158 EXPERIMENTS IN ROAD SURFACING 



A gravel road is one surfaced with material containing a 

 large per cent, of rock, not usually sorted as to size, and a 

 certain per cent, of earth which may be sand, clay, hardpan, 

 or a mixture of two or more of these. 



An earth road is one surfaced with a large per cent, of 

 earth, which may be sand, clay, hardpan, loam, or a mixture 

 of some of these. A very common idea of an earth road is 

 one surfaced with the natural material where the road is built. 

 This description, though gent-rally characteristic, does not 

 give the true distinction between these and gravel ones and 

 may convey an entirely wrong impression. The true dis- 

 tinction lies in the predominance of earth over rock or the 

 reverse in the surfacing material. Again, it will be seen that 

 the gravel road is intermediate between the earth and the mac- 

 adam and that there is no absolute line separating the earth 

 from the gravel or the gravel from the macadam. The latter 

 statement will appear evident if we consider that it makes no 

 difference whether the stone for a macadam road has been pre- 

 pared by a stone crusher or broken by the processes of nature 

 and deposited in gravel banks during the glacial epoch. 



Having defined the standard kinds of road surface we can 

 now profitably discuss the advantages and disadvantages of each. 

 We will assume that proper grades and suitable drainage have 

 been provided and that all surfaces are in a fair condition ot 

 repair. The macadam road is hard and fairly smooth. It 

 will be very smooth when new but is apt to wear rough 

 under average treatn'jent. It is dry during the spring months 

 and will stand up under heavy, though not the heaviest, traffic. 

 For the latter nothing but a pavement will suffice. On the 

 other hand the macadam surface is disagreeably dusty and 

 liable to ravel during dry weather ; is hard on horses' feet and 

 is expensive to construct and maintain. 



The earth road, under favorable conditions of moisture and 

 repair, is the smoothest, most elastic, and most pleasant for 

 pleasure driving of any in existence. It is safest for horses' 

 feet and, where the natural soil is favorable, is by far the 

 cheapest both as regards construction and repair. On the other 

 hand, if it is an ideal summer road, it is reasonably sure to be 

 muddy and rough for perhaps two months in the spring as 



