The Botany of Iceland - 01.12.1914, Qupperneq 151

PHYSICAL GEOGRAPHY
335
The Grimmia-heath formation is co-ordinate with tlie rocky-
flat formation, bnt 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 tliere are sand-drifts Grimmi'a-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, Fiskivötn 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 Grímmia-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; generalty 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 occupjr large areas in the lower part of the pla-
teau, but very few ílowering plants are found there in them; on
the other hand, lichens often occur numerously, especially Cetraria
and Cladonia, not however so numerousljr 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 witli grasses or grass-like
plants may be classified under four heads: grass-slopes (Græsli);
knolly grassland (Græsmo); flat uncultivated grassland; and home-
fields, artiíicially manured soil. Grass-slopcs (Græsli). The lower
son: Gróðrarsaga hraunanna á Islandi (Skirnir, 1906, pp. 150 -163); Vegetation paa
Snæfellsnes (Vid. Medd. Nat. Foren.. 1900, pp. 81—84), 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. Grönlund:
Karakteristik af Plantevæxten paa Island, pp. 30—32.