58 David Milne-Home on Ancient Glaciers. 
the valley, where the Grand Saléve and other mountains are 
situated, whose northern slopes have alpine blocks scattered 
on them. The relative height of these blocks in the different 
parts of this great valley point clearly to such a result. 
The blocks of Monthey, which are only about 300 feet above 
the Rhone, form no ground of objection to this view, because 
they were most probably left by the Rhone glacier as it was 
shrinking to its present dimensions, in which case they would 
not have travelled so far from their parent hills as others; a 
supposition corroborated by the appearance of the blocks 
themselves, all of which are much more angular than the 
generality of the blocks in lower parts of the country. 
2. The great difficulty, of course, is how to account for such 
a change of climate as would produce glaciers on so much 
greater a scale than at present. The question is too large 
to be discussed in all its bearings in this paper. It may be 
sufficient to mention that two causes have been suggested— 
one of which would affect the whole of Europe simultaneously, 
and the other one would affect Switzerland alone. Ac- 
cording to the first hypothesis, a great elevation of land took 
place in northern Europe, in virtue of which (to use the words 
of Sir Charles Lyell, who suggests it) “nearly the whole sea, 
from the Poles to the parallel of 45°, would be frozen over.” 
Switzerland, however, being in latitude 46°, would scarcely 
be reached by such a. cause; and there are other objections. 
According to the second hypothesis, this district of Europe 
alone may have been elevated, and elevated to such a level 
that the Chamouni and Rhone glaciers would require to 
descend to the low country about Geneva before they could 
reach their melting point. 
With reference to this last hypothesis, it may be asked, 
What amount of elevation would be required to produce the 
required extension of these glaciers ? 
They melt now at an average elevation of 4400 feet above 
the sea; and as Geneva is 1335 above the sea, the difference 
of these two levels, 7. ¢., 83065 feet, gives the height to which 
Low Switzerland would require to be raised, to cause such a 
temperature there as to enable glaciers formed in the Alps to 
reach Geneva before melting. | 
