WATER AS A MECHANICAL AGENT. 



235 



firm. The accumulations are stratified, because made from a succession of 

 snow-falls. Surfaces exposed during the intervals between the falls become 

 hardened and often sprinkled with dust, and, in some regions, covered with 

 growths of the minute Protococcus. It may be made straticulate also through 

 the drifting of the snow. Gradually the lower part of the neve becomes 

 consolidated into stratified ice. Besides the dust from the winds, the neve 

 may also contain earth and stones from avalanches ; but it has no surface 

 accumulations of stones, because those that fall upon the neve sink into it. 



204-208. 



Fig. 204. — Part of the glacier-distiict of Mont Blanc, the lighter middle portion of the map 16 miles long 

 out of 22 miles, the whole length ; river on the northwest side, the Arve, in the valley of Chamouni, and those 

 on the southeast side, tributaries of the Dora Baltea; B, Mont Blanc; G, Aiguille du Geant; J, the Jardin 

 T, Aig. du Tour; V, Aig. Verte; a, Argentiere Glacier; ba, Brenva GI.; bn, Bossons Gl.; 6s, Bois Gl. 

 g, Geant or Tacul GL; Z, Lechaud Gl. ; m, Mer de Glace, upper part of the Bois Gl.; mg, Miage Gl. 

 ta, Talefre Gl. ; tr, Tour Gl. ; tt, Trieut Gl. 



Fig. 205. — Section of the Mer de Glace, near m of Fig. 204, or opposite Trelaporte; 206, section of 

 same, near bs of Fig. 204, or opposite Montanvert; 207, view of the Rhone Glacier; 208, profile of same, c, c, 

 etc., being the transverse crevasses, fading out, and becoming curved after passing the cascade at mn. 



