326 



FARM DEVELOPMENT 



travel. If the mixed soil contains considerable clay, 

 coarse gravel mixed in it will improve the body of the 

 crust of the roadbed, and if on top of this is placed some 

 fine hard gravel, a fairly good road will result. If the 

 surface is composed largely of fine clay with very little 

 sand or gravel entering into its composition, a still larger 



Figure 211. Grading subst rupture for a Figure 212. First course of stone on a 

 macadam surface, with shoulders against macadam road as it appears when spread 

 which the rock rests. ready for rolling. 



amount of gravel will be necessary to give the solidity 

 or carrying strength required by the road surface. 



If, on the other hand, the surface of the grade is com- 

 posed of sand, it will often be best to use gravel, or 

 gravel into which a small amount of clay is mixed, or 

 clay alone may be mixed with the sand. Sand really 



-C 



Figure 213. Three courses of a macadam 

 surface, 8 to 12 inches deep. 



Figure 214. Section of macadam 

 3urface. A, 2 to 3-inch rock; B, 1 

 to 2-inch sizes; C, fine rock and dust. 



makes a better substructure than clay, because any water 

 that penetrates the surface can easily percolate down- 

 ward, leaving the roadway dry. 



Where gravel, sand, clay, ashes, shells or other sim- 

 ilar materials are hauled from a distance, much ex- 

 pense can often be saved by using only that amount 

 which, when mixed with the earth already on the road, 



