320 PROCEEDIKGS OF THE GEOLOGICAL SOCIETT. [^P^- 5, 



plains near tlie ends of existing glaciers, wMcli might be presumed 

 to be filled-up lake-basins ; still these cases of glacial erosion, if 

 such they be, are on a very small scale compared with the amount 

 of denudation that this hypothesis requires; and there are many 

 others, as, for example, in the Val del Campo and Yal Viola*, where 

 the great heaps of moraine stuff show the glaciers to have long re- 

 mained just fiUing up the whole of a lateral valley, without any 

 marked effect on the bed behind. 



This difficulty is increased when we examine the bed of an exist- 

 ing glacier, a thing which the rapid diminution of some of the Ober- 

 land glaciers during the last few years has made possible. The 

 surface of the Unter-Grindelwald glacier was (July 1870) aboiit 100 

 feet lower, and the extremity had retreated fuU 500 feet higher up 

 the steep hill-side, than in 1858. Formerly it descended to the level 

 of the valley ; it now rests on a low cliff of rock ; and its stream no 

 longer gushes out from an ice- cave, but runs deep in a rocky gorge. 

 This shows that the glaciation of a valley, and the cutting a gorge 

 in its bed may be simultaneous. (The Eosenlaui glacier affords 

 another example of this.) It can now be seen that the final icefall 

 descends over three or four steps of hard limestone ; the last, and 

 perhaps the tallest of these, together with what we might call the 

 first flag of the valley-floor, being at present exposed. If, then, the 

 glacier has made these steps, if it is plastic enoiigh to mould itself 

 to them (which it is not in all cases), surely it ought, at the base of 

 each wall, to have worn out considerable hollows, analogous to the 

 pot-holes at the foot of a cascade. But there is nothing of the 

 kind to be seen ; the rocks, beautifully polished and scratched in 

 many places, exhibit the usual contours, and after forming an irre- 

 gular lumpy terrace, showing often " Stoss- and Leeseite," round 

 away to the next cliff. 



The steps, not uncommon in valleys, such as those in the Yal 

 Formazza, and that which is visible from near Landro, in the glen 

 which descends from under the Drei Zinnen to the Diirren See, pre- 

 sent similar but still greater difficulties in accepting the hypothesis 

 of glacier erosion. 



Again, how are valleys such as those of the Pusterthal or the 

 Upper Etschthal, to be explained on a theory of glacial erosion ? The 

 former is a well-marked and generally wide trench, about fifty 

 miles long, extending east and west from Miihlbach, where the 

 Eienz turns sharp to the south, to SilUan on the Drave (to say 

 nothing of any further extension to the Gailthal). For the most 

 part it is enclosed by mountains 8000 or 9000 feet high ; and the 

 flat Toblach plateau, which parts these rivers and forms the water- 

 shed between the Adige and the Danube, is 3951 feet above the 

 sea, " sloping gently, almost imperceptibly," in either direction. 

 No one who has seen this great trough, whose sides are steep moun- 

 tains, rising 4000 feet or more on either hand, whose base dips 



* Valleys connecting, on the Italian side, the lower parts of the Bernina and 

 Stelvio Passes. 



