420 OSBORN AND REEDS PREHISTORY OF MAN IN EUROPE 



America and Europe by one of America's leading glaciologists, Frank 

 Leverett, of the United States Geological Survey. This observer on two 

 continents chiefly correlates the glacial and interglacial deposits of 

 Xorth America and Europe ( 1 ) by means of their corresponding strati- 

 graphic position and relations, (2) by the degree of weathering and 

 erosion, which, although it decreases in amount in passing from the 

 oldest to the youngest series of deposits, is practically the same for any 

 one horizon on both continents. 



' The four American drift deposits — Nebraskan, Kansan, Illinoian, and 

 Wisconsin — are thus correlated with the Alpine of Penck and Bruckner, 

 Giinz, Mindel, Kiss, and Wiirm, respectively. These together correspond 

 to the I, II, III, and IV glaciations, respectively. 



Leverett believes that the "Oldest" drift of north Germany, penetrated 

 by well borings near Berlin and near Hamburg, is the product of 

 Glaciation I (Scanian) ; at Berlin it is interbedded with fluvioglacial 

 gravel and sand, the outwash deposits of the earliest ice-sheet. He holds 

 that the "Oldest," "Old," "Middle," and "Young" drifts of the north 

 German plain, left at successive periods by the Scandinavian land ice, 

 may be correlated respectively with the several Alpine glaciations; also 

 with the Nebraskan (Jerseyan), Kansan, Illinoian, and Wisconsin 

 stages, or the I, II, III, and IV glaciations. 



In the "chalky Boulder-clay" of England, Leverett recognizes the 

 westward extension of the "Old" drift of Germany. The "Middle" drift, 

 however, he does not believe has as yet been identified, though it is not 

 improbable that the Scandinavian land ice in this stage extended across 

 the North Sea to the British Isles. 



As to the relative order of magnitude of these glaciations, Leverett 

 believes: (1) that Glaciation I is well represented as far south as 

 Nebraska and New Jersey, but is not extensively exposed in the Alps or 

 in the north German plain, for there it has been concealed in large part 

 by the more extensive later glaciations; (2) that Glaciation II in North 

 America and in Europe was the most extensive of all; (3) that Glaciation 

 III was, in the main, of less extent; (4) that Glaciation IV was still 

 more limited. 



The three American interglacial stages are correlated with three in 

 Europe, namely: 



First Interglacial Stage, the Aftonian of America = the Giinz-Mindel of the 



Alpine region = the Paludinenbank of north Germany = the Norfolkian 



of England. 

 Second Interglacial Stage, the Yarmouth of America = the long Mindel-Riss 



of the Alpine district = the interglacial deposits of central Russia and 



perhaps the Rixdorf horizon of Germany; 



