﻿500 M. A. Hcim on Glaciers. 



elevation of many a central moraine of compound glaciers is 

 produced, not by the underlying ice being protected from melt- 

 ing by the debris, but in such a purely mechanical manner. 

 The central moraine would then, where the mechanical middle 

 wall is rising, increase in height more quickly than further on, 

 where the mechanical dam is already formed and attains no 

 further elevation. 



In the Aar Glacier, for a length of 1200 metres, the whole 

 central-moraine dam is not covered with debris, but only 

 crowned therewith; and this extent commences about 400 

 metres below the confluence — exactly where in the 12000-fold 

 diminished scale of the gypsum experiment a middle wall began 

 to arise. Afterwards the debris slide down the side and cover 

 the previously clear declivity. Whether, as in the gypsum 

 stream, it sinks again, I know not. Fig. 2 (Plate VII.) represents 

 the profile of a transverse section through the middle of the 

 Lower-Aar Glacier, 250 metres below the union of the two 

 principal streams — the Lauteraar (L) and the Finsteraar Glacier 

 (F); figure 3, one at about 1000 metres below the point of union ; 

 and figure 4, one at 3300 metres further down. A peculiarity 

 of the Aar Glacier is, that (as shown in fig. 3) the moraine- 

 crown is not exactly on the centre of the wall, but is displaced 

 towards the left-hand side of the valley. 



Altogether the same as in the Aar Glacier, but much more 

 striking, I found in the Steinlimmi Glacier where it is joined by 

 a powerful arm of the Stein Glacier, which has a precipitous fall 

 between Bocksberg (2640 metres) and Thierbergli (2754). 

 Fig. 7 is a sketch of the moraine of the Steinlimmi Glacier, 

 with its wall clear of debris. Fig. 5 shows the profile where the 

 two lateral moraines are not yet quite united, in about the place 

 which coincides with the middle of fig. 7. 



As in the gypsum experiments, certain irregularities in the 

 form of the bed will always prevent the formation of a di- 

 stinct mechanical middle wall ; thus it does not appear when 

 the two streams are very unequal in magnitude ; hence profiles 

 like the above are by no means to be expected in all compound 

 glaciers. Since my attention was directed to this point, the 

 two glaciers cited are the only ones I have seen of those com- 

 posed of two nearly equal streams. 



It appears to me that it was the observation of such profiles 

 as figures 3 and 5 that misled Charpentier to delineate, as shown 

 in fig. 6, the profile of a moraine as protecting the ice from 

 melting away, and to speak of a "piedestal des moraines superfi- 

 cielles" while with respect to lateral moraines he makes no 

 mention of elevation through ablation of the glacier, and was 

 not yet aware of the widening of moraines by the debris sliding 



