New-York tribune., 1899-04-12
VOLCANOES.
THE EARrH's HOT INTERIOR AND THE
FIssuREs IN ITS CRUST.

mans sons.
Three noteworthy books on this general SUB
feet have appeared within the last two years
Professor Russell. Of the University OF Michi-
gan. confined himself in the main TO Nor'h
America. and limited his detailed descriptions
20 those volcanoes which have been active IN
recent times. Sir Archibald Geikie restricted his
studies to an even narrower field. territorahy
the British Isles-but covered longer period
NJ history. Professor Bonneys work differs
from, that Of his Immediate predecessors partly
IN beine less local in its survey and partly In
discussing more fully than did either Russell or
Geikie the life history and products OF VOL
cano AT one time the notion was entertained
that a volcano is composed chiefly Of strata OF
solid rock that have been thrust upward from
below In such a manner as to carry the centrai
portions thousands Of feet above their FORMER
level and that then they were perforated Ver-
tically. The pipe through which lava ano ous'
and steam were elected. II was thought. dehV-
cred comparatively small quantity or moteh
material on the outer slopes. But II is now be-
lieved that the mass is almost altogether a prod
uct Of eruption Single volcanoes that were
from fifteen thousand to twenty thousand rect
high before the weather began to wear away
their SUBMITS. and which had oreadtn OF
twenty or thirty miles at the base, had such an
origin: and so did volcanic ranges hundreds OF
mile. wide. Of which the Cascades afford a good
example.
These colossal uplifts. considered in connec-
tion with the vast quantities OF volcanic rock
that has been washed away into the ocean out
Of sight. and the enormous intrusions OF lava
into assures OF pre-existng rock (nowforming pa
saltic "dikes") hint strongly at the forces which
have operated to create volcanoes and the ex-
.,.nt OF their share in shaping the earth's sur
face Only a few Of the peaks and ranges that
have been built in this manner have shown any
signs Of disturbance in modern times But
there are evidences that the same sort or Work
has been going on for ages. Professor bonney
thinks that some Of the volcanic rocks OF Great
Britain belong 10 the Cambrian or pre-Cam-
brian era. The writer thus defines volcano:
"It is an oriice in the earths crust. commonly
terminating in a bowl-like hollow called crater
which forms the summit Of a mountain or hili
usually more or less conical in outline. From
the crater are elected sometimes continuously
sometimes at long intervals of quiescence-
but always more or less exposively-gas, steam
or water dust (formed OF comminuted miner
ais or rock). scoria bits Of natural Stag. and
molten rock or lava. Sometimes there is a CEN
trail cone which crowns a lofty mountain mass
~ the action is intermittent and the periods
that elapse between outbreaks are long the
eruption is apt TO he much more violent than II
the action is continuous. This fact was Illus
trated by Vesuvius in the year az. when POM
pen and Hercuaneum were destroyed. AT tnat
time there no record OF the disturbance
next previous. which may have occurred CEN
turies before Occasionally the long pent-up
forces are able to rend mountain to pieces
Such was the fate OF Krakatoa. on a small ISL
and near Java, in the year 1888. The milder
type Of eruption is exemplifed by Stromboli
whose crater contains boiling lake OF lava
whence jets Of steam are forever issuing.
The difference here noted is doubtless due IN
some measure to the amount Of energy that is
at work within. But it is also partly at
trihutable to the size and condition Of the orifces
which serve as outlets. II the pipe of a volcano
is narrow and easily choked ITS activity will be
Suspended now and then. But any check OF this
kind naturally results in a more appalling out
break when the obstacle IS finally overcome.
The higher the pressure at which steam boiler
explodes the greater the havoc.
circumstances to which many geoogists at
tach significance is the comparative nearness
Of volcanoes to the edges of continents and
their frequent development on islands in the sea.
There is. for instance. rude chain OF active or
extinct volcanoes all the way around the Pacific
Ocean, from New-Zeaand up through the East
Indies to the Pnll1pplneS ara Jdpdn tneHCc ~
Kamchatka and tho Aleutian Islands, along
Southern Alaska and down the western coast
OF America across the Isthmus of Panama to
Patagonia. A somewhat similar line. with
broad interruptions extends from Greenland.
Iceland and the Faroes. through the British
Isles TO Portugal. and along the Mediterranean
through Italy and Greece to Asia Minor, Persia,
India and Sumatra.
II lie to be observed however that those shores
OF a continental area which dip abruptly into
the sea are more apt to be the scene of volcanic
action than those which slope more gently into
the ocean as does the Atlantic seaboard. And
though a volcano that is more than hundred
miles inland nyvhere is great rarity, one
which rises In midocean perhaps from depth
OF ~ 600 feet. is not at all unusual. The Sand
wich Islands. the Samoan group and the Azores
are only few instances of this sort
Another curious fact which has been observed
Is that while the composition Of the molten ma
teNal elected from volcanoes varies consider
ably more especially in respect to the amount
Of silica contained. there is tendency to show
larger percentage OF this substance during the
earlier eruptions OF any given region IMAM IN
the later ones. and to betray certain acidity at
FIRST that Is not manifest subsequently, In the
acid lavas one may find as much as ~ or 40
per cent Of silica. whereas in the so-called
basic" lavas the percentage may be only ~
or As. Between these two extremes there are
many gradations. but the distinction is a
notable one. The character Of the lava is apt
10 influence TO some extent the slope of vol
cano. Kilauea. for instance. is covered with
basic lava, and as this is believed to have been
elected when its temperature was far above the
melting point 1t flowed freely and at a small
angle with sea level. Still, a gentle slope does
not always indicate the nature of the rock; for
certain very old volcanoes. long extinct, have
been 80 worn away by the weather as to have
lost their original outlines.
Biologists are not altogether agreed as to the
cause Of a volcanic eruption Professor Shaler.