Ball — On Some Effects Produced by Landslips. 7 



have been transported by glaciers ; and in the particular region in 

 question there are such glacial moraines conveniently situated for 

 comparison. 



These appearances were contrasted with those of the celebrated 

 stone rivers of the Falkland Isles, which Sir Wyville Thompson^ 

 has attributed to the movements of the soil-cap, which has in part 

 derived its motion from the expansion and contraction of the 

 spongy mass, due to varying conditions of moisture and compara- 

 tive dryness. 



Several speakers, when discussing Dr. Ooppinger's Paper, 

 afforded testimony as to the probability of such a cause being 

 capable of explaining many accumulations of blocks and breccias 

 in both recent and early times, while Sir John Hawkshaw showed 

 that movements of the soil-cap, and with it of rooks, were only 

 too familiar to engineers, and that, in some cases, they continued 

 for many years after once the surface had been disturbed- 



In this instance of Patagonia, then, we have a beautiful example 

 of the contemporaneity of two apparently contradictory pheno- 

 mena — (1) a rising of the general mass of the land ; and (2) a sub- 

 sidence of the soil-cap. Generalizing from this, it would perhaps 

 be not too much to say that, given certain relationships between 

 tracts of land and their soil-caps, an upheaval, owing to the dis- 

 turbance of equilibrium, would invariably be followed by a subsi- 

 dence of the soil-cap. Detrital matter which had settled down at 

 its angle of repose must, on the elevation of its sustaining surface, 

 find a new position at a lower level, and thus I believe may, in 

 some cases, be explained the presence of submerged forests and 

 bogs on the one hand, and accumulations of glacial-like debris on 

 the other. 



In regions where there is a heavy rainfall, and also in those 

 where the protecting effects of vegetation have been removed by 

 the cutting down of forest, subsidences of the soil-cap, as is well 

 known, are of common occurrence without any necessary exhibi- 

 tion of regular landslips. There are tracts in the Himalayas 

 where, at the cost of the primeval forests, tea-gardens have been 

 established on the slopes, and where, after a few years, the tea- 



^ Voyage of the Challenger — The Atlantic, vol. ii., p. 245, 



