158 Mr Menge’s Account ofhts Mmerahgical 
gehirge ) in Iceland, as in most other countries, rest on granite, 
and its congenerous rocks, yet here they are less frequently se- 
parated from them by the clay-slate formation than on the 
Rhine, and in the Rhone, and Vogelsgebirge ; yet the limestone 
connected with this slate formation occurs in the Westmanna 
Islands, viz. on the north side of Heyma-Ey and Barner-Ey. 
The limestone is compact and bituminous, with a strong argilla- 
ceous smell. All the lavas on Heyma-Ey and on Eyafialla-Jo- 
kull are melted trap-porphyry, full of crystals of glassy felspar. 
I remarked, in regard to the latter mineral, viz. the glassy fel- 
spar, that it became less and less frequent in the lava as we ad- 
vanced westward, — a circumstance which led me to the conclu- 
sion, that the principal formation of the whole island (which I 
consider to be trap-porphyry) extends from S.E. to N.W., from 
which there may branch out in all directions the different mem- 
bers of the trap series. 
In order to ascertain the accuracy of this inference, it was 
necessary to execute a journey across Iceland from south to 
north, and which I accomplished from Geyser to Skagafiord. 
Unfortunately I obtained in this route but little satisfactory in- 
formation, owing to the great devastation occasioned by fire and 
water in this line of journey. The bounding points of trap-por- 
phyry must be Klofa-Yokull on the south-east, and Hranga- 
Ydkull on the west 
In the Rangaarvalle Syssel, which I passed through on my 
way to Reikiavig, I could not make any observations, because 
the whole plain along the base of Hekla, proved to be an alter- 
nation of marsh, sand, and rapid streams. On the river Thior- 
saa, I observed below a bed of volcanic sand, a species of tuff, 
with an obsidian basis. In the Guldbringe Sjssel, which re- 
sembles a congealed Pandemonium, every rock has been melted. 
Although all the lava here is melted basalt, yet, it is worthy of 
remark, that the lava varies very much in its aspect, and may 
be described as forming three different kinds of terram. The 
first terram is cracked in all directions, and the slaggy masses 
* We recommend the reader to consult the map of Iceland in Henderson’s 
amusing and interesting work, entitled, “ Journal of a Residence in Iceland,” 
and also the map of the south part of Iceland, in the well known work of Sir 
George Mackenzie, Bart. — Ed. 
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