The river press. [volume] (Fort Benton, Mont.) 1880-current, 1912-06-05

successive cultivation of the soil, and
If this soil is used in the construction
of a road it is known as stop soil road
There are many varieties of clay and
consequently a wide variation in the
characteristics of a sand-clay road.
The quality of the sand is a variable
factor, as it may range all the way
from fine, dust-like particles to coarse
grains and gravel and may be perfect
ly clean or mixed with loan n other
material. In consequence of these wid
differences in the materials constitut-
ing sand-clay roads it is impossible to
maintain a uniform standard as to
quality of the road or methods Of con-
struction.
Not all but most sand consists of
tiny grains Of quartz. While quartz
is one of the hardest minerals known,
1t possesses practically no binding or
cementing power. The grains of sand,
instead of cohering in a tough mass
under the impact Of traffic and the ac-
ton of water, remain loose and shift
ing. Fine sand when dry is easily
displaced Ivy the wind, which pro-
duces in this way the ever shifting
sand hills. No road is so difficult to
travel as ore through fine sand.
If clay has been carried in small
quantities by running water and de-
posted as sediment it is known as
"sedimentary clay" If the feldspathic
rock has been disintegrated in place by
x,yofo,. +ho n1or &c lynnyun &c sSroSi6no1
clay" The sedimentary clay, having
been carried in the form of fine par
ticles, is finer grained than the residua!
clay and III more sticky and plastic.
In contrast with sand, which possesses
no binding power, but is very hard,
clay is a powerful binder, but does not
possess the quality of hardness. 1t is
evident that in the construction of a
sand-clay road the important property
in the clay is it's Elasticity or tendency
to become sticky and elastic when
mixed with water. The clays which
are most plastic are called "ball
clays." Another important property
which is possessed by clays in widely
varying degrees is the porosity or ca
pacity for rapid absorption of water.
Clays which possess this quality in
the highest degree fall to pieces under
the action of water. These clays
are called "slaking clays." 1t will read.
lily be seen that the plastic or ball clays
will form a better and more powerful
binder for sand-clay roads than will
the shaking clays; but, on the other
hand, they will be much more difficult
to mix, as they d%isintegrate with fa'
less rapidity.
The shrinkage of clay is an impor'
tant characteristic in connection with
the building of roads. When water is
mixed with clay expansion results, and
when the water evaporates the clay
contracts. This characteristic Of ex
pansion is much mor pronounced In
some clays than in others, and it must
be apparent that the clays which ex
pand the least are preferable for road
building.
The theory Of the sand-clay road Il
very similar to the theory of the mac
adam road. In the latter rock dust
and screenings fill the voids between
the angular fragments Of stone ant
when wet serve as a cement or binder
The grains of sand may be likened tt
the angular fragments of stone an,
clay to the rock dust binder. In thu
most successful sand-clay road just ;
sufficient amount of clay is used to fl
the voids between the grains of sand
In this way the sand sustains thu
wear. while the clay serves as