Broken stone should be clean, hard, and of a size suited to the character
of the work, and the same care in grading should be exercised as in the
case of gravel. Trap, granite, hard limestone, and hard sandstone are
commonly used. The composition and physical character of the stones
should be considered, as some possess qualities that limit their use
under certain conditions (see Substitutes for gravel).
Field stones are common in many localities and their use, when crushed,
may be economical. The finer particles, after the dust is removed, can be
used as sand. Small stone crushers, operated by three or four horsepower
gasoline engines, can be purchased at a relatively low price and may
prove profitable if a large quantity of stone is needed.