Year: 1872

, lands, volcanic regions, and so on-Whlen


are undoubtedly due to the action of sub
terranean forces. The theory advanced BY
J Mr.. Mallet is open TO none of these OBJ


jections. 1t seems, indeed, competent to
explain all the facts which have hitherto
appeared most perplexiDg.


1t is recognized by physicists that our
earth is gradually parting with its heat
As it cools it contracts. Now, if this pro-
cess of contraction took place uniformly,
no subterranean action would result. But,
if the interior contracts more quickly than
the crust, the latter must In some way or
other force its way down to the retreating
nucleus. Mr.. Mallet shows that the hotter
internal portion must contract faster than
the relatively cool crust and then he
shows that the shrinkage of the crust is
competent to occasion all the known phe-
nomena of volcanic action. In the distant
ages when the earth was still fashioning.
the shrinkage produced the irregularities
Of lerel which we recognize in the eleva-
tion of the land and the depression of the
ocean-bed. Then came the period when,
as the crust shrank, it formed corrugationS;
IN other words, when the foldings and
elevations of the somewhat thickened crust
gave rise to the mountain-ranges of the
earth. Lastly, as the globe gradually lost
its extremely high temperature, the contin-
uance of the same process of shrinkage
led no longer to the formation of ridges
and table-lands, but to local crushing down
and dsocation The process is still going
on, and Mr.. MaIlet, not only recognizes
here the origin of earthquakes, and of the
changes of level now in progress, but the
true cause of volcanic heat. The modern
theory of heat as a form of motion here
comes into play. As the solid crust closes
in upon the shrinking nucleus, the work
expended in crushing down and disocat-
ing the parts of the crust is transformed
iuto heat, By which, at the places where
the process goes on with greatest energy,
1.-The material of the rock so crushed and
of that adjacent to it are heated even to
fusion. The access of water 10 such points
determines volcanic eruption


Now, all this IS not mere theorizing.
Mr.. Mallet does not come before the
scientific world with an ingenious specula-
tion, which may or may not be confirmed
By observation and experiment He has
measured and weighed the forces Of which
l
what proportion of the actual energy
which must be developed as the earth con-
tracts is necessary for the production OF
observed volcanic phenomena. 1t is prob
able that nine-tenths of those who have
read these lines would be disposed 20 think
| that the contraction of the earth must be
far o slow to produce effects 50 stipend.
oas as those which we recognize in the vol
cano and the earthquake But Mr. Mallet
Is able to show by calculations which can
not be disputed, that less than one fourth
of the heat at present annually lost by the
earth Is sufficient to account for the total
annual volcanic action, according to the
best data at present in our possession.


This would clearly not be the place to
follow out Mr.. Mallet's admirable theory
into all its details We must content our
selves with pointing out how excellently it
accounts for certain pecularities of the
earth's surface-confguration. Few that
have studied carefully y-drawn charts of the
chief mouatain-ranges can have failed
to notice that the arrangement of these
ranges does not accord with the idea OF
upheaval through the action of int rnal
forces But 1t will be al once recognized
that the aspect of the mountaiu-ranges
accords exactly with what would be ex-
pected to result from such a process of
contraction As Mr. Malet has indicated.
The shrivelled skin of an apple affords no
inapt representation of the corrugated sur
face of our earth, and according to the
new theory, the shriveIling of such a skin
is precisely analogous to the processes at
work upon the earth when mountain-ranges
were being formed Again, there are few
students Of geology who have not found
a source of perplexity in the foldings and
overlappings of strata in mountainous re-
gions. No forces of upheaval seem COM
petent to produce this arrangement. But
by the new theory this feature of the earth's
surface is at once explained indeed, no
other arrangement could be looked for.


1t is worthy of notice that Mr. Mallet's T
theory of volcanic energy is completely .
opposed to ordinary ideas respecting earth T
quakes and volcanoes. We have been +
accustomed vaguely to regard these phe
nomena as due to the eruptive outbursting
power of the earth's interior; we shall I
now have to consider them as due to the
subsistence aud shrinkage of the earth's





heaved but valleys have sunk down. And
in another respect the new theory tends to
modify views which have been generally
in recent times Our most
eminent geologists have taught that the
earth's internal forces may be as active
now as in the epochs when the mountain
ranges were formed But Mr., Mallet's
theory tends to show that the volcanic
energy of the earth is a declining force.
Its chief action had already been excrted
when mountains began to be formed
what remains now is but the minutest
fraction of the volcanic energy of the
era and each year, as
the earth parts with more and more of its
heat, the sources of her subterra
lean energy are more and more exhaust
I'd. Toe thought once entertained by :
that the earth might explode
like bomb, her scattered fragments pro- q
iucing a ring of bodies resembling the
.one Of asteroids, seems further than ever I
rom probability; if ever there was any
langer of such catastrophe, the danger
las long since passed away.-Fronl the
London Spectator.