112 
ISLAND LIFE. 
[part I. 
when the ice was at 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. 1 
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 proofs that 
Scandinavia and all northern Europe have also been covered 
with a huge ice-sheet ; while we have already seen that a similar 
gigantic glacier buried the Alps, carrying granitic blocks to the 
Jura, where it deposited them at a height of 3,450 feet above 
the sea ; while to the south, in the plains of Italy, the terminal 
moraines left by the retreating glaciers have formed extensive 
hills, those of Ivrea, the work of the great glacier from the 
Yal d’ Aosta being fifteen miles across, and from 700 to 1,500 
feet high. 
Glacial Phenomena in North America . — In North America 
the marks of glaciation are even more extensive and striking 
these openings in the valleys that the “ till ” is said to be found, and also in 
the lowlands where an ice-sheet must have extended for many miles in 
every direction. In these lowland valleys the e ‘ till ” is both thickest and 
most wide-spread, and this is what we might expect. At first, when the 
glaciers from the mountains pushed out into these valleys, they would 
grind out the surface beneath them into hollows, and the drainage-water 
would carry away the debris. But when they spread all over the surface 
from sea to sea, and there was little or no drainage water compared to the 
enormous area covered with ice, the great bulk of the debris must gather 
under the ice wherever the pressure was least, and the ice would 
necessarily rise as it accumulated. Some of the mud would no doubt be 
forced out along lines of least resistance to the sea, but the friction of the 
stone-charged “till” would be so enormous that it would be impossible for 
any large part of it to be disposed of in this way. 
1 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 in 
Scotland abounds, and rocks are found in it which must have come from 
Cumberland 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 southwards down the Irish Sea. Ice- 
marks are traced over the tops of the mountains which are nearly 2,000 feet 
high. (See A Sketch of the Geology of the Isle of Man , by John Horne, 
F.G.S. Trans, of the Edin. Geol. Soc. Vol. II. pt. 3, 1874.) 
