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THORODDSEN 



there upon the highest ridges and peaks, which cannot be reached 

 bv the coarser grains of the drifting sand, are seen small patches 

 of soil supporting mosses and a few phanerogams. 



In Iceland blown sand consists almost invariably of decomposed 

 volcanic rocks; quartz-sand does not occur in Iceland. The most 

 common blown sand is palagonite-dust usually of a yellowish-brown 

 colour, which when examined microscopically, is seen to consist 

 of glass-particles, tachylite, palagonite, plagioclase, augite and various 



Fig. 15. Mohella in Kroksdalur, not far from Sandmiiladalsa, (Phot. Heinrich Erkes.) 



finely decomposed zeolitic alteration-products. Volcanic ashes of recent 

 date often occur as blown sand especially in the interior of the 

 lava-wastes; they are heavier and less mobile, consequently, they 

 are not dispersed in quantities beyond the volcanic districts. In the 

 neighbourhood of the great glacier-bearing mountains, considerable 

 tracts of level land are often covered with glacial clay, which when 

 dried, crumbles into dust and drifts beyond the nearer surroundings. 

 Around Dyngjufjoll, especially south-east of Askja, large areas are 

 covered with blown sand, consisting of liparitic pumice-dust which 

 all dates from the eruption of 1875. Moreover, stretches of blown 

 sand consisting of decomposed mussel shells, i. e. calcareous dust, 

 occur here and there along the coast of the north-western peninsula. 



