Crossville chronicle. [volume] (Crossville, Tenn.) 1894-current, 1917-09-26

trar1ly as the dividing line between
sand and gravel and is generally,
though not universally, accepted as
such. Nearly all sand consists essen
TALLY of quartz grains that are very
hard and durable. But there is no Co
herence between the different grains,
and therefore soils composed princi-
pally of sand are unstable, except when
confined in some way. If properly con-
fined and protected from undermining,
sand foundations may. under favorable
climatic conditions, prove entirely sat.
isfactory for almost any type of road
crust, but it is practically impossible,
under any circumstances to make sat
isfactory road surface of sand alone.
Sand roads are at their best when
they are kept moist, and for this rea-
son they should be designed with
view to retaining moisture in the sand
rather than to effective drainage, as is
the case with clay roads. Such roads
sometimes are improved temporarily by
mixing Sawdust, straw, pine leaves or
other similar material into the surface.
but, in general, the sand-clay crust is
the most satisfactory Improvement for
roads of this character.
Loan.
Loan is a soil composed Of clay and
sand, mixed with a considerable per-
centage of finely divided vegetable mat
ter or humus. The quality of loan
from the standpoint of road building
depends very largely upon the proper
tons in which sand and clay are pres
ent and on the character of these ma
terials. Loan that contains about 60
per cent of moderately coarse sand and
from 20 to 80 per cent of good cement
ing clay usually will make an excellent
road surface for light traffic. Material
of this kind is drained easily and Is
fairly stable, even when wet. Another
advantage is that 1t will not become
very dusty under traffic in dry weather
and frequently will cement together
into very hard, compact surface.
Roads surfaced with such material are
commonly called "topsoil" roads, be-
cause the topsoil Of cultivated fields
possesses the desired characteristics
more frequently than that to be OBJ
tanned from any other source.
Gravel.
Gravel is made up of small rounded
particles of stone, which occur In ma
ture and are sufficiently large to be
retained on Observation-Disclosures
screen. Gravelly soils are distributed
widely In the United States, and vary
widely in quality. In general, when q
soil contains as much as 40 to 30 per
cent of gravel and sufficient clay or
other cementing material to bond the
gravel particles together.-it proves a
very satisfactory material for con-
struction of roads, because 1t is drained
easily and is very stable when COM
pacted.
Mari.
Mari is clay containing a relatively
large percentage of carbonate of lime.
1t grades into calcareOus clay and ar
gillaceOus limestone, and its value for
road building is variable. In general
this material has few advantages over
the best varieties of ordinary clay for
use in constructing a road, unless the
percentage Of lime carbonate is suffi-
GENTLY high to give 1t, when compacted,
approximately the character of lime
stone. The best varieties Of mari be-
come very hard and compact when
placed in road surface, and In some
localities this material Is used extern
sively for road surfacing.
- Gumbo.>
Gumbo IS essentially loan contain
ing high percentage each Of clay and
decayed vegetable matter and a very
low percentage Of sand. GumbO has
strong tendency to absorb and hold wa
ter, and therefore is hard to drain. It
is harder to handle in road surface
than clay, because the vegetable matter
Is an added weakness, but If protected
from surface water by proper sys-
TEN Of drainage, 1t may be used to con-
struct fair subgrade for supporting
some type Of impervious road crust.
Gumbo has a relatively high capillary
power, and for this reason its occur
renee in a roadbed usually will necessi-
tate the use Of subdrainage, even under
conditions favorable for surface drain
age.