on Sandy Roads.=--Sand-clay surfaces may be
constructed on naturally sandy roads either by adding clay and mixing
it with the sand to secure the desired composition, or a layer of a
natural sand-clay mixture, caliche or sand-clay-gypsum may be placed
on top of the sand.

The most widely used method is to mix clay or other binder with the
sand. Since there is no need to provide for ditches to carry storm
water on a deep sand soil, the sand is graded off nearly flat across
the road and no ditches are provided. The clay is dumped on the road
in a layer about 8 inches thick and is then mixed into the sand. It is
desired to mix enough sand with the clay to produce a mixture composed
of approximately 1/3 clay and 2/3 sand. The mixing is accomplished in
various ways, the most common being to use a heavy plow at first and
to follow this with a heavy disc harrow. The mixing is a tedious and
disagreeable process, but its thorough accomplishment is
indispensable. The mixing is most readily done when the materials are
saturated with water and in practice it is customary to depend upon
rain for the water, although in the final stages water may be hauled
and sprinkled on the road to facilitate final completion of the
mixing. After the mixing has been completed, the surface is smoothed
with the blade grader and is kept smooth until it dries out. Repeated
dragging will be required, during the first year especially, and to
some extent each year in order to keep the surface smooth, but the
dragging can be successfully accomplished only when the road is wet.

[Illustration: Fig. 14.--Cross Sections for Sand-Clay Roads]

In regions where several months of continued hot, dry weather is to be
expected each year, the sand-clay mixture is likely to break through
unless it is of considerable thickness and generally the surface layer
is made much thicker than for regions where the annual rainfall is
fairly well distributed. This is especially necessary when the binder
is of inferior quality. It is not uncommon in such cases to make the
sand-clay surface as much as two feet thick.

As the mixing progresses it may appear that patches here and there are
deficient in either clay or sand and the mixture in these places is
corrected by the addition of a little sand or clay as may be
required.

If the top-soil is used it is deposited on the sand in the required
quantity and is remixed in place to insure uniformity. If either sand
or clay is neede