EARTH, SAND-CLAY, AND GRAVEL ROADS. 19 
and compact when placed in a road surface, and in some localities 
this material is used extensively for road surfacing. 
Gumbo is essentially loam containing a high percentage each of 
clay and decayed vegetable matter and a very low percentage of sand. 
Gumbo has a strong tendency to absorb and hold water, and there- 
fore is hard to drain. It is harder to handle in a road surface 
than clay, because the vegetable matter is an added weakness, but if 
protected from surface water by a proper system of drainage, it may 
be used to construct a fair subgrade for supporting some type of 
impervious road crust. Gumbo has a relatively high capillary 
power, and for this reason its occurrence in a road bed often will 
necessitate the use of subdrainage, even under conditions favorable 
for surface drainage. 
CONSTRUCTION OF EARTH ROADS. 
The work of constructing an earth road, after the general location 
and design have been decided upon, may be separated into six more 
or less distinct operations, viz : 
(1) The work is staked out in accordance with previously pre- 
pared plans; (2) the right of way is cleared of all trees, brush, 
stumps, etc., which would interfere in any way with the work; (3) 
all necessary bridges, culverts, drains, and other structures which 
extend under the road surface are constructed in accordance with 
proper designs; (4) the roadbed is brought to the required width 
and grade by making excavations and constructing embankments; 
(5) the surface is finished to the required cross section and so main- 
tained until compacted thoroughly; (6) all necessary outlet ditches, 
gutters, guard rails, fences, etc., are constructed in accordance with 
the plans. 
STAKING OUT THE WOEK. 
Before any construction work is started on a road the limits of 
the work should be marked clearly by setting line and grade stakes 
at convenient intervals. The same stakes generally are made to 
serve for both line and grade, and the space between successive 
stakes is made 100 feet. Heavy reference stakes are driven on 
each side of the center line sufficiently far out not to be disturbed 
during the progress of the work. Then, as the work proceeds, such 
supplementary stakes as are necessary for marking the tops and 
bottoms of slopes, ditch lines, etc., may be set from the reference 
stakes by means of a string level and a metallic tape. 
Culvert locations usually are fixed on the ground by means of two 
stakes in the line of the culvert, one near each end. 
