PHYSICAL GEOGRAPHY 335 



The G r i m m i a - h e a t h formation is co-ordinate with the rocky- 

 flat formation, but is not so widely distributed by a great deal as is 

 the latter. As already mentioned, it reaches its fullest development 

 on the lava-streams in the lowlands, especially in the peninsula of 

 Reykjanes, where it occupies vast areas; but it also occurs on many 

 other lava-streams. Where there are sand-drifts Gri/nmia-carpets oc- 

 cur very sparsely or are entirely absent, as Grimmia hypnoides, the 

 most common species, cannot thrive in drifting sand; therefore ex- 

 tensive areas around Hekla, Fiskivotn and several other places are 

 practically bare of mosses. On the vast lava-fields on the plateau 

 mosses occur very sparingly. In several places the Grz/n/nia-heaths 

 on the lava-streams of the lowlands are comparatively quickly trans- 

 formed into soil for higher plants, which are fairly numerous even 

 in the Grimmia-carpet; generally the latter, in the course of time, 

 passes into heather-moor; sometimes into patches of grassland. In 

 several places the Grimmia-heath covers, with its characteristic grey 

 carpet, stony mountain-slopes, and areas strewn with rock fragments, 

 and. as is the case with the rocky flat, forms the foundation of a 

 scattered vegetation of many different species, without any special 

 character, but dependent upon the plant-formations of the neigh- 

 bourhood. Usually the Grimmia-heath develops more quickly into 

 heather-moor or grassland than does the rocky-flat formation, owing 

 to the abundant material for soil-formation supplied by the mosses. 

 Grimmia-heaths occupy large areas in the lower part of the pla- 

 teau, but very few flowering plants are found there in them; on 

 the other hand, lichens often occur numerously, especially Cetraria 

 and Cladonia, not however so numerously that they form a lichen- 

 heath proper, which occurs in Iceland only in patches, and is of 

 no great importance. In the highest parts of the interior of Iceland 

 the Grimmia-heath formation is of much less importance than in the 

 lower part of the plateau. 



Grassland. Ground covered chiefly with grasses or grass-like 

 plants may be classified under four heads: grass-slopes (Graesli); 

 knolly grassland (Graesmo); flat uncultivated grassland; and home- 

 fields, artificially manured soil. Grass-slopes (GraBsli). The lower 



son: Grodrarsaga hraunanna a Island! Skirnir, 1906. pp. 150 163); Vegetation paa 

 Smefellsnes (Vid. Medd. Nat. Foren.. 11)00, pp. 8184), and Vegetation i Syd-Island 

 (Bot. Tidsskr.. 27 Bd., 1905, pp. 53 61). C. H. Ostenfeld: Skildringer af Vegeta- 

 tionen paa Island (Bot. Tidsskr., 22 Bd., 1899, pp. 245 253). Chr. Gronlund: 

 Karakteristik af Planteviexten paa Island, pp. 30 32. 



