PRACTICAL PAPERS—COUNTRY ROADS. 
275 
In tenacious clay soils the margin of the surface of the sub¬ 
structure, on which to place a Macadam road-bed, shonld be at 
least one foot above the bottom of the gutters. It should be 
made smooth and solid, and have an underdrain at each margin 
of the macadamizing from six to twelve inches in depth, and 
an average of twelve inches in width. These drains may 
have a fall each way for five to seven rods, to a low point 
from which a lateral drain should extend under the side road 
to the gutter into which they are to discharge. The longitudi¬ 
nal under-drains are to be made of broken stones, and are to be 
filled up to the level of the surface upon which the macadam¬ 
izing is to rest. The earth-banks on each side of the macadam¬ 
ized portion of the road should be twelve inches in height, 
and be sufficiently sloped to be self-sustaining until the broken 
stone has been applied, which will render them perfectly secure. 
The stone should be so broken that all, or nearly all, the pieces 
will pass through a two-inch ring. This is the rule adopted 
in England, where this kind of road has reached the greatest 
perfection. 
We say “nearly all,” for of course there will occasionally 
be stones which, unless too much time is spent in breaking 
them, will not come up to the standard. This subject is one 
of the utmost importance; and,* if we are to be governed by 
the opinion of Macadam himself, we find him declaring that 
cubes of one and a quarter inch are better than any larger; 
and he affirmed before a committee of the House of Commons, 
that his experience went to prove that the expense of keeping 
roads in repair was almost in the exact ratio of* the, size of 
stone used in each instance. Thus, a road constructed of metal 
broken down to cubes of one and a quarter inch would require 
to keep in repair but one-half the outlay necessary for one con¬ 
structed of cubes of two and a half inches; so that the in¬ 
creased cost of construction in using the smaller broken metal 
will be fully compensated for by the saving in repairs and 
greater durability. Ip speaking of the metal as being in the 
form of cubes, it is not intended to convey the idea that each 
piece of stone must be a perfect cube, and all of equal size; 
