24 H. L. FAIRCH1LD — ICE EROSION THEORY A FALLACY 



sion, who should first prove that it is even possible for a glacier to cut a 

 valley or large basin somewhere, some time, or under some conditions. 

 There are no facts of observation from any living glaciers, nor from any 

 dead glaciers, which justify the idea that they can cut valleys or deep 

 basins in live rock. The sufficient negative proof is given below. 



(11) There seems to be sufficient testimony to the occurrence of small 

 or shallow rock-basins, in crystalline rocks, in the central areas of glacia- 

 tion ; also in cirques or valley heads ; and perhaps in the course of 

 mountain valleys at the foot of steeper slopes. Shallow basins in crys- 

 talline rocks are to be expected, as a product of rock-weathering and 

 glacial removal of the loosened material. This was recognized long ago 

 by Pumpelly* Because a rock-rimmed basin is found to bear glacial 

 stria? on its borders the conclusion does not necessarily follow, logically? 

 that the basin was cut out of the solid rock by ice erosion, although this 

 is commonly assumed. The striae merely prove that glacial ice has 

 passed over the rock. However, since weathering and stream action do 

 not normally produce basins, it is a legitimate theory that ice really had 

 some function in the forming of the basins ; but since there is abundant 

 proof from living glaciers that ice does not cut basins out of solid rock 

 as a habit, it is much more reasonable and scientific to conclude that the 

 ice has usually only developed a structure or form partly due to differen- 

 tial weathering/)* 



The production of small or shallow rock-basins in mountain valleys 

 may be fully admitted without really touching the problem of large lake 

 basins like Chelan or Cayuga. Both quantitatively and in principle the 

 genetic process is entirely different. For example, a river can excavate 

 a plunge-basin at the foot of a cataract, but this gives no warrant for 

 assuming that the river can cut a great basin in its graded valley by its 

 ordinary flow. 



The same statement applies to cirques. J These are a product of an 

 exceptional process of quarrying, due to combination of frost-work and 

 ice-pull at the bergschrund or along deep crevasses. The principle has 

 no application to ice abrasion beneath the glacier in its ordinary flow. 

 The forces involved in cirque-making may have some play alongside the 



*R. Pumpelly: "The relation of rock-disintegration to loess, glacial drift, and rock-basins." 

 Amer. Jour. Sci., vol. 17, 1879, pp. 133-144. 



fit is desirable that reliable observations should be directed to the determination of the question 

 whether undoubtedly glaciated rock-basins occur in sedimentary rocks. 



J For the study of cirques consult specially the following: 



W. D. Johnson : On cirques. Science, new ser., vol. ix, pp. 112-113. 



F. E. Matthes: "Glacial sculpture of the Bighorn mountains, Wyoming." Twenty-first Ann. 

 Rept. U. S. Geol. Survey, 1899-1900, pt. ii, p. 167, et seq. 



H. W. Turner: "Pleistocene geology of the south central Sierra Nevada, with especial refer- 

 ence to the origin of Yosemite valley." Proc. Calif. Acad. Sci., 3d ser., Geol., vol. i, p. 289, et seq. 



A. C Lawson: "Geomorphogeny of the upper Kern basin." Univ. of Calif. Pub., Bull. Dept. 

 Geol., vol. 3, 1904, no. 15, pp. 291-376. (Particularly page 358.) 



