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[ 352 ]
ftalks, and the like. As to its na-»
ture, it is iiliceous ; but feems at the
fame time to contain a different fubftance,
as it diffolves more flowly with
fal fodæ.
The fpring which here burfts forth
ill a very floping diredion towards
the horizon, according to your account,
depofites a kind o f fulphureous
greaie by its hot fteam on the cavities
o f the upper fide ; but I have found
no fpecimen o f this in the colledion
you fent me.
From what I have hitherto faid, we
may gather, that the Icelandic hot
fprings contain very different fubftances
from what are to be met with
ill other places o f the fame fort, efpecially
filiceous earth.
There is no lime at all near
the Geyfer ; but at Laugarnas there
are fome faint traces o f it, partly as
an external covering, and partly as
conftituent parts in the zeolite, of
which more will be faid hereafter.
The balls of lime found at Reykum
are moft probably thrown out by the
I 3 5 3 ]
fpring, and have been rounded on the
furface by the fridion.
O f the Eruptions of Fire,
I HAVE in another * place treated
pretty extenfively o f the dreadful
devaftatlons caufed by fubterraneous
fires oil the furface o f the earth in many
parts o f the world, both in regard to
their caufes and effeds ; I have therefore
not any thing to add in this place
but what particularly relates to Iceland,
and what may ferve to explain
the eruptions that have happened there
from time to time.
Whether Iceland is to be confidered
as entirely produced by volcanos, is a
queftion that moft probably will remain
unreiblved many years. It is true.
Sir, that according to the accounts you
have colleded there, the volcanos have
raged in a great many places, and that
the whole country is in a manner cohered
with traces of their deftrudive
* Verlds beikrifn, § 149.
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