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 ...

200 IMPROVEMENT OF THE SURFACE
ken are placed, resting only on their ends, so that, being
struck sharply in their middle, they break into angular
fragments. Children with smaller hammers can do the
lighter work, so that a whole family may be employed.
The workmen should not be paid by the day, but at an
equitable price per cubic yard. A medium laborer can
break in a day from 1 to 2 yards ef gneiss; but only'
to 3 yard of hard boulders, or " cobble-stones.'
THICKNESS OF THE C^.ATIN^.
Twelve inches of well consolidated, materials on a good
bottom, will be sufficient for roads of the greatest travel,
and will resist all usual weights, and frosts. In the climate of France, ten inches is considered enough for the
most frequented roads, and six or eight inches for others.
The thickness should vary with the soil, the nature of the
materials, and the character of the travel over it; it should
be such that the greatest load will not affect more than
the surface of the shell; and it is for this purpose chiefly
that thickness is required, in order that the weight whicb
comes on a small part only of the road may be spread
over a large portion of the foundation. The severe frosts
of our northern states require the maximum of depth.*
McAdam advocates less thickness than the other English constructors. He considers from 7 to 10 inches sufficient, calling the latter depth of " well consolidated materials equal to carry any thing." He adds, "some new
roads of six inches in depth were not at all affected by a
very severe winter; and another road having been allowed
* Stone broken into fragments of from 1 to 6 inches occupies twice
as much space as in the original solid state; but the broken stone placed
upon the road is reduced by the pressure of the wheels to two thirds
of its former bulk, or more exactly seven-tenths.