262 APPENDIX, NO. I. 



" It was the remarkable similarity of the alternating bands on the 

 mud-slide already described, to the ' dirt-bands ' on Professor Forbes' 

 map of the Mer de Glace, that induced me to take an interest in the 

 matter, and make a drawing of the phenomenon. In the first instance, 

 the curved bands were a mystery to me ; and I could not venture to 

 found any argument on a mere analogy of appearance. The second 

 mud-slide, however, seemed to shew me another step in the process ; 

 and, having explained the one from the other, I was led to ask myself 

 whether the phenomena, to which one class of viscous fluids appeared 

 to be subject, might not be common to another ; in other words, to a 

 glacier. 



" In our first mud-slide we observe, first, the occurrence of curved 

 bands ; and, secondly, a difference of consistency in those bands. Our 

 second mud-slide shews the origin of those curved bands, as far as 

 mud-slides are concerned, to be the previous existence of ridges or 

 wrinkles. Turning, on the other hand, to the glacier, we find curved 

 bands of different consistency and similar appearance, which I have 

 called relatively bands of porous and compact ice. 



" We may then fairly ask, If, in one species of viscous fluid, 

 alternate bands are derived from pre-existing ridges, why should not 

 analogous bands in another species of viscous fluid give rise to a prima 

 facie presumption, that ridges are to be looked for in an earlier stage 

 of that viscous fluid also ? Is not the analogy just so far strong 

 enough as to induce us to examine whether there is any trace of such 

 ridges or waves ; and, if so, whether their correspondence with the 

 alternations of porous and compact ice is sufficient to account for the 

 latter ? 



" It is evident that such ridges or waves, if they do exist, must be 

 very slightly marked, or they would not have been overlooked ; but 

 then, it is to be remembered, that the difference between the two kinds 

 of ice is also very slight in fact, only barely apparent. It will be 

 useless to look for them at the lower parts of glaciers, as they will 

 have disappeared under the effects of atmospheric and other action 

 through the lapse of many years, which will have degraded any exist- 

 ing ridges, just in the same way as in the case of outcropping strata. 



" There is also a tendency to the establishment of an equilibrium as 

 to elevation, to say nothing of the disturbing effect of the lateral 

 friction. It is, therefore, towards the head of the glacier, where the 

 true glacial structure commences, that we are to look for such ridges : 

 the best time, also, will be at the commencement of summer, after the 



