14 PRESIDENTS ADDRESS. 



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 

 eight 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 demon- 

 strates what effects ice can produce when working on land. 



In America also, to which I must now make only a passing refer- 

 ence, great ice-sheets formerly existed : one occupying the district west 

 of the Eocky 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 of 

 New York, but in Ohio, Indiana, and Illinois occasionally leaving 

 moraines only a little north of the 39th parallel of latitude. 1 Of these 

 relics my first-hand knowledge is very small, but the admirably illus- 

 trated reports and other writings of American geologists 2 indicate that, 

 if we make due allowance for the differences in environment, the tills 

 and associated deposits on their continent are similar in character to 

 those of the Alps.* 



In our own country and in corresponding parts of Northern Europe 

 we must take into account the possible co-operation of the sea. In 

 these, however, geologists agree that, for at least a portion of the Ice 

 Age, glaciers occupied the mountain districts. Here ice-worn rocks, 

 moraines and perched blocks, tarns in corries, and perhaps lakelets in 

 valleys, demonstrate the former presence of a mantle of snow and ice. 

 Glaciers radiated outwards from more than one focus in Ireland, Scot- 

 land, the English Lake District, and Wales, and trespassed, at the time 



1 Some of the glacial drifts on the eastern side of the continent, as we shall find, 

 may have heen deposited in the sea. 



2 See the Reports of the United States Geological Survey (from vol. iii. onwards), 

 Journal of Geology, American Journal of Science, and local publications too numerous 

 to mention. Among these the studies in Greenland by Professor Chamberlin are 

 especially valuable for the light they throw on the movement of large glaciers and 

 the transport of dibris in the lower part of the ice. 



3 Here, however, we cannot always be so sure of the absence of the sea. 



