1859.] on the Veined Structure of Glaciers. 75 



Gtfent was in a state of longitudinal compression ; he had also shown 

 that the seams of white ice which intersect this glacier are due to the 

 filling up of the channels of glacier streams by snow, and the subsequent 

 compression of the substance. Here then we have a vast ice-press 

 which furnishes us with a test of the pressure theory. Both in 1857 

 and 1858, the speaker found many of these seams of white ice i rte- 

 sected by blue veins of the finest and most distinct character, their 

 general direction being at right angles to the direction of pressure. 



The speaker next considered the objections which might be made 

 to his conclusions by an advocate of the theory of stratification ; refer- 

 ring to the notions of M. Agassiz as to the turning up of the strata so 

 as to expose their edges at the surface, and also to the acute remarks 

 and arguments of Mr. John Ball. He admitted that these remarks 

 might well tend to cast a doubt upon the pressure theory, by sug- 

 gesting a possible, though extremely improbable, solution of the 

 question, in harmony with the theory of stratification. 



Hence his strong desire to discover some crucial phenomenon which 

 should set this question for ever at rest, and leave no room for doubt, 

 even on the minds of those who never saw a glacier. On Wednesday, 

 the 18th of August, he was fortunate enough to make this discovery 

 upon the Furgge glacier. 



This ice-field spreads out as an almost level plain at the base of 

 MontCervin. The strata pile themselves one above the other without 

 disturbance, and hence with great regularity. The ice at length reaches 

 a brow which forms the termination of a lower valley, shutting up the 

 latter as a cul de sac; and down this brow it is precipitated, forming in 

 its descent four great terraces. Huge blocks of ice stand, like rocking 

 stones, upon the topmost ledge, and numbers, which have fallen, have 

 been caught by the other ledges and occupy very threatening positions : 

 the base of the fall is cumbered with crushed ice, and large boulders of 

 the substance have been cast a considerable way down the glacier. 



On the faces of the terraces horizontal lines of stratification are 

 shown in the most perfect manner. Here and there the exertion of a 

 powerful lateral squeeze is manifest, causing the beds to crumple, and 

 producing numerous faults. Examining the fall from a distance through 

 an opera glass, the speaker thought he could discover lines of veining 

 running through the strata, at a high angle, exactly as the planes of 

 cleavage often run at a high angle to the bedding of slate rocks. The 

 surface of the ice was, however, weathered ; and he was unwilling to 

 accept an observation upon such a cardinal point with a shade of doubt 

 attached to it. Leaving his glass with his guide, who was to give 

 warning should the blocks overhead give way, he advanced to the wall 

 of ice, and at several places, cut away with his axe the weathered 

 superficial portions. Underneath he found the true veined structure, 

 running nearly at right angles to the planes of stratification. 



He afterwards climbed the glacier to the right, and, as he ascended, 

 still better illustrations of the coexistence of the structure and the 

 strata than those which he had observed upon the terraces exhibited 

 tliemselves. Tiie ice was greatly dislocated, and on the faces of the 



