Evening star. [volume] (Washington, D.C.) 1854-1972, 1886-09-25
EARTH THROES.
Forces Acting from the
Eastern Atlantic.

1 AtlSUtics
THE EARTH's CENTRAL FIREs-AGENcY OF
| STEAM IN EARTHQUAKES-THE COOLING
AND CoNrRAcTIoN OF THE GLOBE
From the New York Herald
| Perhaps the best exposition Of the causes and
| characteristics of earthquakes in general, and
specially of our Atlantic seaboard earthquakes,
anywhere to be found Is embodied In the adj
dress delivered by Sir William Dawson, presi-
dent OF the British association, on the night
after the Charleston disaster. This eminent
Canadian scientist, than whom no living man
Is better fitted to expound the formation and
| changes OF the earths crust, gave the probable
history OF the formation of the Atlantic ocean
| ana the continents which bound it. Assuming
That the earth's nucleus, or mass, is solid, not
withstandins the Elasticity of its under crust,
anu that This sub-crust is not in a state of dry
| lSneous fusion, but in that condition of aqueo-
| igneous or hydrothermic fusion which arises
| rom the actIon oil heat on moist substances,
| Professor Dawson argued that the interior sub
| crust Is not homogeneous, but Is composed OF
| Two layers-an upper layer highly siliceous
aud of low specific gravity and a lower layer
hignly charged with iron and igncOus rocks. 1t
IS evident, therefore, that ii this he the double
| structure o1 tile earths under crust, when MS
sureS form in the upper layer the material of
| the lower crust is forced upward by the pres
sure OF the less supported portions OF the
former.
| CAUSE OF VOLCANIC ERUPTIoNs.
| This, of course, would give rise to volcanic
| phenomena, which would be explosive or quiet,
| as determined by contact with water. The
| contraction OF the earth's interior by cooling
ana by the emission of material from below the
/ over crust has caused this crust to bend down.
ward and sidewise, thus forming great bends,
| folds anu plicationS. These great holdings, sub
| sequently modified by surface denudatiOn, con-
| StItute our mountain ranges and piateaus Fol-
lowing this line OF reasoning Sir William conn
pares The earth to ii stone fruit, such Jas plum
| or u peach, somewhat dried up. at has" he
says, - large and intensely hard stone and
kernel, a thin pulp made up OF two layerS-an
| Inner more dense and dark cOlored, and an
outer less dense and lighter colOred. These
constitute the under crust. On the outside it
| mas a. thln membrane over crust. In the
process oi drying it has slightly shrunk So as TO
| produce ridges and hollows on the outer crust,
| and this outer crust has cracked in some
places, allowing portions of the pulp 10 ooze
| Oui.
| A GREAT FORCE ONCE ACTING ON OUR ALLAN
TIC SEABOARD.
Another remarkable fact emphasized bv Sir
William Dawson is that one cannot look at any
geological map of America without perceiving
that the Appalachian ridges which intervene
between the Atlantic ana the st. Lawrence
valley have been driven bodily back by some
mighty force acting from the east, and that
they nave resisted The pressure only where f;ls
III Tie Cult vi st. Lawrence and the Catskill
region Oh New York they have been protected
by outlying MASSES OF very Old rOcks-aS seen
liz the Adirondack region and in NewiOund-
land.
1t is worthy of note that though later in
culture and civilization than some Oh the other
continents, America is, in the view OF geo;ogsts,
''llrst born among the continents. .'Eere, saiu
AsSsZ, ''w;ls the nrSt dry lanui lifted of the
waters, here the FIRST shore washed by the
OCEAN that enveioped all the earth besides; and
while Europe was represented only 10y islands
rising here and there above the sea, America
already stretched an unbroken line OF land rom
Nova Scotia To the iar west" In this case
america, not Europe, is to be regarded as the
"Old World
FUTURE CHANGES IN THE ATLANTIC BED.
bearing these data in mind, we easily see
q
ing to the question OF future changes in the
Atlantic, he says: 1.-The question remains, has
the Atlantic achieved its destiny and finished
its course, or are there other changes i'll store
for ii in the future? The earthS crust is now
tnic~er and stronger than ever before, and its
great ribs Of crushed and folded rock more
liTm and rigid than in any previous period.
