X.] ICE AND ITS WORK. 1C3 



valleys of Switzerland, not now occupied by glaciers, the 

 rocks are rounded, polished, and scratched, showing that 

 the Swiss glaciers must formerly have been of gigantic 

 proportions and that they extended far beyond the limits 

 retained by their present successors. 



On travelling northwards, the snow-line is found to 

 descend until, in the Arctic Regions, it comes down to the 

 very sea-level. Hence, in such regions, the entire surface of 

 land may be enveloped in a mantle of ice. This ice-sheet 

 creeps down towards the shore, until its foot at length 

 advances into the sea. Huge masses of ice then become 

 detached, and are sent drifting away as icebergs. These 

 mountains of ice often assume most fantastic shapes ; and 

 their vast mass produces so great a depression of tempera- 

 ture in the neighbouring air that, when they are carried into 

 the Atlantic, they are usually obscured by a shroud of mist 

 The icebergs, like glaciers, are laden with fragments of rock 

 worn from the land over which the ice-sheet travelled ; and 

 when, on rea,ching warmer waters, they melt, they discharge 

 this freight of stones and earth, which may thus get carried 

 far from their original home. When blocks of rock are 

 borne along by running water, they become rounded by the 

 friction to which they are subjected ; but, when a fragment 

 of rock is transported on an iceberg, it may retain much of 

 its angularity and be dropped upon the sea-bed in an 

 almost unworn state. The finer detritus which the berg 

 carries will be diffused through the water in which the ice 

 melts ; and currents may transport it far away into southern 

 latitudes. If a glacier descends to the edge of a lake, exactly 

 the same thing occurs as in the formation of an iceberg. 

 A tongue ol ice is pushed into the water, and bergs break 

 off and float away, carrying their burden of moraine matter 

 to be strewn over the bottom of the lake on the melting of 



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