152 EXPERIIMENTS IN ROAD SURFACING 



material were its water-worn, rounded surfaces and its lack of 

 homogeneousness because of the presence of a considerable 

 per cent, of softer rock made more or less rotten by being 

 imbedded in the gravel bank for ages. The top layer was 

 composed of sand with a small admixture of clay to make a 

 better binder. The immediate success in securing- a orood 

 hard surface was surprising as well as gratifying. 



Section 15 before surfacing was the muddiest at certain 

 seasons of all, and its treatment was arranged accordingly. 

 About four inches' depth of angular stone, picked up by the 

 roadside, was spread uniformly and then covered with six 

 inches of reservoir gravel. The section has never been muddy 

 since its treatment. 



All of the above described materials were in use in the 

 town for road surfacing, and they were got together in adja- 

 cent plots in order to obtain comparative results. After the 

 work was completed the surface of all the sections was uni- 

 form from top to bottom of hill, except that section 8, with 

 its 9 inches in depth of surfacing material, projected above 

 the general level, and section 14, with nothing, was depressed 

 below. 



Next to No. 15, sections 7, 8, and 9 possessed the most 

 treacherous subsoil, viz. : a clay not underlaid with stone. 

 The lower half of the road treated possessed a flatter cross 

 section than the other, which was one reason why the sur- 

 faced portion was widened here. 



RESULTS AFTER TWO YEARS 



The most striking feature to a person riding over the road 

 at this writing is the existence of depressions over sections 

 6a, 6b, 8a, 11, and 14, of 4 inches, 4 inches, 3 inches, 4 

 inches, and 6 inclies respectively. The depression over No. 

 14 of 6 inches was to be expected. The increase of the 

 depression from 4 inches to 6 inches illustrates the tendency 

 of depressions once started to increase under traflic. The 

 remaining four are the only instances among the whole seven- 

 teen plots where fine gravel or coarse sand was used for sur- 

 facing, and show conclusively that sand, even if mixed with a 

 clayey earth, does not stand up with rock. In short, it lacks 



