Year: 1871

SOlAlD ok FLUID?


Although the doctrine that the earth
molten sphere. surrounded by a thi,
crust OF solid matter. was once almost uni
versaily taught by geologists, there hav
OF late years been brought forward sever
al arguments to the contrary. which. ap
parenfly. are more in favor Of its being ,
solid, or nearly solid mass throughout
and these arguments are fully entitled /.
our consideration. 10 onr Object i. moi. /.
fdefsnd any particular theory, but TO ar
rive. as nearly as We can. ut the truth
will. therefore. in the FIRST place, pro
ceed to scrutinize all which has beer
brought forward in opposition to the older
hypothesis, and then to consider whethe,
any other explanation yet advanced il
more in accordance with the facts ofthe case


First of all, We are to answer the aues
ton as to whether it is possible for such :
thin crust TO remain solid. and not at ono,
to become melted up and absorbed int
the much greater mass of molten matte,
beneath it! This latter would doubles.
be the case, if the fnid mass had any
means of keeping up its high temperature
independently of the amount of heat it &C.
tually possessed when it originally assum
ed the form of an igncous globe. The
question. however, in reality answers it.
self in the negative. since it is evident
that no crust could even commence to form
on the surface. unless the sphere itsel
was at the moment actually giving of
more heat. from its outer surface to the
surrounding atmosphere. than it could
supply from its more central parts, in or.
der to keep the whole in a perfectly fluid
condition so that, when once such a
crust, however thin. had formed upon the
surface, it is self-evident that it could not
again become melted up or re-absorbed
into the fluid mass below.


This external process, Of qualification
due to refrigeration, would then contin-
uc, going on from the outside inwards,
until thickness of crust had been attain
cd sufficient to arrest, or neutralize lowing
to its bad eonductibility of heat) both the
cooling action Of the surrounding air and
the loss of more heat from the molten mass
within: and thus stage would soon be
arrived at when both these actions would
=" counter balance one another, that the
further cooling down Of the earth could
be all but arrested: condition ruling at
the present time. since the earth-surface.
at this moment, so FAR from receiving any,
or more than minute amount of heat
from the interior, appears to depend en-
tirely, as regards its temperature, upon
the heat which it receives from the SUMS
rays.


We have next to consider the argument
that, If the earth's exterior were in reality
only such thin covering, or crust, like
the shell Of an egg. to which it has often
been ikened. that such thickness would
be altogether insufficient to give to it that
stability which we know it to possess, and
that. consequently. it could never sustain
the enormous weight Of its mountain rang
es. such as. for example, the Himalayas
of Asia, or the Andes Of America. which
are, as it were. masses of rock piled up
high above its mean surfacc.le level.


At first sight. this style of reasoning
not only appears plausible, but even seems
to threaten to upset the entire hypothesis
altogether. Il requires but little sober
consideration. however, to prove that it
Is rather, SO to speak. sensational in char
acter than actually founded on the facts
Of the case; for it is only requisite for us
to be able to form in our minds some tan
gible idea of the relative proportion which
the size of even the highest mountain
bears to that Of the entire globe itself, to
convince us. il such crust could once
form and support itself. that it could with
ease support the weight of the mountains
also. The great Himalayan chain OF
mountains rises to n maximum altitude OF
81 500 feet, or six miles above the level
Of the sea; and if the earth could be seen
reduced in scale down to the size Of an
orange, to all inteuts and purposes it would
look like an almost smooth ball, since
even the highest mountains aud deepes;
valleys upon its surface would present to
the eye no greater inequalities in outline
than the little pimpies and hcllcws on the
outside of the skin of an ordinary orange.
IL this thin crust Of the earth can support
itself, it is not at all likely to be crushed
in by the comparatively speaking, insig-
nihcant weight of our greatest mountain
chains: for, in point Of fact. it would b.
quite as unreasonable TO maintain such q
disposition, as to declare tha. the she'll OF
a hens egg would be crushed in by sim.
ply laying piece Of similar esg-shel
upon its outside.


That very thin spheroiial crust, OF
shell, enclosing body of liquid matter,
such as an ordinary fowls egg. does pos.
sess in itself an enormous degree of sta.
bility and power to resist pressure from
without. is easily demonstrated BY mere.
ly leading small portion of its surface
with weights. as long as il does not give
way under them. Even when placed on
its side Cor least strong posi,ion), it is
found that portion Of the shell. only one
quarter Of sn inch square. will sustain
several pounds weight without showing
any symptoms Of either cracking or crush.
ing: or. in other words. this simpie ex.
pertinent indicates that it the external
crust of the earth were but as thick and
strong in proportion as an egy-shell. i,
would he fully capable Of sustaining mass-
cs. equal in volume and weight 10 many
Himalayas. piled up one cop Of another.
| without any danger whatever to it's ssahil-
Iity.--Ertruct from Lecture by Drrid
Forbes, r. X. s.