12 ALBRECHT PENCK 



valley is very slow. This is the case with the Monte Ceneri, which 

 opens in the left side of the valley of the Ticino, and allows one to 

 enter the surroundings of Lugano from the north; with the Pass of 

 Seefeld, through which you reach the valley of the Inn south of 

 Munich; and with the famous Pass of Reschenscheideck, through 

 which 3'0U pass from the lower Engadine to the headwaters of the 

 Adige. The erosion of this pass was carried so far that the floor 

 of the pass reaches the shoulder of the Engadine, and that some old 

 affluents of the Inn were already diverted into the Adige. A further 

 state of erosion of an old pass is shown by the situation of Lake Orta. 

 Here the pass has been totally leveled down, and considerable accumu- 

 lations of moraines south of it force its water northward toward 

 the Alps. Finally, in Valsassina, the long-reversed slope is independ- 

 ent of the terminal moraines south of it. It is a branch of the trough 

 of the Adda valley, which extends here into a side valley where it 

 terminates obtusely. This series of different stages shows us how 

 the watersheds can be moved to the outer rim of the old glaciation. 

 This state, however, has not been reached elsewhere. Its establish- 

 ment depends not only on the intensity of glacial action, but also 

 upon the original features. A pass originally very high will stand 

 far longer than a low one. This fact must be observed in those 

 cases where the valley, reached by a branch of the ice, is overdeepened 

 in a way similar to the main valley. Thus, for example, that branch 

 which branched off the glacier of the Ticino valley at the Monte 

 Ceneri overdeepened the valleys west of Lugano, which are now 

 occupied by the west branch of Lake Lugano, and the branch of the 

 Adda glacier, which branched off at Menaggio, and passed the saddle 

 of Porlezza, has overdeepened the valley of Porlezza and transformed 

 it into the lake basin of Porlezza, which is the deepest part of Lake 

 Lugano. He who considers only the lake basins as the results of 

 glacial erosion will be much puzzled by the interruption of the erosive 

 action of a glacier by a pass. On the other hand, he who follows the 

 whole development of glacial erosion will easily recognize its great 

 effect also on the pass traversed by the ice, and he will perhaps be 

 aware that the erosion on the pass itself was more considerable than 

 that which formed a basin. 



The diffluence of the ice is controlled by the rule of cross-sections, 



