Kk E. C. ANDREWS. 803 



Valleys," as also for an expi,"" nation of these peculiar forms. 

 Russell and McGee had, still eai^'er, called attention to these 

 contours. McGee had also supplied a. explanation. 



Matthes's report of 1899,(20) as also his ^opoc^iaphic maps of 

 Yosemite, are another valuable addition to ou. knowledge of 

 Sierran glaciation, especially in connection with cirque-formation. 



Johnson, in 1904,(19) summarised the main topographic points 

 of the Yosemite, As a result of his excellent observations he 

 he was led to announce a method of cirque-formation by forces 

 acting along lines " curving sympathetically " with those of 

 hergschrunds. 



Tarr in various papers(27,a,6} called attention to the marvellous 

 contours of the Finger Lake and other regions. His latest 

 paper(12) contains very clear statements of the efficiency of ice 

 as a rock-corrader. 



Westgate, in 1905,(30) quotes a concrete case in which a later 

 ice- visitation had, in the main, succeeded merely in aggrading 

 the excavations made during an earlier glacial period. He, 

 however, does not generalise from the observation. 



Thesis. 



The great flood is the main corrasive factor in peneplanation. 

 A " flood " may be defined as that stream-volume which is com- 

 petent not only to utilise the channel-base as a bridge for the 

 transportation of the heaviest stream-material, but has enough 

 residual energy to cut vertically into the live rock of its channel- 

 base. All other stream-volumes are comparatively negligible as 

 regards corrasion. Roadside gutters, brooklet, brook and river 

 valleys, shorelines and glacial canons have dominant shapes all 

 similar and similarly situated. 



Present-day fiord (and some canon) glaciers should be inactive 

 in their channels, with overriding of moraines. 



On the assumption of a recent ice age, many contours may 

 thus be predicted for glacial regions. 

 65 



