sieve should be one and one-half or two inches in diameter, while the
meshes of the other should be three-fourths of an inch. All pebbles
which will not go through the one and one-half inch meshes should be
rejected or broken so that they will go through. All material which
sifts through the three-fourths inch meshes should be rejected for the
road, but may be used in making side paths. The excellent road which can
be built from materials prepared in this way is so far superior to the
one made of the natural clayey material that the expense and trouble of
sifting is many times repaid.

The best gravel for road-building stands perpendicular in the bank; that
is, when the pit has been opened up the remainder stands compact and
firm and cannot be dislodged except by use of the pick, and when it
gives way falls in great chunks or solid masses. Such material usually
contains tough angular gravel with just enough cementing properties to
enable it to readily pack and consolidate, and requires no further
treatment than to place it properly on the prepared roadbed.

Some earth roads may be greatly improved by covering the surface with a
layer of three or four inches of gravel, and sometimes even a thinner
layer may prove of very great benefit if kept in proper repair. The
subsoil of such roadway ought, however, to be well drained, or of a
light and porous nature. Roads constructed over clay soils require a
layer of at least six inches of gravel. The gravel must be deep enough
to prevent the weight of traffic forcing the surface material into weak
places in the clay beneath, and also to prevent the surface water from
percolating through and softening the clay and causing the whole roadway
to be torn up.

Owing to a lack of knowledge regarding construction, indifference, or
carelessness in building or improving, roads made of gravel are often
very much worse than they ought to be. Some of them are made by simply
dumping the material into ruts, mud holes, or gutter-like depressions,
or on unimproved foundation, and are left thus for traffic to
consolidate, while others are made by covering the surface with inferior
material without any attention being paid to the fundamental principles
of drainage. As a result of such thoughtless and haphazard methods the
road usually becomes rougher and more completely covered with holes than
before.

In constructing a gravel road the roadbed should first be brought to the
proper grade. Ordina