PHYSICAL GEOGRAPHY 297 



Lastly some 40 50 foreign species have been found which have 

 not yet gained a permanent footing in the flora, some of which will 

 probably again disappear. 



There can be no doubt that the vegetation has been modified 

 in various ways since man with his cattle-rearing came upon the 

 scene; sheep have especially exerted a great influence upon the 

 coppice- woods and other vegetation; in the few places to which 

 sheep cannot gain access, e. g. in distant valleys surrounded by 

 glaciers and rivers of great volume, on islands in the middle of 

 waterfalls or torrential rivers or in lakes the vegetation is usually 

 far more luxuriant than in other places. In Viftidalur in Lon I had 

 the opportunity of noting an example of the change effected by sheep- 

 rearing. The locality in question is situated 439 metres above sea- 

 level and has a southern exposure; it is surrounded by glaciers and 

 deep river-gorges impossible for sheep and cattle to cross. Formerly 

 the valley had been inhabited for a short time, but in 1840 it was 

 deserted by the inhabitants. I visited the valley in the cold summer 

 of 1882 and found there a very luxuriant vegetation; all the plants 

 had a height quite unusual in Iceland. At the bottom of the valley 

 the grass and the different species of willow usually reached to the 

 horse's belly; especially were Salix phy lid folia, Geranium silvaticum, 

 Bartsia alpina and Archangelica officinalis of considerable size; there 

 was almost a wood of Archangelica which reached a height of 1- 

 2 metres. The old ruins of the huts which were destroyed in 1840 

 by an avalanche were overgrown with Archangelica officinalis and 

 Salix phylicifolia, and from the old fire-place a willow, belonging 

 to the latter species, had grown out, about 2 metres in height, with 

 stem 3 4 cm. in diameter. In 1883 the valley was again inhabited. 

 I revisited the place in the summer of 1894 and found the condi- 

 tions greatly changed owing to cultivation and the influence of sheep 

 and cattle. That tract of land upon which the above-mentioned 

 species had reached their highest development was now laid out 

 as a manured home-field (tun), overgrown by species of grass cha- 

 racteristic of manured fields. These grasses had not, however, yet 

 gained mastery over the wild vegetation; the single plants of grass 

 stood far apart, so that the field only yielded 04 cwt. hay per annum, 

 while in the coastal districts a well cultivated field of the same size 

 would have yielded 240 cwt. Besides, the soil was quite intersected 

 by subterranean portions of former plants, roots of willows, etc. 

 This vegetation w r ould therefore in all probability quickly become 



