316 THORODDSEN 



areas. Mosses often form an edging or fringe around loose stones 

 on gravelly flats or also cushions on heaps of stones or in rock- 

 crevices. On the highest situated and most inhospitable rocky and 

 gravelly tracts, where storms are constantly driving sand and gravel 

 across the surface, not even mosses can thrive, and the ground is 

 quite bare. A few species of lichens (Cladonia and Cetraria) are some- 

 times found in the moss cushions, but usually they occur only as 

 crusts on blocks of rock. Here and there on clayey soil in depres- 

 sions crusts of liverworts occur, especially Anthelia nivalis, often 

 associated with Grimmia hypnoides and Salix herbacea: round pools 

 and along streams, cushions of bright green mosses are often seen, 

 in which some flowering plants have sometimes found a home. In 

 other parts of the country, the three regions mentioned here occur 

 at a lower level, since they are correlated with the altitude of the 

 snow-line in the different parts of the country. 



