The Republican. [volume] (Oakland, Md.) 1877-current, 1894-11-22
GEOLOGY OF ROADS.

DSe 1tSSH 0tOilS DO9S NOT cement ana
tSPoor Material For Road Metal
Tactical information for the
guidance OF all interested in the
go9i roads movement is embodied
IN On important report Of the United
St3es geological survey on the geol-
ogHof the common roads Of the
Un4ed States, prepared by Geolo-
glsIN. S. Shalor. The report out
lin@ the history of American roads,
discusses the geological condition
OF foad materials and reviews the
souices Of supply Of road stones.
fWlth the invention of macad-
am. +" says Professor Shaler, ga new
path in road construction was
oponed. The peculiar advantage
arising from his discovery is that
roads can be constructed at a rela-
lively 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 mass of
broken stones is allowed to lie with
the fragments resting on each other
NO evident trace of cementation
takes place, but if the materials be
| repeatedly traversed by heavy
WHO'S or roller of great weight
then as as soon as it is wet the
concentration sets in.
''This fixing of the bits of stone
together has been attributed to the
interlacing of their rough surfaces
when they are driven together. The
effect, however, is due mainly to the
fact that the friction of bit on bit
produces by the grinding action a
sufficient amount of powdered rock
to form the required cement. The
binding strength of the cement ex-
lists in some measure with all the
species of stone.
"No decayed stone retains the
capacity of concentration when pow
dered, though in some few cases
where material is charged with iron
oxides it may undergo a certain
binding, and no ordinary flnty
gravels free from iron oxides can be
made to form firm roadbed. Peb-
bles, 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
decayed, 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 superficial lavas are the
best fitted for road-making, 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 earth's
surface.
"Almost as important as the
character of the road surface is the
grade, and experience shows that,
except under peculiar conditions, it
is very uproftable to build roads
having five feet Of fall in each 100
feet of LENGTH
In general, the report concludes:
"The greater part of the United
States is characterized by great
seasonal variations and those eli
matte features which most affect the
conditions of carriage roads. There
is preYailingiy an alienation of
heavy rainfall and protracted
drought. During rain periods the
roads are subjected to deep pene-
tration of water and serious wash
ings, In the dry season the upper
surface becomes powdery, and these
conditions make high grade roads
peculiarly necessary and make their
maintenance costly" -Philadel- |
phia Press.