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Page 174:-
[con]clusion seems to be, that air or gas is generated in the
body of the island by decomposition of the vegetable matter of
which it is formed; and this gas being produced most copiously,
as well as being more rarified in hot weather, the earth at
length becomes so much distended therewith, as to render the mass
of less weight than an equal bulk of water. The water then
insinuating itself between the substratum of clay and the peat
earth forming the island, bears it to the surface, where it
continues for a time; till, partly by escape of the gas, partly
by its absorption, and partly by its condensation consequent on a
decrease of heat, the volume is reduced; and the earth gradually
sinks to its former level, where it remains till a sufficient
accumulation of gas again renders it buoyant.
But as the vegetable matter of which the island is principally
composed, appears to have been amassed at a remote period, when
the lake was of less depth than at present, receiving very little
addition from the decay of plants recently grown upon the spot;
it is reasonable to suppose that the process furnishing the gas
cannot from the same materials be continued ad infinitum:
but that there must be a time when it shall have arrived at its
maximum: after which the eruptions will become less extensive or
less frequent.
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