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722 VON TROIL’S LETTERS ON ICELAND.
There is no lime at all near the Geyfer ; but at Laugarnas there are fome faint traces
of it, partly as an external covering, and partly as conftituent parts in the zeolite, of
which more will be faid hereafter. ‘Che balls of lime found at Reykum are molt pro-
bably thrown out by the spring, and haye been rounded on the furface by the friction.
Of the Eruptions of Fire.
I HAveE in another * place treated pretty extenfively of the dreadful devaftations
caufed by fubterrancous fires on the furface of the earth in many parts of the world,
both in regard to their caufes and effects ; I have therefore not any thing to add in this
place but what particularly relates to Iceland, and what may ferve to explain the erup-
tions which have happened there from time to time.
Whether Iceland is to be confidered as entirely produced by volcanos, is a queftion
which moft probably will remain unrefolved many years. It is true, Sir, that according
to the accounts you have collected there, the volcanos have raged in a great many places,
and that the whole country is in a manner covered with traces of their deltruttive ef-
fe&ts: we alfo learn, from undeniable facts, that new iflands have been produced by
volcanos in many places. But all this proves not any thing more than that the moit
dreadful effects have been produced by fiery eruptions in Iceland.
To determine this queftion, it would be indifpenfably neceflary that a naturalift
fhould thoroughly examine all Iceland. Ifa granite, or any other ftone or berg-art,
was found in folid rocks, and not feparate or in loofe fragments, which may have been
brought thither from diftant parts, I fhould entirely diffent from your opinion. But be-
fore thefe and the like difcoveries were made, I believe no conclufions could be drawn.
I may venture to maintain with more certainty, that your collection confirms what I
before concluded from other reafons, viz. that in all volcanos pyrites are found, which
on decompofing produce heat and fire ; and likewile flate that, penetrated with bitumen,
ferves to feed the fire.
12. The flate which you have brought from Iceland fplits into thin plates, which dif-
cover many forts of impreffions, particularly of leaves; the colour is black, and it is
exaétly of the fame nature as the common aluminous flate.
13. ‘The two pieces of furturbrand, or foflil wood, which you brought with you, bear
evident marks of a vegetable compofition ; andI may almoft affirm, with perfect cer-
tainty, that the largeft is a kind of pinus abies; on the outfide are barks and branches,
and in the infide all the rings of the fap appear: the lefler is a piece of rind without
wood; both are black, quite foft, eafily take fire, and flame in burning. After the
flame is extinguifhed, one hundred parts afford forty-two parts of coals, which after being
only calcined yield two parts of yellowifh-brown earth, that is attracted by the magnet,
and partly diflolves with acids: it makes fome effervefcence with borax and fufible
urinous falt ; the fal fodae alfo caufes a little ebullition at firft, but does not entirely dif-
folve it.
Your conje@ure, Sir, concerning the manner in which the furturbrand is produced,
does not feem improbable. I have already obferved a long time with furprife, that
fifhes, othoceratites, lituites, wood, fcc. &c. which are to be found in flate, have been
comprefled or flatted, whilft they preferve their entire form and roundnefs in lime.
This fame circumf{tance may be obferved in the two pieces defcribed above, efpecially
in the larger, which is only an inch and a half in thicknefs, though it is nineteen inches
* Verlds be(krifn, § 149.
in
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