THE ICE AGE AND ITS WORK. 681 



THE ICE AGE AND ITS WORK. 



BY ALFRED R. WALLACE, F. R. S. 



ERRATIC BLOCKS AND ICE-SHEETS. 



I. 



IT is little more than fifty years ago that one of the most potent 

 agents in modifying the surface features of our country was 

 first recognized. Before 1840, when Agassiz accompanied Buck- 

 land to Scotland, the Lake District, and Wales, discovering every- 

 where the same indications of the former presence of glaciers as 

 are to be found so abundantly in Switzerland, no geologist had 

 conceived the possibility of a recent glacial epoch in the tem- 

 perate portion of the northern hemisphere. From that year, 

 however, a new science came into existence, and it was recog- 

 nized that only by a careful study of existing glaciers, of the 

 nature of the work they now do, and of the indications of the 

 work they have done in past ages, could we explain many curious 

 phenomena that had hitherto been vaguely regarded as indica- 

 tions of diluvial agency. One of the first fruits of the new science 

 was the conversion of the author of Reliquiae Diluvianse Dr. 

 Buckland, who, having studied the work of glaciers in Switzer- 

 land in company with Agassiz, became convinced that numerous 

 phenomena he had observed in this country could only be due to 

 the very same causes. In November, 1840, he read a paper before 

 the Geological Society on the Evidences of Glaciers in Scotland 

 and the North of England, and from that time to the present the 

 study of glaciers and of their work has been systematically pur- 

 sued with a large amount of success. One after another crude 

 theories have been abandoned, facts have steadily accumulated, 

 and their logical though cautious interpretation has led to a con- 

 siderable body of well-supported inductions on which the new 

 science is becoming firmly established. Some of the most impor- 

 tant and far-reaching of these inductions are, however, still 

 denied by writers who have a wide acquaintance with modern 

 glaciers ; and as several works have recently appeared on both 

 sides of the controversy, the time seems appropriate for a popular 

 sketch of the progress of the glacial theory, together with a more 

 detailed discussion of some of the most disputed points as to 

 which it seems to the present writer that sound reasoning is even 

 more required than the further accumulation of facts.* 



* The works referred to are : Do Glaciers Excavate ? by Prof. T. G. Bonney, F. R. S. 

 (The Geographical 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. ; 



