80 CARL SKOTTSBERG, A BOTANICAL SURVEY OF THE FALKLAND ISLANDS. 



of East Falklands also belongs to the Devonian, and across it, broadening towards 

 tlie west, stretches a conspicuous folding zone (Pl. V: 1), forming numerous parallel 

 quartzite ridges (Pl. IV: 2), striking E — W and separated by valleys, whose bottoms 

 consist of softer sandstones. To the south, tliis district is limited by the Wickham 

 Heights, which can be follovved right across the broadest part of the island, from 

 Port Stanley to Port Sussex. Its highest point is Mt. Usborne, 683 m. (Pl. V: 1). 

 These qiiarzite-ridges provide one of the most prominent features in the landscape, 

 with their grey or nearly white colour standing out in contrast against the dark heath 

 (Pl. IV: 2). 



The south part of East Falkland, generally called Lafonia, has a rather 

 different (Pl. V: 1—2) nature. It is biiilt iip of sand- and claystones, resting in horizon- 

 tal position, and belonging to the Permo-carbonian. The rocks are all comparatively 

 soft. In conformity with the lithological and stratigraphical character of this forma- 

 tion, Lafonia forms a great plain, in marked contrast to the broken landscape of 

 the rest of the Islands, with their upraised, härd quartzites. Another famous feature, 

 characteristic of the Devonian part of the islands, is also absent here, the stoneruns, 

 or »streams of stones», forming irregular patches, of ten in the form of a network 

 on the hill-sides, and covering the bottom of the valleys with a slieet of great angular 

 quartzite blocks of various shapes and sizes, »varying from that of a man's chest to 

 ten or twenty times as large, and occasionally altogether exceeding such measures», 

 as Darwin expresses himself (Pl. IX, X: 1). 



The origin of these stoneruns has been discussed, as well as by Darwin, by 

 Sir Wyville Thomson, but got its final explanation through the investigations of 

 J. G. Andersson in 1902. They are the resiilt of the period of solifluction, an 

 extra-glacial facies of the great Ice Age. Väst träets of the Falklands were covered 

 by a peculiar semi-fluid soil, formed of sand and clay, delivered by the softer 

 Devonian beds, and with härd, resistent quartzite blocks of all shapes and sizes 

 embedded in this mäss. It moved slowly down the slopes, smaller strips uniting to 

 form the immense mudstreams of the valleys. The finer material was shifted by the 

 action of rain and running water, was removed in some places and collected in others. 

 As the climatic conditions improved and the solifluction finally came to a standstilj, 

 vegetation again commenced to gain ground, and most of the land became covered 

 with meadow, heath or swamps. I have discussed the distribution of associations in my 

 previous paper on the Falklands; I then came to the conclusion, that, taken as a 

 whole, grasses predominate on better soil and that the dark strips of Eiwpetrum-heaih 

 that foUow the inclination of the slopes are strips of ground with more coarse 

 material. Further studies on this subject have not made me abandon this opinion 

 (Pl. IX). 



In some places recent solifluction has been observed, so for example by 

 Andersson, who describes a typical case on Stephens Peak {21, p. 23, Fig. 9). 

 Naturally it is going on on a very small scale in comparison with in old times and 

 only during periods of rain or snow. This recent movement is of great interest as 

 helping U3 to understand the gigantic process that once gave birth to the stoneruns. 



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