The Botany of Iceland - 01.12.1942, Page 21

THE PTERIDOPHYTA AND SPERMATOPHYTA OF ICELAND
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jökull in the south-western part of Vatnajökull has frequently during
the nineteenth century caused large inundations of the neighbouring
lowland, but here the material damage has been of less importance
since only sandy, uninhabited wastes have been inundated.
Mountain peaks projecting above the snow-fields are rare in Ice-
land, and do not usually appear until near the edge of the snow-fields
where summits of the underlying rock may rise above the ice-cap. Such
“nunataks” occur in the southern and south-western parts of Vatnajö-
kull. The vegetation on these peaks is very poor, and altogether very
little known as yet.
Geology and Soil Conditions.
G e o 1 o g y. Iceland is built up almost entirely of volcanic material,
but nowhere does this apparently date farther back than the middle of
the Tertiary period. Basalt and palagonite breccia are the principal
rocks. The basalt formation occupies nearly two-thirds of the area, and
the palagonite, which is composed of breccia, tuffs and conglomerates
of different ages, but, taken as whole, younger than the basalt,
constitutes about one-third of the area. Of much less importance in
the country are other rocks and formations.
The basalt formation attains a thickness of about 3000 m in Ice-
land, and the nature of the underlying rock is as yet practically
unknown.
In many places by the sea coast the basalt mountains rise in pre-
cipitous walls from the sea, up to 1000 metres, and show very fine
profiles of the layers of which they are composed. Between the true
basalt strata there occur beds of tufa and breccia, but in comparison
with the basaltic layers they are of small importance.
As in Ireland and on the Færoes, so also in Iceland there occur, in
the middle of the basalt formation, rather considerable clay deposits
containing impressions and remains of plants from the tertiary forma-
tions, as also lignite and compressed tree-trunks (Icelandic “surtar-
brandur”). The plant-bearing formation has its greatest thickness (up
to 50 m) in the peninsula Vestfirðir; it was originally deposited at
the same level, but was afterwards broken up by dislocations and now
occurs at different heights above the sea. This formation shows that
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