250 Huntington — Road-Making Materials. 
they will be used in the construction of thousands of miles of 
roadway within the next half century. Under such circum 
stances it is well worth while to investigate the most econom¬ 
ical and efficient ways of using the materials at hand. With 
this end in view a series of experiments was begun last fall in 
the laboratories of Beloit College, the results of which, as far 
as they have proceeded, are given below. 
Experience has shown that almost all limestones are too soft 
to make good or economical roads. Although they cement readily 
they quickly wear away producing a disagreeable mud and dust 
and costing a great deal to keep in repair. The glacial drift, on 
the contrary, consists in considerable degree of pebbles which 
are much harder than ordinary limestone but do not ce¬ 
ment readily. This hardness is due to the fact that in the 
process of glaciation the soft parts of any rock are ground to 
powder and only the hardest parts are left as pebbles. In most 
rocks the hardest parts are those which contain the most quartz, 
and in the case of limestone the pebbles which remain in the 
drift contain a great deal of infiltrated silica. While quartz 
gives hardness to a stone, it is a very poor cementing material. 
If we can find some way of firmly cementing the drift we shall be 
able to construct good and cheap roads. In the experiments car¬ 
ried on at Beloit a few tests were made with Trenton limestone, 
but in most cases the drift was the basis of work. The pebbles 
were crushed in the way usually recognized^as best for macadam 
roads, namely into fragments of various sizes, the largest not 
to exceed one and one-half inches in diameter, and the very fine 
material screened off. From six to ten pounds of the crushed 
gravel was taken and to this was added a cement of powdered 
rock sufficient to firmly bind the mass of gravel. The cement 
consisted of several kinds of stone or of mixtures of the various 
kinds. After the crushed pebbles and the fine material were put 
together in a box and thoroughly mixed, the whole mass was 
wet down and pounded and rolled and then allowed to dry. This 
process was repeated several times until the whole became one 
solid mass. When this was thoroughly dry it was broken to 
pieces by allowing to fall upon it a weight so shaped as to give 
a blow as nearly as possible like that of a horse’s hoof. In this 
