468 Prof. T. G. Bonney—Glacial History of Western Europe. 
snow could remain through the summer months, would be carved into 
glens and valleys. Towards the end of that period the Alps were 
affected by a new set of movements, which produced their most 
marked effects in the northern zone from the Inn to the Durance. 
The Oberland rose to greater importance; Mont Blanc attained its 
primacy ; the massif of Dauphiné was probably developed. That, and 
still more the falling temperature, would increase the snow-fields, 
glaciers, and torrents. The first would be, in the main, protective ; 
the second, locally abrasive; the third, for the greater part of their 
course, erosive. No sooner had the drainage system been developed 
on both sides of the Alps than the valleys on the Italian side (unless 
we assume a very different distribution of rainfall) would work back- 
wards more rapidly than those on the northern. Cases of trespass, 
such as that recorded by the long level trough on the north side of 
the Maloja Kulm and the precipitous descent on the southern, would 
become frequent. In the Interglacial episodes—three in number, 
according to Penck and Briickner, and occupying rather more than 
half the epoch—the snow and ice would dwindle to something like 
its present amount, so that the water would resume its work. Thus 
I think it far more probable that the V-lke portions of the Alpine 
valleys were in the main excavated during Pliocene ages, their upper 
and more open parts being largely the results of Miocene and yet 
earlier sculpture. 
During the great advances of the ice, four in number, according to 
Penck and Briickner,! when the Rhone glacier covered the lowlands 
of Vaud and Geneva, welling on one occasion over the gaps in the 
Jura, and leaving its erratics in the neighbourhood of Lyons, it ought 
to have given signs of its erosive no less than of its transporting 
power. But what are the facts? In these lowlands we can see 
where the ice has passed over the Molasse (a Miocene sandstone) ; but 
here, instead of having crushed, torn, and uprooted the comparatively 
soft rock, it has produced hardly any effect. The huge glacier from 
the Linth Valley crept for not a few miles over a floor of stratified 
gravels, on which, some 8 miles below Zurich, one of its moraines, 
formed during the last retreat, can be seen resting, without having 
produced more than a slight superficial disturbance. We are asked to 
credit glaciers with the erosion of deep valleys and the excavation of 
great lakes, and yet, wherever we pass from hypotheses to facts, we 
find them to have been singularly inefficient workmen! 
I have dwelt at considerable, some may think undue, length on the 
Alps, because we are sure that this region from before the close of 
the Miocene period has been above the sea-level. It accordingly 
demonstrates what effects ice can produce when working on land. 
In America alsoto which I must now make only a passing reference, 
great ice-sheets formerly existed: one occupying the district west of 
the Rocky Mountains, another spreading from that on the north-west 
of Hudson’s Bay, and a third from the Laurentian . hill-country. 
These two became confluent, and their united ice-flow covered the 
region of the Great Lakes, halting near the eastern coast a little south 
1 On the exact number I have not had the opportunity of forming an opinion. 
