glaciation in nebraska 493 



Nebkaskan" Glaciation 



The earliest recognized stage of great extension of the ice-sheet upon 

 Canada and the United States has been named Albertan and Jerseyan, 

 from its drift in Alberta and New Jersey. Following a suggestion of the 

 late Prof. Samuel Calvin, the preferable name Nebraskan was proposed 

 by Prof. B. Shimek 2 for this stage. Thus all the series of North Amer- 

 ican ice advances and recessions, if the Champlain stage be excepted, are 

 named from the glacial drift and alternating interglacial beds within the 

 drainage basin of the Mississippi. 



Eroded river valleys have occasional exposures of Nebraskan drift, 

 beneath the Kansan drift and formations of Aftonian age, in eastern 

 Nebraska and in southern and eastern Iowa; but its most western and 

 southern extension in that region was probably everywhere overspread 

 and surpassed by the Kansan icefield. 



East of the Mississippi the early Patrician transportation of copper 

 fragments and drift boulders from the region of Lake Superior to central 

 and southern Ohio seems referable to the Nebraskan stage of glaciation, 

 Belonging originally to Patrician drift, but later carried onward as a part 

 of the Illinoian drift, Prof. G. F. Wright found boulders of red jasper 

 conglomerate near Cincinnati, borne beyond the Ohio Eiver into the north 

 edge of Kentucky, where they were deposited at the extreme boundary of 

 the ice-sheet after a southward glacial journey of about 500 miles from 

 their parent ledges, east of Lake Superior and north of Lake Huron. 



In northeastern Pennsylvania and northern New Jersey the attenuated 

 border of the drift, extending 10 to 25 miles south of the terminal mo- 

 raine, is referred by Chamberlin and Salisbury to the first great stage of 

 our continental glaciation, named by them Jerseyan, probably correlative 

 with the Nebraskan stage and the ancient Patrician drift. It is remark- 

 ably contrasted with the adjoining drift sheet of Wisconsin age, which 

 includes the thick moraine and spreads thence far north upon New York, 

 New England, and eastern Canada. The thin Jerseyan drift remains in 

 patches, and indeed it may have been originally so deposited. Formed 

 mainly by the local snowfall, the thin border of the early icefield probably 

 had low surface slopes, without sufficient movement in many portions for 

 drift erosion, transportation, and deposition. 



Eeaching more than 1,200 miles from the Missouri River to the At- 

 lantic close south of New York City, the southern margin of the most 

 ancient known stage of our continental glaciation fell not very far short 

 of the later maximum icefield in Kansas and Missouri. It attained nearly 



2 Bulletin Geol. Soc. of America, vol. 20, December 24, 1909, p. 408 ; also in Science, 

 January 14, 1910. 



