10 
BULLETIN 23, IT. S. DEPARTMENT OF AGRICULTURE. 
gravel, slag, or broken stone, not less than 3 inches thick, and should 
be provided with a backing of the same material on the shoulder or 
sidewalk side. Figure 1 shows a typical stone curb in place. 
Where suitable stone is not readily available or when from any 
cause the cost of stone curbing would prove excessive, a curb con- 
structed of Portland cement concrete may frequently be advan- 
tageously used. Concrete curbs may be constructed alone or in com- 
bination with either a concrete gutter or a concrete foundation. 
The advisability of constructing the curb in combination with 
the foundation, however, is doubtful. Very little is saved by such 
an arrangement, and the small saving is probably even more than 
offset by the additional difficulty involved in preparing the subgrade 
y/r/?/F/£# 3/t , /c/r 1 
Fig. 1.— Proper method of constructing stone curb. 
without the curb to serve as a guide. Concrete curbs should have 
approximately the same cross-sectional dimensions as stone curbs 
and should be constructed in sections not exceeding about 7 or 8 feet 
in length." Figures 2 and 3 and Plate I show the three common 
methods of constructing concrete curbs. 
Vitrified clay curbing should be set in much the same manner as 
that described for stone curbing. The principal additional require- 
ment is that, since vitrified clay is a lighter material than stone and 
the curb sections are ordinarily shorter, the bedding must be made 
correspondingly more secure in order to prevent displacement. 
THE FOUNDATION. 
A firm, unyielding foundation is one of the most essential features 
of a brick pavement. This fact can be more readily appreciated 
when it is considered that the surface of a brick pavement is made up 
