The weekly Floridian. [volume] (Tallahassee, Fla.) 1867-19??, 1886-09-09

A Theory OF the Earthquake.
Henry l. Grady, of the Atlanta Con-
ssitusion, writes from Charleston to the
N. Y. World. We extract:
PRorKssoR NcoEx's THEORY OF THE CAUSE.
A scientific inquiry ID being made into the
cause of the earthquake by Professor Mc0ee, OF
the Geological Survey, with competent assist
ants Professor McGe2 h rapidly systematizing
the information put in his hands, and to-day
gave your correspondent an interesting talk
His theory of the earthquake, or rather the one
which he adopts as . working theory. Is at entire
seems most reasonable. He says:
1t Is simply q seward slip. In saying this
| assert nothing but state what appears to be
the most intelligent working theory for physi-
cists"
"What Is q seward slip"
ut is movement of the coastal plain towards
the sea- Let me say in round terms that we d.
vide the region this side of the Appalachian
range into two portions. The granite or gneiss
formation is called the Piedmont escarpment,
and extends from the mountain ranges to about
where Columbia is. The region this side of
that is made up of what we call fragmental rock,
and is called the coastal plain. The theory is
that this coastal plain has simply slipped seward
q bit, and the displacement produced the shock
or tremor."
what caused it TO slipf'
There is q tendency in that direction. I'm
agine surface slightly inclined with this coastal
plain everything it. A hundred miles or 80 out
at sea there is sharp depression. The tendency
OF the coastal plain is towards that depression
Were it not for the resistance of friction this
movement would be constant until the tendency
was satisfied. In spite of friction, however, the
coastal plain reaches the point where the pres
sures overcome the resistance, and then slip oc-
1r,rc from fho obi TO IF
the earth's surface constantly going on, or from
the fact that the great rivers flowing out of the
mountain ranges are continually loading the
coastal plain with the deposits they bring. In
this, way the point may be reached, and doubt
lessa has been reached, where the resistance
ours"
Has the seward tendency been noted be-
fore?"
ooh, yes. In the Middle States its work has
been recorded for long time. The movement
there has been 80 gradual that there have been
no very violent shocks. Observations have been
less accurate and widespread in the South At
lantfc States, and less is known of the move
ment"
You have found nothing since coming here
to break your theoryy"
Nothing may say that everything is con-
frmatory as far as have gone. There is absO-
lutely no reason to believe that volcansm has
contrary there is every reason to believe it had
not. l have heard of nothing that cannot be ex
planned by the theory of displacement. The area
of disturbance alone is strong suggestion in this
direction. 1t is perhaps the largest ever recorded
for any earthquake. Volcanic disturbances are
usually local. while the slip OF a coastal plain
hundreds of miles in length may affect half a
continent"
l asked how he explained the twisting of the
railroad track in an opposite direction TO the
slips?
Because there is a refluent motion of the
earth; you sec chimneys that have fallen both
ways. Suppose the Professor continued,
almost entirely through, and holding it at an
angle; the upper piece of this bread was forced
to slide off III lower piece. If had cut it clear
through there would have been no resistance ex-
cept the friction, but as il is joined together at
the end, there is additional resistance in the eff
fort to tear loose. There is produced crink-
ling, or what we call corrugation. This resist
ance would also increase the reaction which
pushes the earth in the opposite direction from
which it had slipped
asked how he explained the shocks which
still continued at Summerville.
Suppose you take" he said, i" fifty saucers
and tie an elastic string TO them. Then pull the
do not follow the elastic Pull in steady mo-
ton. They come in jerky, although you pull
with perfectly steady hand. The jerky mo-
ton is caused by the difference in what is called
starting friction and sliding friction. The jerks
of the saucers, really their stops and starts,
dependeutly of the other. So with every part of
the coastal plain. In responding to the force
that urged it forward, it went in jerks, or by fits
and starts, and these movements are Independent
of each other, and may be more violent or last
longer at one point than another"
49, ~ =
over?"
II do. think the pressure has been satisfied
and that there will be quiet for perhaps long
geologic period The tendency to the sea will
continue, however, and the movement will con-
tinue, but it may be inapprecable to the gener
al public. 1t is probable that no more trouble
will result, and that the slight shocks now notice
able here and there are the subsiding tremors.
Perhaps the movement may be gentle hereafter
in the South Atlantic States, as it has been in
the Middle States.
Some one suggested that the blue mud elected
from the assures and the distinct sulphurOus
smell of the water were volcanic hints
Not at al" he replied. In Florida, nota
bly, and about Charleston also, there are min
eral salts and sulphures in the everything beds or
fragments of rock. There are frequent saline
and sulphur springs and wells. This accounts
for the salty or sulphurous taste of the water
elected from unusual depths in this section. The
blue mud is simply mud which is found deep
down in the earth in this region. 1t is about
5000 feet to solid rock in this region. The enor-
nous composite above the slide rock is the frag
mental or coastal plain that has suddenly been
displaced. Imagine such a mass hundreds of
miles in length and breadth, slipping forward
Calculate the friction of this mass it is forced
forward over the surface of the bed rock and
you can form an idea of the disturbance it
makes. Consider that this moving mass is elias
tic, of different thickness and composition, you
see how the movement is irregular and how, on
finally adjusting itself after its dislocaton, there
may be prolonged minor tremOrs and Quak-
ings in certain localities"
asked if the granite section or the Piedmont
escarpment was not safer from earthquakes than
the coastal plain.
"That is doubtful" he replied "Granite con-
veys tremor or vibration much more distinctly
than fragmental rock does. While the granite
is not in the area OF displacement, the tremOr is
often sent backward from the line OF fault, as
we call it. The granite region is stable and has
no seward tendency, but as the coastal plain is
granite, as in this case. You remember there
were shocks in the coastal regions at Augusta
and Charleston several days before the displace-
ment actually occurred. These were not felt in
the granite region. When the slip come, how
ever, there were tremors in the Piedmont es-
carpment. There was probably fitting of the
granite edge as the weight of the coastal plain
was shifted further seward"
THE SHATTERED BUILDINGS.
Let me attempt to give an idea of the stua-
ton: You take carriage in any part of the
city, and order your driver TO proceed immedi-
ately. You pass sidewalks piled knee high with
debris. Every other house, and for blocks every
house. has lost its coping, porticos and often its
entire front. Great cracks from an inch 10 two