468 



Farm Mechanics. 



and the readiness with which it may often be obtained, 

 leads to its occasional use as a binding material in macadam 

 road. The coarse silicious sands, however, have very little 

 cementing quality, they do not retain water well enough 

 cither to make the road shed the rains nor give the surface 

 tension of water much opportunity to bind the grains to- 



PIG. 221. View showing the binding material or screenings being applied to the 

 foundation layer of crushed rock . 



gether firmly; consequently the best results cannot be se- 

 cured when it is used. 



If loam is used there is danger that it will pack in the 

 upper surface of the layer of stone and prevent even the 

 combined use of water and the roller from working it to 



