Bd. III; 2) CONTRIBUTIONS TO THE GEOLOGY OF THE FALKLAND ISLANDS. 
37 
Addendum. 
As the physical conditions under which solifluction takes place are very 
imperfectly known, I sent two samples collected from flowing soils in the Falkland 
Islands for examination to Dr. A. Atterberg in Kalmar, who has executed a 
series of brilliant investigations into the characteristics of different types of soils. 
In the course of the correspondence dealing with these specimens Dr. Atter- 
BERG has sent me some general remarks on the process of solifluction which are 
of such great interest, especially as hints to future researches, that they ought to 
be quoted here. 
»The transition», Dr. Atterberg writes, »of a soil into fluid or semifluid condi- 
tions may be due to several reasons. 
When the mass consists chiefly of particles smaller than 0,002 mm. diameter, 
then, according to my experience ^ the circulation of water in this soil is very slow. 
If such a mass is mixed with water to the amount of 25 — 35 % of its weight, the 
water shows no tendency to separate, but the mixture remains homogenous — 
plastic clay. When the amount of water is larger, the mass is fluid like a porridge 
or pap which, when left undisturbed, remains in the same condition without any 
tendency to divide into a bottom-deposit and a superstratum of water. 
When the mass consists of particles coarser than 0,002 mm., but smaller than 
0,02 mm., pure water circulates more easily in the interspaces between the particles, 
and the mass does not remain plastic, but divides into a compact bottom deposit 
and an overlaying stratum of water. 
However, this is the case only with pure water. In saliferous water such min- 
ute particles do not settle into a hard, compact deposit, but form a soft, fluid mass 
that contains much water and only very slowly packs, or even fails altogether to 
pack, into a more coherent deposit. 
Evidently these phenomena are of high importance in nature. At the coasts of 
Kurisches Haff in the Baltic there are formed .sand-deposits which are so mellow that 
it is perilous to try to walk on them. The flowing clays in Bohuslän (W. Sweden) 
which have repeatedly inundated the railway-embankments are other instances of 
the same process. Also coarser sand can sometimes settle in fluid conditions. At 
the coasts of the isle of Oland the sand is generally deposited in coherent masses. 
But inside a compact sand-ridge I often found the sand to be entirely fluid (pos- 
sibly acid extracts out of the sea-ware have caused this condition of the sand). 
' Atterberg, Studier i Jorclanalysen. Svenska Landtlmiks Akad. Handi. 1903. R. 206. 
