162 H. MØLHOLM HANSEN 
swamp) the soil is protected from the frost and therefore even; in 
mo, jadar, and (myri) the frozen surface will crack in the spring, as 
in Denmark, and form greater or smaller polygons which will 
furnish a foundation for the formation of knolls. How this latter 
takes place 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 clayey 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, and the frozen crust will 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, the more marked is this phenomenon. If the 
Icelandic formation of knolls is a result of the same forces, it may 
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 jadar in 
the highlands where precisely these two conditions are present. 
According to this view the knolls (in mo and jadar) 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 the knolls is peculiarly loose, 
almost like flour. 
If there is a continued formation of knolls it will, in regions 
much exposed to wind, become a starting point for solifluction. The 
surface of the knolls will break on the side exposed to the wind, 
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 solifluction. 
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 these in connection with a simultaneous 
phytogeographical investigation a better understanding of these fac- 
tors, so important to Icelandic farming, might no doubt be gained 
