ROAD-MAKING. 199 



been laid for some time, under the pressure of Jieavy carts and waggons 

 passing over them, the stones become to a considerable extent mixed 

 with the soil. If, therefore, the soil is a stiff' clay, the bed for the recep- 

 tion of the stones should be slightly rounded, keeping it a few inches 

 higher in the centre ; but where this is not the case, I would recom- 

 mend the bed to be made flat. In those roads which I make I next 

 proceed to cart large flat stones and lay them as they are in the bottom 

 without being broken, unless they stand higher above the surface than 

 six inches ; this being done, I then cart the broken stones and empty 

 them above those already put on, and lay them so that they will be eight 

 inches thick at the sides and have a slight slope upward toward the 

 centre, but not making the slope more than 1 in 30, as shown in the 

 sketch. Those stones put on the top should be broken to such a size as 

 they will all pass through a ring two and a half inches in diameter. 



Where there are hollow places in the road, and where it may be neces- 

 sary to lead the outfall from either of the side drains across the road, it 

 is always advisable to have a strong culvert built to bear the weight of 

 heavy vehicles. 



It may be advisable to make these cross drains frequently, as it is not 

 judicious to allow the water to run a long distance in the side drains 

 without checking it, as it gains force in the open drains on an incline, 

 and cuts the bottom of the drains. The opening of the cross drains or 

 culverts, as shown in fig. 73, should not be less than eight inches square. 



FIG. 75. 



Where the open side drains are let into the cross drains or culverts, it 

 will be necessary to cover the inlet with a small grating, to prevent leaves 

 or other substances, which might choke the drain, being carried into it. 



In some districts large stones cannot be got to break for road-metal, 

 but gravel may be plentiful. In this case the gravel should be put 

 through a screen of three-quarter-inch mesh ; the large gravel or stones 

 will do well for forming the surface of the road, if mixed with a little 

 soil. If the round pebbles are put on without anything to assist in 

 binding them, they will shift about and not bind for a long time. The 

 surface of any road should always be as much exposed to the free action 

 of the sun and air as possible ; when rain falls upon them, it is very 

 quickly evaporated, and thus the surface is soon dry again. A great 

 many of our existing English roads are always in a bad condition, caused 



