ON THE STRUCTURE OF GLACIER ICE 499 



which I am acquainted. The sketch was taken by myself from the 

 point marked k on the map in July 1842," — Travels, 2nd Ed., p, 203. 



It must at once strike any one conversant with the ordinary 

 •character of the veined structure, that at the distance of the point on 

 the mule-road from which Prof Forbes's view is taken any veins of 

 the usual dimensions must be totally invisible ; and I therefore 

 approached La Brenva with the desire, if not the hope, of making the 

 acquaintance of glacier structure on a new and gigantic scale. 



Viewed from the mule-path, or from the old moraine at the com- 

 mencement of the pine wood celebrated by De Saussure, the lower 

 part of the glacier of La Brenva exhibits numerous crevasses, which 

 appear to run nearly parallel with its length, so that the icy mass is 

 divided into a series of parallel crests or ridges. The lateral faces of 

 these ridges form perpendicular cliffs of ice, and present dark stripes 

 directed in a longitudinal and nearly horizontal direction ; but where 

 an end view of a ridge is obtained, the stripes run either horizontally 

 and transversely (as in the more central parts of the glacier), or are 

 curved up towards the sides (as in the more lateral parts). 



These markings are evidently those described and faithfully figured, 

 as the " structure " of the glacier, by Prof Forbes ; but I cannot say I 

 should have called them bluish-green. They looked to me simply 

 dark and dirty. But I should state, that the weather, when I visited 

 the glacier, was wet and cloudy. 



Nevertheless, on descending on to the glacier itself, I found its 

 structure, though very beautifully developed, to be in nowise 

 remarkable for the size of its veins, which varied in length from an 

 inch to eight or nine feet, and in breadth from a fraction of an inch 

 to nine or ten inches. Veins of the latter dimensions, however, 

 were rare ; the majority having a thickness of less than an inch. 

 The lenticular form was very well marked, and the veins were 

 ■commonly separated by less than their thickness of white ice. I 

 need hardly say that these veins became indistinguishable at a very 

 short distance. 



The streaks so conspicuous a long way off, on the other hand, 

 became less sharply defined as I approached, and at length showed 

 themselves to be nothing more than accumulations of the fine dirt — ■ 

 spread more or less over the whole cliff-like wall of ice, — in streaks of 

 four to ten inches in breadth, and of variable length. They ran 

 parallel with one another and with the structure, at a distance varying 

 from a few inches to six or seven feet ; and they were entirely super- 

 ficial, the dirt never extending deeper than the weathered superficial 

 Jayer. 



K K 2 



