The Mankato free press. [volume] (Mankato, Blue Earth County, Minn.) 1879-1924, 1912-05-03

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
number of times. During each OF
these periods or continental submer-
gence the harder rock remanents along
the inner margins of the oceans adj
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. "s .... ....
Gravel roads and macadam roads
alike have often received sweeping con.
formations as unsatisfactory when the
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
Tn nj. of grading
and drainage and other details In con-
nectiOn' with tile construction or q
gravel road should be done with as
much care and thOroughness as in the
case Of a macadnm road. Moreover, in
the one case as in the other specifica-
lions must be adapted to varying local
conditions. Of course, the gravel itself
must be selected with care. That which
contains sufficient quantity of bind
ing material so that it stands as ver-
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. e ~ "2
There are three important qualities
which should be possessed by road
building gravel hardness, toughness
and cementing or binding power. or
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 ana
in part to the angular shape and size
of the pebbles composing the gravel
Blue gravel is universally conceded to
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 or
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 it is very hard. Therefore
gravel which contains an exception
ally large percentage of quartz will not
prove successful, as it will fail to con-
solidate unless it contains binding ma
terial, or unless good binder Is added
In order that the material may bind
readily the pebbles should be angular
and should vary in size so that the
smaller fragments may fill the vOids
between the larger pieces. Gravel OBJ
tanned from streams is usually inferior
to pit gravel for the reason that the ac-
ton of the water has worn the pebbles
smooth and practically all the fine
binding material has been removed by
the same agency. Even If clay or loan