The Botany of Iceland - 01.12.1942, Síða 29

THE PTERIDOPHYTA AND SPERMATOPHYTA OF ICELAND
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however, are the stony deserts (melar) bare of vegetation (cp. Weis,
table nos. I, II and V), from which a soil formerly covered with vegeta-
tion has been removed by solifluction or wind, and the sands which
have not yet been bound by any vegetation. Weis maintains that the
content of organic matter is high in moors (mýri) and heaths where raw
humus layers have accumulated in the course of time.
More surprising is the great content of mineral substances (fine sand
and clay particles) in the peat. This is due to the frequent sand-storms
blowing from adjacent areas destitute of vegetation.
Weis also points out the peculiarity that there is often a very large
amount of humus in the apparently pure mineral soil. Thus in two
samples the humus content was 12.08 and 12.70 p.c. respectively, though
the soil resembled brownish-yellow mineral dust with apparently no
traces of roots or leaves. According to Weis the organic matter must
here be present in a colloidal state forming gel films around the mineral
dust particles.
This abundance of organic material is very valuable. Not only does
it give the soil its water-holding and base exchange capacity, but it
furnishes a corresponding supply of nitrogen.
On the whole, the investigations made by Weis, as well as by others,
show that the content of plant nutrients in Icelandic soils is, generally
speaking, hardly smaller than in the soils of similar types from Central
Europe and Scandinavia. Even though CaCO:., and marl are lacking
in most of the Icelandic soils, the calcium content (silicates and sul-
phates) tends to be higher than in soils from Central Europe.
The material from which Icelandic soils originate, volcanic rock,
especially basalt and liparite, lava and volcanic ash as well as palagonite
breccia and tufa is apparently excellent. As a rule it disintegrates quickly
to very fine soil particles, so fine indeed that they are easily blown by
the wind and deposited as loess. A great deal of the material is carried
off as clay suspensions in glacial streams and is later deposited else-
where.
Analyses of 4 different important Icelandic soil types are presented
in the following table 2 (cp. Weis, loc. cit. p. 3). For comparison 4 types
of Central European soils are also represented. As will be seen, the
black soil (Tschernosiom) is here taken as a parallel to the Icelandic
peat soil, because thc Icelandic bog soils differ in many respects from
northern and central European moor soils, and in their chemical com-
position more closely resemble the famous rich “black soils”.
The figures in table 1 are quite dissimilar from the pjq -value of