and Glacier Fluctuations. 539 
‘‘ So natural was the association of ice and cold, that even celebrated 
men assumed that all that is needed to produce a great extension of 
our glaciers is a diminution of the sun’s temperature. Had they gone 
through the foregoing calculations they would probably have demanded 
more heat instead of less for the production of a glacialepoch. What 
they really needed were condensers sufficiently “powerful to congeal 
the vapour generated by the heat of the sun.’ According to 
the temperature theory the condensers which Tyndall demands are 
furnished by the increased areas over which the whole of the snow- 
fall does not melt each year, these increased areas being produced 
by the fall of the snow-line as a result of lower atmospheric tempera- 
tures. The precipitation in the Glacial period may have been rather 
less per square yard than it is now; but this was more than made 
up for by the increase in the size of the alimentation areas. 
Paschinger! is of opinion that the determining factor in the height 
of the snow-line is above all the temperature of the air, and as 
a result of the study of the precipitation and temperature of the 
earth he considers that, in general, both in the longitudinal direction 
and in the latitudinal direction the influence of warmth on the 
height of the snow-line is greater than that of precipitation. He 
shows that in the Swiss Alps the snow-line is much higher on the 
warm south side than it is on the colder north side. 
There is one important consideration which has caused many to 
reject the precipitation theory as an explanation of the glaciation of 
Switzerland. In the Swiss valleys one can often see where the 
upper limit of the old ice-fields stood. Below the limit the rocks are 
more or less smoothed and levelled; above they are broken and 
craggy. If such a valley has glaciers and snow-fields at its source, it 
will be noticed, as one passes up the valley, that the craggy ridges 
are continuous with these that rise above the neve, and that the 
névé abuts directly against them. There are no ‘signs in these 
elevated regions that the névé was ever thicker than it is now; and 
the view taken is that during the Glacial period the névé-covered 
region was greatly extended in area, but that the higher regions then 
presented much the same appearance they do now. Had the snow- 
fall in the past been much greater than it is at present, signs of 
thicker ice and névé would now be visible at the higher as well as 
the lower levels. 
The more carefully the question of the cause of glacier advances 
and retreats has been studied in the field the more certain it 
has appeared that all considerable glacier fluctuations have been 
due to fall of temperature, accompanied, perhaps, by a slight decrease 
in the precipitation per square yard. Much more snow is converted 
into ice, but this has been due to the greater area over which it did 
not entirely melt. Thereis good reason to believe that in Switzerland 
the snow-line was so low in the Glacial period that even the great 
mass of ice which covered the region of Lake Geneva rose share its 
and that, therefore, the whole of the Rhone Glacier trunk, and 
 Peterman’s Mitteilungen, i, pp. 57-60, 1911, and Pet. Mitt. Ergangungsheft, 
No. 173, Gotha, 1912. 
