Stratification of the Neve. 127- 



entire surface, and as far down in the crevasses as the eye could 

 distinguish, was composed of compact snow, or snow changed 

 to icy particles resembling hail and having in reality but few of 

 the properties of ordinary snow : it might properly be called 

 neve ice. Usually the thickness of the layers varied from ten to 

 fifteen feet. Separating them were dark lines formed by dust 

 blown over the surface of the glacier and buried by subsequent 

 snow-storms, or by thin blue lines formed by the edges of sheets 

 of ice and showing that the snow surface had been melted during 

 bright sunny days and frozen again at night. The horizontal 

 stratification so plainly marked in all the crevasses in the neve 

 was almost entirely wanting, or at least was not conspicuous, in 

 the lower portion of the glacier, where, instead, we found those 

 narrow blue and white bands already mentioned, the origin of 

 which has been so well described and explained by Tyndall. 



The center of the Marvine glacier, as in most similar ice- 

 streams, is higher and less broken by crevasses than its borders. 

 The crevasses at the side trend np stream, as is the case with 

 marginal crevasses generally. In the present instance the courses 

 of these rents could be plainly distinguished on each border of 

 the glacier, when looking down upon it from neighboring slopes. 

 The crevasses occur at quite regular intervals of approximately 

 fifty feet, and diverge from the bank at angles of about 40°. In 

 the banks of snow bordering the glacier similar crevasses diverge 

 from the margin of the flowing glacier and trend down along its 

 banks. The marginal crevasses and the crevasses in the border- 

 ing snow-fields, to which no special name has been given, fall 

 nearly in line ; but between the two there is a series of irregular 

 cracks and broken snow, sharply defining the border of the 

 moving n6ve. 



The origin of the marginal crevasses trending up stream was 

 explained during the study of the glaciers of Switzerland. The 

 following diagram and explanation illustrating their development 

 are copied from Tyndall : 



" Let A C be one side of the glacier and B D the other ; and let the direc- 

 tion of motion be that indicated by the arrow. Let ^S' Tbe a transverse 

 sHce of the glacier, taken straight across it, say to-day. A few days or 

 weeks hence the slice will have been carried down, and because the center 

 moves more quickly than the sides it will not remain straight, but will 

 bend into the form S^ T' . Supposing T i to be a small square of the original 

 slice near the side of the glacier ; in the new position the square will be 

 distorted to the lozenge-shaped figure T^ l^. Fix your attention upon the 



