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broken-stone road-coverings, except in cases of a very 

 heavy traffic, or where the Substratum of the road is of a 

 very yielding character. They also give less thickness to 

 the road-covering than the English engineers of Telford's 

 school deem necessary ; allowing not more than six to 

 eight inches to road-coverings for light traffic, and about 

 ten inches only to the heaviest traffic. 



"If the soil upon which the road-covering is to be 

 placed is not dry and firm, they compress it by rolling, 

 which is done by passing over it several times an iron 

 cylinder about six feet in diameter and four feet in 

 length, the weight of which can be increased, by addi- 

 tional weights, from six thousand to about twenty thou- 

 sand pounds. The road material is placed upon the bed, 

 when well compressed and leveled, in layers of about 

 four inches, each layer being compressed by passing the 

 cylinder several times over it before a new one is laid on. 

 If the operation of rolling is performed in dry weather, 

 the layer of stone is watered, and some add a thin layer of 

 clean sand, from four to eight tenths of an inch in thick- 

 ness, over each layer before it is rolled, for the purpose 

 of consolidating the surface of the layer, by filling the 

 voids between the broken-stone fragments. After the 

 surface has been well consolidated by rolling, the road 

 is thrown open for travel, and all ruts and other dis- 

 placement of the stone on the surface are carefully 

 repaired, by adding fresh material, and leveling the 

 ridges by ramming. 



"Great importance is attached by the French en- 

 gineers to the use of the iron cylinder for compressing 

 the materials of a new road, and to minute attention to 



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