044 Prof. T. G. Bonney—Alpine Passes and Peaks. 
deepened the valley between the Tofana and the Cristallo massif, 
it gradually cut away the rocky wall which once closed the glen to 
the west of Schluderbach. 
But the head of the Pusterthal itself presents us with a somewhat 
similar anomaly, and this, singularly enough, finds a parallel at the 
head of the Etsch. The watershed in the former, though between 
the Adriatic and the Danube, is curiously ill defined. It is a flattish 
drift-covered plain, barely 4000 feet above the sea, perhaps a third 
of a mile wide, guarded on the one side by the slopes and crags of 
the crystalline schists of the central range of the Tyrol, on the other 
by the magnificent dolomitic cliffs of the southern range. On the 
west—from Welsberg to Niederndorf (4 miles) there is a rise of 
about 260 feet; from the latter place to Toblach (8 miles) a further 
rise of 150 feet; and from Toblach to Innichen, on the east side (2 
miles), a descent of less than 100 feet. Thus the floor of the trough 
for some five miles does not rise and fall more than about 100 feet, 
and the average slope is less than 1 in 100. In the next eight miles 
the fall is only about 225 feet, which is still more gentle. But then 
it becomes more rapid; the valley contracts, its floor descends more 
sharply as the river passes through the Lienzer Klause, a defile cut 
into the crystalline schists and about nine miles long. Lienz itself, 28 
miles from Toblach, is about 1750 feet below that place, while 
Untervintl, which is about the same distance on the western side, is 
some 3800 feet higher than it. Here, then, I conclude that the 
original watershed must be placed to the east of the Toblacherfeld, 
and that the Drave has cut its way back into the upper part of the 
glen of the Rienz. 
The pass of the Reschen Scheideck, which leads from the upper 
part of the valley of the Etsch to the Finstermiinz in the valley of 
the Inn, exhibits a structure in some respects similar to that which 
has just been described. The Malser Heide, on which the pass lies, 
is a long and comparatively level trough, the watershed of which is 
less than 5000 feet above the sea (4898 feet). Thence the road 
declines gradually to Nauders (4468 feet), and then drops rapidly 
down to the gorge of the Inn, the level of that river being about 
3700 feet above the sea. 
To explain the structure of the region, I must go back to the 
time when the Inn had excavated a valley which was both shallower 
and narrower than that which it now occupies. Suppose that its 
bed was then about 5000 feet above the sea, on the level of the 
Reschen Scheideck ; at that time the head waters of the Etsch may 
have descended from a ridge, the watershed of which lay near to 
the channel of the Inn. Gradually, as the latter river deepened 
and enlarged its valley, the ridge would be eaten away, until at last 
the head of the Reschen Scheideck trough was exposed. Then the 
brow of the declivity towards the Inn (as the rocks here are not 
very durable) would be rounded off, so that the edge of the old 
trough would not remain sharp, as in the case of the Maloya, but 
would be gently bevelled in the upper part, and thus the actual 
watershed would travel slowly and almost imperceptibly eastwards. 
Instances where apparent anomalies may be explained by the 
