Polk County observer. (Monmouth, Polk County, Or.) 1888-1927, 1907-02-15

SPREADING CHERT MATERIAL ON ROAD
appearance The two rocks differ ma
terially in their origin. Cherts occur
usually in chalk and limestone forma
tions and are generally believed to bG
formed by chemical precipitation
from sea water. Novaculites, on the
other hand, are thought to be true sed
lmentary rocks, having been formed by
deposits of very fine material-slt and
sand-in sea water and subsequently
solldified The useful qualities of no
vaculitcs as oilstOnes for sharpening
fine tools are well known and are due
to the hardness and smoothness of this
rock.
In order that road may bind we'll
its surface must be composed of fine
particles of suitable rock which form
the bond. If these partieles'are blown
or washed away they must be replaced,
or the bond will be broken and the
road will ravel. Whcn roads are sur
faced with limestone or ebert com
paratively light traffic can be depend
ed upon to supply enough binder to
keep the road from raveIiug. For this
reason these materials ara better adapt
ed to light traffic thar harder and
tougher rocks.
When bank cherts are first spread
upon the road they are sometimes soft
and brittle and apparently almost use
less as road material, but when
the materials are exposed to the action
of traffic and the elements the surface
soon becomes a solid, compact mass.
Cherts and novaculites are Invariably
found in sedimentary formations. The
material Is also found sometimes com
pletely covering the ground, sometimes
In the beds Of streams and narrow val
leys, where it has been deposited by
the action of the water and again in
banks and pockets on hill and noun
tain sides. Cherts are usually found
in nodular masses, but, like novacu-
lltes, may occur in angular fragments,
varying in size from about one to six
inches.
Where these materials ale found in
banks or the beds of streams they are
commonly called gravel Creek gravel,
formed from ebert or novaculite. Is
usually of uniform size and compara-
lively clean, while the bank gravel
often contains earthly matter and fine
particles of the same material. The
creek gravel usually wears the best,
but it does not bind so readily Or form
as smooth a surface as the bank de
posits. Where both creek ana bank
gravel is available good results can
be obtained by using the former for
foundation and the latter for wearing
or binder course. The writer used
this method at Florence, Ala, with
marked success.
Where the material is plentiful and |
where a good quality of bank gravel
Is available for binder it is unneces-
sary to go to the trouble and expense
OF cutting out subgrade or to pre-
pare earth shoulders, as is done for
regular macadam. If the shoulders
are dispensed with, however, it is abb
solutely essential that the surface
course contain a sufficient quantity of
good binding material; otherwise the
Dond will soon be broken, the material
VIII spread, and much of it will even.
tually be forced or washed into the
side bitches. The rOadbed shopId of
course be shaped with a road machine
betore the material is placed and given
a Slight crown of from three-eigbtbs to
Ohe-half Of an inch to the foot from
the center to the sides The founda.
uon Should then be rolled and the mate.
rial for the first course spread in two
layers and rolled and sprinkled in tbe
usual manner. The spreading Of the
material can be accomplished by the
use OF a road machine, provided the
gravel Is not too large. The total
depth of material may vary from four
TO nine inches at the center as sofI
and traffic may require, and grodua7.
" diminish in thickness to what Is
commonly called a feather edge" AT
lne sides If the most approved meth
oa Is followed, shoulders should be nro.
Vided to hold the material In pIace
Inc material should then be spread to
uniform depth from the center 10
Iides. "