The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1899-06-25

and should possess by all means cement
ing and recementing qualities. For the
Southern states, where there are no ffoStS
to contend with, the best qualities of
limestone are considered quite satisfac-
tory so far as the cementing and re-
cementing qualities are concerned, but
In most cases roads built of this class
of material do not stand the wear and
tear of traffic like those built of trap
rock. and when exposed to the severe
northern winters such material disinte-
CRATES very rapidly. For broken rock,
niger heads" technically known as
diabase and dioritess are considered by
most road engineers of long experience
to be the very best stones for road build
ing. Trap rocks as a rule possess all the
qualities most desired for road stones.
They are hard and tough, and when prop
erly broken to small sizes and rolled
thoroughly, cement and consolidate into
a smooth, hard crest which Is impervious
to water, and the broken particles are
so heavy that they are not readily blown
or washed away@Gg -
Unfortunately the most useful stones
for road building are the most difficult to
prepare, and as Crap Brooks are harder
TO break than any other stones they
usually cost more, The foundation or
lower courses may Be formed of some of
the softer stones, like gneiss or lime
SNOiAO' NuI Trap TOCk SHOULD. De uSeO TOT
the wearing surface, If possible, even If
1t has to be brought from distance
AS to construction of smacadam roads
Mr.. Potter says
In the construction of a macadam road
In any gwen locality, the question of
economy generally compels US to use
material found near at hand and where
a local quarry does not exist field stone
and stone gathered from the beds of
rivers and small streams may often be
made to serve every purpose. Many of the
stones and boulders thus obtained are
OF trap rock, and in general it may be
said that all hard field and river stones
IL broken. to proper size, will make fair
ly good and sometimes very excellent
ROAD metal. No elaborate test is required
to determine. the hardness of any given
specimen. steel hammer in the hands
OF an Intelligent workman will reveal in
general way the relative degree of
toughness of tive or more pieces of rock.
Field, and river stone offer an additional
advantage in that they are quickly
handled, are generally OF convenient size.
and are more readily broken either by
hand or by machine than most varie-
ties OF rock which are quarried in the
usual way
The size to which stone should be
broken depends upon. the quality OF the
stone. the amount OF traffic to which the
ROAD Will be subjected and to some ex-
tent upon the manner in which the stone
is put in place If a hard toug! stone
IS employed it may be broken into rough
cubes or pieces of, ebolt one and one-half
inches in largest face dimensions. and
when broken to such a size the product
of, the crusher- may generally be used
to good. advantage without the trouble
of screening, since dist 'tailings" and
fine stuff do noeS accumulate in large
quantities in. the breaking of the tougher
stone.
If only moderate traffic is to be pro-
vided for the harder Iimestones may be
broken so the pieessSwfl1 pass through
two-1nch ring, though Szes running from
two and one-Quarter to two and one-half
inches will lDsureGat more durable road
way, and If, ,steamf roller is used in
compacting the metal. it will be brought
to a smooth surface without much trou..
BILE. AS rule it may be said that to ad-
here closely to a Size running from two
and one-quarter 10 two and one-half
inches in largest f9ees dimensions, and to
use care In excluding toe large a proper
ton of small stuff as well as all pieces Of
excessive size, will ENSURE a satisfactory
and<durable macadamiroad. :" '@
Macadam Insisted that no large stone
should ever be employed in road making,
and, indeed, most modern road builders
practice his principle that small angular
fragments are the cardinal require
& ments.'' AS a general rule it has been,
stated that no stone larger than a walnut
should be used for the surfacing of roads.
MACADAM AND TELFORD.
Stone roads are, built IN most cases
according to the principles laid down by
John L. Macadam, while some are built
aby the methods advocated by Telferd.
The sTaest9 Important difference. between
these two principles. of construction re-
lates to the propriety, or necessity of a
paved foundation beneath the crust of
broken stone. Telford advocated this
principle, while Macadam strongly denied
its advantages. r.
The macadam road consists of mass
triangular fragments of rock usually in
layers upon the eroadbed or prepared