SCREENING GRAVEL I 55 



the traveled way. The gravel mixes with the material stirred 

 up by the machine, and together tliey consolidate into a fairly 

 smooth road surface. A second graveling the next year, 

 when the ground is soft in the spring, or later, if rains are 

 abundant, will produce a very excellent road, and tiiereafter, 

 if the first use of the machine has been thorough, there will be 

 no further need of its employment, as a little gravel, applied 

 every few years as needed, will keep a first-class surface. In 

 following numerous such examples, I have noted a verv gen- 

 eral practice of employing too fine a material. If the ground 

 is soft and the soil heavy, the sand will mix with the natural 

 earth and improve the surface, though not as much so as if a 

 coarser gravel were used. It becomes, in such case, merely a 

 question of comparative cost of the two materials. It should 

 be remembered, however, that if sand is used it must be put 

 on in small quantities at a time, and the greater necessity 

 exists of having it consolidated early in the spring. With an 

 average New England condition as to rain-fall, a coarser 

 gravel may be easily consolidated without sensible waste at 

 almost any season. With sand, however, especially on a 

 grade, a considerable portion will be found in the side ditches 

 unless almost immediately consolidated with the natural earth 

 beneath, and this can only be accomplished when such earth 

 is reasonably soft, as in the spring. If there is no washing 

 away of the sandy material, and no heavier soil with which it 

 may form a mixture, it will make a loose, sandy road, very 

 disagreeable for travel, and requiring nearly the maximum of 

 animal force to accomplish a given amount of work. 



It is often advisable to haul upon a road a layer of clay or 

 hardpan before the gravel is put on. Nothing short of a 

 pavement, not even a macadamized surface, will withstand 

 the washing of heavy rains upon a steep grade better than a 

 properly compacted combination of clay and gravel. 



SCREENING GRAVEL 



Early in the above experiments it was seen that the ques- 

 tion of a uniform size of product for each layer of surfacing 

 material would be an important one, and when in the fall of 

 1898 an opportunity offered to experiment with screened 



