SNOW-LINES. 445 



selves however, as a result of our researches into existing 

 data we are disposed to regard this estimate as somewhat 

 overstated, if we are to regard that as the ordinary 

 limits of perpetual snow in those regions, which accounts 

 show might probably be fixed with greater accuracy at 

 about 18,000 feet. But the snow-lines on mountains 

 are apt to vary considerably from year to year accord- 

 ing to the nature of the seasons. Some years when 

 the average rainfall has been light it will be much 

 higher than at ordinary times. Mr. Whymper, in his 

 late work upon " Mountaineering among the Andes " of 

 Ecuador, suggests that it would be better to abandon 

 the attempt to fix a perpetual snow-line upon 

 mountains, because, as he explains at some length, 

 he regards it as misleading on account of the difficulty 

 in determining what the snow-line really is, or the 

 quantity of snow which would entitle a mountain to 

 be classed as one having a permanent snow-line. * 



The term however is a convenient one, provided that 

 it is clearly understood to mean merely the approxim- 

 ate limits of perpetual snow which exist upon ordinary 

 occasions, according to the best available data ; bearing 

 in mind that, like the depth of a river, it is liable to 

 constant variations it is conceivable for instance, that 

 a violent storm beating upon a particular point, might 

 denude a considerable area of newly fallen snow, and 

 as we know, large extents of exposed ridges and steep 

 slopes are often seen at very great elevations, surrounded 

 by eternal snows, t but remain themselves kept quite 



* See Travels among the Great Andes of Ecuador, by Edwd' 

 Whymper, 1892, pp. 346 to 348. 



f See The Alpine Guide to the Central Alps, by John Ball, F.R.S., 

 p. Ixi of Introduction. (Such instances are also to be seen upon most 

 lofty mountain ranges). 



