278 THE ICE AGE AND ITS WORK. 



which it seems to the present wi'iter that souiul reasoning is even 

 more re([uire(l than tlie i'urther aecnmnlation of facts.* 



In the hist centnry Swedenborg, Linna'ns, Pallas, De Lnc, and 

 many other eminent writers took notice of the remarkable fact tluit 

 in Scandinavia, Enssia, Germany, and iSwitzerland detaclied rocks or 

 bowlders were found, often in great abundance and of immense size, 

 and of a kind that did not exist in situ in the same district, but which 

 were often (mly to be discovered in remote localities, sometimes hun 

 dreds of miles away. Tbose who ventured to speculate on the origin 

 of these travelled rocks usually had recourse to water power to account 

 for their removal; and, as their large size and often elevated position 

 required some unusual force to carry them, there arose the idea of enor- 

 mous Hoods sweeping over whole continents; and for a long time this 

 diluvial theory was the only one that appeared to be available, although 

 the difticulties of its application to explain all the phenomena became 

 greater the more closely those phenomena were studied. Still, there 

 was apparently no otlier known or conceivable means of accounting for 

 them, and for the enormous mounds of gravel or clay intermixed with 

 bowlders which often accom})anied them; and the ehbrts of geologists 

 were therefore directed to the discovery of how the water power had 

 acted and by what means the supposed Hoods could have been pro- 

 duced. 



There were not wanting men who saw that no action of water alone 

 could account for the facts. Sir James Hall iiointed 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 

 parallel grooves and iiutings runningfornearly amile 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 i^roblem till 1822, when Venetz, 

 a Swiss engineer, finding that existing glaciers varied in extent from 

 year to year and that historical records showed them to have consider- 

 ably increased during the last eight centuries, 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 Hel- 

 vetic Society of Natural History, and urged that glaciers once stretched 



* The works referred to are: Do Glaciers Excavated by Prof. T. G. Bonuey, F. R. S. 

 (The Geograpliical Journal, vol. i. No. 6) ; The Glacial Nightmare and the Flood, by Sir 

 H. H. Howorth, M. P., F. R. S. ; Fragments of Earth Lore, by Prof. James Geikie, F. R. 

 S. ; Man and the Glacial Period, by Prof. G. F. Wriiilit, F. G. S. A. ; La P&iode Glaciaire, 

 by A. Falsan ; and the Glacialists' Magazine, edited by Percy F. Kendall, F. G. S. ; 

 from which Avorks, ami from those of Lyell, Ramsay, Geikie, and the American ^ideolo- 

 gists, most of the facts referred to in the present article are derived. 



