ctions of Giezier, I may now add the
information which we have received in consequence of a new voyage from
this country to Iceland.

When Sir Joseph Banks returned from his expedition to Iceland, he landed
at this place; and, having brought specimens of the petrifications of
Giezer, Dr Black and I first discovered that these were of a siliceous
substance. I have always conjectured that the water of Giezer must be
impregnated with flinty matter by means of an alkaline substance, and
so expressed my opinion in the Theory of the Earth published in the
Transactions of the Edinburgh Royal Society. We have therefore been very
desirous of procuring some of that water, in order to have it analysed.

An opportunity favourable to our views has occurred this summer. Mr
Stanley set out from this place with the same purpose of examining
Iceland. He was so good as to ask of Dr Black and I what inquiries we
would incline that he should make. We have now, by the favour of this
gentleman, obtained specimens of the petrifactions of Giezer; and, what
is still more interesting, we have procured some of the water of those
petrifying boiling springs.

It appears from these specimens, that the boiling water which is ejected
from those aqueous volcanoes, if we may use the expression, is endued
with the quality of forming two different species of petrifaction or
incrustation; for, besides the siliceous bodies, of which we had before
received specimens, the same stream of water incrustates its channel
with a calcareous substance. All the specimens which I have seen consist
of incrustation, some purely siliceous, some calcareous, and others
mixed of those two, more or less.

Dr Black has been analysing the water; and he finds in it siliceous
matter dissolved by an alkaline substance, in the manner of liquor
silicum[44]. My conjecture has thus been verified.

[Note 44: See Trans. of the Edin. Royal Society.]

It must not be alleged that nature may operate in the mineral regions,
as she does here upon the surface in the case of Giezer. Such an
argument as this, however sound it may be in general, will not apply to
the subject of which we treat at present. There is no question about
the limiting the powers of nature; we are only considering nature as
operating in a certain determined manner, viz. by water acting simply
upon the loose materials of the land deposited at the bottom of the
sea, and accumulated in regular strata, one upon another,