Page:Historic highways of America (Volume 15).djvu/153

 thicker the crust the more uniformly will the load be distributed over the foundation.

Macadam earnestly advocated the principle that all artificial road-building depended wholly for its success upon the making and maintaining of a solid dry foundation and the covering of this foundation with a durable waterproof coating or roof of broken stone. The foundation must be solid and firm; if it be otherwise the crust is useless. A road builder should always remember that without a durable foundation there is no durable road. Hundreds of miles of macadam roads are built in the United States each year on unimproved or unstable foundations and almost as many miles go to pieces for this same reason. Says Macadam:

"The stone is employed to form a secure, smooth, water-tight flooring, over which vehicles may pass with safety and expedition at all seasons of the year. Its thickness should be regulated only by the quality of the material necessary to form such a flooring and not at all by any consideration as to its own independent power