ness
generally predominate. Intermixed with the pieces of rock there is
likely to be clay or other soil, the quantity varying greatly in
different deposits and even in various places in the same deposits.

Often there are found deposits of material which are by the layman
termed gravel, which are really clayey sand or sand containing a few
pebbles, but which are of value to the road builder for the sand clay
type of surfacing. The term gravel is exceedingly general and unless
specifically defined, gives little indication of the exact nature of
to which it is applied.

TABLE 7

SHOWING CEMENTING PROPERTIES OF SEVERAL SAMPLES OF
GRAVEL

-----------------+----------------------------
| Cementing Value
Per Cent Clay by +---------------+------------
Weight | As Received | Washed
-----------------+---------------+------------
4.4 | 276 | 43
6.4 | 105 | 285
5.1 | 241 | 70
14.5 | 500 | 279
8.5 | 500 | 112
10.1 | 300 | 267
14.8 | 500 | 107
7.5 | 184 | 198
16.5 | 500 | 428
2.0 | 185 | 239
1.5 | 500 | 500
4.5 | 212 | 204
2.5 | 116 | 363
-----------------+---------------+------------

The value of any gravel for road surfacing depends upon the degree to
which it possesses the properties of an ideal gravel for road
surfacing. Ideal gravel is seldom encountered, but a consideration of
its characteristics serves to establish a measure by which to estimate
the probable value of any deposit.

=The Ideal Road Gravel.=--The ideal road gravel is a mixture of
pebbles, sand and earthy material, the pieces varying from coarse to
fine in such a manner that when the gravel is compacted into a road
surface the spaces between the larger pebbles are filled with the
finer material. The pebbles are of a variety of rock that is highly
resistant to wear so that the road surface made from the gravel will
have the quality of durability. The gravel possesses good cementing
properties, insuring that the pieces will hold together in the road
surface. The cementing property may be due to the rock powder in the
deposit or