FOUNDATION AND TOP SURFACE. 221 



road-making, which consists in giving every road two component 

 parts ; one, — the foundation, — to be solid, unyielding, porous, 

 and of large material ; the other — the top surface — to be made 

 up of lighter material, and to be made to bind compactly and 

 evenly over the rough foundation. This constitutes the whole 

 principle to be followed ; and let it be repeated, that to dump 

 the road material directly on the ground, without first prepar- 

 ing a foundation for it, as is so frequently done, is a waste of 

 time, labor and materials, by no possibility resulting in a good 

 road. On this one fundamental idea, which is never abandoned, 

 however, there are a number of variations. Besides these 

 roads, whose characteristic is the foundation they are all built 

 on, we have paved roads, or pavements, of a great many kinds, 

 and roads with trackways, also of various kinds. 



Foundation Roads. 



The roads of this kind, with macadam for the top surface, 

 are called Telford roads by English writers, from Telford, who 

 first built them in England. The Central Park " gravel roads " 

 belong under this head, gravel taking the place of the macadam 

 of the Telford roads. These foundation roads are of far greater 

 importance than any other kind for State, county or town roads, 

 also for parks and driveways. The top surface of all these 

 roads must have a certain inclination, to cause efficient surface 

 drainage. Various authorities give various rules for the 

 amount of this inclination or side-slope. It would seem just 

 that it should depend on the nature of the top covering, being 

 less for more solid than for looser or softer materials, and also 

 on the grade of the road. 



In Baden, one of the smaller German States, but which is 

 worthy to be taken as a model in matters of road-building, and 

 in France, the rise at the centre is given as ^q-^q of the width 

 of the road, according to the nature of the material; that is, 

 inclinations of 1 in 20, and 1 in 30. The rules in Prussia pre- 

 scribe inclinations of 1 in 24 for roads falling more than 4 in a 

 hundred ; 1 in 18 for roads on a grade of between 2 and 4 in a 

 hundred ; and 1 in 1 2 for those on a grade of less than 2 in a 

 hundred. When first built, the centre should be made some 

 four inches too high, to allow for after settling. 



