April 2, 1915] 



SCIENCE 



511 



Penck's ourve^ page 1168, "Die Alpen im Eis- 

 zeitalter," 1909, expresses graphically the climatic 

 oseillations of the alpine district for Pleistocene 

 and post-Pleistocene time. The key to the four 

 glaciations and the three interglacial stages indi- 

 cated in the curve was found in the four outwash 

 deposits of glacio-fluvial streams on the northern 

 foreland of the Alps in the vicinity of Ulm and 

 Munich. Along the present stream valleys the 

 glacio-fluvial deposits are arranged in terraces, the 

 oldest occupying the highest position and the 

 youngest the lowest level. When the key was car- 

 ried in mind to the French and Italian Alps the 

 remarkable association of these deposits on the 

 northern foreland was found to he applicable 

 throughout. Hence the names of four small tribu- 

 taries of the Danube which cross the outwash de- 

 posits on the Bavarian plateau, G-iinz, Mindel, Eiss 

 and Wiirm, were applied by Penck and Briickner 

 to the first, second, third and fourth glaciations. 

 The deposits of the third or Riss glaciation in the 

 Swiss and French Jura extend farther out on the 

 foreland than the deposits of the other glacial ad- 

 vances, but in other districts the morainal deposits 

 of the second or Mindel stage extend beyond that 

 of any other, hence it is regarded as the most ex- 

 tensive of the four alpine glaciations. The mo- 

 rainal and outwash deposits of the first or Gvinz 

 glaciation are least in evidence while those of the 

 fourth or Wiirm glaciation, the last, are most in 

 evidence. 



That the temperature of the alpine region was 

 considerably colder during the stages of glaciation 

 than during the interglacial stages and the present 

 which is at the close of the retreating hemicycle of 

 the last glaciation, is shown conclusively by the de- 

 pressed snow lines. Penck has determined their 

 position in the Alps for all four glaciations. They 

 have a distribution parallel to that of the present 

 snow-line, but occupying lower levels, namely, 

 Giiinz, 1,200 meters, Mindel, 1,350 meters, Riss, 

 1,300 meters, and Wiirm, 1,200 meters below the 

 present snow-line. During the interglacial stages 

 the snow-line was approximately 300 meters higher 

 than the present one. From the Hottinger Breccia 

 near Innsbruck Penck determined that there was a 

 temperature variation of 1° G. for every 200-meter 

 change in the altitude of the snow-line. 



The unit of measurement which Penck used in 

 estimating the duration of the Pleistocene period 

 is the retreating hemicycle of glaciation of the 

 fourth or Wurm stage, better known as the post- 

 glacial period. In the alpine district Penck and 



Briickner found that in this retreating hemicycle 

 there were three minor advances called the Biihl, 

 Gsehnitz and Daun stadia. These advances were 

 preceded by a prominent minor retreat of the 

 Achen oscillation. From the lignite deposits of 

 Diirnten, the deposits of the Muota deltas and the 

 turf deposits in many of the glacial swamps it has 

 been possible to estimate the duration of this hemi- 

 cycle of glaciation in years, as follows: 



Subdivisions of Post-Glacial Time 



Years 



Achen oscillation 9,000 



Biihl advance and retreat 5,000 



Gsehnitz advance and retreat 4,000 



Daun advance and retreat 3,000 



Age of copper 1,000 



Post-copper time 3,000 



Total 25,000 



The estimate on the duration of post-glacial 

 time in America is based chiefly on the recession 

 of the waterfalls of Niagara and St. Anthony. Re- 

 cently Coleman* made an estimate based on the 

 rate of wave erosion on the shore of Lake Ontario 

 and glacial Lake Iroquois. Twenty-five thousand 

 years is a figure which falls within the estimates 

 made by Coleman, Taylor, Lyell, Chamberlain and 

 Salisbury. It is a bit under those of Fairchild, 

 Sardeson and Spencer and above those of Gilbert 

 and Upham. It is considered a conservative figure. 



Penck states that it must have been 16,000 to 

 24,000 years from the Etihl stadium to the present, 

 with 20,000 years as an average, and 25,000 to 40,- 

 000 years from the beginning of the Achen re- 

 treat to the present. In selecting a figure, however, 

 which shall be used as a unit of measurement in 

 calculating the duration of the entire Pleistocene 

 period, he chooses 20,000 years as the length of 

 post-Wiirm time. 



The correlation of the mountain glaciations of 

 the Alps with those of the Scandinavian continental 

 ice fields of Pleistocene time has not been worked 

 out in all regions, but there is sufficient informa- 

 tion at hand to say that there were four advances 

 of the continental ice over northern Europe which 

 correspond to the periods of ice advance upon the 

 alpine forelands. Geikie remapped in 1914 the 

 second, third and fourth glaciation distribution in 

 Europe. G. de Geer delimited the retreating stages 

 of the fourth glaciation in the Scandinavian penin- 

 sula in 1912. 



A correlation of American with European glacial 

 deposits has been made by Leverett. By consid- 



* Coleman, A. P., Proceedings, Twelfth Inter. 

 Geol. Cong., Canada, 1913. 



