100 



ICE AND GLACIERS. 



the valleys, filling them throughout their entire breadth, and 

 often to a considerable height. They thus follow all the cur- 

 vatures, windings, contractions, and enlargements of the valley. 

 Two glaciers frequently meet the valleys of which unite. The 

 two glacial currents then join in one common principal current,, 

 filling up the valley common to them both. In some places, 

 these ice-currents present a tolerably level and coherent surface,. 

 FIG. 13. 



but they are usually traversed by crevasses, and both over the 

 surface and through the crevasses countless small and large 

 water-rills ripple, which carry off the water formed by the 

 melting of the ice. United, and forming a stream, they burst, 

 through a vaulted and clear blue gateway of ice, out at the 

 lower end of the larger glacier. 



On the surface of the ice there is a large quantity of blocks 

 of stone, and of rocky debris, which at the lower end of the 



