126 



HOBBS— CHARACTERISTICS OF THE 



[April 22, 



shear off and sink vertically into the water, disappear for some seconds, and 

 then rise again almost to their original height before turning over. If there 

 were any projection within 300 feet of the surface this mass would have 

 struck it and been overturned so that it could not have arisen vertically out 

 of the water. 



Fig. 41. Origin of bergs as a result especially of wave erosion (after 

 Russell). 



Reid thinks there are three ways in which bergs come into exist- 

 ence at the end of a glacier: 



(a) A piece may break off and fall over— this is the usual way with 

 small pinnacles; (h) a piece may shear off and sink into the water — this is 

 the usual way with the larger masses ; or, again, (c) ice may become 

 detached under water and rise to the surface. 



The supposed successive forms of the ice front, according to Reid, 

 are .shown in Fig. 42. 



JfWr^\ 1 



Fig. 42. Supposed successive forms of a tide-water glacier front (after 

 Reid). 



