146 A CENTURY OF SCIENCE 



an absolutely trivial work. There is not a particle of direct 

 evidence, so far as I can see, to warrant the belief that these 

 U-shaped canons were given their peculiar form by other means 

 than the actual ploughing erosion of glaciers. ..." 



These contributions from the Cordilleras corroborat- 

 ing the conclusions of Ramsay (1862), Tyndall (1862), 

 Jukes (1862), Hector (1863), Logan (1863), Close (1870), 

 and James Geikie (1875), made little impression. The 

 views of Lyell (1833), Ball (1863), J. W. Dawson (1864), 

 Falconer (1864), Studer (1864), Murchison (1864, 1870), 

 Ruskin (1865), Rutimeyer (1869), Whymper (1871), 

 Bonney (1873), Pfaff (1874), Gurlt (1874), Judd (1876), 

 prevailed, and the conclusions of Davis in 1882 72 fairly 

 expressed the prevailing belief in Europe and in 

 America : 



"The amount of glacial erosion in the central districts has 

 been very considerable, but not greatly in excess of pre-glacial 

 soils and old talus and alluvial deposits. Most of the solid rock 

 that was carried away came from ledges rather than from val- 

 leys; and glaciers had in general a smoothing rather than a 

 roughening effect. In the outer areas on which the ice advanced 

 it only rubbed down the projecting points; here it acted more 

 frequently as a depositing than as an eroding agent." 



During the past quarter-century the cleavage in the 

 ranks of geologists, brought about by Ramsay's classic 

 paper, has remained. Fairchild and others in America, 

 Heim, Bonney, and Garwood in Europe argue for insig- 

 nificant erosion by glaciers ; and Gannet, Davis, Gilbert, 

 Tarr in America followed by Austrian workers present 

 evidence for erosion on a gigantic scale. A perusal of 

 the voluminous literature in the Journal and elsewhere 

 shows that the difference of opinion is in part one of 

 terms, the amount of erosion rather than the fact of 

 erosion ; it also arises from failure to differentiate the 

 work of mountain glaciers and continental ice sheets, of 

 Pleistocene glaciers and their present diminished repre- 

 sentatives. The irrelevant contribution of physicists has 

 also made for confusion. 



It is interesting to note that the criteria for erosion 

 of valleys by glaciers has long been established and 

 by workers in different countries. Ramsay (1862) in 





