Earth Roads. 459 



gravel is too coarse, to run it through the crusher so as to re- 

 duce the material to a more uniform si/e and at the same 

 time to increase the angularity of the fragments will make 

 a much better road material to use either by itself, or 

 tempering material. 



FTG. 216. Champion rock crusher and screen. 



572. Some Gravels Contain Too Much Clay. There are 



many deposits of gravelly clay which it might appear would 

 make a good road material, but the principle must be kept 

 always in mind that too much of a too fine material will 

 take in and retain so much water that the binding quality 

 of the water is lost. These gravelly clays occur in many 

 of the hills of the glaciated portions of the United States 

 and through which roads are often cut. 



573. Gravel Roads. In the construction of a gravel road, 

 as in that of a stone road, it is of prime importance to se~ 

 cure first of all a properly shaped and thoroughly rolled 

 and firmed road-bed before any gravel is laid on. When 

 this has been done, and a suitable gravel has been found, 

 the next step is to spread evenly over the surface and thor- 

 oughly roll a layer which, when finished, will measure three 

 inches thick. 



