1848.] ORIGIN OF THE WRINKLES ON THE GLACIER. 217 



ample stream which furnishes it. We perceive here nothing 

 like an annual recurrence ; and this circumstance at first puzzled 

 me, the intervals between the dirt-bands of the Mer de Glace 

 (which are evidently the same with the wrinkles) being, as ob- 

 served by me at the very time of their first discovery, so nearly 

 consistent with what I supposed to be the annual motion of the 

 ice stream, and which was afterwards -confirmed by direct 

 experiment, as scarcely to allow us to suppose the coincidence 

 fortuitous. 



But an easy experiment establishes the analogy perfectly. 

 If the stream of plastic matter already supposed be not uniformly 

 supplied, but arrive in gushes, every such overflow, by the rapid 

 rise of the head, throws off a wrinkle in the most regular manner. 

 So that, for example, on examining those plaster models, for- 

 merly repeatedly described by me, in which cupfuls of white 

 and of blue plaster of Paris were alternately poured down an in- 

 clined channel, each separate flow was found to constitute a 

 wave or crease. In a glacier, especially in its higher regions, 

 the difference of summer and of winter velocity is sufficient to 

 produce what may be called (relatively) a gush ; and I suppose 

 that the wrinkles are formed in most glaciers at the foot of the 

 steeps of the neve (as Mr. Mil ward also believes), where a pres- 

 sure d tergo is produced by the heat of the short summer, suf- 

 ficient to overcome the incalculable resistance which a mass of 

 half-frozen snow, hundreds of feet thick and hundreds of yards 

 wide, presents, to be squeezed and moulded, after the manner 

 of a semifluid, into a convex wrinkle. Of the fact there is no 

 doubt. Each wrinkle, then, is nothing else than a local swel- 

 ling, such as those figured by M. Collin, taking place at the 

 moment when the upward and forward force due to the quasi- 

 hydrostatic pressure of the mass becomes insupportable, and 

 gives rise to the forced separation of the cohering substance by 

 countless fissures, constituting the frontal dip of the veined 

 structure of the glacier, whose position, taken in connection with 

 the wrinkles, is shewn in Plate IX. fig. 5. 



I farther beg leave to direct your attention to a very 



