IV THE ICE AGE AND ITS WORK 61 



gravel or clay intermixed with boulders which often accom- 

 panied them ; and the efforts of geologists were therefore 

 directed to the discovery of how the water-power had 

 acted, and by what means the supposed floods could have 

 been produced. 



But there were not wanting men who saw that no action 

 of water alone could account for the facts. Sir James Hall 

 pointed this out with regard to erratics on the Jura, 

 whose source was undoubtedly in the far distant Alps ; 

 and Mr. Grainger, in America, described some of the par- 

 allel grooves and flutings running for nearly a mile in Ohio, 

 strongly arguing that no action of running water could 

 have produced them, but that an agent was required the 

 direction of whose movement was fixed and unalterable for 

 long distances and for a great length of time. No light 

 was, however, thrown on the problem till 1822, when 

 Venetz, a Swiss engineer, finding that existing glaciers 

 varied in extent from year to year and that historical re- 

 cords showed them to have considerably increased during 

 the last eight 3enturies, was further led to observe that, long 

 before the historical era the glaciers had been immensely 

 more extensive, as shown by the smooth and rounded rocks, 

 by longitudinal scratches and grooves pointing down the 

 valleys, and by numbers of old moraines exactly similar in 

 form and materials to those deposited by existing glaciers. 

 He read a paper before the Helvetic Society of Natural 

 History, and urged that glaciers once stretched down the 

 Rhone valley as far as the Jura, and there deposited the 

 erratic blocks which had so puzzled the diluvialists to 

 explain. 



Other writers soon followed the clue thus given. In 

 1835 Charpentier, after a close study of the erratic blocks 

 and of their sources, adopted the views of Venetz. Agassiz 

 followed, and by his strenuous advocacy did much to spread 

 correct views as to the former extension of the Alpine gla- 

 ciers, and their capability of explaining the numerous super- 

 ficial phenomena which in all northern countries had been 

 thought to afford proofs of enormous floods and of the 

 submergence of a large part of Europe under a deep sea. 

 He has, therefore, gained the reputation of being the 



