CHAPTER L. 



GLACIAL PERIOD. 



THE Quaternary Age is divided into the Glacial, the Champlain, 

 and the Terrace periods. 



The glacial, or ice period, like other geological phenomena, seems 

 to have come on gradually. In the early part of the tertiary, the 

 climate of Central Europe and North America was sub-tropical, 

 and flowering plants and shrubs were growing within the Arctic 

 circle. During the extensive changes in the crust of the earth 

 which occurred in the tertiary, the northern parts of the conti- 

 nents seem to have been gradually elevated to a height of some 

 1,000 to 2,000 feet above the present level. With this elevation 

 the climate gradually became more severe, until the ice and snow 

 had crowded the shrubs and flowering plants far toward the 

 south, and were occupying the greater part of North America, 

 north of the Ohio river, and the northern and central portions of 

 Europe, and parts of Asia and the glacial period was in full 

 progress. 



Then followed periods when the ice seems to have retreated 

 and advanced several times, as if the climate were alternately 

 warmer and colder. One retreat was so great, that many speak 

 of the next advance as a second glacier. But at length the ice 

 retreated to the confines of the polar zone, and temperate climates 

 prevailed over Central Europe and North America. 



The glaciers of the Alps and the Pyrenees, those that linger in 

 Norway and cover Greenland, the glaciers of Alaska and the 

 Rocky Mountains, are but the remnants of the great ice sheet 

 that dominated the northern part of both continents for untold 

 centuries. 



From a study of these existing remnants, and the work they 

 do, we may gain some idea of what were the conditions of our 

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