MATERIALS OP A ROAD-BED. 271 



Road-Bed. 



Quite equal in importance to the grade is the surface to be 

 driven over. 



Theoretically this should be unyielding, smooth, and impervi- 

 ous to water. It should be a roof, shedding the water each way 

 from the centre, from eighteen to twenty feet wide, except in or 

 near villages, where it may be thirty feet, or even fifty. An ele- 

 vation of six inches at the centre is required, and the lateral 

 slopes should be planes^ rather than curves as is usual, that the 

 water may be carried off more quickly. We mean by the " road- 

 bed " simply the drive-way, and this should be as narrow as per- 

 fect safety and convenience will permit, on the score of economy, 

 both of construction and maintenance. Bars across the road 

 for turning the water into the ditches are only necessary on the 

 heavy grades of inferior surface, or of such roads as are not 

 kept in good repair ; and when needed, should be built V shape, 

 with the angle up the grade, if practicable, that they may strike 

 both wheels at once. An exception to this rule would occur 

 when it is desirable to turn all the surface water to one side ; 

 and in that case the slope of the surface would fall one foot in 

 the width of road-bed to the same side. Such a shape of road- 

 bed is desirable in very short turns, as in zigzag roads up steep 

 mountains, and around sharp angles of hills, where the width 

 of driving surface should be a few feet greater, and the slope 

 inward. 



The materials of the road-bed must be the best that can be 

 afforded to approximate as nearly as possible to the true theory 

 of a perfect road surface. 



The importance of this is evident from the facts established 

 by experiments, that from two to three times as much can be 

 hauled on a broken stone road as on one of gravel, both being 

 in equally good order ; and from four to five times as much upon 

 a good pavement of rectangular blocks of stone. 



The broken stone road, and the block pavement, have been so 

 long in use, both in this country and in Europe, and in fact 

 throughout the civilized world, and their modes of construction 

 and repair so fully discussed in treatises on road making, even 

 to the minutest details, that it would be superfluous to dwell 

 upon the subject here. It may be remarked however that the 

 Nicolson pavement of wood, or its essential principle which 



