PARRY — ALPINE FLORA. 535 



surface become heated, vegetation starts with unwonted 

 vigor from its long winter sleep of nine months' continuance ; 

 rivulets gush freely from the contracting edges of snow drifts, 

 swelling the alpine brooks, and pouring their united tributes 

 of melted snow water through the lower valleys to the dis- 

 tant plains. In this condition of things there is of course no 

 opportunity for the development of glacier phenomena ; no 

 accumulated body of snow above to exert pressure on the 

 mass beneath, thus converting its neve to glacier ice. In 

 fact the higher peaks and crests being more exposed to the 

 action of fierce winds, afford the scantiest space for the falling 

 snow to rest upon, and are generally the first to become 

 bare; besides, having no source of supply but what is derived 

 directly from the atmosphere, all that is borne down by the 

 wind is so much taken from its power of resisting the con- 

 tinued action of the sun's rays. It is, indeed, possible that 

 this transporting agency of wind may constitute the process 

 by which, in this region and the more elevated districts of 

 Mexico and the South American Andes, the culminating 

 points are prevented from accumulating that local amount of 

 winter snow which would otherwise be sufficient to establish 

 a definite snow line, and thus give origin to that slower pro- 

 cess of descent represented by the glacier phenomena of the 

 old world. It is in the higher mountain slopes above the 

 timber line that the evidences of ancient glacier action are 

 most conspicuous, being here less obscured by the mingled 

 product of subsequent surface denudation. Some of the 

 upper valleys thus exhibit, in their deeply scooped bed and 

 polished rocky sides, the traces of ice movements, that have 

 since given place to the ordinary abrading action of running 

 water derived from melting snows. At many other points 

 along the irregular slopes of the highest crests, we meet with 

 what are termed in the expressive language of mining prospec- 

 tors as sags, representing, as it were, slips, scooped out from 

 the sides of the mountain ridges, and which may be properly 

 regarded as incipient valleys, abandoned in their present un- 

 finished state by their parent glaciers, and now only affording 

 a bed in which the light-drifting snows of winter may find a 

 resting-place. 



The outweathering of the natural rock exposures, as ex- 

 hibited on the peaks and flattened summits of the highest 

 elevations, is instructive as showing the combined effect of 

 frost and atmospheric denudation. Nowhere do we meet 

 with extensive smooth surfaces of level rock, such as we 

 might suppose would result from uniform surface abrasion, 

 but, instead of this, loose angular blocks of all sizes, and piled 

 in every conceivable form, either loosely, leaving extensive 

 cavities, or imbedded in a coarse granitic sand. These de- 

 tached blocks, variously spotted over with lichen, serve to 



