170 



ISLAND LIFE. 



[part I. 



an entire country there would be no moraines, and that rocks or 

 dShris are very rarely seen on icebergs. But during every 

 glacial epoch there will be a southern limit to the glaciated 

 area, and everywhere near this limit the mountain-tops will 

 rise far above the ice and deposit on it great masses of debris ; 

 and as the ice-sheet spreads, and again as it passes away, 

 this moraine-forming area will successively occupy the whole 

 country. But even such an ice-clad country as Greenland is 

 now known to have protruding peaks and rocky masses which 

 give rise to moraines on its surface ; ^ and, as rocks from Cumber- 

 land and Ireland were carried by the ice-sheet to the Isle of Man, 

 there must have been a very long period during which the ice- 

 sheets of Britain and Ireland terminated in the ocean and sent 

 off abundance of rock-laden bergs into the surrounding seas ; 

 and the same thing must have occurred along all the coasts of 

 Northern Europe and Eastern America. 



We cannot therefore doubt that throughout the greater part 

 of the duration of a glacial epoch the seas adjacent to the 

 glaciated countries would receive continual deposits of large 

 rocks, rock-fragments, and gravel, similar to the material of 

 modern and ancient moraines, and analogous to the drift and the 

 numerous travelled blocks which the ice has undoubtedly scat- 

 tered broadcast over every glaciated country ; and these rocks 

 and boulders would be imbedded in whatever deposits were then 

 forming, either from the matter carried down by rivers or from 

 the mud ground off the rocks and carried out to sea by the 

 glaciers themselves. Moreover, as icebergs float far beyond the 

 limits of the countries which gave them birth, these ice-borne 

 materials would be largely imbedded in deposits forming from 

 the denudation of countries which had never been glaciated, or 

 from which the ice had already disappeared. 



But if every period of high excentricity produced a glacial 

 epoch of greater or less extent and severity, then, on account of 

 the frequent occurrence of a high phase of excentricity during 

 the three million years for which we have the tables, these 

 boulder and rock-strewn deposits would be both numerous and 

 extensive. Four hundred thousand years ago the excentricity 

 1 Nature, Vol. XXI., p. 345, " The Interior of Greenland." 



