222 MASSACHUSETTS AGRICULTURE. 



Macadam Top. — The cross section of such a road is about as 

 <^J^awii '■> "^'^"' i 7. y ^^^' the 



thickness of the foundation 6=a, the thickness of the top cov- 

 ering at the centre, and is six, four or five and three and one- 

 half inches in thickness for first, second and third class roads. 

 If the stone for the foundation — for which most anything will 

 do, and that kind should be taken which is cheapest to procure 

 — happens to be got out cheapest in larger pieces than the 

 above dimensions, it will do no harm. This foundation course 

 is sometimes set so as to present an inclination on top, and the 

 cover then put on of a uniform thickness over the whole 

 breadth. This is perhaps best, but is somewhat more expensive. 

 It will do, in nearly all cases, to set the foundation course on a 

 level, or as near so as the stones will allow, and then make the 

 top crowning, by making the covering say three-quarters of an 

 inch or an inch less thick at the edges than in the centre. The 

 stones forming the foundation should not be set in rows, nor 

 ever laid on their flat sides, but set up on edge and made to 

 break joints as much as possible ; that is, set up irregularly. 

 After they are set up, the points that project aboye the general 

 level may be broken off, and the interstices generally filled with 

 small stone. More or less care and work are necessary in this 

 part of the operation, according to the importance of the road 

 and the depth and character of the material used for the top 

 covering. To roll the road at this stage is to be recommended ; 

 afterwards it becomes a requisite. The point never to be lost 

 sight of, is that this foundation course must remain porous, 

 must be pervious to water, so that all rain-water that shall 

 soak through the top covering will find, through it, means of 

 escape to the ground underneath ; thence, according to the na- 

 ture of the subsoil, it is left either to soak into the ground,^ or 

 must be further led away by appropriate drains. 



Of very great importance is the material used for the top or 

 road covering. In the order of their value for macadam, we 

 have. 



I. Basalt. 

 II. Syenite and Granite. 



III. Limestones. 



lY. Sandstones. 



