230 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



The North German School of Diluvial geologists looked 

 with a certain favour upon this explanation, but believed still 

 more in the efficacy of water action. The Berlin physicist, 

 Wrede, in 1802 gave his opinion that the granite "foundling 

 blocks " on the German plain had been brought upon ice-floes 

 from the Silesian mountains. Leopold von Buch in 1810, and 

 one or two later authors, proved, however, that Scandinavia had 

 been the original home of most of the North German erratics; 

 they assumed that gigantic floods had been the chief agent of 

 transport, and that the scratches on the rocks and pebbles had 

 been caused by the friction of the sand, pebbles, and larger 

 fragments during transportation. 



Bernhardi, Professor in the Academy of Forestry in Dreis- 

 sigacker, without any knowledge of the researches of Venetz 

 and Charpentier, by his own insight arrived at the true solution 

 of the problem (Neues Jahrb. fur Miner., 1832). He said the 

 polar ice had extended to the southmost edge of the German 

 plain now bestrewn with erratics, and that in the course of 

 thousands of years the polar ice had gradually withdrawn to 

 its present reduced dimensions and more limited fields of 

 glaciation. Before Bernhardi, the Norwegian geologist, Jens 

 Esmarch, in 1824 had suggested there had been a far greater 

 extension of the Norwegian glaciers than now existed. But 

 the tide of influence and authority in Germany at the time ran 

 in other directions; an Esmarch or a Bernhardi might say 

 what they thought, but there the matter ended ; none listened 

 while a Von Buch and a Sefstrom said differently. The Swede, 

 Nils G. Sefstrom, was the most extreme of the diluvialists. 

 He taught that the northern floods had spread diluvium over 

 Scandinavia, Finland, Russia, and Germany, and borne frag- 

 mented rock-material and big boulders from the northern areas 

 as far south as the foot of the Alps, 



During the years 1839-43, a brilliant group of British 

 geologists, Lyell, De la Beche, Darwin, and Murchison, 

 thoroughly acquainted with the results of the polar explorations 

 made by Parry, Scoresby, and Ross, founded the "Drift Theory," 

 which appeared to be a satisfactory explanation of all the 

 phenomena. They attributed the transport of erratics and 

 the formation of the thick surface deposits or "boulder forma- 

 tions," known under various local terms in Great Britain, most 

 commonly as "till," or "boulder-clay," to floating icebergs 

 which had drifted far southward from Polar regions. The 



