OUR COMMON ROADS—MURPHY. 443 
Gravel Roads.—The American as well as the European prac- 
tice, is to screen pit gravel before applying it to the surface 
layer. Two wire screens, one with wire 1 to 2 inches apart, the 
other $ to ?-inch apart, are necessary. The pebbles that will 
not pass the larger screen are rejected, and are afterwards broken 
up into smaller fragments, while the earth, gravel and sand that 
pass through the smaller one, although unsuitable for the road 
surface, will answer for blinding or for a sub-layer or side walk 
covering. 
A layer from 4 to 6 inches thick of good unscreened pit gravel 
in its natural state is first spread upon the road bed, which is 
then thrown open to travel, until it becomes tolerably well con- 
solidated, after which a second layer of screened gravel is added 
of sufficient depth to suit the requirements of traffic. The whole 
is generally consolidated by a roller. The aggregate thickness 
of the layers does not exceed 8 to 10 inches. 
The sides of the road should be rolled first to such a degree of 
firmness that when the roller is placed upon the highest portion 
along the middle, the tendency of the gravel to spread and work 
off towards the side gutters will be resisted. A gravel road, 
carefully constructed in the manner above described, will possess 
all the essential requisites of a good road. 
McAdam and Telford roads have been already described. A 
few remarks on rolling of McAdam roads, by Mr. William H. 
Grant, Superintending Engineer of the New York Central Park, 
in his report on the park roads, are so interesting that I quote 
them: “At the commencement of the McAdam roads, the experi- 
ment was tried of rolling and compacting the stones by a strict 
adherence to McAdam’s theory—that of carefully excluding all 
dirt and foreign materials from the stones, and trusting to the 
action of the roller and the travel of teams to accomplish the 
work of consolidation. The bottom layer of stone was sufficiently 
compacted in this way to form and retain, under the action of 
the rollers (after the compression had reached its practical limit), 
an even and regular surface, but the top layer, with the use of 
the heavy roller loaded to its utmost capacity, it was found im- 
practicable to solidify and reduce to such a surface, as would 
