THE FORMER EXTENSION OF GLACIERS. 
H3 
from a great distance. No similar rock occurs in the 
neighbourhood, and it is often possible to determine 
the locality from which they have been derived. 
For instance, near the Katzensee is a block con- 
sisting of a peculiar variety of Granite only known to 
occur at Ponteljes-Tobel above Trons in the valley of 
the Rhine. Many blocks of the same rock occur on 
the right bank of the Lake of Zorich, and they can 
be followed all the way to their source. Not one 
occurs to the left of the lake. This could hardly be 
the case on any other theory than that of transport 
by a glacier. Again, the “Ploughstone” already men- 
tioned agrees with the fine-grained Melaphyre of the 
Gandstock in the middle of the Canton of Glarus. 
The block of Steinhof near Soleure, which 
measures 65,000 feet, is probably from the Val de 
Bagnes. 
The Pierre a Bot, as already mentioned, is of 
Protogine, and has come from the St. Bernard. 
It is probable that the ancient glaciers moved 
more rapidly than their comparatively diminutive de- 
scendants of the present day; but at the existing rate 
Of movement the Pierre a Bot would have taken 
1000 years to travel from its original home on the 
chain of Mont Blanc to its present site near Neu- 
chatel; Whymper calculated that the blocks at Ivrea 
