A CENTURY OP SCIENCE 



by the agency of wind in a region of steppe vegetation is 

 now all but universal. 



Glacial Sculpture. 



Within the present generation sculpture by glaciers has 

 received much attention and has involved a reconsidera- 

 tion of the ability of ice to erode which in turn involves 

 a crystallization of views of the mechanics of moving ice. 

 The evidence for glacier erosion has remained largely 

 physiographic and rests on a study of land forms. In 

 fact, the inadequacy of structural features or of river 

 corrasion to account for flat-floored, steep-walled gorges, 

 hanging valleys, and many lake basins, rather than a 

 knowledge of the mechanics of ice has led to the present 

 fairly general belief that glaciers are powerful agents of 

 rock sculpture. The details of the process are not yet 

 understood. 



Erosion by glaciers enters the arena of active discus- 

 sion in 1862-63. The possibility had been suggested by 

 Esmark (1827) and by Dana (1849) in the description of 

 fiords and by Hind (1855) with reference to the origin 

 of the Great Lakes. It appears full-fledged in Ramsay's 

 classic, which was published simultaneously in England 

 and in America. 68 The argument runs as follows: 

 There is a close association of ancient glaciers and lakes 

 especially in mountains ; glaciers are amply able to 

 erode; evidences of faulting, special subsidence, river 

 erosion, and marine erosion are absent from the lake 

 basins of Switzerland and Great Britain. To quote 

 Ramsay : 



"It required a solid body grinding steadily and powerfully in 

 direct and heavy contact with and across the rocks to scoop out 

 deep hollows, the situations of which might either be determined 

 by unequal hardness of the rocks, by extra weight of ice in 

 special places, or by accidental circumstances, the clue to which 

 is lost from our inability perfectly to reconstruct the original 

 forms of the glaciers. ' ' 



"I believe with the Italian geologists, that all that the glaciers 

 as a whole effected was only slightly to deepen these valleys and 

 materially to modify their general outlines, and, further (a the- 

 ory I am alone responsible for), to deepen them in parts more 

 considerably when, from various causes, the grinding power of 



