1882.] 21 [Davis. 



Before going farther, we may note the development of the idea 

 that glaciers have a strong erosive effect on the surface over which 

 they move. 



Roches moutonnees and polished rock-surfaces, at first considered the 

 result of floods, were shown by de Charpentier 1 in 1834 to be the product 

 of glacial friction. In 1837, Agassiz 2 explained rock striations in the 

 same way, and pointed out how they might be distinguished from slieken- 

 sides and land-slide scratches ; they had been taken by de Saussure to be 

 the effect of crystalline structure, like the parallel lines on the side of a 

 quartz prism ; and by Hall 3 and Sefstrom 4 as the result of a flood. 

 Glacial mud, the result of the production of striated and rounded rocks, 

 was noticed by de Charpentier, 5 but first considered of much importance 

 by Collomb 6 . 



In 1821, Venetz 7 suggested that the smaller Alpine lakes owed their 

 preservation to having been cleaned out by glaciers ; an idea since carried 

 farther by de Mortillet, 8 and extended by Ramsay 9 to the making of rock- 

 basins. Esmark 10 first proposed that the Norwegian fjords had been shaped 

 by glaciers ; Chambers n went farther in claiming that land ice had pro- 

 duced great general denudation. In 1858, K'amtz 12 suggested that the 

 Swiss and Scandinavian glaciers had been self-destructive by wearing 

 away their mountain supports ; Tyndall 13 repeated this in 1862, and at the 

 same time stated his belief that without glaciers the Alps would have had 

 no valleys. Finally, in 1874, Campbell u compared a glacial scratch and a 

 Norwegian fjord as differing in size but not in kind. One cannot well 

 imagine anything more excessive than these latter views. 



With reference to subglacial streams, de Charpentier 15 referred the for- 

 mation of lap iaz (karrenf elder) to their action; Agassiz 16 added pot-holes, and 

 thought also that Alpine valleys of erosion had been cut out by streams 



i Annales des Mines, vm, 1835, 231. 



2 Soc. Helv. Actcs, xxn, 1837, p. xn ; Etudes sur les Glaciers, 1840, 195. 



3 Edinb. Trans, vn, 1815, 183. 



4 Pogg. Ann. xxxvni, 1836. 614. 



5 Essai sur les Glaciers, 1841, 89. 



6 Soc. Geol. Bull, vi, 1848-49, 492. 



7 Soc. Helv. Denkschr, i, (2) 1833, 33. 



8 Soc. Geol. Bull, xvi, 1859, 888. 



9 Peaks, Passes, and Glaciers, 1859, 466 ; Geol. Soc. Journ., xvm, 1862, 185. 

 io Edin. New Phil. Journ., n, 1826-27, 118. 



11 Id. liv, 1853, 252. 



12 Wien, Geogr. Ges. Abhandl. II, 1858, 241-243. 



13 Phil. Mag., xxiv, 1862, 172. 



1 4 Geol. Soc. Journ., xxx, 1874, 221. 



1 5 Annales des Mines, vm, 1835, 232. 

 i6 Soc. Helv. Acjes, xxn, 1837, p. xiii. 



