Earthquake Theories [pp. 516-523]

E EAR THQUA KE THE ORIE S.
the most solemn manner that they have
felt the ground shaking under them
violently; while others are equally pos itive that no such thing ever took place.
It is the fact, however, that during the
heaviest shocks that have ever been ex perienced in San Francisco, when houses
of the most substantial construction
were shaken to such an extent that all
their occupants rushed out in terror and
fright, the most credible of those found
on the streets-the persons most likely
to keep their wits under any excitement
or in the presence of any danger-assert
that they felt no motion at all in the
earth, and had no idea that an earth quake had taken place until they had
seen the commotion of the people in the
houses. A usual remark is, that the
earthquake was felt more sensibly in
those portions of the town which are
known as " made ground," than on the
solid and natural earth; but this does
not prove the internal fire theory as much
as it does the fact that houses were
shaken there more violently because of
their less secure foundations. Another
is, and it is usually used as an argument
against the supposition that the ground
was not disturbed at all, that horses have
been known to have been thrown down
during the prevalence of a shock; but
the reply to this is simple enough. The
force that can sway a four-story brick
building ought to be sufficient to knock
even a more powerful quadruped off his
feet than a horse. The ground would
have to be trembling, indeed, in a manner about which there could be no possibility of controversy, to prostrate any
living animal.
But we prefer to place this matter
upon higher and more scientific grounds.
That stores, and lighter structures, in
San Francisco, have been subjected to
a sort of twisting process does not admit
of any doubt. If the motion was in the
earth, and was communicated from it to
the edifices upon it, it may be asserted,
without fear of contradiction, that cobble,
planks, and loose materials generally,
would have been sent whirling round
with dangerous velocity. It is not pos sible for the earth to be shaken up in the
form of eddies without the derangement
of a single particle on the surface, and
without leaving any trace behind. It is
not like water, which assumes its origi nal condition as soon as the disturbing
cause is removed. Again, if the motion
extended, as is often the case, over a
large tract of land, the area of its opera tionI ought in all cases to be clearly
marked and defined, for there were at
either end and on both sides irregular
lines, where there were particles in re pose and particles in motion. But there
is no pretence that any of the Califor nia earthquakes have left behind them a
clearly defined boundary offissures. Up on the rumbling noise which has so fre quently been heard either before or after
the shock, it will not be necessary to
enlarge. That it could have come from
the bowels of the earth is entirely incom patible with any of the known laws of
acoustics. It maybe stated that earthy
matter, closely packed, is not a good
conductor of sound.
The earthquake of the twenty-first of
October, the most violent that we ever
experienced, has left behind it a handwriting which, by a little study, can easily be deciphered. There are hundreds of
chimneys moved out of their position,
while the houses on which they are
erected maintain their original lines.
If the force came from the interior of
the earth, it must have been communicated to the house before it reached
the chimney; but the house furnished
no evidence of a change of position.
There is a hiatus of force then, which is
totally inexplicable upon the subterranean hypothesis. But this is not all.
A walk through that portion of the city
which lies east of Montgomery street,
will reveal many curious facts. This is
the section of the city which is known
as "made ground." It was originally a
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