478 THE HANDBOOK FOE PEACTICAL FARMERS 



fact, trap rock, ''nigger heads," technically known as diabase, 

 and diorites, are considered by most road engineers of long 

 experience to be the very best stones for road building. 



Macadam construction. — The macadam road consists of a 

 mass of angular fragments of rock deposited usually in layers 

 upon the roadbed or prepared foundation and consolidated to a 

 smooth, hard surface produced by the passage of vehicles or by 

 use of a road roller. The thickness of this crust varies with the 

 soil, the nature of the stone used, and the amount of traffic which 

 the road is expected to have. It should be so thick that the 

 greatest load will not affect the foundation. The weight usually 

 comes upon a very small part of the surface, but is spread over 

 a large area of the foundation, and the thicker the crust the more 

 uniformly will the load be distributed over the foundation. 



Telford construction. — The character of the foundation 

 should never take the place of proper drainage. The advisabil- 

 ity of underground or subdrainage should always be carefully 

 considered where the road is liable to be attacked from beneath 

 by water. In most cases good subdrains will so dry the founda- 

 tion out that the macadam construction can be resorted to. 

 Sometimes, however, thorough drainage is difficult or doubtful, 

 and in such cases it is desirable to adopt some heavy construction 

 like the telford; and, furthermore, the difficulty of procuring 

 perfectly solid and reliable roadbeds in many places is often 

 overcome by the use of this system. 



In making a telford road the surface for the foundation is 

 prepared in the same manner as for a macadam road. A layer 

 of broken stone is then placed on the roadbed from five to eight 

 inches in depth, depending upon the thickness to be given the 

 finished road. As a rule this foundation should form about two- 

 thirds of the total thickness of the material. The stone used for 

 the first layer may vary in thickness from two to four inches 

 and in length from eight to twelve inches. The thickness of the 

 upper edges of the stones should not exceed four inches. They 

 are set by hand on their broadest edges lengthwise across the 

 road, breaking joints as much as possible. All projecting points 

 are then broken off and the interstices or cracks filled with stone 

 chips, and the whole structure wedged and consolidated into a 

 solid and complete pavement. Upon this pavement layers of 

 broken stones are spread and treated as for a macadam road. 



Dirt roads on the farm. — An ideal, hard surface road is a good 

 thing to have. But most of our roads for a long time to come 

 will be dirt highways. This being the case, we may spend time 



