Evening star. [volume] (Washington, D.C.) 1854-1972, 1894-09-07
THE GOOD ROADS MOVEMENT
Practical Information Embodied in a Geo.
logical Survey Report.
The Binding Force Of PulverixeN
Stone - The Question of Grade
an Important One.

Practical information for guidance Of all
interested in the good roads movement 4
embodied in an - -. -
rret s;stes feolcxicaI survey on the
eeology OF re common roads of the United
Stated, prepared by Geologist N. C. shaler
The report outlines the history of Ameri-
can roads. discusses the geological relations
Of common roads. and the geological con-
dition Of road materials. and reviews the
sources of supply of road stones.
The Macadam InventiOn.
with the invention Of Macadam," says
Prof. Shaler. "a new path in the road con-
struction was opened. The peculiar ad-
vantage arising from this discovery is that
roads can be constructed at a relatively
small expense as compared with pavements
made Of blocks. and the work can be done
In many regions where suitable paving
blocks cannot be obtained. If a mass. Of
broken stones Is allowed to lie with the
fragments resting on each other no evident
trace OF cementation takes place. but II
the materials be repeatedly traversed by
heavy wheels or a roller of great weight
then as soon as II Is wet the cementation
sets % IN. This fixing Of the bits of stone
together has been attributed to the inter-
iacing OF their rough surfaces when they
are driven together. The effect however
IS due mainly to the fact that the friction
VI oiI O1l Ott pTOOuCeS Dy tne STlnOln& 6c-
ton sufficient amount Of powdered rock
to form the required cement. The binding
strength Of the cement exists in some
measure with all the species Of stone No
decayed stone retains the capacity Of ce-
mentation when powdered, though in some
few cases where material is charged with
iron oxides 1t may undergo a certain bind
ing. and no ordinary fiinty gravels free
from iron oxides can be made to form
firm road bed. Pebbles, even though they
cannot be made to cement in their natural
state. will do so when broken into bits.
Thus the Macadam invention can be applied
in three Ways: breaking stone, which Is
taken from the quarry; using stone broken
by natural processes, and which is not de-
cayed, and by rebreaking pebbles, which. in
their natural state, cannot be made to unite
by the cementing processes.
The volcanic rocks, the dyke stones and
large crystalline masses and the superb
eial lavas are the best fitted for road max
Ing, and Of these the material known as
basalt Is much the best. The lavas which
have cooled in assures are stronger than
those found on the esrth's surface.
The Grade Question.
'.Alrncst as important as the character of
the road surface is the grade, and exper-
ience shows that except under peculiar con-
ditions 1t II very improbable to build roads
having five feet of fall in each 100 feet of
length"
In general, the report concludes: "The
create part Of the United States is char
acterized by great seasonal variations and
those climatic features which most affect
the conditions of carriage roads, There is
prevailingly an alienation Of heavy rain
fall and protracted drought During rain
periods the roads are subjected to a deep
penetration OF water and serious washings.
In the dry season the upper surface be-
comes powdery, and these conditions make
high-gIade roads peculiarly necessary, and
make their maintenance costly.
The great range of temperature is a con-
siderable disadvantage to our roads. An
other disadvantage arises from the fact
that almost half the area Of this country
that part Of 1t having nine-tenths Of its
crop giving value, lacks adequate materials
for highway construction.
'Our railway authorities should be brought
to realize the importance to the develop
ment Of their ways in favoring the trans
portation over their lines Of roadmaking
materials. The greater number Of roads
In this country are, in effect, branches of
one or more railways. So far only a few
railways have been disposed to foster the
betterment Of highways by fixing the
charge for materials for their construction
at actual carriage cost"