328 THORODDSEN 



flats; they have a characteristic vegetation consisting of Koenigia 

 islandicctj Sedum villosnm , Juncus alpinns, J. biglumis and J. trigln- 

 mis; moreover, Epilobium palustre, Spergula arvensis, Sagina pro- 

 cumbens, S. nodosa, Stellaria crassifolia, Polygonum aviculare, Equise- 

 tum palustre, Triglochin palustris, Agrostis alba, Luzula spicata and 

 some other species occur frequently, which are distributed according 

 to the water content, etc. of the clayey flats 



The vegetation of mountain- si opes is often only an extension 

 of that of the rocky flats, with the difference that greater variations 

 occur at the base of the mountains, the conditions there being more 

 highly diversified: the stony tracts alternating with bogs, springs, 

 grass-slopes, heather-moors, coppice-woods, etc. But frequently moun- 

 tain slopes consists mainly of downward-gliding gravel-masses or an- 

 gular rock-fragments, with little or no vegetation, the stone-covering 

 being too unstable to permit plants to gain foothold; in other places 

 are heaps of loose blocks of rock (urd) or solid rock-terraces or 

 -faces; in many places mountain-streams excavate channels or deep 

 ravines, and at the base of mountains they cause the formation of 

 broad gravel-cones with branching streamlets with mosses and other 

 plants connected with springs, or \vith transitions to bog-formations. 

 On the rock terraces there is sometimes a soil-layer which, accord- 

 ing to the conditions of moisture, supports either GramineaB or 

 Cyperacese. Therefore, on mountain-slopes, many different plant- 

 formations are found in patches close to one another in many transi- 

 tional stages. In the rock-detritus on mountain slopes which are 

 not too steep, plants common on rocky flats occur, but none that 

 are really characteristic: the following have been noted: Sllene acanlis, 

 S. maritima, Alchimilla alpina, Dryas octopetala, Thymns serpyllnm, 

 Cerasthim alpinum, Armeria maritima, Saxifraga ccespitosa, S. hyp- 

 noides, S. stellaris, PotentiUa macnlata, P. anserina, Sedum acre, Erige- 

 ron alpinuSj Veronica saxatilis, Poa glauca, P. alpina, and several 

 others. Nor are there many characteristic plants in the vegetation 

 of the rock-faces. Tuff and breccia mountains are generally richer 

 in plants than basalt mountains, their surfaces having many more 

 crevices and hollows in which plants can gain foothold. The fol- 

 lowing plants occur on steep mountain-sides: Archangelica offwinalis, 

 Rhodiola rosea, Haloscias scoticnm, Polypodium uulgare and Woodsia 

 ilvensiSj also Cochlearia officinalis, especially on sea-fowl cliffs; Saxi- 

 fraga Cotyledon grows only on rocks in south-eastern Iceland. More- 

 over, in rock-clefts various ferns occur, most frequently Cystopteris 



