The Botany of Iceland - 01.12.1914, Síða 35

PHYSICAL GEOGRAPHY
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observed afTording evidence of an upheaval of the land in our own
day. Shortly after the Giacial period the climate was somewhat
milder than it is now; in northern Iceland abundance of Purpura
lapillus has been found in shell-mounds, and this still lives in the
sea south of Iceland, but not in the colder water along the north
coast. In bogs on the northernmost headlands, where birch woods
no longer thrive, remains of Betula alba are found, wliile Betula
verrucosa, which no longer grows in Iceland, has been found in
the bogs of South Iceland.
Volcanoes and Lava-streams. Iceland is one of the most
volcanic countries in the world; as mentioned above, the island
throughout has been built up by volcanic activity which began
early in Tertiary times and has continued to the present day.
There are records to hand of 138 eruptions from 30 volcanoes within
historic times, but many eruptions undoubtedly took place in early
times which either were not recorded or occurred in the inland
wastes and snow-fields without being noticed by the inhabitants.
At the present time, 130 post-Glac.ial volcanoes are known in Iceland,
and several volcanic vents have undoubtedly still to be found, or
else have been eflaced or destroyed by erosion. All tlie numerous
volcanoes liave, in the course of time, since the Glacial period, dis-
charged enormous quantities of lava, and the post-Glacial lava-fields
of Iceland cover an area of about 11 200 square km.; they occur
over the country in vast expanses around the volcanoes from
which they have originated. The majority of these lava-fields haye
been produced nol by one but by numerous eruptions at various
times, and the greater part of the lava dates from pre-historic out-
bursts. The largest lava-stream which has been poured forth during
a single eruption within liistoric times, is that which issued from
the craters of Laki — a row of craters formed in 1783; this stream
covers an area of 565 square km.; and its mass occupies about
12l/s cubic kilometres; it is probably the largest lava-stream upon
the surface of the earth which, within historic times, has been
known to flow out during a single eruption. The largest continuous
lava-field in Iceland is Odáðahraun on the plateau north of Vatna-
jökull (600—1200 metres above sea-level); it was produced by nu-
merous eruptions from more than 20 volcanoes, and covers an area
ot about 4000 square km. The lava-field, next in size, which origi-
nated from the many large craters near Veiðivötn, west of Vatna-