Practical Road Building

in character all the way from a sand-clay road to a road of cementitious gravel. The top soil which is used for road purposes is composed principally of sand, gravel, clay, and a small proportion of silt, with some decayed vegetable matter included. In the sections where this top soil is found in a proper mixture for road purposes the subgrade is usually of sand or gravel; or, if there are spots where the sand or gravel does not appear, there are gravel pits near enough to make a sand-gravel subgrade by a short haul of the material. It is held by those who have given the top-soil road the most careful study that under favorable conditions it is the cheapest and yet the most durable and satisfactory road that can be built. The top-soil road has reached its highest development, apparently, in the state of Georgia, though many miles have been built elsewhere. Reports fromthe work in that state are fragmentary by reason of the fact that Georgia has no state highway organization, the only practical information obtainable being through personal investigation by the author, and occasional scientific addresses or reports on the subject by members of the faculty of the University of Georgia. Practical experience has shown that while the sand- clay road, described in Chapter XII, requires a careful selection of sand and clay for its success, the top-soil road may be successful with a wider range of materials, amounting at times almost to a reversal of the principle...