33() THORODDSEN 



slopes of mountains are often grass-covered, especially when the rock 

 is tuff or breccia; in South Iceland the tuff mountains are often en- 

 tirely grass-covered, at least on the southern side, and sometimes 

 they are covered with a thick layer of soil without knolls proper, 

 which occur only on the clay ground of the lowlands. But some- 

 times wavy rows of small knolls, or narrow ripple-like ledges occur 

 in the lowest part of the grass-slope, and sometimes above these, 

 for a great distance up, the surface of the soil is undulating and 

 wave-like; this is undoubtedlv due to mud-flows in the clavey soil- 



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covering. On basalt mountains the grass-vegetation extends upwards 

 in tongues or occurs in patches in depressions or on ledges, se- 

 parated by considerable tracts of stones and gravel. On such a 

 grass-slope, in addition to the grasses, many other kinds of herbaceous 

 plants are more or less numerously represented. In South Iceland, 

 according to H. Jonsson, the following are the dominant species: 

 Agrostis vnlgaris, A. canina, Anthoxanthnm odoratnm, Festiica ouina, 

 Poa alpina, P. nemoralis, Geranium silvaticum, Trifolinm repens, Brn- 

 nella vulgaris and Leontodon autumnalis; less common, but often 

 occurring locally in great abundance: Spircea nlmaria, Linnm ca- 

 tharticum, Rubus saxatilis, Gentiana campestris, Myosotis arvensis, 

 Parnassia palnstris, and many others: in Fljotshlid Carum carvi is 

 very common and in Myrdalur and Sida Succisa pratensis. The 

 vegetation is rich in species and is rather mixed, although grasses 

 preponderate. In other parts of the country where basalt is domi- 

 nant the grass vegetation of the mountain-slopes consists of similar 

 species, but is not so luxuriant as in South Iceland. The following 

 species are common: Agrostis vulgaris, A. alba, A. canina, Anthoxan- 

 thum odoratum, Nardus stricta, Aira flexuosa, A. ccespitosa, Phleum 

 pratense, Poa alpina, Hierochloa borealis, Festnca rnbra, etc. A spe- 

 cial Nardzzs-association and an A/7//?oxa/?//?Z7m-association often occur. 

 Knolly grassland (Graesmo). By this is understood dry, ex- 

 tremely knolly stretches of clayey ground intermixed with humus, 

 occurring on level land and in valleys with a mixed vegetation of 

 Graminese, Juncaceae and Cyperaceae; it may therefore differ con- 

 siderably in appearance, according to which of these families pre- 

 dominates. When grasses predominate the "Grsesmo" resembles 

 grassland, but sometimes Jnncns trifidns and Ely no. Bellardi are so 

 dominant that large stretches attain a brownish tint like that of a 

 heather-moor. Usually, the vegetation of the knolls differs from that 

 of the depressions; in the depressions, mosses and some Carices 



