326 Professor J, fyndall, [Jan. 23, 



moraine of the Aar glacier. In fact, the association of pressure 

 and lamination is far more distinct in the case of a glacier than in 

 the case of slate rock. We know that in the latter case pressure 

 is the sufficient cause of the lamination ; are we not justified in 

 concluding that it is also the cause in the former? The oblique 

 position of the veins near the sides, the transverse lamination of 

 the centre, the lenticular structure, the relation of the veins to the 

 crevasses, are all in harmony with this compression theory of the 

 veined structure of glacier ice. Unless, indeed, we suppose the 

 compacted mountain snow to be perfectly homogeneous in a me- 

 chanical point of view, — a supposition plainly opposed to common 

 sense — some portions of it will when under violent pressure, be 

 rendered more compact than others, and the blue veins are the 

 natural consequence.* 



In the investigation, the well-known " dirt bands," to which so 

 much theoretic importance is attached, were finally considered, and 

 an explanation of these bands, as they are seen upon the glaciers of 

 Grindelwald and of the Rhone, was attempted. On the former 

 glacier the bands were particularly well developed, and a portion 

 of the glacier where they did not exist was presented simultaneously 

 with the bands upon another portion. Their proximate origin and 

 final completion were thus observed at once ; and to account for 

 them the following explanation is proposed : these bands, wherever 

 they have been observed, are, it is believed, first developed at the base 

 of an ice cascade. The dirt, scattered by winds and avalanches over 

 the upper regions of a glacier, is redistributed by the passage of 

 the glacier through a precipitous gorge, where the ice is shattered 

 and the dirt broken up into detached patches. On reaching the 

 bottom, where the force becomes one of longitudinal compression, 



* I have recently ti'ied to reproduce the blue veins on a small scale by 

 compressing snow. In some cases the section of the mass perpendicular to the 

 surface, on which the pressure was exerted, exhibited in a feeble, but distinct 

 manner, an appearance the same in kind as that of the veined structure of 

 glacier ice. Stripes more transparent than the surrounding ice were observed 

 at right angles to the direction of pressure. It is well known that the ice 

 structure sometimes exhibits a true cleavage, and since the above discourse was 

 given I have succeeded in impressing upon a perfectly transparent prism of ice 

 a cleavage, the perfection of which surprised me. As in the case of the glacier 

 and of slate rocks, the cleavage is perpendicular to the direction of pressure. 

 On placing a specimen of the squeezed ice before a friend, he at first sight 

 imagined it to be a bit of gypsum. The case then, as regards slaty cleavage 

 and the structure of glacier ice, stands thus : — the testimony of independent 

 observers proves that both ice and slate are laminated at right angles to the 

 direction of pressure ; and the question occurs, Is this pressure suJQBicient to pro- 

 duce the lamination ? P^xperiment replies in the affirmative. I have reduced 

 slate rock to an almost impalpable powder, and reproduced from it the 

 lamination by pressure. The experiments above referred to prove the 

 sufficiency of the pressure to produce the cleaved structure of the glacier ice. 

 By combining the conditions of nature we have produced her results. 



