PHYSICAL GEOGRAPHY 339 



on the roofs and in some places Achillea millefolium; in various 

 districts Rhodiola rosea has been planted on the walls, and in the 

 northermost districts Cochlearia officinalis often occurs in abundance 

 upon the houses, and in some places Saxifraga rimilaris. At their 

 base the house-walls are green with Prasiola crispa; various mosses 

 also grow 7 upon the houses, especially Bryiim argentenm l . 



Heather moors are extensively developed in Iceland both in the 

 lowlands and valleys, on mountain-sides and on hills to a height of 

 about 400 metres; they are not recorded from higher levels. On moun- 

 tain-sides and on hill-slopes the heather moor is almost flat, on level 

 land it is usually knolly; it is best developed upon old lava-streams 

 and it often forms the ground vegetation of birch coppices. The 

 dominant species are Empetrum nigrnm, Vaccimum uliginosum, V. 

 myrtillus, Arctostaphylns uva ursi and Calluna vnlgaris; the last 

 species is fairly common in many districts, but never occurs so abun- 

 dantly as the others. Moreover, among the heather there is usually 

 an abundance of Dry as odopetala, Juniper us communis, Betula nana, 

 Rubus saxatilis and Salix herbacea. In heathy tracts at higher levels 

 and also above these in scattered patches, are found Loiseleuria pro- 

 cumbens, Cassiope hypnoides and Sibbaldia procumbens. On the penin- 

 sulas on either side of Eyjafjordur patches of Phyllodoce coerculea 

 which is not recorded from more southerly habitats - - are no\v and 

 then found. There is a great variation in the distribution of the 

 different character-plants in the heather moor; sometimes they all 

 occur mixed with each other; sometimes each occurs 'separately in 

 large or small patches, so that the different areas may be designated 

 Vaccimum heaths, Empetrum heaths, Calluna heaths, Arctostaphylus 

 heaths, etc. Between the heather, as ground vegetation, other plants 

 occur in abundance, especially immigrants from the knolly grass- 

 land from which the knolly heather-land often appears to have 

 been derived for instance, Juncus tri/idus, Elyna Bellardi, Luzula 

 multiflora, L. spicata, Nardus stricta, Agrostis canina, A. alba and se- 

 veral other Gramineae, also Salix lanata, S. glauca, S. phylicifolia, 

 Silene acaulis, Thymus serpyllum, Bartschia alpina, Alchimilla alpina, 

 Thalictrum, Galium, Hieracium, and many others. In addition, there 

 is very often a moss-carpet of Grimmia hypnoides beneath the heather. 



Willow coppices. Although the various species of willows 

 lare widely distributed they rarely form coppices proper, and willow 



1 As regards the moss-vegetation on old house-walls see Helgi Jonsson's 

 above-mentioned paper on the vegetation of South Iceland. 1905, p. 54. 



