GLACIAL PERIOD. 
19 
which descended from the southern slopes of 
the Alps into the plain of Northern Italy. 
Moreover, these boundaries are not yet ascer¬ 
tained with the same degree of accuracy as 
those of the northern and western slopes ; 
though very accurate descriptions of some of 
them have been published, with illustrations 
on a large scale, by MM. Martins and Gastaldi, 
and of others by Professor Ramsey. I have 
myself examined only the upper part of that 
of the valley of Aosta. 
The evidence concerning the ancient glaciers 
of the Alps, especially within the limits of 
Switzerland, is already so full that it affords 
ample means for a comprehensive general view 
of the subject. When a stretch of time or 
space lies between us and a matter we have 
oiice studied more closely, we often see it as a 
whole more vividly than when our nearness to 
it forced all its details upon our observation. 
In my present position, separated by the lapse 
of many years from my personal investigation 
of the ancient and modern glaciers of Europe, 
I look back upon them from another continent, 
and it seems to me that I have, as it were, a 
bird’s-eye view of their whole extent. I con- 
