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692 VON TROIL’S LETTERS ON ICELAND.
We were now arrived at one of the higheft fummits, when our conductor, who did
not take great pleafure in the walk, endeavoured to perfuade us that this was the higheft
part of the mountains. We had juft finifhed our obfervations, and found by them that
Ramfden’s barometer ftood at 24-238, and the thermometer, fixed to it, at 27°, when
happily the clouds divided, and we difcovered a ftill higher fummit. We loft no time
in deliberation, but immediately afcended it, and when at the top difcovered a fpace of
ground, about eight yards in breadth, and twenty in length, entirely free from fnow ;
the fand was however quite wet, from its having lately melted away. Here we experi-
enced, at one and the fame time, a high degree of heat and cold, for in the air Fahren-
heit’s thermometer was conftantly at 24°, and. when we fet it down on the ground, it
rofe to 153. ‘The barometer was here at 22-247, and the thermometer at 38.
We could not with fafety remain here any longer, though we were very much in-
clined to it; and defcended, after having confidered the laft opening there, one of the
fides of which was entirely overturned, and the other quite covered with afhes and grit.
In our return we obferved three confiderable openings, in one of which every thin
looked as red as brick. From another the lava had flowed in a ftream of about fifty
yards in breadth, which the Icelanders call Stenaa, or Stone Flood ; and at fome diftance
from thence the ftream divided into three broad arms. Further on we found a large
circular opening, at the bottom of which we obferved a mountain in the form of a fugar-
loaf, in throwing up of which the fire feemed to have exhautted itfelf.
The laft eruption of mount Heckla happened in 1766; it began the fourth of April,
and continued to the feventh of September following. Flames proceeded from it in
December 1771, and in September 1772, but no flowing of lava, &c.
The mountain does not confift of lava, but chiefly of fand, grit, and afhes, which are
thrown up with the ftones, partly melted, and partly difcoloured by the fire. We like-
wife found feveral forts of pumice, and among them one piece with fome fulphur in it.
‘The pumice was fometimes fo much burnt, that it was as light as tow; their form and
colour was fometimes very fine, but at the fame time fo foft, that it was difficult to
remove them from one place to another: of the common lava we found both large
pieces and fmall bits, as likewife a quantity of black jafper, burned at the extremities,
and refembling trees and branches. Among the ftones thrown out of the mountain we ~
faw fome flate of a deep red colour.
LETTER XXI.—tTo proFEssoR BERGMAN.
Of the hot fpouting Water-/prings in Iceland.
Stockholm, O&. 3, 1774.
Amonc all the curiofities in Iceland, which nature prefents to the eyes of an attentive
fpe€tator to raife his admiration, nothing can be compared to the hot fpouting water-
fprings with which this country abounds. The hot fprings at Aken, Carlfbad, Bath,
and Switzerland, and feveral others which are found in Italy, are confidered as very re-
markable ; but to my knowledge, except in the laft-mentioned country, the water no
where becomes fo hot as to boil; noris it any where known to be thrown fo high as at
the hot {pouting water-{prings in Iceland.
All thofe jets d’eau which have been contrived with fo much art, and at fo enormous
an expence, cannot by any means be compared with thefe. ‘The water-works at Herren-
haufen throw up a fingle column of water, of half a quarter of a yard in circumference,
to the height of about feventy feet ; thofe on the Winterkalten, at Caffel, throw it up, but
in amuch thinner column, one hundred and thirty feet ; and the jet d’eau at St. Cloud,
which
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