230 



AW^'ALS l^EW YORK 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 Dllrnten, and he subsequently advanced a theory 

 of three glacial stages. James Geikie (1871-1894) developed the hj'poth- 

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

 In 1883 Boule from his observations along the Mediterranean coast main- 



YoungSi . 



Middle Drift limit -I 



Old Drift Limit ♦-!• 



Scale rs.ooaooD 



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



This map shows the drift and terminal moraines of Glaciations I-II. Scanlan + iiax- 

 onian (old drift), III Polandian = Riss (middle drifts IV ^[ecklenhurglan = Wtirm 

 (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 properlw 

 within the Pleistocene. The firm foundation of the quadruple theon^ in 

 Europe was laid, however, by the researches of Penck and Briickner^® 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 



" Pexck^ Albrecht, and BRfCKXER, Edouard : Die Alpen im Eiszeitalter. III. Die 

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



