A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

194 IMPROVEMENT OF riIE SURFACE.
A coating of four inches of gravel should be spread
over the road-bed, and vehicles allowed to pass over it
il it becomes tolerably firm, and is nearly, but not entirely, consolidated; men being stationed to continually
rake in the ruts, as fast as they appear. A second coating of 3 or 4 inches should then be added and treated like
the first; and finally a third coating. A very heavy roller
drawn over the road will hasten its consolidation. Wet
weather is the most favorable time for adding new materials.
A very erroneous practice is that of putting the larger
gravel at the bottom, and the smaller at the surface; for,
from the effects of tile frost, and of the vibration of carriages, the larger stones will rise to the surface and the
smaller ones descend, like the materials in a shaken sieve,
and the road will never become firm and smooth.
3. BROKEN-STONE ROADS.
Broken-stone roads have been the subjects of violent
partisanship on many disputed points, and the most important of these questions relates to the propriety or necessity of a paved foundation beneath the coating of broken stones. McAdam warmly denies the advantages of
this, while Telford supports and practises it. Brokenstone roads may therefore be conveniently divided into
McAdam roads and Telford roads.
McADAWM ROADS.
Mr. McAdam, who first brought into general use in
England roads of broken stone, and from whom they derive their popular name, is said* to have deduced the
* Millington, p. 234.