454 FEXXELL : SOME PHYSICAL FEATURES IN ICELAND. 
The diagram represents a plateau, on which we have pebbles 
and boulders of lava and basalt embedded in soft brown earth 
in a curious mosaic-like pattern as shown. The question to be 
answered is, How came they to be thus distributed? Some 
present may read the solution at a glance, or perhaps have 
seen the same thing elsewhere. I think the diagram makes it 
easier to solve the difficulty than when looking at the enlarged 
reality. 
Dr. Thoroddsen, who has travelled over Iceland more than 
anyone else in search of matters of geological and scientific 
value, was much interested to hear of these markings, which 
he had never noticed. 
Iceland is subjected to severe changes of climate, and, in my 
opinion, this plateau of lava-earth has been thoroughly wet and 
turned to mud, which has afterwards been baked and cracked 
in a hot sun, like the bottom of a dried-up farm pond in a hot 
summer, or it is possible that the constituents of the soil are 
such that mere drying would cause the surface to crack in 
this way owing to contraction. 
The cracks might no doubt be considerably widened and 
deepened by climatic changes, but be this as it may, given the 
cracks, it is very easy to now picture that in the summer, 
when the ground is baked hard, or in the winter months, when 
the ground is frozen, one of the terrific gales so well known 
in Iceland arises, setting stones and boulders rolling along the 
hard surface which fall into the cracks previously formed, and 
fill up every crevice therein, the rest being blown on to find 
a resting-place elsewhere. In summer we find the soft earth 
surrounded by the boulders which, in my opinion, mark out 
the exact sites of former cracks on the hard surface. 
