162 Mr Menge’s Account ofliis Mineralogkal 
rocks prevented all research. On the west side of the summit 
of Tindastoll, I found obsidian in roundish pieces, and in 
every possible variety. I was struck with the perfect resem- 
blance of these to the varieties found in Mexico. I had the 
good fortune to find a great number of specimens of the schiU 
lerende^ indigo-blue, green and striped kinds. The rocks in the 
vicinity of the obsidian appeared to be somewhat slaggy, and 
resembled those of the pseudo-volcanic class. The amygdaloidal 
beds were intersected by an opening several hundred paces 
wide, which I conceived might have formerly been filled with a 
vein of obsidian, thus affording a miniature representation of the 
great volcanic track which extends across the island, intersecting 
the trap-rocks. This appearance would enable me to explain 
the origin of obsidian from siliceous-sinter ; the more particular- 
ly, as I had observed at the Geyser, and on the Huarevellir, the 
siliceous-sinter inclining to obsidian. 
On the way from Tindastoll to Skagastrand, I discovered in 
Haller Valley a vein of obsidian. The obsidian appeared to 
pass into that coal which we often find in beds of flinty-slate. 
The principal formation around Skagastrand is greenstone, 
which, like basalt, forms large groupes of columns. Nearly the 
whole of Spakonefell is composed of’ this greenstone, which very 
much resembles that of the Meissener in Hessia, diflPering from 
it only in containing augite in place of hornblende. At Spa- 
konefell, I observed several beds of amygdaloid resting on 
the greenstone, in which the cavities were lined with the most 
beautiful crystallizations of analcirae, chabasite, and meso- 
type. On my departure from Skagastrand, at the entrance 
of the Valley of Laxa, I rode over a vein of pitchstone, 
several hundred feet wide. In this mountain-chain, I cross^ 
ed a valley named Vide, which appeared one of the most in- 
teresting geognostical spots in Iceland, but stormy weather, 
and want of time, prevented me from examining it. The most 
beautiful trap-porphyry, with magnificent crystals of glas- 
sy felspar ; splendent calcedonies, pumice-porphyry, and mas- 
ses of quartz-slate, with crystals of iron-pyrites; and the va- 
rious colours of the rocky walls, all intimated very interest- 
ing phenomena in the district. From this to Liosavatn, I 
observed alternations of porphyry and amygdaloid. On the 
