ROAD MODELS. 13 
Section I> shows the first course 4 of gravel spread and rolled to a 
thickness of about 1 inches at the center and 3 inches at the sides. 
Section C represents the finished road after the second course of 
gravel has been spread and compacted. The second course when 
compacted is 2 inches in thickness at the center and 1 \ inches at the 
sides. 
Many gravels as found in nature are not suitable for use on t In- 
road, unless modified by the addition or elimination of certain ma- 
terials. The products of some pits are deficient in bonding materials, 
such as sand or clay, and at the same time may have an excess 
of large pebbles. In general, the gravel should be screened and the 
graded material laid in courses according to the manner of macadam 
road construction. 
MACADAM ROADS. 
WATER-BOUND MACADAM ROADS. 
Plate VII, figure 1, illustrates the construction of a water-bound 
macadam road 16 feet wide, 6 inches thick at the center, and 4 inches 
thick at the sides when rolled. The crown of the finished road as 
shown is one-half inch to the foot. The road is graded for a width of 
33 feet. 
Section A represents the prepared subgrade properly crowned and 
rolled; section B, the first course of broken stone, 4 inches thick 
compacted; section C, the second course, 2 inches thick compacted; 
and section D, the finished road. 
In preparing for the construction of a road of this type, the pro- 
cedure given on page 7, for foundation, or subgrade, and shoulders, 
should be followed. After the subgrade has been prepared, a layer 
of broken stone of approved size and quality for the first or bottom 
course should he spread evenly over it to such depth that it shall 
have, when rolled, the required thickness. The depth of the loose 
stone may be gauged by laying upon the subgrade cubical blocks of 
wood of the proper size, and spreading the stone evenly to conform 
to them. 
The roller should be run along the edge of the stone backward and 
forward several times on each side of the road before rolling the 
center. If a filler is desired for the bottom course it should be clean, 
coarse sand, or stone screenings supplemented by the product of the 
crusher not otherwise used in top or bottom courses. It should be 
spread uniformly over the surface and then swept in and rolled dry. 
This process must be continued until no more will go in dry, when 
the surface should be sprinkled to more effectually fill the voids. Any 
irregularities or depressions may he made good with broken stone of 
the size used in the bottom course, and screenings or filler should not 
be used for this purpose. 
