It is impossible, adds Herschel, but that this increase of pressure in
some places and relief in others must be very unequal in their bearings.
So that at some point or another our planet's floating crust must be
brought into a state of strain, and if there be a weak or a soft part a
crack will at last take place. This is exactly what happened in the
earthquake which originated the Allah Bund, or God's Wall, in Cutch.
Volcanic eruptions are easily explicable on this principle,--the volcano
being simply a vent for the passage of heated and molten matter, which
the elevating pressure of the liquid below tends to eject. It is a
well-known fact that volcanoes and earthquake-centres are nearly all
situated on the borders or in the immediate neighbourhood of seas and
oceans; and the reason would seem to be, that at such positions the
accumulation of transported matter would necessarily attain its maximum,
to whatever cause it might be due. Then again, as Herschel points out,
the eruption of scorite and lava from the mouths of volcanoes, the
result of the upward movement of the fiery liquid below, compensates in
some degree for the downward transfer of material by detritus and
alluvial deposits.
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