The Botany of Iceland - 01.12.1914, Qupperneq 26

210
THORODDSEN
Thorisvatn — cover an area of only about 100 square km. eacli:
the lake-surfaces occupy therefore only a very small part of the
entire area of the country. The lakes are of very diverse origin,
the basins having been formed by tectonic movements, ice-erosion,
volcanic action and other natural agents. On the plateau where
the outlet is sliglit, especially in the neighhourhood of the large
Jökulls (ice-mountains) many lakes occur, in some places gathered
in large groups, as Fiskivötn on Arnarvatnsheiði NW. of Lang-
jökull, and Veiðivötn W. of Vatnajökull; the melting snow and ice
from the glacier-edges disappear in the nearest lava-streams and
sandy tracts and then reappear and gather into basins many kilo-
metres away from the glaciers from wrhich they originated. In other
places the lakes occur in the immediate neighbourhood of the glacier-
edge, as Hvítárvatn and Hagavatn near Langjökull and Langisjór
near Valnajökull; the glaciers project into these lakes and calve
their ice-bergs there; the water in these lakes is milky-w'hite as in
the glacier rivers. In some places lakes occur in between the glaciers
(Grænalón near Skeiðarárjökull) or are dammed up in valleys by
glacier-tongues. The best-known lake in Iceland is Thingvallavatn
(105 square km.); it is situated in a new volcanic district bounded
on the S. and W. by steep tuff-mountains and on the N. and E.
bv lava-streams which originate from the volcano of Skjaldbreið;
these streams have afterwards flowed dowm between the two well-
known fissures — Almannagjá and Hrafnagjá. It was here that the
Icelandic Althing met in the time of the Republic. It appears as if
the basin of the lake of Thingvalla was originally formed by sub-
sidence along lines of fracture from SW. to NE.; this lake has a
depth of 110 metres. In North Iceland Mvvatn is the best-known
lake; it is formed in a depression in the lava-stream and has a
depth of only 2—7 metres; its bottom is lava and several craters
project above its surface Iike islands, while the surroundings are
very volcanic. Mývatn has received its name from the mosquitoes
(mý) which are often quite a plague there. As in Thingvallavatn,
trout are plentiful in this lake, but it is especially known as the
abode of numerous birds, especially many different species of ducks.
The group of lakes called Veiðivötn consists for the most part of
crater-Iakes, of which the largest is called Stórisjór. In other places
valley-Iakes occur — deeply hollow'ed basins in the basalt — as
Skorradalsvatn in Borgarfjörður and Lagarfljót in East Iceland, the
surface of w'hich latter lies 26 metres above sea-level while its bottom