THE TOPOGKAI'HV OF LAKE SHORES. 53 



margin, and by the winter's oscillation of tL'niperatnrc can be thrust land- 

 ward only to a certain distance, determined by the size of the lake and 

 the local climate. There is thus for each locality a definite limit beyond 

 which the projection of boulders cannot be carried, so that all are de- 

 posited along a common line where they constitute a ridge or wall." 



Shore walls are not conspicuous about the margin of large lakes for 

 the reason that they seldom freeze over and also because the winter's ice 

 work is usually obliterated by the more active waves and currents at 

 other seasons. They are not formed about deep lakes for the reason that 

 such water bodies do not become ice-covered, and for the same reason 

 they do not occur in Avarm climates. 



In tliis brief sketch of the topograph}' of lake shores, an attempt has 

 been made to direct attention to the main processes by which the results 

 have been reached, and to describe briefly the character of some of the 

 more striking forms produced, without attempting an exhaustive analysis 

 of the subject. To the reader who would go farther in the studies here 

 outlined, I most heartily recommend G. K. Gilbert's attractive paper on 

 the t<)[)0gra})hy of lake shore, in the 5th Annual Report of the U. S. Geo- 

 logical Survey, and the more special volume l)y the same author on Lake 

 Bonneville, forming Monograph No. 1 of the publications of the U. S. 

 Geological Survey. 



