The Botany of Iceland - 01.12.1914, Síða 61

PHYSICAL GEOGRAPHY
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Owing to the variability of the wind-conditions, tlie dunes in the
blown-sand districts are usually small and irregular in form; tliey
are rarely higlier tlian 3—4 metres, usually much less, and they
are bound together by lyme grass and a few creeping dwarf willows.
Sandy levels with low waves of sand are of general occurrence, and
when moisture comes into play, the surface is cracked into numerous
polygonal cakes by the action of desiccation or frost. Tlie cracks are
filled with drifted sand, so that the surface resembles a kind of mosaic.
Fig. 16. Soil torn up bv the wind. Large tracts in Landsveit are occupied by these loess-like
formations. Here several square miles of land. which were formerly wood-covered, are torn
up bv the north-east wind. The district of Landsveit, west of Hekla. (Phot. Th. Thoroddsen.)
In tuff districts proper older and younger æolian formations
are the thickest and most widely distributed, and often alternate
with volcanic and glacial formations; but the tuff-dust is also car-
ried to the basalt districts, where they initiate the formation of the
loess-like layers known in Iceland as “móhella.” Smaller layers of
“móhella” occur everywhere in valleys and lowlands alternating
witli older and more recent glacial formations, with peat and lava-
streams, but they decrease in thickness Ihe further they are away
from the large stretches of blown sand in the tuff districts. “Mó-
hella” usually resembles a íine, easily crumliled, yellowish-brown
or grey tuff, which is often traversed by stems of plants and red
tuff-tubes wliich have been formed around the decayed stems; they