e. A very good general notion of the
probable durability of gravel can therefore be obtained by a careful
visual examination of the material and classification of the rock
varieties represented by the pebbles.

=Utilizing Natural Gravels.=--Gravel road construction is advantageous
only when it can be accomplished at low first cost. This usually
presupposes a local supply of gravel that can be utilized, or at any
rate a supply that need not be shipped a long distance. In the nature
of things, such deposits are likely to be deficient in some of the
desirable characteristics, and may be deficient in most of them. By
various means, the defects in the materials can be partially corrected
while constructing the road.

If the gravel deposit consists of layers of varying composition as
regards size and clay content, the material may be loosened from the
exposed face and allowed to fall to the bottom of the pit thereby
becoming mixed to a sufficient extent to produce a reasonably uniform
product. If deficient in clay, it often proves feasible to add a small
part of the clay over-burden, thereby insuring enough binder.
Sometimes adjoining deposits will consist one of relatively fine
material, the other of relatively coarse. These may be mixed on the
work by first placing the coarse material in a layer about 5 inches
thick and adding the finer material in a similar layer. The two will
mix very rapidly during the operations of spreading and shaping.

When deposits contain pebbles larger than will pass a 3-1/2-inch ring,
these larger stones will prove to be undesirable if placed on the
road, as they are almost sure to work to the surface of the gravel
layer and become a source of annoyance to the users of the road.
Oversize stone can be removed while loading the gravel or while
spreading it, if care is exercised and not too large a proportion is
oversize. It is preferable however to remove the oversize by means of
screens at the pit. Usually on large jobs the oversize is crushed and
mixed with the supply so as to utilize what is really the best part of
the material.

Gravels deficient in bonding material are often encountered in
deposits where there is insufficient overburden to give enough
additional binder or where the overburden is of a material unsuitable
for binder. Such materials may be utilized by adding binder in the
form of clay after the gravel has been placed on the road.

Almost any gravel deposit can be utilized i