CLOUDS AND RIVERS, ICE AXD GLACIERS. 99 



and above the ice-falls of the Geant and the Talefre 

 begin as narrow cracks, which open gradually to 

 crevasses. We are thus taught in an instructive and 

 impressive way that appearances suggestive of very 

 violent action may really be produced by processes so 

 slow as to require refined observations to detect them. 

 In the production of natural phenomena two things 

 always come into play, the intensity of the acting force, 

 and the time during which its acts. Make the in- 

 tensity great, and the time small, and you have sudden 

 convulsion ; but precisely the same apparent effect may 

 be produced by making the intensity small, and the 

 time great. This truth is strikingly illustrated by the 

 Alpine ice-falls and crevasses ; and many geological 

 phenomena, which at first sight suggest violent con- 

 vulsion, may be really produced in the selfsame 

 almost imperceptible way. 



§ 37. Icicles. 



252. The crevasses are grandest on the higher neves, 

 where they sometimes appear as long yawning fissures, 

 and sometimes as chasms of irregular outline, 

 delicate blue light shimmers from them, but this is 

 gradually lost in the darkness of their profounder 

 portions. Over the edges of the chasms, and mostly 

 over the southern edges, hangs a coping of snow, and 

 from this depend like stalactites rows of transparent 

 icicles, 10, 20, 30 feet long. These pendent spears 



