STRATIGRAPHICAL GEOLOGY. 539 



members, and until about thirty years ago geologists were 

 content to treat the series comprehensively as one group of 

 deposit. Buckland originally defined the upper limit of the 

 Diluvium and beginning of Alluvium as coeval with the 

 appearance of man on the earth, but the prehistoric researches 

 conducted in the latter half of the century showed that man 

 had been a contemporary of some of the extinct Mammals. 

 Palaeolithic implements have afforded traces of man's existence 

 in the latter part of the Pleistocene age. The study of the 

 Diluvial Mammals led Lartet, in 1863, to establish three 

 periods: the oldest is characterised by the predominance of 

 Elephas antiquus. Rhinoceros Mercki^ and others ; the middle 

 period by the Mammoth, Rhinoceros tichorliinus, Ursus 

 spelceus, Bison priscus ; and the third and youngest by the 

 occurrence of forms still living in high latitudes, such as rein- 

 deer, musk-ox, Canadian elk, and beaver. 



Research on Diluvial deposits was imbued with fresh interest 

 when the glacial theory was established by Venetz, Charpentier, 

 and Agassiz (1829 to 1840). It was then rendered possible, 

 not only to understand the conditions under which the various 

 deposits had taken origin, but also to classify the deposits 

 according to their age as preglacial, interglacial, and post- 

 glacial. The first researches from this standpoint were carried 

 out in Switzerland, Scotland, and Wales (cf. p, 231). Tn 

 Germany, it was not until Otto Torell had broken the spell of 

 the Drift Theory (1875) that an active impulse was given to 

 detailed investigations of the Pleistocene deposits on the 

 North German plains. The results are apparent in the newer 

 geological maps, which show the great diversity in the lithologi- 

 cal character and age of the deposits belonging to this epoch. 



The discovery of glacier scratches on the Muschelkalk of 

 Riidersdorf first suggested to Torell the idea that an 

 extensive ice-sheet had covered the North German plain. 

 German geologists have since demonstrated the occurrence 

 of similar grooves and scratches on the rock-floor at several 

 localities in the plain, especially in Saxony. The sands and 

 gravels and boulder-clays have also undergone a careful 

 exploration in the light of the glacial theory. Structures 

 identical with the ground-moraines of recent glaciers have been 

 recognised, and the pebbles and boulders contained in them 

 v ave been examined with reference to their derivation from 

 ndinavia, Finland, and other northern territories. The 



