316 



PROF. W. MORRIS DAVIS ON 



[Aug. 1909^ 



theoretical discussion as are the corresponding and more familiar 

 changes through the advance of a cycle of normal erosion. 



Under conditions such as are here outlined, let the newly estab- 

 lished or young glacier of fig. 14 continue its work until it becomes 

 the well-established, sub-mature glacier of fig. 17. It will then 



have a large neve-reservoir 

 Fi g> 17 .—Diagram of a later stage or cwm enclosed by cliffs, 

 of fig. U (p. 313). some parts of which may 



rise to meet the correspond- 

 ing cliffs of an adjacent 

 reservoir : there the pre- 

 Glacial rounded spur will 

 be converted into a sharply 

 serrated arete ; elsewhere 

 the rounded summit-forms 

 may resemble those of pre- 

 Glacial time, although they 

 will have been weathered 

 down somewhat during the 

 Glacial Period. Along the 

 valley-sides which rise from 

 the glacial stream to the 

 ridge - lines, there will be 

 undercut slopes which may 

 be weathered to ragged and 

 cliff-like walls in the resistant rocks, but may be weathered back to 

 smooth grade in the less resistant rocks. Although the changes 

 due to superglacial weathering, as here considered, are not to be 



Pigs. 18 and 19. — Diagrams of successively later stages 

 of fig. U (p. 313). 



directly charged to ice-action, they are nevertheless so systematically 

 related to the other erosive work of the Glacial Period that they 



