ICO 



ANCIENT BRITISH GLACIERS. 



surfaces are indubitable evidence of ancient glacial action. They 

 abound in Switzerland and the north of Europe, and in our own 

 country are excellently seen in North Wales about Snowdon, in the 

 valleys of the Lake district, along the west coast of Scotland, and on 

 both flanks of the Grampians. The morainic matter from the old 

 British glaciers is spread along the country, and known to us as 

 Boulder Clay. Where the mountain districts show marks of glacial 

 action, they commonly exhibit vast blocks of stone perched in posi- 

 tions from which tidal waters would at once have swept them down. 

 These masses, well seen in the Pass of Llanberis, are termed blocs 

 perches. They are portions of moraines which were carried by glaciers 

 moving over the places where they occur, and as the ice melted away 

 beneath them, they were deposited on the sides of the valley, on any 

 ledge broad enough to afford them resting-ground. 



Some small lakes are dammed up with terminal moraines. This 



Fig. 48. Conical Boulders (Arran) 



is the case with Llyn Llydaw on Snowdon, and Llyn Idwal in Nant 

 Francon, and many others in the lake district of Cumberland. Numerous 

 mountain tarns which lie in true rock basins thoroughly glaciated, 

 appear to have been excavated entirely by the erosive action of 

 ancient glaciers. 



Professor Eamsay has detected polished and striated boulders in the 

 Permian Breccias of Enville in Worcestershire, the Abberley Hills, 

 Clent and Lickey Hills, and other localities. In all cases the fragments 

 are angular, and have been carried twenty-five to forty-five miles from 

 the parent rock. These deposits testify to ancient glaciation. 



Where a glacier runs into the sea, as in the Arctic Regions, and is 

 buoyed up by the density of the water, the terminal fragment breaks 

 off as an iceberg, loaded with the stones which have fallen upon it 

 from the sides of the valley along which the ice travelled. As these 

 icebergs are carried by currents into warmer water they melt, and 



