Charles Davison—Stone- Rivers, Falkland Islands. 391 
occupies the axis of the valley; and here and there, where a space 
between the blocks is unusually large and clear, a quivering reflection 
is sent back from a stray sunbeam.” The inclination of the surface 
of the stone-rivers is very small, and this is their most remarkable 
feature. ‘On the hillsides,” says Darwin, “I have seen them 
sloping at an angle of ten degrees with the horizon, but in some of 
the level, broad-bottomed valleys, the inclination is only just sufficient 
to be clearly perceived.” The actual movement of the blocks does 
not seem to have been noticed. ‘As far as I can ascertain,” Dr. 
Coppinger remarks, ‘“‘no attempt has ever been made to estimate 
the rate of movement (if any) of these ‘runs,’ and there is no 
evidence whatever of their motion during the present century.” 
The origin of the blocks themselves has been clearly pointed out 
by Sir Wyville Thomson. ‘The beds of quartzite are of very 
different hardness: some are soft, passing into a crumbling sand- 
stone; while others are so hard as to yield but little to ordinary 
weathering.” Being worn away unequally, the harder bands 
project, and at last the joint-formed blocks fall over. The 
difficulty, however, is to account for their present position and 
arrangement, and, for this purpose, the following theories have been 
proposed :— 
1. The action of earthquakes, hurling the blocks down the slopes, 
and then levelling them out into continuous sheets (C. Darwin, 
A. J. Pernéty). 
2. The movement of the soilcap enclosing the stones, the soil 
being afterwards washed away by the streamlets in the valleys (Sir 
C. Wyv. Thomson). 
3. The former movement of “earth-glaciers,’ which, owing to a 
change of climate, became desiccated, the earth being afterwards 
washed away by rain and streams (J. Geikie).’ 
4. The action of frost and snow, the alternate freezing and 
thawing of rain (Sir J. D. Hooker).? 
5. The action of glaciers. ‘I believe it will not be difficult to 
explain their origin in the light of the glacial theory, and I fancy 
they may turn out to be ground moraines similar to the ‘horse- 
backs’ of Maine” (J. R. L. Agassiz). 
6. The alternate expansion and contraction of the blocks under 
changes of temperature taking place mainly down the slopes, being 
assisted by gravity in that direction (C. Davison).* 
It is not my purpose to discuss these suggestions here; but I may 
remark that, according to Thomson, ‘ice had no hand whatever in 
the production of these grand ‘moraines’ of the Falkland Islands.” 
The second theory has been criticised adversely by Prof. J. Geikie 
1 The Movement of the Soilcap: Nature (March 8, 1877), vol. xv. pp. 397-398. 
* Himalayan Journals (1854), vol. ii. p. 179 (footnote). 
% Louis Agassiz: His Life and Correspondence, edited by E. C. Agassiz, vol. ii. 
pp- 694-695. Extract from a letter to Prof. B. Peirce, dated Feb 20,1871. It 
should be noted that Agassiz’s intention of visiting the Falkland Islands was never 
carried out. 
4 Note on the Movement of Scree-material: Quart. Journ. Geol. Soc. (1888) vol. 
xliv. pp. 232-237. 
