542 Prof. T. G. Bonney—Alpine Passes and Peaks. 
J regard it as anterior in its dominant features to the extension of 
the ice. J suppose that when it was made no glacier intruded on to 
its floor; perhaps there were no glaciers among the peaks; at any 
rate, I do not suppose that the region of snow and ice was more 
extensive than at present. I believe, for I can find no other 
explanation, that in this part of the valley of the Inn we have a 
true valley of erosion, comparable, let us say, with the upper part 
of the Val Rosegg, one of those steps which not unfrequently 
precede the final ascent to the watershed. But I suppose that the 
watershed in this case once lay some distance further south, perhaps 
not very far away from the present frontier-line between the Enga- 
dine and Italy, say passing somewhere above the site of Vico 
Soprano. From this ridge the Inn then flowed towards the north- 
east, while on the other side the Maira descended towards the south- 
west. At the present time the Maira falls about 2500 feet between 
Vico Soprano and Chiavenna, a distance of about 12 English miles, 
say full 200 feet a mile, and the Maloya Kulm is nearly 2400 feet 
above Vico Soprano, a distance of about 5 miles as the crow flies, 
giving a total fall of almost 5000 feet in some 18 miles of the river 
course, say 5 in 100 on the average; while the Inn, as has been 
said, descends at first almost imperceptibly, and between St. Moritz 
and the Finstermiinz only falls 94 in 10,000, which is rather less 
than 1 in 100. 
Obviously, then, apart from any consideration of rainfall, the 
erosive force of the Maira would be far greater than that of the Inn. 
Thus the streams of the former would bite more deeply into the 
dividing range than those of the latter. The intervening mountain 
mass was quarried away far more rapidly on the southern side, until 
at last the corrie at the head of the Maira ate its way back through 
the dividing ridge, and actually cut away the slopes by which the 
streams descending towards the Engadine were formerly fed. Thus 
I regard the floor of the Upper Innthal as the decapitated remnant 
of a very ancient valley, which, while important changes have been 
occurring on either side, has remained comparatively unchanged, 
because denudation must needs cease when its motive forces are 
gone. When the weapons are snatched from the hand of the 
destroyer, when his arm is paralysed, then he must cease from 
troubling and the weary may rest. 
If we examine a good map of the district, we find an interesting 
confirmation of the explanation just offered. The tributary glens 
of a river system bear a general resemblance, as every one knows, 
to the branches of a tree—they tend to converge in the direction of 
the flow, as twigs unite to branches, and branches to the trunk. It 
is true that the changes from valleys of strike to valleys of dip give 
rise to sharp turns and “kinks,” not unlike those in the boughs of 
an aged oak; but we rarely find a valley running almost in the 
opposite direction to that of the stream to which it is a tributary. 
Yet the long glens occupied by the Albigna and the Forno glaciers 
run due north, while the Maira for some distance is flowing almost 
exactly in the line of the former glen, but in the opposite direction. 
