536 TRANS. OP THE ACAD. OP SCIENCE. 



give a peculiar aspect to the scenery, and the present irregu- 

 lar position can only be satisfactorily explained by referring 

 it to the action of melted snow penetrating the fissures, which, 

 by subsequent freezing, quarry out the immense blocks which 

 strew the surface. These once detached from their bed are 

 readily subjected to the displacing movements of underlying 

 bodies of ice, melting unevenly according to differences of 

 local exposure, and hence frequently poised in unstable equi- 

 librium, rendering the footing insecure, and at times danger- 

 ous. Along the mountain slopes these features are of course 

 modified by the action of running waters and occasional 

 avalanches of snow and loosened rocks, all confusedly mixed 

 up with the results of ancient glacier action. Hence it is 

 not uncommon along the flanks of the snowy range to en- 

 counter extensive tracts completely bedded with fragments 

 of rock of all sizes, and variously shaped by attrition. Over 

 these traveling can only be accomplished by a succession of 

 leaps from one rock to another, while in the burrowing re- 

 cesses and crevices the peculiar alpine plants, and animals, 

 find needful shelter from the rigors of an arctic winter. 

 Through these loosely aggregated beds the melted snow 

 waters percolate, and work their sinuous course by unseen 

 channels to form the alpine brooks below. Occasionally a 

 shallow basin accumulating in its bed the finer sediment 

 washed down from above, supports a rank growth of vegeta- 

 tion, being thus gradually converted into an alpine morass. 

 At other points smooth slopes are covered with a rich alpine 

 sward, composed of densely tufted plants, with spreading 

 fibrous roots and matted foliage, whose variously colored 

 flowers complete an enameled carpet, attractive alike to the 

 eye and foot of the mountain traveler. 



These several enumerated points comprise the main fea- 

 tures of scenery presented during the summer months on 

 these bare exposures, wonderfully varied, it is true, and of 

 which a mere verbal description can give but a very inade- 

 quate conception. 



THE TIMBER LINE, AND THE UPPER LIMIT OF THE GROWTH OF SHRUBS. 



No feature of Rocky Mountain scenery is more strongly 

 marked than that which determines the upper limit of the 

 growth of trees. This can be readily traced by the eye from 

 a distant view, embracing a wider scope of mountain ex- 

 posure, in which the slighter inequalities are smoothed down 

 to a more uniform level, and thus presents a well marked 

 horizontal line. 



This feature is most distinctly marked when the green 

 foliage of the upper pine growth is brought in contrast with a 

 background of glittering snow, such as prevails during the 



