LIFE IN THE ALPS. 323 



land. South-westerly winds, on the other hand, come 

 charged with the vapour contracted during their passage 

 over vast tracts of ocean. Such winds, in England, 

 produce the heaviest rains. 



And now we approach a question of very great in- 

 terest. The condensed vapour which reaches the low- 

 lands as rain, falls usually upon the summits as snow. 

 To a resident among the Alps it is interesting to ob- 

 serve, the morning after a night's heavy rain, a limit 

 sharply drawn at the same level along the sides of the 

 mountains, above which they are covered with snow, 

 while below it no snow is to be seen. This limit marks 

 the passage from snow to rain. 



To the mountain snow all the glaciers of the Alps 

 owe their existence. By ordinary mechanical pressure 

 snow can be converted into solid ice ; and, partly by its 

 own pressure, partly by the freezing of infiltrated 

 water, the snow of the mountains is converted into the 

 ice of the glaciers. 



The great glaciers, such as the one now below me, 

 have all large gathering grounds, great basins or 

 branches where the snow collects and becomes gra- 

 dually compacted to ice. Partly by the yielding of its 

 own mass, and partly by si ding over its bed, this ice 

 moves downwards into a trunk valley, where it forms 

 what De Saussure called 4 a glacier of the first order.' 

 Such a glacier resembles a river with its tributaries. 

 We may go further and affirm, with a distinguished 

 writer on this subject, that ' between a glacier and a 

 river there is a resemblance so complete, that it would 

 be impossible to find, in the one, a peculiarity of motion 

 which does not exist in the other.' 



Thus, it has been proved that owing to tbe friction 

 of its sides which holds the ice back, the motion of a 



