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BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 
the case of first-class macadam roads. The materials used should con- 
form in all respects to the ordinary requirements for similar mate- 
rials used in constructing such roads; that is, the stone should be 
clean, hard, tough, and 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 uni- 
form 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 
Fig. 3. — Making provision for expansion joint. 
surface of the pavement. Broken stone should be compacted 
in the usual manner by rolling the base with a power roller weighing 
not less than about 10 tons, and sufficient clean stone chips 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 uni- 
form 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 
