The Botany of Iceland - 01.12.1914, Síða 32

21(5
THORODDSEN
have been produced before the surface assumed its present form,
others have been formed after the country had in all essentials
acquired the sculpture it has to-day; several of them have flowed
down through vallej’s and hollows. Reykjavík is built upon such
a doleritic lava-stream, and there the dolerite is much used for
building purposes. In severai places the glacial lavas are of con-
siderable thickness (100—200 metres and more). Some larger vol-
canoes, which have been in eruption as lale as within historic times
(Eyjafjallajökull, Snæfellsjökull, Öræfajökull), began their activity
even during the Glacial period and at that time discharged doleritic
lava-streams. In several places in West and South Iceland large
deposits of conglomerates occur, with rolied gravel and sand, alter-
nating now and then with moraine material and ice-striated Iavas;
these resemble the “Nagelíluh” of the Alps and wcre perhaps formed
in a similar manner.
During the Glacial period the whole island was wrapped in a
sheet of inland-ice through which only a few small peaks projected
here and there near the edges. The Jökulls (snow-íields) of the
mainland probably extended on all sides down to the sea, for the
bottom-moraines of that time are found everywhere, both on the
plateau and in the lowlands; the lateral and terminal moraines
which occur in the valleys and lowlands, date from a later period
when the ice was retiring; it appears also that large masses of
moraine-material occur here and there on the sea-bottom off the
mouths of the fjords. The north-western peninsula was probably
covered with a separate ice-sheet, from which numerous small
glaciers, with intervening ridges free from ice, descended to the sea.
The ice-sheet of the Glacial period had, on the interior plateau, a
thickness of 700—800 metres. Ice-striated rocks occur all over the
island, both in the high land, in tlie valleys, and in the lowlands,
as also on islands and skerries. Large and small erratic blocks are
found in thousands scattered over the wliole of Iceland.
As mentioned above, it is assumed that Iceland, in the begin-
ning of Tertiary times, was connected by a broad land-bridge
with Greenland, the Færöes and Scotland; this land-bridge was a
volcanic higliland or plateau-land formed by innumerable lava-
streams which originated principally from rows of craters and from
íissures. The plateau, which had a height of 3000—4000 metres
above sea-level, was towards the end of the Miocene period broken
up and depressed; by this subsidence, perhaps in conjunction with