14 BULLETIN 691, U. S. DEPARTMENT OF AGRICULTURE. 
concrete or well-compacted broken stone or gravel foundation 
to such depth that it will yield a uniform layer two inches in 
thickness after thorough rolling. A seal coat of the hot asphalt 
should then be applied at the rate of 0.4 to 0.6 gallon per square 
yard and covered with a sufficient amount of stone chips to just 
absorb the excess bitumen. Roads of this character may be 
maintained with oil-surface treatments using the materials and 
methods given under specifications OC— 2 or OH-1. The latter is 
usually to be preferred. Such maintenance treatments should be 
applied whenever the wear comes directly upon the wearing course 
rock. 
