52 DYNAMICAL GEOLOGY. 



kind are formed by land-destroying, of the other kind by 

 land-forming action of waves. The one are the scattered 

 remnants of an old coast-line, the other the beginnings of 

 a new coast-line. 



\r> 



SECTION III. ICE. 



Ice may act either as land-ice glaciers, or as floating 

 ice icebergs. 



Glaciers. 



The action of glaciers can not be observed by every one 

 in his own locality, since they exist only in very high 

 mountains or in high latitudes ; but the subject is a very 

 fascinating one, and some knowledge of it gives additional 

 interest to mountain-travel. 



The summits of high mountains, especially in cool, 

 moist climates, are not only covered with perpetual snow, 

 but from this snow-cap there extend down the valleys, 

 far below the region of perpetual snow, solid masses of 

 ice, which are in continual, slow motion downward. 

 These valley prolongations of the snow-caps these moving 

 masses of ice, these ice-streams are called glaciers. 



All mountain-peaks and mountain-ridges are trenched 

 on the sides with radiating or transverse valleys. Now, 

 if we imagine such a peak or ridge to be covered deeply 

 with snow and ice, and if we imagine, further, that ice is 

 a stiffly viscous substance like pitch, so that under the 

 heavy pressure of the thick mass it runs slowly down the 

 slope of the valleys to half-way down the mountain, then 

 we have the condition of things as they exist in the Alps, 

 or in any other glaciated region. In most mountains the 

 valleys are occupied by rivers ; in glacial regions they are 

 occupied in their upper parts by glaciers, and in their 

 lower parts by rivers. As rivers, so glaciers, have their 



