The river press. [volume] (Fort Benton, Mont.) 1880-current, 1912-06-12

pits, which are frequently termed gla-
cial gravels on account of their direct
or indirect association with ice action,
are quite widely distributed, and these
have been and may be used to a
greater or less extent In road improve
ment.
During recent geological history of
the continent the Atlantic and gulf
borders have been submerged at inter
walls. The ocean has advanced inland
a number of times. During each of
these periods of continental submer-
gence the harder rock remanents along
the inner margins of the oceans ad
vance have been rounded, worn down.
deposited and redeposited with vary
ing proportions of sands and loans
and clays, thus forming beds Of gray
ell, which are today available for road
building purposes.
Gravel roads and macadam roads
alike have often received sweeping con-
formations as unsatisfactory when he
cause Of failure was poor construction
and not the character Of the material
used. The need of care in grading and
drainage in the construction of macad-
am roads is being quite generally rec
ognized, but unfortunately many anna
teur road builders seem to think that
gravel roads may be constructed by
simply piling gravel on the surface and
leaving it to be packed by the passing
traffic. In point Of fact, the grading
and drainage and other details in con-
nection with the construction of a
gravel road should be done with as
much care and thoroughness as in the
case Of a macadam road. Moreover, in
the one case as in the other speciica-
lions must be adapted to varying local
conditions. OF course, the gravel itself
must be selected with care. That which
contains "a sufficient quantity Of bind
ing material so that it stands as a YER
teal wall when it is being excavated
is generally the best, for the reason
that this same binding material will
re-cement the gravel when used for
road building.
There are three important qualities
which should be possessed by road
building gravel-hardness, toughness
and cementing or binding power. OF
these three qualities the last is the
most important. This binding quality
Is due in part to the presence Of oxide
of iron, lime or f~errugineous clay and
in part to the angular shape and size
of the pebbles composing the gravel
Blue gravel is universally conceded tt
be the best for road construction, be
cause it is usually derived from traI
rock. AS the pebbles composing thu
gravel retain the characteristics which
they formerly possessed as a part o.
the larger rock itself, it follows that al
trap rock is considered an excellen
material for road building, trap rocl
gravel should occupy the same RELATIVE
rank among the gravels. Limestone is
generally speaking, a soft rock, an
consequently limestone gravel, whicl
is quite rare, will usually be fount
soft and will wear rapidly. Quart
possesses practically nc binding power
although it is very hard. Therefor
gravel which contains an exception
ally large percentage Of quartz will no
prove successful, as it will fail to con
solidate unless it contains binding ma
terial. or unless a good binder is added
In order that the material may bin
readily the pebbles should be angula
and should vary in size so that til
smaller fragments may fill the void