THE GLACIAL PLRIOD AND ITS RLCORDS 



be seen near the southern end of Green Bay, in Wisconsin; in 

 Dickinson, Marquette, Deha and Menominee counties, the 

 Les Cheneaux Lsland area, and in tlie Grand Traverse region, 

 in Michigan; as well as in western and central New York. 



All this plaster of rock waste quite foreign to the forma- 

 tions on which it lies — these moraines, kames, eskers, drum- 

 lins, outwash plains, till plains, mixed accumulations of all 

 sorts, sizes and shapes of rock fragments — limestone, sand- 

 stone, jasper, granite, gneiss, chunks of copper, iron ore, rare 

 flakes of gold, even a few diamonds, beds of clay, sand, gravel 

 — spread over the glaciated region, is collectively known as 

 drift, because early geologists believed it to have been spread 

 by drifting currents and icebergs in an ancient sea. Its thick- 

 ness varies widely; in some places it is very thin or entirely 

 lacking and in others it is from 800 to 1,200 feet thick. 



A large area in southwestern Wisconsin was never covered 

 by the ice. Not because it was too high, but for some other 

 reason, the ice deployed around it, leaving the famous Drift- 

 less Area in which the beautiful and interesting Dells of the 

 Wisconsin River have been cut by that stream in the red- 

 brown Cambrian sandstones. A small peak of rock standing 

 like an island above a glacier is known by the Eskimo name 

 "nunatak." Around such a nunatak in Ontario the ice de- 

 ployed in its forward march and formed the Huron and Erie 

 lobes, and in the retreat the nunatak separated these lobes. 

 Highlands in the Northern Peninsula once covered by the ice 

 became nunataks for a time during the retreat. 



As the glacier retreated northward, the melt water from 

 the ice escaped in broad channels leading southward to the 

 Ohio River and thence to the Mississippi. These channels, 

 now the wide flat valleys of too-small rivers, furnisjied the 

 routes for man-made canals in the heyday of canal building 

 in Ohio. The great volume of glacial water reached the Ohio 

 and vastly increased the size and activity of that river. Ad- 

 vance of the ice had pushed the river southward in the vicinity 



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