OSBORN, REVIEW OF THE PLEISTOCENE 291 



Fourth Glacial Stage — Wurm, Mecklp^j^burgian, Wisconsin 

 beginning oe the reindeer and cave period 



The Fourth Glacial Stage, like the First, is believed to have been 

 nearly contemporaneous in Europe and North America, consequently the 

 estimates of Postglacial time in one country have an important bearing 

 on the other. The First Maximum of the Fourth or Wtinn glaciation in 

 the Alps is estimated by Penck as occurring 40,000 years ago. It was 

 followed by the slight recession known as the Laufenschwankung, a tem- 

 perate retreat followed in turn by the Second Wiirm Maximum, which is 

 estimated as occurring 20,000 years ago. Similarly in America the 

 "early Wisconsin" is followed by a recession interval {Peorian), and 

 this in turn by the "late Wisconsin" which is the final great glaciation in 

 America. The contemporaneous Mechlenburgian of the North German 

 lowlands gave rise to the "Upper Drift, '^ which in some respects bears a 

 striking resemblance to the A¥isconsin Drift of America both in its sys- 

 tems of moraines and in its topography. This stage also includes appar- 

 ently the "Upper Drift" of northern England with which the drift of 

 the Alps correlates well. The Upper Drift of England covered also a 

 large part of Wales. In Germany glaciation also occurred in the Eie- 

 sengebirge and the Black Forest. 



In America part of the "Upper Drift" is loess-covered and in the opin- 

 ion of Koken and Schmidt the Upper Drift of Germany is also partly 

 covered with the "Newer Loess." The Postglacial Stage did not exhibit 

 a steady amelioration of climate after the culmination of the Fourth 

 Glacial Stage, but there is evidence of great oscillations and renewed 

 glacial advances both in northern Britain and Scandinavia and in Ger- 

 many. These Postglacial advances, as most clearly defined in the Alpine 

 region, have been termed by Penck the Buhl, the Gschnitz and the Daun, 

 They are correlated by palaeontologists and anthropologists quite closely 

 with the successive faunae and arch^ological implements of Postglacial 

 time. 



Period of the Final Glacial Maximum, — The length of time which has 

 elapsed since the close of the Fourth great glacial advance is estimated 

 in America by the recession of the Falls of Niagara. This recession 

 began with the end of the Wisconsin glaciation which is believed to have 

 been contemporaneous with the Wtirm. As early as 1829 Bakewell esti- 

 mated that since the Falls of Niagara were receding by the erosion of the 

 Niagara gorge at the rate of three feet annually about 10,000 years had 

 elapsed since the end of the Glacial Epoch. Lyell visited Niagara in 

 1841 and after consideration of all the data of erosion conchided that 



