398 
Roads and Highways : their History, 
of gearing attached to the wheels, and being placed at a slight 
angle with the axle, delivers the material swept up in a con- 
tinuous heap at the side and along the course of the machine. 
The cost of this machine is 211. 
Materials. — The statute width of a highway is 30 feet, of 
■which about 20 is metalled, the chief wear and tear being con- 
fined to a space of 12 feet at the crown of the road. 
The materials used for repair vary with the locality, and con- 
sist principally of limestone, sandstone, gravel, flint, sea-shingle, 
and the harder rocks. 
Limestone is an expensive and bad material for roads. In 
damp weather in summer it makes a pleasant road for use, but 
after a continuance of fine weather the stone is converted into 
dust. In winter, owing to the action of the frost, the stone is 
soon changed into mud, which has to be scraped off at great and 
constant expense. 
Flint-gravel makes a clean road. If used in sufficient quan- 
tities, and properly attended to, it gives a firm surface. If, 
however, the gravel consists of rounded pebbles, the road never 
consolidates, but becomes covered with loose round stones, 
extremely dangerous for horses. 
Round gravel is the worst material that can be used for 
repairs, it always makes a loose, bad road. If the gravel be- 
comes consolidated during the winter, it is certain to work loose 
again in the following summer. The constant tendency of the 
stones, as the weight is brought on them, is to roll round one 
another, and so to work loose. 
All material should therefore be angular, and all round stones 
require to be broken into angular fragments before being placed 
on the road. 
The chief requisites for a road-material are that it should be 
not only hard but also tough, and that the chemical composi- 
tion be such that it shall not be affected by the weather ; in 
shape the fragments must be angular, so as to bed well together. 
Flint is very hard, but it is brittle^ Limestone is tough, but 
when exposed to the weather, soon decomposes. Water-worn 
pebbles, composed of hard sandstone and older rocks, are both 
hard, tough, and not easily affected by the atmosphere ; but 
owing to their shape, they never bed together. The only really 
good road-material which contains all the above qualities is 
composed of fragments of the granitic and trappean rocks, 
broken so as to pass through a two-inch gauge. The angular 
shape of the stones and their uniform size cause them to fit 
together in a compact body, so that the surface of the road is 
bonded together like the bricks in a very flat arch, and the 
