and glistering, ^-om its being thrown out to the surface, 

 (Paterson s Letters, ^fc 44. 48. 84.) 



3607. Thorough drainage, Stevenson observes, " should pervade the whole system of 

 the formation of roads. The smaller drains, connected immediately with the road, must 

 vary in their number, direction, and description, according to the judgment of the 

 engineer. They consist of what are technically termed box and rumbling drains ; the 

 former of which are built, and the latter consist of a stratum of rubble stones, simply 

 thrown into an excavation made for their reception, through which the moisture is 

 allowed to percolate. Where the road is to be made through a boggy or marshy soil, 

 which is generally pretty level, the opportunities for drainage are less obvious; nor 



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