The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1886-09-05
EARTHQUAKE THEORIES.
Professor MCGEE Holds that the Coastal PIasl
Has Slipped Seaward.

Professor MCGEE Holds that the Coastal Plain
Has Slipped Seaward.
Charleston Special.
Professor McGee's theory of the earthquake,
or rather the one which he adopts as a working
theory. is at entire variance with the accepted
opinion here, but seems most reasonable HIS
says: 1T is simply a seaward slip. In saying
this assert nothing, but state what appears to
be the most intelligent working theory for phys
cists"
What is seaward slipq
1t is movement of the coastal plain toward
the sea. Let me say in round terms that we di
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 fraemental rock, aud
is called the coastal plain The theory is that
this coastal plain has simply slipped seaward a
bit, and that the displacement produced the
shock tremor."
''What caused it to sipa'
There is a tendency in that direction. I'm
agine surface slightly inclined with this coastal
plain everything it. A hundred miles or so out at
sea there is sharp depression. The tendency
OF the coastal plain is toward 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 a slip
occurs. This may come from the readjustments
of the earth's surface constantly going on, or
from the fact that the great rivers flowing out of
the mountain ranges continually loading the
coastal plain with the deposits they bring. In
this way the point may be reached. and doubt
less has been reached, where the resistance is
overcome and the forward movement occurs"
Has this seawar6 tendency been noted be-
foreq"
ION, yes; in the Middle States its work has
been recorded for a long time The movement
there has been so gradual that there have been no
very violent shocks. Observations have been
less accurate and widespread in the South Allan
tic States, and less is known of the movement
"You have found nothing since coming here to
break Your theory2"
Nothing; may say that everything is confirm
atory as far as l have gone There is absolutely
no reason to believe that volcanicsm has any
thing to do with this earthquakes On
the contrary, there is every reason to
believe 1t had not. | have heard of
nothing that cannot be explained by the theory
of displacement The area of disturbance alone
IS strong suggestion in this direction. 1t is,
perhaps, the largest area recorded for any earth
quake. Volcanic disturbances are usually local
while the slip of a coastal plain hundreds Of
miles in length may affect half continent"
asked how he explained the twisting of rail
road track in opposite directions to the slips.
D6CduSC Gu0Eo Is d FenuGub mOttOu OL LuO
land, just as there is of a wave. You see chin
neys that have fallen both ways. Sup
pose" the Professor continued, taking a
piece Of bread and cutting it in twa
almost entirely through and holding i.
at angle, ''the upper piece of this bread
was to slide on the lower piece If had cut IL
clear through there would have been no resist
arce except the friction, but as it is joined to-
gether at the end there is additional resistance
in the effort to tear loose; there is produced
crlnEinp what call C0rruUatjOn This
slstance would also Cause 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 ''ffty saucers
and tie an elastic string to them, then pull the
saucers by the string You will find the saucers
do not follow the elastic. Pull in steady mo-
perfectly steady hand The jerky motion is
caused by the difference in what is
called starting friction and sliding
friction. The jerks of the saucers and their
stops and starts would not be synchronous. Each
would act Independently OF the other. So with
every part of the coastal plain In responding
to the force that urged il 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 a. one point than at an.
other
''Do you think the general movements overf4
II do. / think the pressure has been satisfied.
and that there will be quiet for perhaps long
geological period. The tendency TO the sea will
continue, however and the movement will con-
tinue, but it may be nappreciable to the general
public. 1t is probable that no more trouble will
result and that the slight shocks now notable
here and there are the subsiding tremors. Per-
haps 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 eiscted
from the assures and the distinct sulphurous
smell Of the water were volcanic hints.
mot at all" he replied sin Florida notably.
and about Charleston, also. there are mineral
salts and sulphurets in the everything beds OF
fragmental rock. There are frequent saline and
sulphur springs and wells. This accounts for
the salty or sulphurous taste of the water eject
ed 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
three thousand feet to solid rock in this region.
The enormous composite above the solid rock is
the fragmental or coastal plain that has sudden
ly been displaced Imagine such a mass. hun
dreds of miles in length and BREADTH slipping
forward. Calculate the friction of this mass as
it is moved forward over the surface of the bed
rock, and you can form an idea of the disturb
ance it makes. Consider that this moving mass
is elastic, of different thicknesses and compost
tion You see how the movement is irregular,
and how, on finally adjusting itself after its dis
location, there may be prolonged minor tremors
and quakings in certain localities"
asked if the granite section or the Piedmon'
escarpment was far safer from earthquakes
than the coastal plain.
''That is doubtful" he replied. "Granite con-
veys the tremor or visitation much more dis
tinctly 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 seaward tendency, but as the coastal
plain is displaced reactonary tremcfs will reach
the granite as in this case You reIaember there
were shocks in the coastal region at Augusta
and Charleston several days before the displace-
ment actually occurred These were not felt in
the granite region. When the slip came, how
ever, there were tremors in the Piedmont es-
carpment There probably fitting of
granite edge. as the weight of the coastal plain
was shifted further seaward."
Tracing the Shake tn the Mediterranean.
CHARLESTON, s. c., Sept. 4-The Nows and