The Botany of Iceland - 01.12.1949, Síða 10

8
EMIL HADAC
1 o e s s, less common are the slope-loess, strand sand, aeolic sand (ori-
ginating in the interior of the Peninsula by weathering of palagonite
formation), talus-gravél, alluvia etc. There are two original materials
for the originating of the soil in the area investigated: basalt lava and
palagonite formation. Lava weathers very slowly: it is covered
generally by vegetation. Palagonite formation weathers very rapidly:
it is generally bare of vegetation. The two formations hardly differ in
their chemical composition, their chief difference is found in their
physical nature.
Chemical composition of palagonite may be seen from the following
table, quoted from Rosenbusch: Elemente der Gesteinslehre, Stutt-
gart 1923, p. 434:
Si02 38.96
A1203 11.62
Fe2Oa 14.75
MgO 6.29
CaO 9.13
NaaO 0.68
K20 0.72
H2o 17.85
Several articles have been written on the Icelandic loess. S t e i n
E m i 1 s s o n in his interesting study quotes different definitions of
loess together with his own results and comes to the conclusion that
lcelandic loess should be classified as something quite different from the
ordinary loess. The chief differences are according to Emilsson the
greater grains, layers of volcanic ashes, and impenetrability for water.
This is true from the point of view of soil-science; but the term
“loess” is used mainly in a geological sense. It is therefore more suitable
to use the criterium of origin than of structure or texture of the soil in
question. The loess may then be defined as follows: Loess is an
aeolic sediment with more or less angular grains.
The grain diametre is about 0.01—0.05 mm. Icelandic loess may be
classified as a special case (greater grain diametre, ash horizons,
chemical properties like palagonite).
Walter Iwan deals with a more complicated problem. He
travelled in different parts of the country and records “Fetzen des
Lössmantels”—slices of the loess-cover—in all visited places of the
Island with the exception of the most recent lava fields. Aeolic sedi-
ments are lying not only on lava fields, but also on morainic material as
well as on “sandar”. These districts are to be classified as accumulation