THE NONMETALLIC MINERALS. 483 



The cost of macadamized roads from necessity varies ajinost indefi- 

 nitely. The primary factors are (1) cost of labor, (2) accessibility of 

 materials, and (3) character of country. From $2,000 to $2,500 a 

 mile is perhaps an average figure for localities where materials are 

 available close at hand. 



The collections are intended to show only the average sizes employed 

 and the varying nature of materials. 



