curing suitable foundations for
the broken stone road are largely eliminated, but it may be observed
that this type of surface is not suitable for such climates unless
some sort of bituminous binder is employed to hold the stones in
place. The cementing power of the stone dust is inadequate when the
surface is continually dry.

[Illustration: Fig. 17.--Cross Section for Macadam]

=Telford Foundation.=--When the Telford type of foundation is
employed, the earth subgrade is prepared and then the Telford stone
placed carefully by hand. The spaces between the large stones are
filled with the spalls broken from the larger stones in fitting them
in place. When completed the base is rolled with a heavy roller to
secure a firm unyielding layer. The thickness is generally about eight
inches. Any fairly sound stone may be used for the Telford base.

=Placing the Broken Stone.=--It has been found impracticable properly
to roll a greater thickness than about 5 or 6 inches of loose stone,
therefore, the stone for the macadam surface is usually placed in two
layers, the first or lower layer being rolled before the next layer is
placed. The stone is hauled in dump wagons, trucks or dump cars,
dumped on the road bed and spread by hand rakes or by means of a blade
grader and is then rolled. To insure the proper thickness the loads
are accurately spaced to spread to the proper thickness.

=Rolling.=--A three-wheeled or "macadam" type of roller, of the
self-propelled type, is best for compacting the broken stone road. The
weight varies from eight to fifteen tons, but for most conditions the
ten or twelve ton size seems to be preferable. On Telford base
construction, a heavier machine is desirable and for very hard stone
it may be successfully employed.

The first trip with the roller is made along the edge of the stone and
each successive trip is made a little nearer the middle until finally
one half of the strip of stone has been rolled. The roller is then
taken to the opposite side of the roadway and the operation repeated
on the other half. The rolling is continued until the stone is
thoroughly compacted, which is evidenced by the fact that the roller
makes but a slight track in the surface.

The second layer of stone is then placed and rolled in the same manner
as the first.

=Spreading Screenings.=--After the upper course has been rolled, the
screenings are spread on it from piles alongside the road, enough
being used to fil