36 
BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 
Table 7. — Mileage of sand-clay roads in several ^representative States for 1909 
and 191^. 
States. 
Sand-clay mileage. 
States. 
Sand-clay mileage. 
1909 
1914 
1909 1914 
None. 
186 
1,107 
561 
1,151 
1,916 
Kansas 
202 
730 
2,254 
758 
Virginia 
North Carolina 
4,313 
3,684 
The construction of sand-clay roads is essentially a matter of em- 
ploying locally available materials to the best practicable advantage 
in producing an improved earth road surface. To do this involves 
an intelligent selection from the local materials and an adaptation of 
the construction method employed to the material selected. These 
two features of the work will be taken up separately in the order 
mentioned. 
SELECTION OF MATERIALS. 
•The questions that ordinarily must be given principal considera- 
tion in the selection of materials for a sand-clay road surface are: 
(1) Is the soil composing the roadbed such that, if local sand or 
clay were admixed with it in proper proportion, a durable road 
surface can be produced? (2) Is topsoil of a suitable character 
available for use as a surfacing material? (3) Can a sufficient quan- 
tity of natural sand-clay subsoil for surfacing the road be obtained 
conveniently? (4) Can the two constituent materials be obtained 
separately and mixed in place on the road? (5) If a variety of 
materials are available, what selection or combination would give 
the best results and prove most economical in the long run? In 
deciding these questions, there are three ways in which the judgment 
may be assisted materially. These are, in the order of their impor- 
tance, by means of service comparisons, field examinations, and labo- 
ratory tests. The questions and the customary manner of deciding 
them will be discussed briefly in the following paragraphs. 
THE SOIL OF THE EOADBED. 
Iii order to determine whether the soil of a given roadbed may 
be incorporated advantageously in a sand-clay road surface, it is 
necessary, of course, to consider the quality of the other local ma- 
terials available for mixing with it, since the fitness of the roadbed 
soil for use in the surface necessarily must be limited by the quality 
of the other constituent material. In general, there are two condi- 
tions where the soil of the roadbed may be used advantageously in 
constructing the surface. One is where the roadbed is very sandy 
and plastic clay is more readily available for use in the surface than 
