The St. Charles herald. [volume] (Hahnville, La.) 1873-1993, 1883-11-10
HAHNvHLE LOUISIANA, SATURDAY, NOVEMBER TO- 1885,

tide. Some have concluded from these
facts that the interior of the earth is in
a fluid condition beneath thin crust,
and that this fluid matter is affected by
the tide generating forces of the sun
and moon. But Prof. Le Conte has
said of this theory: Z" If it were true
the effect ought to be far greater than
we find it, and he concludes that il IS
better to regard the position of the
moon as an incidental phenomenon.
1t may be regarded, however, as al
most established that the forces which
produce earthquakes and volcanic erup-
tions are closely allied. Eruptions, es-
pecially if explosive, are often preceded
or accompanied by Ell thquakes. Earth
quakes also cease after eruptions from
neighboring volcanoes, and vice versa
For instance, Stromboli ceased erupting
during the famous Calabrian earth
quake, and the earthquake in which
Riobamba was destroyed and 10000
people persisted took place under SINH
lar circumstances. An earthquake map
prepared by Prof. Mallet shows that
the distribution of earthquake centres
Is much the same as that of volcanoes
Elevation and depression of great
6ACdo VI tl0 Ctbthn utt COnUttIeu
with earthquakes. After the South
American earthquake in 1855 the coasts
of Chill and Patagonia were elevated
from two to ten feet, and old beach
marks are found there from 100 to |, 300
feet above the sea level, indicating that
the whole southern end Of South
America has at some time been elevated
to this extent. In the Mississippi val
ley earthquakes there was tissure, one
side Of which dropped lower than the
other, thus forming what is now called
the "Sunk Country" around the mouth
of the Ohio.
From the phenomena of volcanic
eruption and of the movements of great
areas two separate theories have been
formed Earthquakes, it is sad, orig
mate by the sudden subterraneous for
nation or escape of vapor. This will
account for local earthquakes, but not
for the movements of large areas. Both
! phenomena seem to be covered by the
following theory There is greater con-
traction in the interior of the eal tn than
on the crust, consequently the crust is
forced upon itself by horizontal pres
sure, and where the crust resists II
yields suddenly by the formation of ifs
sures. The yielding produces jar in
the interior of the earth the jar pro-
duces an earthquake the earth wave
reaches the surface at what is called the
epicentrum, and spreads from that
point.
The wave theory explains many phe.
nomena. For instance, in great earth
| quakes the velocity with which the
| shock travels rarely axceadq txvaptV
miles minute; in small earthquakes it
runs up TO 140 miles. In great EARTH
quakes the trough of the wave is deep,
and consequently 1t is continually strik-
ing inelastic strata, whereas in slight
earthquakes the wave trough is shallow
and meets few interferences. The inter-
ferences gradually break the force of
the wave. Again, in all earthquake re-
gions there are districts called bridges
which are not affected. In these dis
tricts the original wave strikes an inc
lastic stratum before emerging and
is detected. Other phenomena are ex-
| planned by the wave theory.
The great sea waves which sometimes
accompany earthquakes are formed oy
the point of emergence of the original
earth wave being on the sea bed, the
sudden upheayal of which lifts the mass
of water above, which in falling spreads
| like other waves. This great wave
reaches the shore after the earth
waves, which travel faster have
| wrought their destruction. Thus half
dan hour after Lisbon was destroyed by
IL earthquake great sea wave sixty
e high came. rushing mn X Snn.