The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1912-07-10


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 n
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
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
demnatious as unsatisfactory when the
cause of failure was poor construction
and not the character OF the material
used. The reed 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 II 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 rs
much care and thoroughness as in the
case of macadam road. Moreover in
the one case as In the other specified
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 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 cementmg 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 ferrugineous clay and
In part TO the angular shape and size
OF the pebbles composing the gravel.
Blue gravel is universally conceded 10
be the best for road construction. be-
cause it is usually derived from trap
rock. AS the pebbles composing the
gravel retain the characteristics which
they formerly possessed as a part OF
the larger rock itself. it follows that as
trap rock Is considered an excellent
material for road building. trap rock
gravel should occupy the same relative
rank among the gravels. Limestone IS
generally speaking. soft rock. and
consequently limestone gravel. which
Is quite rare. will usually be found
soft and will wear rapidly. Quartz
possesses practically no binding power.
although Il is very hard Therefore
gravel which contains an exception
ally large percentage Of quartz will not
prove successful. as il will fail to con
Solidate unless Il contains binding ma
terial. or unless a good binder Is added
In order that the material may bind
readily the pebbles should be angular
and sh0nld vary in size so that the
smaller fragments may an the voids
between the larger pieces. Gravel OBJ
tanned from streams is usually inferior
TO pit gravel for the reason that the &C
ton Of the water has worn the pebbles
smooth and practically al the fine
binding material has been removed by
the same agency. Even II clay OF loan
Is mixed with river OF creek gravel the
result is not likely 10 be as satisfactory
as that obtained by the use Of pit gray-
e. Pit gravel frequently contains too
much clay OF earthly matter while river
gravel may have too much sand In
such cases r. Is sometimes advisable to