The new North-west. [volume] (Deer Lodge, Mont.) 1869-1897, 1884-09-19

EARTHQUAKES.

| earthquakes.
Prof Samuel Knceland. A. NJ, M D.,
of Boston. says 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-
| PLANTATION, 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 aud the sedimentary de-
posits 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 on
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 bo mentioned
that the 1894 eruption of Vesuvius
yielded 46. 000.0 600 cubic feet of lava,
that of Etna, in 1869, twice that
amount, and that of Skaptar Jokul, in
Iceland, in two years, lwcnty-one cubic
miles. Where the heat generated by
friction of subsistence IS not sufficient to
liquify the rocks, mud volcanoes. rs in
Java and Hawaii. are produced; and as
the volcanic energE lessons, geysers and
hot springs denote tho expiring forces.
Though in such localities you may ex-
pect the earthquake, as n rule you need
not fear an outburst.
The theories of earthquakes are nu-
merous. and fanciful in tho extreme.
No satisfactory connection with at
mospheric conditions has been proved,
except rs mere accessory; they occur
everywhere at all seasons of the year
and in all 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 wave past an observ-
er, in any direction, with force and
velocity depending on the activity of
the cause and the nature of the strata
through which it passes-a vibratory
movement like that of wave of sound,
transmitted. reflected and refracted by
the earth; it may originate beneath the
sea, causing destructive tidal wave
hundreds OF miles distant This wave
can be measured by cunningly devised
instruments.
Having visited the earthquakc-rent
districts of Iceland, the Sandwich and
Philippine Islands apd the Meditterra-
mean basin, | am Of the opinion that al
most all OF the extended modern earth
quakes have been the result of subsid-
encc and not of explosions.
Wherever in the cooling. shrinking
crust support is taken away by con-
traction. pressure, chemical action.
emission OF laras, 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 a shock which may be transmit
ted to great distances by land or be-
meath the water. In certain fractures
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 II flow of lava. This
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," were doubtless accompanied |
by earthquakes and were then their
most common cause; but, rs the tension |
and pressure which formed the then i'm |
mense folding have in a great measure
ceased, subsistence may be n more sat
isfactory explanation than upheavaL