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ANNALS NEW YORE ACADEMY OF SCIENCES 



America the hypothesis of several glacial advances of varying duration 

 and severity alternating with interglacial temperate periods during which 

 the ice retreated and conditions of climate prevailed which in some in- 

 stances were even milder than the present in the same latitudes. 



As early as 1856 Morlot observed a relatively warm flora between two 

 Swiss glacial deposits at Diirnten, and he subsequently advanced a theory 

 of three glacial stages. James Geikie (1871-1894) developed the hypoth- 

 esis of a succession of six glacial and five interglacial stages and climates. 

 In 1883 Boule from his observations alone; the Mediterranean coast main- 



Fig. 3. — Glacial map of northern Germany and the Netherlands 



This map shows the drift and terminal moraines of Glaciations I— II, Scanian + Baas- 

 oni'an (old drift), III Polandian = Riss (middle drift), IV Mecklenburgian = Wiirm 

 (upper drift). After Leverett, 1910. 



tained that there is evidence of three great glacial advances, the first fall- 

 ing within the close of the Pliocene Epoch, the second falling properly 

 within the Pleistocene. The firm foundation of the quadruple theory in 

 Europe was laid, however, by the researches of Penck and Bruckner 16 in 

 the Alpine region, published in 1909. According to this classic work the 

 entire Glacial Epoch is assigned to the Pleistocene or Quaternary Period. 

 Its deposits include the entire "Diluvium" and "Drift" of earlier geolo- 

 gists. 



All the river gravels, boulder-clays and moraines of the Glacial Epoch 



16 Penck, Albrecht, and Bruckner, Bdodard : Die Alpen im Eiszeitalter. III. Die 

 Eiszeiten in den Sndalpen und im Bereich der Ostabdachnng der Alpen. Leipzig, 1909,, 



