12 
BULLETIN 373, U. S. DEPARTMENT OF AGRICULTURE. 
the case of first-class macadam roads. The stone should be durable. 
and should be graded in size between certain reasonable, fixed limits. 
It should be uniformly spread on the road, either from dumping 
boards by means of shovels or from wagons especially designed to 
spread the material as it is being dumped. Where whole loads are 
dumped in one place and then spread out to the required depth, it is 
very difficult to obtain uniform density. Usually those spots where 
the loads are dumped are more densely compacted than the rest of 
the base, and this lack of uniformity very soon manifests itself by 
producing unevenness in the surface of the pavement. The broken 
stone should be compacted in the usual maimer by rolling with a 
Fig. 3. — Making provision for expansion cushion. 
power roller weighing not less than about 10 tons, and sufficient 
stone screenings and coarse sand to fill the voids should be spread 
and flushed into the base while the rolling is in progress. When 
complete the base should present a surface uniform in grade and 
cross section and parallel to the proposed surface of the finished 
pavement. 
Concrete bases are unquestionably better adapted for brick pave- 
ments than any other type. They are practically monolithic in form, 
nearly impervious to water, and possess a relatively high crushing 
strength. All of these qualities may be obtained with a relatively 
" lean " concrete if the subgrade has been properly prepared. Under 
ordinary circumstances a satisfactory base mav be constructed of 
