ITS THIRD STAGE. 237 



plants or animals, and these in all likelihood of "boreal 

 habits, like those now inhabiting the borders of the arctic 

 regions. How long this period of descent continued rela- 

 tively to the other stages, it is difficult to determine, 

 though, on the whole, it appears to have been the longest 

 stage, and that which has most impressed its character on 

 the terrestrial surface. The extent to which the subsi- 

 dence took place is variously estimated at from 1700 to 

 2000 feet, for from that limit down to the existing sea- 

 shore, the land-surface is marked with rounding and smooth- 

 ing, polishing and scratching, glacial moraines and clays, 

 ice- borne blocks and boulders. One cannot turn to the 

 higher districts of our own islands, to the north of Europe, 

 or to Xorthern America, without perceiving on every hand 

 traces of this long-continued ice-action the bouldery clays, 

 the rounded blocks and boulders, the scratched and polished 

 rock-surfaces, the rounded outlines of the hills and knolls, 

 all bespeaking its presence as incontestably as the existing 

 surface of the Alps, the Scandinavian mountains, or the 

 uplands and shores of Greenland. 



But the forces that govern the external conditions of our 

 planet are never at rest. Change succeeds change, and cycle 

 follows cycle. The downward tendency of the land ceases, 

 and an upward movement commences. Along with this 

 gradual elevation, new distributions of sea and land begin 

 to appear, and with these changes the intensity of the gla- 

 cial epoch seems to come to a close. Glacier and ice-sheet, 

 however, still shroud the land, and icebergs drift away 

 from the shores. Other currents, however, are evidently 

 setting in, a more genial climate begins to prevail, and with 

 this higher temperature the ice disappears frum the seas 

 and lower grounds, and only clings to the higher bills in 



continent as 39 N. lat. ; in Europe it has been variously stated at 40, 

 42% and even 44 N. lat. 



