, 1886-10-02
r4g PHENOMENA Of EAarsou.kes.


V "
whatever part of the world observed.
and whether from a volcanic vent on
land O beneath the ocean, is accom-
panied by earthquake shocks of greater
or less violence and duration; while, on
the other hand. those observing earth
quakes speak of them as accompanied by
volcanic eruptions. and of their often
being stopped on the opening of volcanic
vents. 1t is. however, an important
fact that, although regions of active vol
canic action are those of most frequent
earthquake movements, yet the most
violent earthquakes do not appear to
have occurred in those regions, but, on
the contrary, in districts lying some de-
grees AVA from the worst volcanic ac-
ton.
The phenomena connected with earth
quakes have been ~variously described.
Many writers refer to appearances in the
heavens of changes in the atmosphere.
Others tell of Irregularities in the season
preceding or following the shock; of
sudden gusts of wind, interrupted by
sudden Gains; OF violent rains at unu-
sual seasons; of a reddening of the suns
disk and of a haziness in the air, often
continued for months. But these are so
irregular in their appearance, and have
been 50 seldom observed associated with
more than a single earthquake, that, in
the absence of any decided reason to the
contrary, there seem good grounds for
believing they have no real connection
with the earthquake. 1t is different with
underground noises, which frequently
precede, accompany or succeed the &C.
currencer of earthquakes, or some of the
shocks of them. They are undoubtedly
intimately connected with the shock, yet
earthquakes occur, even of the greatest
violence, which are unaccompanied by
any sound whatever. Different descrip-
tions have been givon of these subter-
ranean noises. In some earthquakes
they are likened to chains pulled about,
increasing to thunder; in others the
sound is like the rumbling of carriages,
growing gradually louder, until it equals
the loudest artillery; or like heavy
wagons running away upon a road; or
like the kissing produced by the quench-
ing of masses of red-hot iron in water;
like the rush of wind underground.
The more intimate earthquake phe-
nomena are more uniform. Sometimes
there is nothing else felt than a trem-
bling or gentle motion of the surface,
without producing any injury. In Sc
we're earthquakes the almost invariable
succession of phenomena is first a trem-
bling, then a severe shock, or a success
sion of shocks, and then a trembling,
gradually becoming insensible.
violent shocks are instantan
very few in number. In the ii IS
between, these smaller shocks or trem-
blings take place. The severe shocks do
the mischief. AT the point or line Of
greatest disturbance the shock has a dis
tinctly v~erticle direction, coming from
below upward. Leaving this point the
direction of the motion becomes more
horizontal, gradually, also, decreasing
in intensity until it becomes insensible.
This progressive movement is produced
by an earth wave, or true undulation of
the solid crust of the earth. The whole
mass of the area is not moved at once,
but only the wave-crest.
In the case of the earthquake at Lis
bon the progress of the wave was
roughly calculated. 1t was shown to
have had a very great velocity and to
have lasted only for an instant at any
one spot. The area affected on this oc-
casion vas very extensive. The shock
was felt on the one side as far as the
southern shores of Finland, and on the
other it reached beyond the st. Lawr-
ence in Canada, and was observed in
some of the West India islands-an area
of no less than 1900, 900 square miles.
The force required to move this must
nave been enormous, for, s%upposing the
thickness of the earth's crust moved to
have been no more than twenty miles,
then $50, 900. 900 cubic miles of solid
matter were moved. The influence of
this earth wave is communicated to the
sea when the earthquake is near the
shore or on the bed of the ocean. Tho
sea swells and slightly %retires from the
beach, and then a great wave rolls in
upon the shore. AT the Lisbon earth
quake this wave ose to the height of
sixty feet at Cadiz.
The regions that are far removed from
active volcanoes, yet specially subject to
earthquake shocks, are, in the order of
the severity of the phenomena, the
Himalaya mountains and India, Syria,
Algeria, the west coast of North Amer
lea, the Mississippi valley, Scotland, New
England and the st. Lawrence valley.
The regions that are at present COM
paratively free from sensible earth
quakes are Egypt and the eastern and
southern portions of Africa, northern
Europe and Asia, Australia, many por-
tions of North America, the eastern por-
portion Of South America, and Green
land.
OF sudden changes produced by
earthquakes nay be noticed the eleva-
tions during the earthquake at Concep-
cion in 1885, and the depressions attend
ing the shock at Lisbon in 1875. OF
slow movements examples are found in
the upheaval of the Scandinavian
peninsula, which is now proceeding at
the rate on its eastern coasts of five feet
per century. About one half of the
islands in the Pacific ocean are believed
TO be rising, as also the island of Spitz-
bergen, the West Indies. and the whole
of the west coast of South America.
Among the most remarkable slow de
pressions are the cases of the southern
portion Of Greenland, the numerous
coral-reefed islands inc atolls of the
Pacific, and the countries of Holland,
Belgium, Denmark, and the south shore
OF the Baltic sea. In North America
the most notable well defined case of de-
preston is that now in progress along
the Atlantic coast from Cape Cod to
Cape Hatteras. which region is calcu-
lated to be sinking at the rate of about
two feet per century.-Chicago Herald.
Waterspouts occur almost daily of
Key West.