MODERN GEOLOGY 



become surrounded on all sides by stones which ulti- 

 mately form a sort of crown around the summit when- 

 ever the glaciers decrease or retire completely. Water 

 currents never produce anything like this ; but, on the 

 contrary, whenever a stream breaks itself against a 

 projecting rock, the stones which it carries down are 

 turned aside and form a more or less regular trail. 

 Never, under such circumstances, can the stones re- 

 main either at the top or at the sides of the rock, for, if 

 such a thing were possible, the rapidity of the current 

 would be accelerated by the increased resistance, and 

 the moving bowlders would be carried beyond the ob- 

 struction before they were finally deposited. 



"3. The polished and striated rocks, such as have 

 been described in Chapter XIV., afford yet further evi- 

 dence of the presence of a glacier; for, as has been said 

 already, neither a current nor the action of waves upon 

 an extensive beach produces such effects. The general 

 direction of the channels and furrows indicates the 

 direction of the general movement of the glacier, and 

 the streaks which vary more or less from this direction 

 are produced by the local effects of oscillation and re- 

 treat, as we shall presently see. 



"4. The Lapiaz, or Lapiz, which the inhabitants of 

 German Switzerland call Karrenf elder, cannot always 

 be distinguished from erosions, because, both produced 

 as they are by water, they do not differ in their ex- 

 terior characteristics, but only in their positions. 

 Erosions due to torrents are always found in places 

 more or less depressed, and never occur upon large in- 

 clined surfaces. The Lapiaz, on the contrary, are 

 frequently found upon the projecting parts of the sides 



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