The Botany of Iceland - 01.12.1945, Blaðsíða 26

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STEINDÓR STEINDÓRSSON
called Stórihvammur. This is a fairly luxuriant slope situated
in the upper part of the ravine of Jökulsá, and mainly with a west-
ward exposure. The greater part of the slope is covered by a rather
vigorous Salix scrub or by heath. In the depressions grow vigorous
Juniperus bushes and some few Betula pubescens bushes. As this
locality is situated at c. 660 m above sea-level, it must be one of the
highest localities of the birch in Iceland.
2. Eyvindarver is a tract of mýri or flói on thc east side
of Þjórsá, south of Hofsjökull. Here I especially investigated a “flá”,
which will be described in more detail below.
2. GEOLOGICAL REMARKS
Here the main geological features of the regions mentioned above
will be briefly summarised.
A. Landmannaafrjettur.
This area lies in the palagonite formation of Iceland. Thus the
mountains Loðmundur, Sáta, Kýlingar, and Hellisfell are built up of
tuff and breccias. On the other hand, Kirkjufell and the mountains
around Jökulgil and Laugar are made up of liparite, and the lava
fields occurring in this region of obsidian lava. The whole westem part
of the region is much ravaged by blown sand. No observations on the
influence which the different rocks occurring in Iceland may have
exerted on the vegetation were made, but here as in other regions
under similar conditions there is a great difference between the vegeta-
tion of the tuff mountains and that of the liparite mountains. Thus
the former are always more or less covered with vegetation, if they are
not ravaged by blown sand, and fairly luxuriant slopes, mainly clad
with grass, occur there, whereas the liparite mountains are almost or
entirely devoid of vegetation. I suppose that the paucity of plants on
the liparite mountains has two causes; one is that since the rock
weathers rather easily, the mountain sides are covered by scree, which
is in constant motion and does not permit a vegetation of any im-
portance to gain a foothold; the other, I should think, is to be found
in the chemical composition of the liparite, notably its content of silica.
However, these are only suppositions, since no investigations have been
made in this respect.