Evening journal., 1907-02-13

SPREADING oHERT MATERIAL ON A ROAD.
appearance. The two rocks differ ma
terially in their origin. Cherts occur
usually in chalk and limestone forma-
tons and are generally believed to be
formed by chemical precipitation
from sea water. Novacultes, on the
other hand, are thought to be true sed-
imentary rocks. having been formed by
deposits Of very fine materlal--sllt and
sand-ln sea water and subsequently
solidihed. The useful qualities Of no
vacultes as oilstones for sharpening
fine tools are well known and are due
to the hardness and smoothness Of this
rock.
In order that a road may bind we'll,
its surface must be composed OF fine
particles Of suitable rock which form
the bond. II these particles are blown
or washed away they must be replaced,
or the bond will be broken and the
road will ravel. When roads are sur
faced with limestone or ebert a com
paratively light traffic can be depend
ed upon to supply enough binder to
keep the road from ravellng. For this
reason these materials are better adapt
ed to light trahic than 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 a 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 sedlmentary formations. The
material is also found sometimes CON-
pletely covering the ground. sometimes
In the beds OF streams and narrow val
leys, where II 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 noduiar masses, but, like novacu-
lites, may occur In angular fragments.
varying in size from about one to six
inches
Where these materials are found In
banks or the beds Of streams they are
commonly called gravel Greek 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 II does not bind so readily or form
as smooth a surface as the bank de-
poslts. Where both creek and bank
/ rnT Il
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 a binder II is unneces-
sary to go TO the trouble and expense
Of cutting out a subgrade OF to pre-
pare earth shoulders. as Is done for
regular macadam II the shoulders
are dispensed with, however, Il is abb
solutely essential that the surface
course contain sufficient quantity of
good binding material; otherwise The
bond viii soon be broken, the material
will spread, and much Of Il will even
/ tually be forced or washed into the
side dltches The roadbed should Of
course be shaped with a road machine
before the material Is placed and given
a slight crown OF from three-elghkls TO
one-half OF an inch to the foot from
the center TO the Sides The founda-
ton should then be rolled and the mate
rial for the first course spread In two
layers and rolled and sprlnkled ia the
usual manner. The spreading OF the
material can be accomplished by the
use OF 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 soil
and traffic may require. and gradual
/ ~ diminish in thickness to what is
! commonly called a feather edge" at
the sides. II the most approved meth
cd is followed. shoulders should be pro
vided to hold the material in place.
The material should then be spread to
a uniform depth from tbs caateE to
sides.