FOUNDATION AND COVERING. 291 



It is made of gravel and lime in the proportion of five or six 

 parts of clean gravel to one of lime. The lime is finely ground, 

 the materials thoroughly mixed, and the concrete is made on the 

 surface of the road. 



The depth of the concrete bed when applied is six inches ; 

 upon which a layer of stone or gravel three inches in depth is 

 spread, before the concrete has set. 



Afterward, and before the travel is permitted to go over it, 

 another layer of material is spread, and the whole consolidated 

 by rollers. 



In some instances the concrete foundation has been success- 

 fully tried in cases where no other means were effectual in mak- 

 ing the road solid. 



The method of making a foundation of rough paving intro- 

 duced into England by Mr. Telford has been extensively used in 

 Europe, and to some extent in this country. 



This is formed by laying down broken stone of not more than 

 twelve inches in their greatest dimensions, nearly parallel-sided, 

 and not more than seven or eight inches in depth. 



The stones are laid close together broadest side down with the 

 longest way across the road, and then are wedged together with 

 thinner stones and chips, after which projecting points are broken 

 off with a hammer, and the surface evened by filling the hollows, 

 and crevices with stone-chips. 



Road-coverings based upon foundations of paving, or concrete 

 are so superior, and so much more durable as to justify their use 

 wherever the traffic is large, and the saving in the wear of ma- 

 terial and the labor of repairs will, in time, more than compen- 

 sate for the extra cost of constructing. 



They receive the pressure from loads, transferred by the frag- 

 ments composing the covering, without yielding ; thus checking 

 any tendency to movement amongst them, and prevent their be- 

 ing forced into the soil below, and the soil from working up, and 

 mixing with them. 



With such foundations a less amount of material will be re- 

 quired for the covering, which need not exceed five or six inches 

 in depth, whether made of broken stone or gravel. 



The covering placed upon the earthy surface, with no inter- 

 vening stratum, will need a depth of eight or ten inches, and 



