200 THIRTEENTH LETTER ON GLACIERS. [1846. 



light upon this question, and I shall state the result of iny 

 observations there nearly in the words in which I recorded 

 them immediately after they were made. A little higher up 

 than the usual passage of the glacier to the Jardin, or near the 

 upper limit of the sketch, Plate VIII. fig. 2, the annual layers of 

 the N&ve are seen. But these wholly disappear further down ; 

 the great body of the ice in the hollow of the basin exhibits 

 little sign of structure ; only near the lateral and medial moraines 

 the structure is icy and vertically veined, elsewhere it is decidedly 

 snowy, with hardly any trace of bands either vertical or horizontal. 

 This is true even as far down as the line of stations W in the 

 figure. The general disposition of the structural lines where 

 they exist (which, it is to be recollected, are almost vertical), is 

 seen in the same figure [to be] perpendicular to the crevasses. 

 From these facts I conclude, first, That the vertical structure 

 is too close to the original strata of the Neve to allow of the sup- 

 position that these have all of a sudden turned up vertically in 

 some parts of the glacier, and disappeared in the remainder. 

 2dly, That where the vertical bands are not developed in the 

 higher glacier, the structure remains snowy and undefined. 

 3 dly, That the conversion into ice is simultaneous, and in this case 

 identical with the formation of the Hue lands. thly, That these 

 bands are formed where the pressure is most intense, and where 

 the differential motion of the parts is a maximum, that is, near 

 the walls of the glacier ; but being once formed, it still continues, 

 at least for a time, to be observed under the medial moraine, and 

 this may even be traced throughout the ice-fall of the Talefre. 



I am satisfied then (and it is only after long doubt that I 

 venture this confident expression), that the conversion of snow 

 into ice is due to the effects of pressure upon the loose and 

 porous structure of the former ; that the very first effect is to 

 annihilate the annual strata of the Neve, and that the most 

 rapid glacification is effected by the kneading or working of the 

 parts upon one another, by the differential motions which the 

 semi-fluid law of glacier progression occasions, and which also 

 necessarily takes place under intense pressure. 



