OUR COMMON ROADS—MURPHY. 435 
the whole was covered with 14 inches of good clean gravel. 
At Coventry he covered the pitching with a six-inch layer of 
Nuneaton stone, broken to a gauge of 24 inches, and well raked 
into the surface of these a covering of good gravel blinding 14 
inches in thickness. 
The method introduced by Mr. McAdam was as follows (see 
Fig. 2): He dispensed with the foundation of large stones, and 
if anything preferred a soft substratum to a hard artificial one, 
and selected angular fragments of granite, basalt, or whinstone, 
broken sufficiently small to pass through a ring 2} inches in 
diameter, preference being given to stones from 1 to 2 ounces in 
weight, and he in no case allowed the use of stone exceeding 6 
ounces, the larger ones being broken to the regulation size, which 
after much experience and many carefully experiments, was still 
further reduced to cubes of 1 inch to 14 inches in every direc- 
tion. 
If we compare Telford’s mode of pavement with Tresaguet’s 
method of constructing roads as described by the latter and gen- 
erally adopted in France sixty years before Telford’s time, we 
cannot help but surmise that he borrowed his system, or that 
it was evolved largely from the French. Tresaguet says, so early 
as 1775; “The bottom of the foundation is to be parallel to 
the surface of the road. The first bed on the foundation is to be 
placed on edge and not. on the flat, in the form of a rough pave- 
ment, and consolidated by beating with a large hammer, but it 
is unnecessary that the stones should be even one with another. 
The second bed is to be equally arranged by hand, layer by layer 
and beaten and broken coarsely with a large hammer, so that the 
stones may wedge together and no empty spaces remain. The 
last bed 3 inches in thickness, is to be broken to about the 
the size of a nut with a small hammer on a sort of anvil, and 
thrown upon the road with a shovel to form the curved sur- 
face. Great attention must be given to choose the hardest stone 
for the last bed even if one is obliged to go to more distant quarries 
than those which furnish stone for the body of the road; the 
solidity of the road depending on this latter bed, one cannot be 
too scrupulous as to the quality of materials which are used 
in it.” 
