ON THE CONSTRUCTION OF ROADS. 135 



Probably a pavement made of small flat cobble stones, carefully 

 picked and properly set on edge, in a bed of concrete or beton, would 

 be found to be the most satisfactory pavement, until we get some 

 arrangement of iron which will serve a better purpose. 



Asphalte, a sort of mineral tar, which is found in various localities, 

 has been used with very great success in Paris and in other European 

 cities. It has been employed to a small extent with us, but has not 

 met with so much favor as it deserves, probably owing to the imper- 

 fect manner in which it has been applied. 



The asphalte should be melted and mixed with about one half its 

 weight of small clean gravel, and while hot poured upon the surface 

 prepared to receive it, immediately sprinkled with a little sand, and 

 smoothed off with a flat wooden patter or paddle. The mistake which 

 is frequently made in laying it is in providing a hard unyielding sur- 

 face, such as a cobble-stone or brick pavement, on which it is soon worn 

 out. A smooth surface of gravel or sand should be prepared to receive 

 it, or if a more rigid foundation should be required, concrete carefully 

 rammed and smoothed off may be used. When finished, an asphalte 

 pavement presents a smooth, partly elastic, surface, almost like that 

 of hard India rubber, or of oil cloth, over which the feet of the horses 

 and the wheels of the carriages move almost noiselessly. It presents a 

 continuous surface without openings and cracks, and being waterproof, 

 is admirably adapted for roadways, or for coverings over stone bridges, 

 for which purpose it has been extensively used. 



In Paris the sidewalks are almost all made of it, and in front of the 

 Merchants' Exchange, and several of the theatres, where the noise of 

 passing vehicles would be objectionable, the middle of the street is 

 covered with it. It has also been used in France with considerable 

 success on common roads. Its cost, and a tendency to soften under the 

 intense heat of the summer sun, are the principal objections to its 

 general use. For the pavements of court yards and stables it is supe- 

 rior to a,ny other material. 



A few years ago it was supposed that plank roads, especially in 

 wooded countries, would be found to be very cheap and satisfactory. 

 In many localities they have been used with great success, although 

 the opinion is gaining ground among engineers that they are inferior 

 in every way to good gravel roads, provided that that material can be 

 obtained at any reasonable price. They are usually made by laying 

 two longitudinal sills of timber about six inches square four feet eight 

 inches apart, filling up carefully with earth to their upper surfaces, 

 and then laying three-inch plank of any width upon them. The gen- 

 eral practice is now to lay them at right angles to the line of the road, 

 and not to spike them. Every fifth or sixth plank has its end pushed 

 out a few inches on alternate sides to make it easy to bring a wagon 

 back on to the planks if it runs off. 



