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.^ 

 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, canying 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 

 Val 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 ''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 foand 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 Home, 

 F.G.S. Trans, of the Edin. Geol. Soc. Vol. 11. pt. 3, 1874.) 



