462 Farm Mechanics. 



causeways outside of which, on each side, were unpaved 

 side-ways each eight feet wide, and the paved way some- 

 times had an aggregate thickness of three feet. 



575. Macadam Roads. The use of crushed rock in road 

 building is at least as old as Roman history ; but as, during 

 the dark ages, little road building of a permanent character 

 was practiced, the art had to be revived in modern times 

 and about 1764 the French engineer Tresaguet appears to 

 have introduced into France the type of road represented in 

 Fig. 218, consisting of a stone pavement covered with two 

 or three inches of crushed rock as a facing material. After 

 being introduced into England and Scotland, where the de- 

 tails were modified and perfected by Telford about 1820, 

 this type of stone construction came to be known as the 

 Telford road. 



FIG. 218. Type of road introduced into France by Tresaguet about 1764. 

 (After Shaler.) 



Macadam's work began somewhat earlier than Telford's 

 in 1816, and to him apparently is due the idea that when 

 any road-bed is thoroughly under- drained, so as to remain 

 permanently hard, then crushed stone alone may be used, 

 the pavement of Roman practice becoming unnecessary. 



576. Construction of Macadam Roads. After the founda- 

 tion for the stone road has been completed the border is 

 left with a shoulder of earth on each side as represented in 

 Fig. 219, between which the road-bed is covered with a 

 layer of crushed rock as nearly one size as possible and 

 three or four inches thick. This layer is next thoroughly 

 rolled and then covered with enough of finely crushed rock 

 to fill the voids between the larger fragments. This ma- 

 terial is worked in with the roller and water until a solid 

 bed has been formed. 



