Page:Popular Science Monthly Volume 46.djvu/507

Rh manner possible. The work is essentially economic, and, owing to its intimate relations to geology, is considered to be directly germane to the work of the survey.

Highways. The geology of highways embraces the study of the materials entering into their construction. It is distinct from the engineering problem of the mechanical construction of highways—a subject that is not intended to be taken up by the survey. The main questions have to do with the choice and manipulation of materials. Experience has shown that many kinds of rocks, which are not suitable for road-building when used alone, may be combined with other materials in such wise as to give good results. It is well known that in many districts great expense has been incurred in building roads on the best known engineering principles of road construction, with the result of producing dusty roads in summer and muddy roads in winter. This outcome is the result of ignorance in regard to the character of the rock necessary for the production of good roads. Inferior materials have sometimes been used when there were other materials in the immediate vicinity which alone or in combination would have produced a solid roadbed. A large part of the country, including the greater portion of the southern States and some portions of the Mississippi basin, has been thought to be essentially destitute of materials suitable for the construction of good roads. The inquiries that have been made by geologists have shown that in many places within these regions there are hidden deposits of gravel and other sorts of rocks which, when properly used, might give excellent highways; and that around the margin of this great area, often within the limits of convenient railway distribution, there are abundant supplies of rock well fitted for such use. It only remains to discover the supply of such rocks as are cheapest and best for each region. This information can be obtained in practical form for each district as the work of the survey advances.

The movement for the betterment of roads and the obtainment of information relating to the materials available for the purpose has not yet taken a national character; but it is believed. that, by establishing a laboratory in connection with the Federal survey, a great impulse may be given to the improvement of highways. Such a laboratory should be arranged to obtain information as to the character of the material best adapted to road construction, tests being made of specimens sent to the survey by the various road commissioners immediately interested, by geologists surveying areal geology, and by public spirited citizens interested in the making of good roads. During the present year the survey is temporarily using a laboratory, under the direction of Prof. N. S. Shaler, at the Harvard