Gregory — Progress in Interpretation of Land Forms. 125 



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 

 the ice was unusually powerful, especially where, as in the low- 

 lands of Switzerland, the Miocene strata are comparatively soft." 



Whittlesey (1864) 69 considered that the rock-bound 

 lakes and narrow bays near Lake Superior were partly 

 excavated by ice. LeConte (1875) 70 records some sig- 

 nificant observations in a pioneer paper on glacier 

 erosion^ which has not received adequate recognition. 

 He says : 



"... I am convinced that a glacier, by its enormous pressure 

 and resistless onward movement, is constantly "breaking off large 

 blocks from its bed and bounding walls. Its erosion is not only a 

 grinding and scoring, but also a crushing and breaking. It 

 makes by its erosion not only rock-meal, but also large rock- 



