134 A. Milward, Esq., on the 



but there are not at present sufficient data for investigating 

 the effects of any such difference of viscous nature. After 

 the surface has been long dry, experience shews that the 

 lower parts may be very wet, and leads us to conclude, that 

 the establishment of an equilibrium does sometimes result 

 from that fact. It is matter for investigation and discussion, 

 how far this and the preceding remarks may, or may not, be 

 applicable to glacial motion. I trust that the careful illus- 

 tration of an actual phenomenon — important in itself and in 

 its bearings — may be found of sufficient interest to justify 

 me in having thus trespassed upon the time and attention of 

 the Section. 



An Attempt to illustrate the Origin of " Dirt-hands^^ in Gla- 

 ciers. By A. Milward, Esq. Communicated by the 

 Author. 



It will be remembered, that Professor Forbes, in his inte- 

 resting work on the Glaciers of the Alps, describes the " dirt- 

 bands" to be nothing more than curved bands of porous ice, 

 the surface of which affords a readier receptacle to the drift 

 of the glacier. He found the dirt to be superficial, and merely 

 an indication that the glacier is made up of two kinds of ice, 

 the one more porous than the other ; so that the dirt lodges 

 in the one more readily than in the other. The question to 

 be determined is, how we are to account for the existence of 

 the different kinds of ice thus regularly alternating. The dirt 

 being merely accidental to this subject of inquiry, it will be 

 better to speak of the dirt-bands, and the intervals between 

 them, as the alternating bands of porous and compact 

 ice.* 



The dirt -bands are found to follow the direction of the hy- 

 perbolic curves marked out by the outcrop of the structural 

 planes, — known by the name of the ribbon-structure. The 

 ice forming the dirt-bands is made up of that structure, in 

 the same way as the other ice ; and depends, of course, upon 



* These terms are, of course, only relative. 



