Bd. III: 2) CONTRIBUTIONS TO THE GEOLOGY OF THE FALKLAND ISLANDS. ig 
or a few heads of the graceful drooping chrysanthemum-like Chabræa sua- 
veolens. 
These ‘stone-rivers’ are looked upon with great wonder by the shifting popula- 
tion of the Falklands, and they are shown to visitors with many strange speculations 
as to their mode of formation. Their origin seems however to be obvious and 
simple enough, and on that account their study is all the more instructive, for they 
form an extreme case of a phenomenon which is of wide occurrence, and whose 
consequences are, I believe, very much underrated. 
There can be no doubt that the blocks of quartzite in the valleys are derived 
from the bands of quartzite in the ridges above, for they correspond with them in 
every respect; the difficulty is to account for their flowing down the valley, for the 
slope from the ridge to the valley is often not more than six to eight degrees, and 
the slope of the valley itself only two or three, in either case much too low to 
cause blocks of that form either to slide or to roll down. 
The process appears to be this. The beds of quartzite are of very different 
hardness; some are soft, passing into a crumbling sandstone, while others are so 
hard as to yield but little to ordinary weathering. The softer bands are worn away 
in process of time, and the compact quartzites are left as long projecting ridges 
along the crests and flanks of the hill-ranges. When the process of the disintegra- 
tion of the softer beds has gone on for some time the support of their adjacent 
beds is taken away from the denuded quartzites, and they give way in the direc- 
tion of the joints, and the fragments fall over upon the gentle slopes of the hill- 
side. 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 in- 
dicates that the loose blocks ai'e embedded beneath it. Once embedded 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 comparatively dry, and while with the expan- 
sion 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 re- 
moval. 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 after- 
wards removed and the blocks left bare. This, I have no doubt, is effected by the 
stream in the valley altering its course fi'om time to time, and washing away the 
soil from beneath. 
