200 
Frank Carney 
ture has generally grown less polemical with the increase of field ji 
knowledge. At the present time the belief in glacial erosion, | 
locally even profound erosion, is almost universal. 
It is many years since attention was first directed to the deepen- 1 
ing of valleys as an evidence of glaciation. But for a long time 
no convincing proof was adduced. Perhaps the earliest observa- j 
tion approximating proof, and even this was not credited by many [| 
geologists, was King’s description^ of certain Cordilleran valleys '! 
which, passing downstream, change from a U-profile, ice-carved, 
to a V-profile, water-made. An appreciation of the distinction | 
between the ice-modified and the water-made valley was of slow j 
development. McGee^ in 1883 briefly mentioned the relation- || 
ship produced when ice makes a major valley wider, thus removing |i 
the terminal part of a tributary; but this intimation of the ‘‘hang- j 
ing valley” condition apparently did not fix an impression in the i| 
minds of glacialists. In 1887 Russell gave a very accurate descrip- [ 
tion of this relationship, but concluded that “the great inequality I 
in the depth of the main glacial troughs and of their lateral bran- ! 
ches is too great a work to be ascribed to the erosive power of I 
ice.”^ The first description of an ice-produced discordance be- | 
tween a major and its tributary valley, given in sufficient detail i 
and explicitness to merit acceptance, is that of Tarr in his “Lake 
Cayuga, a Rock Basin. 1 
i 
1873 J. LECONTE. I 
Leconte says the fact that the Yosemite and other similar canons ll 
in the Sierra Nevada “have been occupied by glaciers, makes it [l 
almost certain that they have been formed by this agency.” “I | 
must believe that all these deep perpendicular slots have been | 
sawn out by the action of glaciers. ”® ! 
i 
^ Geological Exploration of the Fortieth Parallel, vol. i, p. 478, 1 ^ 73 ’ | 
^ W. J. McGee, Proceedings of the American Association for the Advancement j| 
of Science, p. 238, 1883, |, 
^ 1 . Russell, U. S. Geological Survey, Eighth A nnual Report, part i, p. 352, 1889. ji 
° Bulletin of the Geological Society of America, vol. v, pp. 339-5^) 1894. 
® Quoted from Davis, Proceedings of the Boston Society of Natural History, vol. j 
xxii, p. 46, 1882. Leconte’s statement appeared in American Journal of Science, |j 
vol. V, p. 339, 1873. 
