80 THE GLACIER EPOCH OF AUSTRALASIA. 
the prominences, leaving the rounded rocks, as well as the 
striz we still see marking the direction of its motion. . 
The present glaciers of the Alps being confined to valleys 
which carry off a large quantity of drainage water lose this mud 
(sticky, tenacious clay) perhaps as rapidly as it is formed; but 
when the ice covered the whole country there was com- 
paratively little drainage water, and thus the mud and stones 
collected in vast compact masses in all the hollows, and espe- 
cially in the lower flat valleys, so that when the ice retreated, 
the whole country was more or less covered with it. It was 
then, no doubt, rapidly denuded by rainsand rivers, but, as 
we have seen, vast quantities remain to the present day to tell 
the tale of its wonderful formation. There is good evidence 
that when the ice was its maximum it extended not only over 
the land but far out to sea, covering all the Scottish islands, 
and stretching in one connected sheet to Ireland and Wales, 
where all the evidences of glaciation are as well marked as in 
Scotland, though the ice did not of course attain quite so 
great a thickness.” ‘“ That the ice sheet was continuous from 
Scotland to Ireland is proved by the glacial phenomena in the 
Isle of Man, where ‘ till’ similar to that of Scotland abounds, 
and rocks are found in it which must have come from Cum- 
berland and Scotland, as well as from the north of Ireland. 
This would show that glaciers from each of these districts 
reached the Isle of Man, where they met and flowed south- 
wards down the Irish Sea. Ice marks are traced over the 
tops of mountains which are nearly 2,000 feet high.” Dr. 
Wallace concludes with the statement that “ It is evident that 
the change of climate requisite to produce such marvellous 
effects in the British Isles could not have been local, and we 
accordingly find strikingly similar proof that Scandinavia and 
all Northern Europe have also been covered with a huge ice 
sheet. In North America the marks of glaciation are even 
more striking than in Europe, stretching over the whole of 
Canada, and to the south of the Great Lakes as faras latitude 
39°. There is in all these countries a widespread deposit, like 
the ‘till’ of Scotland, produced by the grinding of the great 
ice sheet when it was at its maximum thickness; and also 
extensive beds of moraine matter, true moraines and travelled 
blocks left by glaciers as they retreated towards the mountains, 
and finally withdrew into the upland valleys.” After combating 
objections, he concludes thus :—‘‘ There is perhaps no great 
conclusion in any science which rests upon a surer foundation 
than this; and if we are guided by our reason at all in de- 
ducing the unknown from the known, the past from the pre- 
sent, we cannot refuse to assent to the reality of the glacial 
epoch of the Northern Hemisphere in all its more important 
features.” 
