1858.] o?t, tite Merde- Glace. 545 



The law first established by Prof. J. D. Forbes, that the central 

 portions of a glacier moved faster than the sides, was amply illus- 

 trated by the deportment of lines of stakes placed across the Mer- 

 de-Glace at several places, and across the tributaries of the glacier. 

 The portions of the Mer-de-Glace derived from these tributaries 

 were easily traceable throughout the glacier by means of the 

 moraines. Thus, for example, that portion of the trunk stream 

 derived from the Glacier du Geant, might be distinguished in a 

 moment from the portion derived from the other tributaries, by the 

 absence of the debris of the moraines upon the surface of the 

 former. The commencement of the dirt formed a distinct junction 

 between both portions. Attention has been drawn by Prof. Forbes 

 to the fact, that the eastern side of the glacier in particular, is " ex- 

 cessively crevassed ;" and he accounts for this crevassing by sup- 

 posing that the Glacier du Geant moves most swiftly, and in its 

 effort to drag its more sluggish companions along with it, tears 

 them asunder, and thus produces the fissures and dislocation for 

 which the eastern side of the glacier is remarkable. The speaker 

 said that too much weight must not be attached to this explanation. 

 It was one of those suggestions which are perpetually thrown out 

 by men of science during the course of an investigation, and the 

 fulfilment or non-fulfilment of which cannot materially affect the 

 merits of the investigator. Indeed, the merits of Forbes must 

 be judged on far broader grounds ; and the more his labours are 

 compared with those of other observers, the more prominently does 

 his comparative intellectual magnitude come forward. The speaker 

 would not content himself with saying that the book of Prof. Forbes 

 was the best book which had been written upon the subject. The 

 qualities of mind, and the physical culture invested in that excellent 

 work, were such as to make it, in the estimation of the physical 

 investigator at least, outweigh all other books upon the subject 

 taken together. While thus acknowledging its merits, let a free and 

 frank comparison of its statements with facts be instituted. To 

 test whether the Glacier du Gt^ant moved quicker than its fellows, five 

 different lines were set out across the Mer-de-Glace, in the vicinity 

 of the Montenvert, and in each of these it was found that the point 

 of swiftest motion did not lie upon the Glacier du GtJant at all ; 

 but was displaced so as to bring it comparatively close to the 

 eastern side of the glacier. These measurements prove that the 

 statement referred to is untenable ; but the deviation of the point 

 of swiftest motion from the centre of the glacier will doubtless be 

 regarded by Prof. Forbes as of far greater importance to his theory. 

 At the place where these measurements were made, the glacier 

 turns its convex curvature to the eastern side of the valley, being 

 concave towards the Montenvert. Let us take a bolder analogy 

 than even that suggested in the explanation of Forbes, wliere lie 

 compares the Glacier du Geant to a strong and swiftly flowing 

 river. Let us inquire how a river would behave in sweeping round 

 a curve similar to that here existing. The point of swiftest motion 



