108 
ISLAND LIFE. 
[part r. 
"head of the Lake of Geneva, since it spread over the whole of 
the great valley of Switzerland, extending from G.eneva to 
Neufchatel, Berne, and Soleure, and even on the flanks of the 
Jura, reached a maximum height of 2,015 feet above the valley. 
The numerous blocks scattered over the Jura for a distance of 
about a hundred miles vary considerably in the material of 
which they are composed, but they are found to be each trace- 
able to a part of the Alps corresponding to their position, on 
the theory that they have been brought by a glacier spreading 
out from the Rhone valley. Thus, all the blocks situated to the 
east of a central point G (see map) can be traced to the eastern 
side of the Rhone valley ( l e d) } while those found towards 
Geneva have all come from the west side (p h). It is also very 
suggestive that the highest blocks on the Jura at G have come 
from the eastern shoulder of Mont Blanc in the direct line 
h B F G. Here the glacier would naturally preserve its 
greatest thickness, while as it spread out eastward and westward 
it would become thinner. We accordingly find that the 
travelled blocks on either side of the central point become lower 
and lower, till near Soleure and Geneva they are not more than 
500 feet above the valley. The evidence is altogether so con- 
clusive that, after personal examination of the district in com- 
pany with eminent Swiss geologists, Sir Charles Lyell gave up 
the view he had first adopted — that the blocks had been car- 
ried by ice during a period of submergence — as altogether 
untenable. 1 
The phenomena now described demonstrate a change of 
climate sufficient to cover all our higher mountains with 
perpetual snow, and fill the adjacent valleys with huge glaciers 
at least as extensive as those now found in Switzerland. But 
there are other phenomena, best developed in the northern part 
of our islands, which show that even this state of things was 
but the concluding phase of the glacial period, which, during 
its maximum development, must have reduced the northern 
half of our island to a condition only to be paralleled now in 
Greenland and the Antarctic regions. As few persons besides 
professed geologists are acquainted with the weight of evidence 
1 Antiquity of Man, 4th Ed. pp. 340-348. 
