The Botany of Iceland - 01.12.1945, Síða 27

THE VEGETATION OF CENTRAL ICELAND
369
B. Brúaröræfi.
This area is likewise situated within the palagonite formation, but
its eastern portion borders on the basalt formation of the east country.
No liparite occurs here. The factor that exerts the greatest influence
is no doubt the wind, traces of its intense erosion being visible every-
where. Large stretches, formerly entirely covered with vegetation, are
now destitute, and the blown sand incessantly devastates the few and
small oases that are still left. The vegetation only holds its own in places
where the moisture of the soil is capable of counteracting the devasta-
tions of the wind.
C. Snæfells- and Lónsöræfi.
The westernmost part of this area, that around Snæfell, is built
up of the palagonite and the basalt formation in conjunction, with
some admixture of liparite near Snæfell. The easternmost part, Kol-
lumúli and surroundings, however, is made up of liparite, but other-
wise the surface consists of basalt. Here the difference between the
vegetation of the liparite mountains and that of the basalt mountains
is very conspicuous. Although the latter are not particularly densely
covered with vegetation, the liparite mountains are still barer. In the
highland between Jökulsá í Fljótsdal and Víðidalur solifluction is very
conspicuous, especially above 600 m above sea-level. It is distinctly
visible that whole hills and ridges are, as it were, flattened out, and
on the outskirts screes of the coarsest stony material are formed. This
moving soil, as might be expected, supports only a very poor vegetation,
but where the material is more fine-grained, some vegetation is found
on the slopes affected by the solifluction. It is in these cases that terraces
are formed on the mountain sides, and the vegetation mainly gains a
foothold in the front parts of these terraces; it is always characterised
by the rather deep snow-covering here. On larger horizontal gravel
flats both here and in other places of the highland, polygon soil
is widely distributed. Systems of fissures are formed, which mostly make
pentagonal or hexagonal polygons often of considerable size. The
coarsest stone material is gathered along the fissures, especially at the
corners of the polygons. The polygon flats are rarely entirely horizontal,
but bulge slightly, sloping on all sides towards the fissures, along which
a scattered vegetation is often found, while the polygon flat itself is
entirely bare.