THE FORMS OF TVATEP 



251. It is difficult to believe that the for. 

 midable fissures, among which you and I 

 havu so often trodden with awe, could com- 

 mence in this small way. Such, however, is 

 the case. The great and gaping chasms on 

 and above the ice-fails of the Geaut and the 

 Talcfre begin as narrow cracks, which open 

 gradually to crevasses. We are thus taught 

 in an instructive and impressive way that up 

 pearances suggestive of very violent action 

 may really be produced by processes so slow 

 as to require refined observations l > detect 

 them. In the production of natural phe- 

 nomena two things always conic into play, 

 the inteiixity of Ihe acting force, and I he time 

 during which it acts. Make the intensity 

 great and the time small, an 1 you have sud- 

 den convulsion ; but precisely the same ap- 

 parent effect may be produced by making the 

 intensity small and the time great. This 

 truth is strikingly illustrated by the Alpine 

 icv-falls and crevasses ; and many geological 

 phenomena, which at first sight suggest vio- 

 lent convulsion, may be really produced in 

 the self-same almost impercepiibb way. 



37. ICICLES. 



2/52. The crevasses are grandest on the 

 higher neves, where they sometimes appear 

 as long yawning fissures, and sometimes as 

 chasms of irregular outline. A delicate blue 

 light shimmers from them, but this is grad- 

 ual ty 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, 

 80 feet long. These pendent spears consti- 

 tute one of the most beautiful features of the 

 higher crevasses. 



253. How are they produced ? Evidently 

 by the thawing of the snow. But why, 

 Avhen once thawed, should the water freeze 

 again to solid spears ? You have seen icicles 

 pendent from a house-eave, which have been 

 manifestly produced by the thawing of the 

 snow upon the roof. If we understand these 

 we shall also understand the vaster stalactites 

 of the Alpine crevasses. 



254. Gathering up such knowledge as we 

 possess, and reflecting npuii it patiently, let 

 us found on it, if we can, a theory of icicles 



255. First, then, you aie to know that the 

 air of our atmosphere is hardly heated at all 

 by the rays of the sun, whether visible or in- 

 visible. The air is highly transparent to all 

 kinds of rays, and it is only the scanty frac- 

 tion to which it is not transput cut that ex- 

 pend their force in warming it. 



256. Not so, however, with the snow on 

 which the sunbeams fall. It absorbs the 

 solar heat, and on a sunny day you may see 

 the summits of the high Alps glistening with 

 the water of liquefaction. The air above 

 and around the mountains may at the same 

 time be many degrees below the freezing 

 point in temperature. 



257. You have only to pass from sunshine 

 into shade to prove this. A single step 

 suffices to carry you from a place where the 



thermometer stands high to one wneie it 

 stands )ow ; the change being due, not to 

 any difference in the temperature of the air, 

 but simply to the withdrawal of the ther- 

 mometer from the direct action of the solar 

 rays. Nay, without shifting the thermome- 

 ter at all, by interposing a suitable screen, 

 which cuts off the sun's rays, the coldness of 

 the air may be demonstrated. 



258. Look now to the snow upon your 

 house-roof. The sun plays upon it and 

 melts it ; the water trickles to the cave and 

 then drops down. If the eave face the sun 

 the water remains water ; but if the eave do 

 not face the sun, the drop, before it quits its 

 parent snow, is already in shadow. Now the 

 shaded space, as we have learned, may be 

 below the freezing temperature. If so, the 

 drop, instead cf falling, congeals, and the 

 rudiment of an icicle is formed. Other 

 drops and driblets succeed, which trickle 

 over the rudiment, congeal upon it in part 

 and thicken, it at the root. But a portion of 

 the water reaches the free end of the icicle, 

 hangs from it, and is there congealed before 

 it escapes. The icicle is thus lengthened. In 

 the Alps, where the liquefaction is copious 

 and the cold of the shaded crevasse intense, 

 the icicles, though produced in the same way. 

 naturally grow to a greater size. The drain- 

 age of the snow after the sun's power is with- 

 drawn also produces icicles. 



259. It is interesting and important that 

 you should be able to explain the formation 

 of an icicle ; but it is far more important 

 that you should realize the way in which the 

 various threads of what we call Nature are 

 woven together. You cannot fully under- 

 stand an icicle without first knowing that 

 solar beams powerful enough to fuse the 

 snows and blister the human skin, nay, it 

 might be added, powerful enough, when con- 

 centrated, to burn up the human body itself, 

 may pass through the air and still leave it at 

 an icy temperature. 



38. THE BERGSCHRUND. 



260. Having cleared away this difficulty, 

 let us turn once more to the crevasses, taking 

 them in the older of their formation. First 

 then above the neve we have the final Alpine 

 peaks and crests, against which the snow is 

 often reared as a steep buttress. We have 

 already learned that both neves and glaciers 

 are moving slowly downward ; but it usual- 

 ly happens that the attachment of the high- 

 est portion of tho buttress to the rocks is 

 great enough to enable it to hold on while 

 the lower portion breaks away. A very 

 characteristic crevasse is thus formed, called 

 in the German-speaking portion of the Alps 

 a Beryschrund. It often surrounds a peak 

 like a fosse, as if to defend it against the as- 

 saults of climbers. 



261. Look more closely into its formation. 

 Imagine the snow as* yet unbroken. Its 

 higher portions cling to the rocks and move 

 downward with extreme slowness. But its 

 lower portions, whether from their greater 

 depth aud weight or their less perfect at" 



