682 THE POPULAR SCIENCE MONTHLY. 



In the last century, Swedenborg, Linnaeus, Pallas, De Luc, and 

 many other eminent writers took notice of the remarkable fact 

 that in Scandinavia, Russia, Germany, and Switzerland detached 

 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 only to be discovered in remote 

 localities, sometimes hundreds of miles away. Those who ven- 

 tured to speculate on the origin of these traveled rocks usually 

 had recourse to water power to account for their removal ; and 

 as their large size and often elevated position required some un- 

 usual force to carry them, there arose the idea of enormous floods 

 sweeping over whole continents ; and for a long time this diluvial 

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

 the difficulties of its application to explain all the phenomena be- 

 came greater the more closely those phenomena were studied. 

 Still, there was apparently no other known or conceivable means 

 of accounting for them, and for the enormous mounds of gravel 

 or clay intermixed with bowlders which often accompanied them ; 

 and the efforts of geologists were therefore directed to the discov- 

 ery of how the water power had acted, and by what means the 

 supposed floods could have been produced. 



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 un- 

 doubtedly in the far-distant Alps ; and Mr. Grainger, in America, 

 described some of the parallel 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, how- 

 ever, thrown on the problem till 1822, when Venetz, a Swiss en- 

 gineer, 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 Helvetic Society of Natural History, and urged 

 that glaciers once stretched down the Rhone Valley as far as the 



Man and the Glacial Teriod, by Prof. G. F. Wright, F. G. S. A. ; La P6riode Glaciaire, by 

 A. Falsan ; and the Glacialist's Magazine, edited by Percy F. Kendall, F. G. S. ; from which 

 works, and from those of Lyell, Ramsay, Geikie, and the American geologists, most of the 

 facts referred to in the present article are derived. 



