MR. MILWARD ON DIRT-BANDS IN GLACIERS. 263 



disappearance of the snow, and before the confusion of the surface 

 occasioned by the sun's influence. 



u 1. It has been suggested to me, that in the case of the mud-slide, 

 there maybe an original difference of consistency in the bands of mud, 

 which is only increased by the action of the drainage water ; and that 

 the ridges and intervals are the outcropping of these beds which com- 

 pose the mud-stream. If there be such a tendency in viscous fluids 

 to separate into beds of different consistency, such a difference of con- 

 sistency may exist in glaciers, although the actual ridges may never 

 be sufficiently developed to be apparent. Such a peculiarity of viscous 

 structure would account for the bands of porous and compact ice, 

 whether the ridges be found or not. 



" At present, however, we have no proof of such an internal struc- 

 ture, and may therefore dismiss it. 



" 2. If, however, ridges or waves are found to exist, the case be- 

 comes precisely analogous to that of the mud-slide : The lower extre- 

 mity of each ridge will be more broken up than the other parts, just 

 as we see the ridges and lower extremities of the several mud-streams 

 to be broken up and more porous. From these high and broken 

 parts, the water will drain and saturate, to a greater extent, the sur- 

 faces below. The ice thus saturated will become, by the action of 

 frost, more compact than the rougher ridges. This fact, that satu- 

 rated ice produces the most compact glacier, appears to have been 

 already assumed (either from experience or otherwise), in the explanation 

 which is given of the formation of the transparent blue bands of the 

 ribbon -structure. An objection to which this explanation is open, 

 will be found in the very different width of the porous and compact 

 bands on the glacier ; whereas in the mud-slide they are nearly equal. 



" In any case, however, it seems that there is sufficient ground why 

 we should look for such ridges or waves ; but at the same time, it is 

 quite possible that they may be proper to a peculiar condition of vis- 

 cous matter, to which class the glacier does not belong, or it may be 

 that special resistance and obstruction prevents the development of 

 such peculiarity in the case of glaciers. If this be so, the direct ana- 

 logy between the glacier and the mud-slide in this respect vanishes. 



" 3. From the manner in which the second mud-slide explains the 

 first, depending, it will be remembered on the drainage of water 

 altering the character of the mud another deduction may, I think, 

 be drawn as applicable to glaciers, although not exactly in the same 

 way. The result to which I am about to draw your attention musf, 



