winter or wet seasons, by their retention of | 
water, and dripping upon the road, as well as 
preventing its becoming dry when the rain has 
ceased. A good piece of road overshadowed by 
trees, is a thing of very rare occurrence. 
It only remains to speak of the manner of ren- 
dering roads hard and durable after they have 
been set out and formed as before directed, and 
this can only be accomplished by covering them 
with hard materials. What these materials will 
be must in general depend on the locality of the 
road, and its happening to be in a completely in- 
land country, or one that has the advantage of na- 
vigation. There is no doubt but that the hardest 
flint stones make the best road, and next to them 
the whin stone, trap and basaltic formations, but 
they are not procurable in all places, and there- 
fore the best materials that can be obtained in 
the immediate neighbourhood must be resorted 
to, and in their selection, hardness and tenacity 
are the great objects to be regarded. When 
countries are near navigable rivers or canals, it 
often proves more economical to transport hard 
materials from a distance, than to use the softer 
ones with which a country abounds. No material 
igs more universally distributed over the face of 
the earth than what is called gravel, and accord- 
ingly that is generally used for making roads. 
Gravel is a general term applied to all stones 
that have the form of pebbles, whatever their 
composition may be, therefore it is not admitted 
as the name or character of any particular stone 
in mineralogy. The hypothesis usually held re- 
specting pebbles is, that they are fragments of 
rock broken or separated from the large masses, 
by decay of parts, or by some great convulsion 
of nature, and that they have been rounded by 
having their points and sharp edges worn off by 
attrition in the sea, from whence they have been 
deposited, by means of which we have no record, 
in various parts of the dry land, and frequently at 
elevations far above the present reach of the sea. 
These pebbles, therefore, vary much in quality, 
even in the same parcel of gravel, but they are 
almost universally hard, because the process they 
must have undergone to bring them to the form 
of pebbles would grind the softer materials to a 
state of powder, producing either sand or com- 
mon soil; and as flint is the hardest of all com- 
mon or ordinary stones, so the pebbles of gravel 
are usually of this material. What may be desig- 
nated under the general name of gravel, is divided 
into several classes, by names dependent only on 
the magnitude of the component parts. Thus 
large rounded pebbles, which are never quite 
round, but are flattened on their two opposite 
sides, and which are found abundantly on many 
sea shores, of a magnitude varying from that of 
a man’s fist to his head, are called boulders, and 
these are picked up separately and reserved for 
the purpose of paving streets. What is generally 
understood by gravel has no stones in it larger 
than the fist, but it has all gradations of smaller 
eT ae Na a NV n dA NN Oe LO CPL 
hese eee 
Oo ee I 
Sn 
ones down to sand. The sort always used, or at 
any rate preferred for road making, is termed 
clean, or screened gravel, that is to say, the 
mixed gravel passed through a screen or sieve 
composed of very strong iron wires, or rather 
thin rods of iron placed at from half to three- 
quarters of an inch asunder. All that will not 
pass through such a screen is termed screened 
gravel, and that which does pass through is, by 
workmen, termed hoggin. The first is alone used 
for road making, and the latter for covering 
causeways, footpaths, and gravel walks; it con- 
sists of a mixture of sand and small pebbles, 
which bind together and produce a hard, smooth, 
and compact surface. 
The old system of road making, cr rather road 
covering and repairing, as followed in England, and 
which is still persevered in in many places, was, after 
having prepared the ground or sole of the road by 
giving it its proper crown or convexity, slope, water 
tables, and so on, to cart and spread as much screened 
gravel, without any previous preparation, as would 
cover the whole road to a depth of from nine to 
twelve inches, and then to cover this with a thin 
coat of hoggin, in order to fill up the interstices, and 
cause the gravel to bind or become compact. ‘This 
produced a very rough road at first, but by time and 
use it would become compact and tolerably smooth. 
In this way it was left until it needed repair, and 
that repair consisted in first scraping off all soft mud, 
and then applying another coat of screened gravel 
without hoggin, so as to cover the old road to a 
thickness of two or three inches, spreading it by 
rakes or shovels, to make the surface as even as 
possible, and to fill up the old ruts and inequalities, 
and this was repeated every fall or autumn. This 
practice was continued until Mr. M‘Adam, of Scot- 
land, drew the attention of the public to its waste 
and impropriety, and introduced his improved system 
of road making, which he began about the year 1810, 
and which is now almost universally followed. He 
was led to the consideration of this subject by ob- 
serving the effect that took place when a heavy car- 
riage, such as a loaded stage-coach, passed over a 
newly formed road. The wheels being thin and 
narrow, cut or sunk into the new gravel to a consi- 
derable depth, so as to make the draught enormously 
heavy, and they were permitted thus to sink in, on 
account of all the gravel pebbles being hard and 
round, which allowed them to roll about and displace 
each other, thus completely counteracting any ten- 
dency they might have to bind or unite together into 
a hard mass. Every vehicle that passed in succession 
produced a new disturbance or displacement of the 
materials, to such an extent that it might almost be 
compared to ploughing up the road; nor did the road 
begin to assume a good and hard aspect, until by the 
repeated passage of heavy carriages over the materials 
they were broken and partly reduced to powder. In 
the sare way when a road was repaired by giving it 
a new coat of coarse gravel, without disturbing the 
old surface, the wheels constantly made their way 
through that new coating down to the old surface, 
displacing the new gravel, unless it was applied in a 
very thick and expensive manner, and thus the re- 
pairs never availed until the new material was partly 
worn out, as it was supposed, by becoming broken. 
In the formation of his system he was guided alone 
by what he saw going on in nature. If the road did 
not become hard and good until the stones were ir- 
regularly broken by the frequent passage of heavy 
carriages over them in process of time, why impose 
the duty of breaking the stones upon the carriages, 
Ji 
