540 Prof. T. G. Bonney—Alpine Passes and Peaks. 
TV.—Tue Scutrrure or ALPINE Passes anp Praxs.! 
By Pror. T. G. Bonney, D.Sc., LL.D., F.R.S., F.G.S. 
HERE are two facts which are closely connected with the present 
condition of the Alps—(1) that the rainfall on the Alpine 
slopes on the Italian side of the watershed, as a rule, is heavier than 
that on the other side, and (2) that the valleys also are steeper. It 
is indeed true that the distance from the watershed of the Central 
Pennines to the lakes on either side, north or south, is not very 
different, but the level of those on the latter is some 700 feet below 
that of those on the northern. This difference of level is especially 
marked in the upper part of the valleys, places correspondingly 
situated being always lower on the southern than on the northern 
face ; for instance, Zermatt is rather above Macugnaga, but as the 
crow flies it is more than double the distance from the watershed. 
For both the above reasons denudation will proceed more rapidly 
on the slopes of the Alps facing southwards or eastwards, that is, 
towards Italy, and thus the valleys in them will be cut back more 
quickly and be more precipitous at their heads than in the northern 
or western slopes. From this results a singular configuration of the 
uppermost parts of a valley, which is commonly exhibited by the 
passes selected for the construction of high roads. The usual form 
of a pass in the higher Alps, as every climber knows, is this: you 
follow a valley which at last leads you by a final ascent, more or less 
steep, to a gap or saddle between two peaks, on the other side of 
which a similarly formed valley is found to descend. Of such passes 
every variety exists, from the depression which must be reached by 
climbing a rocky wall, like the east side of the Strahleck or the south 
side of the Sella Pass, to those like the Col de la Valpelline, where 
the final acclivity is comparatively slight. Occasionally, however, 
we meet with a type of pass of which the Maloya, at the head of the 
river Inn, may serve as an example. Noted as one of the lowest 
gaps across the watershed of the Alps, for its summit is barely 6000 
feet above sea-level, its structure offers a problem which at first 
sight is sufficiently perplexing. The valley of the Inn ascends, on 
the whole gradually, to Samaden, where the river is joined by a 
torrent which carries the drainage from the northern face of the 
Bernina group. But though this brings the greater volume of water, 
it occupies a glen which is, orographically, of secondary importance, 
and the main valley continues onwards in a south-westerly direction 
towards the Maloya Pass. Samaden is about 5600 feet above the 
sea; from it a rather steep but short ascent brings us to the level of 
the St. Moritzersee, the elevation of which is about 5800 feet. We 
have now entered a rather broad and almost level valley, enclosed 
between mountains which rise on either side from 4000 to 6000 
feet above it, the floor of which is occupied to a considerable extent 
by a group of shallow lakes. This trough is more than nine miles 
long ; yet the Silsersee at its upper end is only 66 feet higher than 
_ } An extract from one of the “ Tyndall Lectures” delivered at the Royal Institution 
in 1888, by Prof. T. G. Bonney, D.Sc., F.R.S. 