TN the other hand, il is known that
movements OF elevation, along with local de-
pressons, are i'll progress in The Arctic regions,
anu great weight OF new sediment is being de-
posted along the borders of the Atlantic. espe-
cisliy ON its western side, and this Is not im-
probably connected with Tile earthquake shocks
! and slight movements OF depression which have
occurred i'll North America. 1t is possible that
| these slow and secular movements may go on
uninierrupteGiy until considerable changes are
produced but ~ Is quite as likely that they
| may be retarded or reversed. He adds: at is
possible, on the other hand, that after the long
period OF qulescence which has elapsed there
may be Il new settlement OF the ocean bed, ac-
| companied with iOldiEgs of the crust, especially
| ON the western side OF the Atlantic, and pOs,i.
| bly, with renewed volcanic activity OH its east
ern margin. In either case loug time rela-
lively To our limited human chronology may
intervene before the occurrence OF any marked
change
Is THE EARTH'S INTERIOR HOT AND FLUID?
n most important question underlying all
chronological inquiries is whether the interior
OF our globe is a molten mass. Until compare
| lively recent times physicists almost unani-
mously agreed tina. the process of sOldifcation
| began by radiation from the cooling of the
| earth s surface exposed to the atmosphere, and
that the particles near the center continued hot
| and Huld. Fourier, Laplace, humboldt and
| many great names are associated with this
| theory. The i.eat OF the water which flows
| from deep borings (artesian weiIs), direct ex-
periInents regarding the temperature OF rocks
In mines, above all, the volcanic activity of the
! earth, shown by the How oil molten masses from
open assures, afford unquestiOnable evidence"
| said humboldt, "OI the increase OF heat tor
| very considerable depths from the upper
strata" II the observations on increase OF neat
| below the earth surface afford amy light the
thermal state OF great subterraucan depths, it
| follows that granite rocks lying 30 miles under
our feet Will De In d state Oi fusion.
| Sir William Thomson while contending that
much the larger part10t the cartn's interior is
| bowels great seas OF tin molten matter which is
occasionally beicncd forth from voIca mic cones
| 1t is certain that this is actually the case in
called volcanic districts and Within the "circies
OF fire. which have been traced by volcanic
Graters emerging rom tue grand oceanic basins.
| noted by the great ply sicist Fortress that Iavas
! from VesuviuS, from Hecia, from the Adde'S
| from Japan and from New Zealand present
! such agreement in essential particulars as can
| seemingly be accounted for only OH the hypoth-
esis that they all emanate from one vast COM
mon source.
But In the light now attained or attainable by
the most eminent physicists 1t would be absurd
| to assert the absolute nuidity or absolute SOL
| Idly of the earth's central mass.
| CAUSE OF EARTHQUAKES.
Among the ingenious theories devised to ex-
plain seismic disturbances is the attractive in
| fiuences OF the moon and sun. Professor Percy
| q great chronological student, held the view
that earthquakes Ielt at certain seasons OF tine
/ year were possibly due TO the sun and moon
| producing d tide in the fluid interior OF
the globe, and that this tide pressing against
| the solid crust caused fractures Though the
/ theory gained most credence on account of Its
adoption by Percy, IL was enuciated long be-
/ fore his day, and has since been ampified by
Falb. Though not fully accepting Perrey's and
| Ealb's views, Professor Milne argues that 1--WE
| nevertheless have travelling round our earth.
! following the attractions OF the sun and moon,
u tidal stress. This stress, imposed upon an area
/ III "A critical STATE, may cause II To give way,
| and thus be the origin vi an earthquake. Earth
| when these stresses are the greatest And
| again, this high authority says: ''rhat earth
Quakes are slightly more numerous at these
| particular periods tOf maximum stress or great
est pull eXerted by the moon and SUM-. e.
perigee and periheiiOn-and again when they
strong reason for believing that the attractions
OF the moon and sun enter into the list OF causes
producing these phenomena"
HIGH TIDE JUST BEFORE THE CHARLESTON
| SHOCK.
1t is very interesting to notice AZ DOint ted ont