52 TWELFTH REPORT. 



Andersson's observation that solifliiction is a pheuomenon particularly 

 characteristic of inhospitable regions, seems to be confirmed by the 

 observation of Howe in the Eocky Mountains. The rock streams which 

 he has described from that region are always found originating beneath 

 the steep walls of abandoned glacial cirques in high altitudes. 



Nordenskj(31d has brought out the interesting fact that the debris 

 stripes are always developed below the rim of a great snow drift, 

 which in melting has so saturated the debris as to transform it into a 

 thick paste, and thus allow it to slide slowly down the slope. 



In the month of August, 1909, the writer discovered identical strij^ed 

 debris zones on the steeply inclined side sloijes of the Asulkan Pass 

 above the n^v^ of the Asulkan glacier (see plate 1, A). Here, also, the 

 stripes ran in gently curving courses in the direction of the steepest 

 slopes, making their start at the lower edge of a drift of snow. Thus 

 the observation is in eveiT way confirmatory of those made by Nor- 

 denskjold. The dark lines in the illustration are slight trenches within 

 which no larger rock fragments are found, and they appear to corre- 

 spond to lines of maximum near-surface flow of the rock paste, here 

 largely of mud. The flat rock fragments lying between the trenches, 

 form an imperfect plating of the intei"vening ridge so that it sheds the 

 water as does a pent-house. 



Upon the Asulkan n^v^ below the pass the surface layer of the 

 snow has been grooved by a process which perhaps has something in 

 common with that which arranged the debris in parallel bands. The 

 eft'ect of this surface striping, or venation, is brought out in Plate 1, B. 

 Starting from near the upper margin of the n^v^, nearly parallel ridges 

 and grooves descend so as always to conform to the lines of steepest 

 gradient upon the surface, eventually coalescing to form a somewhat 

 larger trunk groove which follows the lowest line of the n^v^ surface. 

 Unlike a drainage system the tributaries travel beside the trunk for a 

 considerable distance before making junction with it. This surface 

 grooving or venation upon the n^v6 is best shown upon the plate near 

 the left, and also near the right-hand margin of the newer snow. That 

 it is due to water drainage is evident from the fact that the lines do not 

 continue beyond crevasses which intersect their course. It is suggested 

 that the melting of the outer zone of the ii6y6 granules by filling up the 

 spaces between them with water, affords temporary conditions similar 

 to those of a thin layer of sand partially saturated with water and 

 lying upon a slope. There is thus considerable resemblance between 

 the surface venation of the n^ve and the striping in the rock debris on 

 steep slopes below summer snow drifts. 



This phenomenon of soil strij)ing in debris which has been saturated 

 with water, can hardly be considered apart from the well-known "bar- 

 rancas" which develop on volcanic tuff cones after each new eruption, 

 so soon as the first rains have saturated the material with water (See 

 plate 2 A). Here also the strii>es follow the steepest slope. A compar- 

 ison of the Asulkan and Greenland soil stripes with the great barrancas, 

 suggests that the width of tlie ridges which develop is in some way a 

 function of the viscosity of the rock paste, which in turn is doubtless 

 dependent u])on the nature, form, and size of the materials, the degree 



