to a bearing by passing the unballasted
road roller a number of times over every portion of the surface of the
section.

In level countries and with narrow roads, enough material may be
excavated to raise the roadway above the subgrade in forming the side
ditches by means of road machines. If not, the required earth should be
obtained by widening the side excavations, or from cuttings on the line
of the new roadway, or from pits close by, elevating graders and modern
dumping or spreading wagons being preferably used for this purpose. When
the earth is brought up to the final height, it is again harrowed, then
trimmed by means of road levelers or road machines and ultimately rolled
to a solid and smooth surface with road rollers gradually increased in
weight by the addition of ballast.

No filling should be brought up in layers exceeding nine inches in
depth. During the rolling, sprinkling should be attended to wherever the
character of the soil requires such aid. The cross section of the
roadway must be maintained during the last rolling stage by the addition
of earth as needed. On clay soils a layer of sand, gravel, or ashes
spread on the roadway will prevent the sticking of the clay to the
roller. As previously explained, the finishing touches to the road
surface should be given by a heavy roller.

Before the earth road is opened to traffic, deep and wide side ditches
should be constructed, with a fall throughout their entire length of at
least one in one hundred and twenty. They should be cleaned and left
with the drain tiling connections, if any, in good working order.

Clay soils, as a rule, absorb water quite freely and soften when
saturated, but water does not readily pass through them; hence they are
not easily subdrained. When used alone, clay is the least desirable of
all road materials, but roads constructed over clay soils may be treated
with sand or small gravel, from which a comparatively hard and compact
mass is formed which is nearly impervious to water. Material of this
character found in the natural state, commonly known as hardpan, makes,
when properly applied, a very solid and durable surface. In soil
composed of a mixture of sand, gravel, and clay, all that is necessary
to make a good road of its kind is to "crown" the surface, keep the ruts
and hollows filled, and the ditches open and free.

[Illustration: Sand Clay Road in Richland County, South Carolina

[_Sand soil with nine inches of cla