The Botany of Iceland - 01.12.1930, Side 172

162
H. X10LHOLM HANSEN
swamp) the soil is protected from the frost and therefore even; in
mo, jaðar, and (mýri) the frozen surface will crack in the spring, as
in Denmark, and form greater or smaller polj'gons which will
furnish a foundation for the formation of knolls. How this latter
takes [>lace is still uncertain. It seems natural to suppose that it
is due to the action of frost which may also be observed in Den-
mark when clayej' or boggy soil freezes. On such soil, which has
been exposed to a long period of frost, the surface will be observed
to have been raised in various ways, aud the frozen crust wrill be
seen to consist of alternate layers of ice and frozen earth. When
the water freezes the whole mass of soil expands upwards, either
in the shape of a large cake or as a radiating system of branches
of ice and earth. The greater the moisture and the longer the
action of the frost, tlie more marked is this phenomenon. If the
Icelandic formation of knolls is a result of the same forces, it majr
be anticipated to be most pronunced on moderately moist soil and
in regions where frosts are frequent. And, as a matter of fact, the
formation of knolls attains its handsomest development in jaðar in
the highlands wrhere precisely these two conditions are present.
According to this view' tlie knolls (in mo and jaðar) should be
a kind of “frost-baked earth-balls”, for which the polygonal soil
forms the point of departure. Frost is the agent and water
the expanding factor which, on freezing to ice, changes
the internal structure of the knoll from a relatively com-
pact to a more porous state. In accordance herewith it will,
in fact, be observed that the interior of tlie knolls is peculiarly loose,
aimost like flour.
If there is a continued formation of knolls it will, in regions
much exposed to wrind, become a starting point for solifluction. The
surface of the knolls will break on the side exposed to the wrind,
and will at last be entirely eaten up by erosion. In areas where
the action of the frost is relatively strong, as in melar, knolls will
form the starting-point for solitluction.
The above considerations are merely of a sketchy nature. On
the basis of general observations and the knowledge of external
factors drawn from phytogeographical investigations I have attempted
to correlate a series of peculiar soil phenomena. By a more me-
thodical investigation of tliese in connection writh a simultaneous
phytogeographical investigation a better understanding of these fac-
tors, so important to Icelandic farming, might no doubt be gained