OUR COMMON ROADS—MURPBHY. 453 
considers their preservation from decay is largely due to their 
partial submersion in the bog and the tannic acid which it con- 
tains. Vehicles seem to pass easily over it, the bending and 
cross-breaking tendency of the road produces no sensible effect, 
there is no movement in the body of the road, and the wear is 
confined to the grinding and crushing of the surface of the planks, 
and although there is a continuous stream of daily traffic, the 
wear does not seem to have the same effect as on planked cover- 
ing in other situations. In localities where lumber is cheap, and 
stone and gravel scarce and expensive, planked roads might be 
judiciously employed in crossing peaty stretches or bog or swamp. 
EARTH OR CLAY ROADS. 
Clay is a poor substitute for road covering. If we could only 
bake it and drive off the water, in combination with the oxide of 
iron which it contains, we might obtain a crust more impervious 
to water. Frequent attempts have been made to burn and calcine 
clay for railway ballast and road material in situations remote 
from stone or gravel, and it is said with some degree of success. 
It is, however, a costly operation, which we would not be justified 
in adopting. We are not ripe enough for costly experiments, 
and must content ourselves with other and cheaper means. We 
may, however, reason thus :—Sand stones are made from sand by 
some slow process, clay stones from clay, and so on, for all 
geologists believe that rocks are made from secondary causes. 
Now we can pretty thoroughly imitate rock-making by an ad- 
mixture of lime and sand, or by the use of certain natural and 
artificial cements we can consolidate such material into solid rock 
in a short space of time, six or seven days, and the induration 
will improve in time. Adobe for roads, as well as for buildings, 
may yet be capable of practical application. At present in our 
climate we need a harder and more endurable material than clay 
or earth to sustain any sort of heavy traffic in the spring and 
fall seasons. Nevertheless, the writer has seen within our own 
borders several effective attempts to maintain clay roads, where 
the traffic is light, by material which is always within easy 
distance in Nova Scotia. By taking the tops of spruce or fir 
