Ellsworth American. [volume] (Ellsworth, Me.) 1855-current, 1907-01-16
CONCERNING EARTHQUAKES.
Readjustments of Weight That Alter
the Earth Crust.

Readjustments of Weight That Alter
the Earth Crust.
The earth's crust is composed Of hetero-
geneous elements; but all possess one inn
portant property, flexibility, though in
varying degrees. Alike In very moderate
elevations and in lofty mountain chains,
the rocks are seen to have been thrown
into arches and troughs and even to have
been crnmpled and folded like sheets OF
paper or dislocated or broken up by the
enormous strains and stresses they have
been subjected to. These are the strikes,
dips, synclinals and anticlinals, faults,
folds, upthrows and downthrows OF geol-
ogists, modest examples Of which can be
seen anywhere in cliffs and even in quar-
res and railway cuttings.
OF these conditions prevailing beneath
the crust we know far less. When pits
are sunk the temperature increases pro-
gressive rate with the depth, boiling
springs are encountered, some making
their way to the surface, red-hot stones
and ash and molten rocks are violently ex-
truded through vents, but most signifi-
cant Of all to the geologist is the meta
morphism of rocks, which must have been
melted at relatively moderate depths, but
are now exposed on the surface in every
quarter of the globe.
There is thus the certainty that the
cooled surface is underlain at some not al
together inaccessible depth by rock in q
molten state, both fluid and pasty,
through heat. Below this is the intensely
heated solid sphere, to which astronomers
| assign the rigidity and density of steel,
and which is kept solid by compression OF
the external layers. Between the super
heated nucleus, kept solid by compression
and the cool enveloping shell in which
lies the COMPRISING force, some interme-
date condition must exist. With lessen
ing pressure nearer the surface normal
conditions must prevail, and rocks at'their
melting temperature must be in the liquid
state OF Stag from smelling furnace.
Our globe would therefore consist of an
outer cooled heterogeneous and flexible
crust, with a temperature increasing
downward and passing into rocks and
above the melting point in a liquid state,
which in turn overlie the heated nucleus,
kept solid by compression and of the
rigidisy of steel.
If the crust were undisturbed, the
molten layer upon which it rests would
be inactive; but atmospheric agencies,
frost and rain, are ceaselessly at work
transporting weight from the hills and
depositing it under the sea, decreasing
the pressure here and adding to it there.
The rivers debauch into the sea charged
with silt, which is eventually deposited
outside the influence of the surf, and the
breakers acting like rasp along the base
OF the cliffs, contribute their quota of
sediment, eroding and breaking up the
coast, the material being carried out by
the waves to swell the deposits forming
parallel to the shore within the littoral
zone.
Geology reveals that these deposits may
in time reach thousands of feet in thick
ness. simultaneously the removal of
weight by the breakers impairs the resist
ing power of the crust along the actual sea
margin. Thus two parallel lines are con-
tinually forming, the one of increasing
pressure and the other of decreasing re-
sistance.
Is the crust so flexible as to be sensible
to such readjustments of weight? In a
past age when perhaps man was already
among its inhabitants the earth suffered
in places from glacial period, when vast
ice caps formed over the elevated regions.
Under one of these accumulations the
hole ,f Wo1n nr,ly hon hal nxyn
| rising again to its existing height as the
ice melted away. In hotter regions
masses of coral are forming reefs and
atolls, rising in some cases from water
hundreds of fathoms deep. The polyps
| forming the coral can only live in surf
near the surface, and unless subsistence
had continuously kept pace with deposit
ton no such masses could have been
| formed.
Many Of the great rivers empty into
bays sheltered from coast currents and
there form deltas which have been proved
by behring's to be thousands of feet thick,
yet each foot has been formed in water a
few feet deep, as proved by the angle of
bedding, the fauna, drifted land debris
and the sorting action OF the waves. In
all these cases the crust must have sagged
under the increasing load of added ma
terial, and did it not similarly give way
under the additions of weight along the
littoral zone, every island and continent
would be surrounded for miles by shoals
no deeper than the disturbing motion of
the waves. When the crust says out to
sea the column of water over it deepens,
augn enting the pressure. The pressure
acting on the molten layer tends to squeeze
it not seward, where the water is deeper,
but toward the shore, where line of least
resistance is already prepared by the
breakers.
The effect of steadily increasing lateral
pressure acting on long and relatively
weak shore line of heterogeneous materials
must be extremely complex. The molten
matter is able to eat its way up