or Saussurite-smaragdite Gabbro of the Saasthal. 249 



But the blocks may also be traced up the slopes some height 

 above the bed of the Saasthal'* and are carried down the 

 valley of the Rhone to beyond Geneva, though of course they 

 become much less numerous in the lower part, even of the 

 Vispthal. If, however, the glaciers extended only as far as 

 Stalden, at least a considerable portion of the ridge would be 

 concealed, and during no small fraction of the Ice Age it 

 must have been completely buried. In my opinion, we are 

 not materially helped by assuming that a large area of gabbro 

 may be buried beneath the present glaciers f ; for I am not 

 aware of any evidence which would justify us in assuming 

 that masses of rock can be, to any great extent, gripped and 

 torn ofT by the lower part of a glacier and then transported 

 beneath the ice. At the present time, as probably at all times, 

 most boulders of any size begin their journey on the surface 

 of the glacier, i. e. have fallen upon it from crags. Is it pos- 

 sible that, during a long period anterior to the " Great Ice Age," 

 the Alpine glaciers either were much smaller than they are at 

 present, or perhaps had entirely disappeared? As I have 

 elsewhere shown J, a rise of only 6° F. in the mean tem- 

 perature of Switzerland would suffice to remove them from 

 many districts and reduce them, even in this part of the 

 Pennines, to comparative insignificance. If so, blocks doubt- 

 less might be accumulated by the ordinary processes of 

 mountain destruction over an area much more extensive than 

 is now exposed, and these might be gradually swept onwards 

 by the advancing ice. Some of these also must have been 

 lifted vertically, for, as I have said, they occur at least 500 

 feet above the bed of the Vispthal. But even this hypothesis 

 does not appear to me to remove the difficulty, for where the 

 boulders are most abundant they lie as if they had been 

 dropped during the retreat of the ice. So we must suppose 

 that the glacier kept depositing them on the bed of the valley 

 and - then over-riding them ; a process which I find not very 

 easy to understand, and one which, if acknowledged, would 

 be extremely difficult to reconcile with that excavating power 



* I have only seen them up to 500 or 600 feet above the river, "but very 

 likely they go higher. I have not had a good opportunity of searching* 

 for and determining their vertical range. 



t At the lower end of the ridge we appear to he approaching the inferior 

 limit of the mass, for Mr. Eccles informs me that in 1890 he saw (but 

 could not actually touch) a dark green rock (either serpentine or the 

 " green schist" of the district) below the euphotide and above the surface 

 of the glacier. The ridge does not appear at the present time to give rise 

 to any well-marked moraine. 



X " The Growth and Sculpture of the Alps," ' Alpine Journal/ vol. xiv. 

 p. 233. 



