10 



PLIOCENE GLACIERS 



qSSSt g , laCierS ' and the lce - b °me character of Alpine boulders 



TabTe^ase ! *?* ° n the Jura ' there was a P owerf »l reaction among 

 in Recess 41. geologists ; the true doctrine fell into discredit, and most 



writers adhered to the dogma that the heterogeneous mix- 

 tures that cover a great part of the northern continents 

 were the result of mighty sea waves, which rushed from 

 the north across Europe, Asia, and America, scattering 

 rocky fragments, which polished and grooved the rocks 

 over which they passed. More correct views, however, 

 at length prevailed ; and there are now few geologists who 

 have studied the effects of ice, but will readily recognise 

 its familiar indications and more especially those of glacier 

 action in the Highlands of Scotland, in Cumberland, Wales, 

 Ireland, and the mountains of the Vosges. 



It is nearly universally allowed that all the more impor- 

 tant general contours of hill and valley in the continents of 

 the old and new world were the same as now previous to the 

 glacial epoch. Much of the land was then slowly depressed 

 beneath the sea ; and as it sank, its minor features were 

 somewhat modified, for terraces were formed on old shores, 

 and icebergs drifting from the north, and pack-ice on the 

 coasts, as they ground and grated along the coasts and sea 

 bottoms, smoothed and striated the rocky surfaces 

 which they passed, and deposited, in the course of many ages, 

 clay, gravel, and scattered boulders over wide areas that 

 had once been land. The grooves and striations on the ice- 

 smoothed rocks (except where locally deflected) still bear 

 witness to the general southward course of the winds and 

 ocean currents that bore the ice from its birth-place into 

 milder climates. 



The intensity and wide-spreading effects of cold in what 

 a™ now temperate climates is one of the greatest marvels 

 of Tertiary geology. In our own latitudes these effects 

 were clearly not confined 



over 



to mountain regions when 



at 



their present elevation, or when perhaps by further up- 

 heaval of the land, they attained a still greater height; 

 for it is certain that in Wales the drift rises on the mountains 



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