EARTH, SAND-CLAY, AND GRAVEL ROADS. 35 
which are constructed of such soil, and it happens occasionally that 
for a considerable distance along a road the soil contains just the 
proper proportions of sand and clay to produce an excellent road 
surface for moderate traffic under all weather conditions to which the 
road is subjected. But, in general, such soils occur only for limited 
distances, and to secure a continuous surface of this kind, the neces- 
sary material must be hauled to the road, spread, and compacted 
after the grading is completed otherwise. More generally, perhaps, 
the soil composing the roadbed is deficient in only one of the neces- 
sary constituents, sand or clay, and it frequently may be economical 
to construct the surface by supplying the necessary sand or clay 
and mixing it with the natural soil of the roadbed, rather than to pro- 
A T ide a surface of natural sand-clay material. It may happen, also, 
that the roadbed contains no material suitable for use in constructing 
the surface, and that sand and clay are more readily available sepa- 
rately than ready mixed. In such case both materials may be hauled 
to the road and mixed in place to form the surface. 
In order to distinguish between common earth roads, which are 
constructed wholly of the natural soil as it occurs along the road, and 
those which have been surfaced with especially selected or especially 
prepared earth which contains sand and clay mixed in such propor- 
tions as to increase the resistance to wear of the surface as described 
above, the latter are designated sand-clay roads. This designation 
evidently includes most of the so-called " topsoil " roads, because 
topsoil which is especially suited for use in road surfaces generally 
possesses that quality by virtue of the sand and clay which it 
contains. 
The sand-clay method of construction has produced its best results 
in the Southern States, where deep freezing is not a serious factor 
and where materials suitable for such construction probably are more 
widely distributed than in any other section of the country. There 
are many sand-clay roads in the South Atlantic and Gulf States 
over which heavy loads of cotton and other farm products are hauled 
throughout the year and which remain continuously in good condi- 
tion with a comparatively very small outlay for maintenance. And 
there are innumerable cases where sand-clay surfaces, constructed 
of even rather inferior materials, have so improved intolerable 
stretches of sandy or muddy road as to provide for at least fairly 
comfortable travel throughout the year. Examples of the latter 
kind are by no means peculiar to the Southern States, but are to 
be found in nearly every section of the country. Table 7 shows the 
mileage of sand-clay roads in several representative States for 1909 
and 1914, respectively, and illustrates how the popularity of this 
type of construction is increasing. 
