SOLIFLUCTION 99 



of their adjacent beds is taken away from the denuded quartzites, and they give 

 way in the direction of the joints, and the fragments fall over upon the gentle 

 slopes of the hillside. The vegetation soon covers the fallen fragments, and 

 usually near the sloping outcrops of the hard quartz, a slight inequality only 

 in the surface of the turf indicates that the loose blocks are imbedded beneath it. 

 Once imbedded in the vegetable soil, a number of causes tend to make the 

 whole soil-cap, heavy blocks included, creep down even the least slope. I will 

 only mention one or two of these. There is constant expansion and contraction 

 of the spongy vegetable mass going on, as it is saturated with water or com- 

 paratively dry, and while with the expansion the blocks slip infinitesimally down, 

 the subsequent contraction cannot pull them up against their weight; the rain- 

 water trickling down the slope is removing every movable particle from before 

 them; the vegetable matter on which they are immediately resting is undergoing 

 a perpetual process of interstitial decay and removal. In this way the blocks are 

 gradually borne down the slope in the soil-cap and piled in the valley below. 

 The only other question is how the soil is afterwards removed and the blocks 

 left bare. This, I have no doubt, is effected by the stream in the valley altering 

 its course from time to time, and washing away the soil from beneath.^ 



This explanation given by Sir Wyville Thomson, referring the 

 formation of the stone-rivers to the slow removal of the waste down 

 the slopes, must be willingly accepted by everyone who has studied 

 the "stone-runs" in nature. The only objection, and that a very 

 essential one, is against the idea of the phenomenon as a product 

 of present conditions and of the process as still working with full 

 effectiveness underneath the vegetation that now partly covers 

 the stone-rivers. It ought to be noticed that long before I visited 

 the Falkland Islands and studied in detail one of the stone-rivers, 

 James Geikie, knowing these tracts only from the descriptions of 

 Darwin and Thompson, had already expressed the opinion that 

 the stone-runs were comparable to the rubble-drifts of England, 

 or otherwise that they were formed in a bygone period, characterized 

 by a climate more severe than the present.^ 



When I came to the Falkland Islands in 1902, I did not know 

 of the ingenious comparisons made by James Geikie, but with my 

 earlier experience from Bear Island it was easy to go straight to 

 a full understanding of the thing. 



Solifluction, in its quite typical form, is still at work in the Falk- 

 land Islands, but only on a small scale in favorable localities where 



^Ibid., pp. 246-48. 



^Geikie, The Great Ice Ag", 3d ed. (London, 1874), pp. 722, 723. 



