DUST PREVENTION AND ROAD PRESERVATION, 1914, 13 
One purpose of this experiment was to provide a basis of compari- 
son between the various bituminous treatments and a well-constructed 
coralline-rock road. Another and more important one was to demon- 
strate, if possible, that the principal defect in the existing roads, 
the rapid development of an uneven surface, could be overcome by 
proper methods of construction. By the method here used a surface 
of uniform strength is secured by reason of the uniform strength of 
the subgrade and the uniform depth and consistency of the screened- 
rock course. Such uniformity can be obtained in no other way, 
apparently, than by screening the rock and following the general 
method of construction used in this experiment. 
In the cost data, which follow, the cost of bituminous materials 
was taken from bid prices for carload lots. 
