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VON TROIL’S LETTERS ON ICELAND, 719
indeed one of the moft daring enterprizes which the proud reafon of man ever propofed
toitfelf; and, more than any other attempt, fhews his weaknefs and arrogance. All
thefe imaginary fyf{tems have been by little and little overturned, though the greatelt
pains were exerted to compare them with nature, and examine their exiftence. Their
arguments were then difcovered to be founded on a few infufflicient obfervations, or,
what is ftill worfe, on uncertain, and fometimes evidently falfe principles.
You, Sir, will therefore readily excufe my timidity; for inftead of endeavouring to
difcover all at once, as it were 4 priori, though without any certainty, the manner in
which nature works, and forms+things in fecret, I prefer the more laborious method of
difcovering it gradually with certainty, by experiments founded on due obfervations ;
and fhall not hefitate to confefs my ignorance, wherever thefe guides in the ftudy of
nature ceafe their inftructions. I do not, however, reject all conjectures and propofed
opinions, whenever they lead to new refearches, provided they are offered as mere con-
jetures, and not obtruded on usas certain trutns, or determined opinions.
From what I have hitherto faid, you will, I believe, conceive my method ; therefore
I fhall enter upon the fubjeét, and briefly treat of it under feparate heads, in the follow-
ing manner.
Of the Hot Springs.
Your defcription of the Icelandic fprings, the moft extraordinary which have hither-
to been difcovered in the known world, was extremely agreeable to me, partly on ac-
count of the furprizing force of them, and partly on account of the great light obtained
in mineralogy by the cruftated ftones formed in them. How thefe {prings may be ac-
counted for, I hope I have fuffictently explained in another place * ; I fhall, therefore,
entirely pafs it over here. But now | will communicate to you what [ could not then
eal, namely, the true nature of thefe depofitions.
You have prefented me with the following fubftances from the Geyfer:
t. The fubftance of which the water has prepared itfelf a bafon to run from.—It
confifts of a hard, rough, greyith, and irregular flaty, and generally martial cruftated
ftone, over which acovering of fmall cryftallizations has formed itfelf, that refembles
the lichen fruticulofus, or rather the Stahliteindrufe found in the Welterfilverberg ;
that is called the flos ferri or Eifen bluthe. Thefe precipitations are opaque, without of
a whitifh grey, blacker within, and plainly fhew the formation of feveral crufts on one
another. Each of thefe flos ferri, as wellas the cruftated ftone, has the hardnets of a
flint ; however they are not fo compact or {trong as to {trike fire with the fteel.
The ftrongeft acids, the fluor acid not excepted, are not fufficient with a boiling heat
to diffolve this fubftance. It diflolves very little if at all by the blow-pipe with the
fufible alcali, a little more with borax, and makes a {trong effervefcence with fal fode.
Thefe effets are peculiar only toa filiceous earth, and therefore there remains no doubt
concerning the real nature of this cruftated {tone. Neverthelefs, I have melted it in the
erucible ; firft, by weight, with half as much alcaline falt, and likewife with three times
as much ; and have obtained in the firft cafe a fixed glafs, and in the fecond one, which
in diffolving, yielded a common liquor filicum. The glafs of the cruftated ftone is of
amore yellowifh brown than that of the cryftallizations ; and this difference is caufed
by the greater quantity of irony particles.
2. The porous cruftated ftone or finter, which is found in the moor furrounding the
border of the bafon, is light, whitifh, and here and there fpotted with a ruft colour: it
* Inmy Phyfika befkrifning om Jordklotet, ult. edit.
8
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