The Magnolia gazette. [volume] (Magnolia, Miss.) 1872-current, 1883-10-04

dinary food tide and Of highest flood
tide. Some have concluded from these
facts that the interior Of the earth is in
fluid condition beneath thin crust,
and that this fluid matter is affected by
the tide-gcnorating forces OF the sun
and moon. But Prof. lie Conte has
said of this theory II il were true
the effect ought to be far greater than
we find II, y 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 il explosive, are often preceded
or accompanied by earthquakes. Earth
quakes also cease after eruptions from
neighboring volcanoes, and vice versa.
For instance, Strombol ceased eruptng
during the famous Calabrian earth
quake, and the earthquake in which
Riobamba was destroyed and 10000
people pershcd took place under simi-
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
areas Of the earth crust are connected
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 10 300
feet above the sea level, indicating that
tho whole southern end of South
America has at some time been elevated
to this extent. In the Mississippi val
ley earthquakes there was iissure, one
side of which dropped lower than the
other, thus forming what is new 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, II is said, orig
mate by the sudden suhterrancous 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 earth than
on the crust, consequently the crust is
forced upon itself by horizontal pres
sure, and where the crust rcsists 1t
yields suddenly by the formation Of fis-
sures. The yielding produces jar in
the interior Of the earth the jar pro-
4 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 phc.
nomena. For instance, in great earth
/ quakes the velocity with which the
shock travels rarely exceeds twenty
miles minute in small earthquakes It
runs up to 140 miles. In great earth
quakes the trough Of the wave is deep,
and consequently it is continually strik-
4 ing inelastic strata, whereas in slight
earthquakes the wave trough is shallow
andmeets 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
ltricts the original wave strikes an ine-
lastic stratum before emerging and
/ is DETECTED, Other phenomena are ex-
planned by the wave theory
i The great sea waves which sometimes
accompany earthquakes are formed 1y
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
an hour after Lisbon was destroyed by
an earthquake a great sea wave sixty
feet high came rushing iD.--M u SIN.