The Manitowoc pilot. [volume] (Manitowoc, Wis.) 1859-1932, 1884-08-28
Earthquakes.

Prof Samuel kneeland, a. NJ, M. ID. 4,
of Boston, saws in lecture on earth
quakes:
The old theories of the causes of vol
canoes have gradually lost the conf
dence of Geologists. Mallet's theory is
now generally admitted as the best ex-
planation, to-wit, that in cooling from
highly heated nebulous matter, the
crust OF the earth has shrunk upon the
center, more readily according TO its
thinness, and the most so, therefore. in
former geological ages; this shrinking
and falling in of strata of immense ex-
tent and thickness. by the motion, de-
velop a great amount of heat, sufficient
to melt rocks and the sedimentary de-
posts between the crust and the nucle-
us, which, by the agency of steam from
the admitted waters, are brought TO the
surface in the form of lavas.
That the same cause has produced
both the elevations and depressions or
the earth's surface may be inferred
from the fact that the height of the
loftiest mountains and the depth of the
deepest ocean are about alike. AS con-
nected with the cause of earthquakes
here maintained, it may be mentioned
that the 1874 eruption of VeSuvius
yielded 46. 900, coo cubic feet of lava,
that of Etna, in 1869, twice that
amount, and that OF Skaptar Jokul, in
Iceland, in two years, twenty-ono cubic
miles. Where the heat generated by
friction of subsistence is not sufficient 20
liqUify the rocks, mud volcanoes, as n
Java and Hawaii, are produced; and rs
the volcanic energy lessons, geysers and
hot springs denote the expiring forces.
Though in such localities you may ex-
peet the earthquake, as a rule you need
not fear all outburst.
The theories of earthquakes are nu-
merous, and fanciful in the extreme
No satisfactory connection with at
mospheric conditions has been proved,
except as a mere accessorv; they occur
everywhere at all seasons of the year
and in ali geologic formations and
times. They seem to follow no law of
periodicity, and are apparently indie
pendent of volcanoes. The theory of
their nature now usually accepted is
that OF Mallet, viz, that an earthquake
Is the passage Of u wave past an opserv-
er. in any direction, with q force and
velocity depending on the activity of
the cause and the nature of the strata
through which it passcs-a vibratory
movement like that OF wave of sound.
transmitted, reflected and refracted by
the earth; il may originate beneath the
sea, causing a destructive tidal wave
hundreds of miles distant This wave
can be measured by cunningly devised
instruments.
Having visited the earthquake-rent
districts of Iceland, the Sandwich and
PHILIPPINE Islands and the Medtterra-
mean basin. | am of the opinion that al
most all OF the extended modern earth
quakes have been the result of subsid-
ence and not of explosions.
Wherever in the cooling. shrinking
crust, support is taken away by con-
traction, pressure, chemical action,
emission of lavas, corroding and heated
waters, occasional explosions, aided
possibly by terrestrial, meteorological
or astronomical causes, the strata fall
in; these may be hundreds of miles in
area and leagues in thickness, with
more or less violent depression, pro-
ducing shock which may be transmit
ted to great distances by land OF be-
hCtiIi tlC NtlCl. LII CGEIIlu lEdCIuIcS
OF the crust, produced even in remote
geological ages and in favorable strata,
much heat and consequent chemical
action may liquefy the surrounding
rocks and cause Il flow of lava. This
undermining or corrosion | conceive TO
be the predisposing cause of earth
quakes. the shock being the effect car
rled for long distances, with violence
and direction depending on the elastic
character OF the strata.
In old geological times the disloca-
tions or uplifts of strata, called
faults. y were doubtless accompanied
by earthquakes and were then their
most common cause; but, Us the tension
and pressure which formed the then i'm
mense folding have in a great measure
ceased, supsidence may be q more sat-
isfactory explanation than upheaval