332 



THORODDSEN 



Where the sand becomes more stable, or there is shelter, Elymns 

 arenarius appears, often associated with Festuca r libra v. areuaria; 

 not until the sand becomes somewhat fixed do other species appear, 

 e. g. Juncus balticus, Carex iucurua, Agrostis alba, Festuca oviua, 

 Sileue maritima, Salix lauata, S. glauca and occasionally Haliauthus 

 peploides in localities not too far away from the coast. Extensive 



Fig. 32. Sali.r lanata and. in the background, Betula odorata growing in black blown-sand 

 (volcanic ashj near Jokulsa, between 'As and Svinadal ; July, 1909. 



(Phot. A. Hesselbo.) 



tracts are covered with different Salices, especially in Fjallasveit, 

 where in some places on sandy flats Carex iucurua also occurs in 

 abundance; moreover, in Myvatnsorsefi, Sudurarbotnar, Rangarvellir, 

 and several other places. Where the soil is broken up and re- 

 moved by sand-storms as deep down as to the underlying gravel, 

 as in several places in the southern lowlands in the neigbourhood 

 of Hekla, small tufts of Festuca rubra and F. ovina are the first to 

 appear, then come Juncus balticus, Equisetum arueuse, Agrostis alba, 

 Sileue maritima, Salix lauata and S. glauca; then gradually several 

 species of grasses make their appearance until at last a grassy wil- 

 low-flat is formed which makes an excellent sheep pasture. Here 

 and there on the plateau are damp flats of old blown-sand inter- 



