36 IOWA DEPARTMENT OF AGRICULTURE. 



a road firm is to keep it constantly damp. This can be done by planting 

 shade trees along its sides to prevent the evaporation of water, or by 

 growing upon the surface of such sand roads a thick turf, preferably 

 Bermuda grass. Roads running through loose sand may be improved 

 by mixing clay with the sand and slightly crowning the surface. 



For the temporary improvement of earth or sand roads, any strong, 

 fibrous substance, especially if it holds moisture, such as refuse of sugar- 

 cane or sorghum, and even common straw, flax, swamp grass or pine 

 needles will be useful. Spent tan bark is sometimes beneficial and wood 

 fiber in any form is excellent. Enough sand or earth should be thrown 

 over such roads to keep them damp and to protect them from catching 

 fire. 



IMPORTANCE OF ROLLING. 



Earth is composed of small, irregular fragments which touch each 

 other at points, leaving voids between. When the earth is broken up 

 and pulverized these voids are almost equal in volume to the solid par- 

 ticles, and as a result the earth will absorb almost an equal volume of 

 water. In the building or maintaining of earth roads it is, therefore, 

 very desirable that these small, irregular particles be pressed and packed 

 into as small a space as possible, in order that surplus water may not 

 pass in and destroy the stability of the road. To this end rolling is very 

 beneficial. The work of maintaining dirt roads will be much increased 

 by lack of care in properly rolling the surface. (Fig. 17.) 



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aSEM 





Fig. 17.— Section of unrolled earth road showing a loose, soft surface. 



After the material has been placed on the surface, it should not be 

 left for traffic to consolidate or for rains to wash off into the ditches, 

 but should be carefully surfaced and then rolled. If loose earth is left 

 in the middle of a road, the narrow-tire wheels will cut it and knead it 

 into uneven ridges and ruts, which hold water, and this ultimately re- 

 sults, if in the winter season, in a sticky, muddy surface, and in dry 

 weather in covering the surface with dust. If, however, the surface be 

 crowned with a road machine and properly rolled with a heavy roller 

 (Fig. 18), it can usually be made sufficiently firm and smooth (Fig. 19) 

 to sustain the traffic without deep rutting and to resist, in a large meas- 

 ure, the penetrating action of the water. Such work should be done while 

 the soil is in a plastic state, when it will pack. The rolling not only 

 consolidates the small particles of earth and leaves less space ^or water, 



