60 BULLETIN 724, U. S. DEPARTMENT OE AGRICULTURE. 
fairly well by particles of stone crushing under the roller and in such cases the 
addition of sand or screenings may not be necessary. The character of the 
road crust also should be considered in deciding this point. 
6. In order to lock the particles of stone together satisfactorily it frequently 
is necessary to sprinkle a moderate amount of water over each layer of the 
foundation while the rolling is in progress. This is especially true of limestone 
where screenings are added after the stone is spread. In all cases .where 
water is used it is merely to flush the fine chips and dust into the interstices 
and by no means to produce a grouted surface, and it should be applied gently 
and in such quantities as not to saturate the subgrade and should be done only 
on sections of the foundations where rolling is in progress. 
COST OF CRUSHED-STONE FOUNDATION^. 
The cost of constructing a crushed-stone foundation, after the 
stone has been delivered on the work, usually can be estimated with a 
fair degree of accuracy when the conditions affecting the work are 
understood. If the stone is hauled out in suitable dump wagons and 
the -price of labor is about 20 cents per hour, the spreading can be 
done at an average total cost of from 6 to 8 cents per cubic yard. 
Where the stone is dumped on boards and spread by hand this cost 
ordinarily will be just about doubled. 
The cost of rolling varies with the quality of the stone used. If 
a hard limestone or trap is used, about 100 cubic yards can be com- 
pacted per 10-hour day with a 10-ton roller, while with sandstone or 
soft limestone the quantity compacted per 10-hour day may be as 
much as 150 or 175 cubic yards. Assuming the loose depth of the 
foundation at 9 inches and the cost per day of a roller, including 
labor, fuel, and depreciation, at 812, the total cost of rolling would 
average from 2 to 3 cents per square yard. The cost of spreading 
and rolling combined would average from 3 \ to 5 cents per square 
yard. 
The cost of quarrying and crushing varies with the character of 
the stone, the layout of the quarry, and the equipment employed. 
Some of the largest producers of crushed limestone market their 
product at about 50 cents per ton, or 65 cents per cubic yard, while 
in other cases, where the quarry face is shallow and the plant is small, 
the actual cost of quarrying and crushing sometimes is more than 
$1 per cubic yard. The following record is of a limestone quarry in 
Loudon County. Tenn.. operated under the supervision of the Bureau 
of Public Eoads in connection with a single road improvement 
project, may be of assistance in estimating costs for similar work 
in other localities. The quarry had been faced up. but required 
heavy stripping, and the presence of numerous clay seams made 
drilling and blasting expensive. The stone is a dark-blue, tough 
limestone, very similar in appearance to Knoxville dolomite. The 
depth of quarry face was from 12 to 18 feet. Blasting was done 
