are not rigid. Stones
having one dimension about 8 inches and the others not over 10 or 12
inches are satisfactory.

=Earth Work.=--A thoroughly drained and stable earth foundation is
essential to success with the macadam type of surface. Before placing
the stone, the road must be shaped to the proper cross section and
all grade reduction work completed. Preferably heavy fills should have
a year to settle before the macadam surface is placed. Side ditches,
necessary culverts and tile drains should be constructed as required
for drainage. The earth work is often carried out in connection with
the construction of the macadam surface, being completed just ahead of
the surfacing. In that case, the fills must be carefully rolled as
they are placed. The road bed may be shaped in connection with the
other earthwork. If the road has been brought to a satisfactory grade
some time prior to placing the macadam, the road bed for the broken
stone will be prepared as needed for placing the stone.

=Foundation for the Macadam.=--Macadam surfaces are quite generally
placed in a trench as described in the trench method for placing
gravel. It is an almost universal practice to compact the layer of
stone by rolling with an 8- or 10-ton power roller, and if the stone
is not held between substantial earth berms or shoulders, the rolling
merely serves to spread the stone out over the road bed instead of
compacting it. If an attempt is made to roll broken stone which has
been placed on a yielding foundation, no benefit results, but on the
contrary the stone is likely to be forced down into the soil. To
insure that the layer of broken stone can be compacted by rolling, it
is first necessary to roll the earth foundation until it becomes hard
and unyielding. If soft or yielding places appear during the rolling
these should be corrected by tile drains or by removing the earth from
the spongy place and back-filling with material that will compact when
rolled.

It is not always easy to determine why these soft places exist in what
appears to be a well drained roadway, especially since they are as
likely to be found on fills as anywhere else. Apparently they are due
to local pockets of porous soil held by denser soil so that the water
does not readily drain away. It is usually true that such places are
observed during the season of frequent precipitation more often than
during other seasons of the year.

In dry climates, the difficulties of se