ROADS AND PATHS 37 



fresh gravel or broken stone that has been properly 

 screened or otherwise prepared. 



Graveled roads have been found to be well suited for 

 country places, although they are not generally as reli- 

 able at all seasons as those made of broken stone and 

 screenings. The clay that is necessarily left in the 

 gravel for the purpose of binding it will always tend, in 

 certain seasons, under the wheels of carriages, to grind 

 into mud. It is difficult, often, to secure just the right 

 kind of gravel for road-making, for clean material con- 

 sisting of round pebbles will not pack, because a certain 

 admixture of clay and some angularity of the stones are 

 necessary to secure a proper bond. It has been found 

 that seaside and riverside gravels are too clean, and 

 ordinary pit gravel is too dirty or clayey. 



By using two wire screens of the proper size we can 

 secure with many pit products what has been found to be 

 the best kind of gravel; namely, a moderately clean 

 article containing no stone less than half an inch in dia- 

 meter and none more than an inch and a half. This is 

 done by placing one screen above the other, the lower 

 one allowing everything smaller than half an inch to pass 

 through and the upper one retaining everything over an 

 inch and a half. It is no objection, and rather an advan- 

 tage to the screened gravel, that considerable clay is 

 sure to adhere to the stones, for on the presence of this 

 clay depends the capacity of the material to properly 

 bind together. Much skill is required to secure just the 

 right admixture of this clay in order to prevent as much 

 as possible both mud and dust. 



On ordinary soil, an excavation to the depth of ten or 

 twelve inches will suffice to make a gravel road, and you 

 may, in dry ground, where the travel is light, construct 



