138 A. Milward, Esq., on the 



passed more quickly down them will accumulate to a greater 

 extent than if there had been no elevation behind, on account 

 of the change of inclination. Now, during the summer 

 months, the saturation thus taking place will be greatest, 

 because of the large quantity of water then coming down. 

 At this period of the year, likewise, the motion of the glacier 

 is also greatest, and a large advance of the saturated body 

 occurs. This, during the winter frosts, is consolidated, and 

 formed, I imagine, into more compact ice than would have 

 resulted from less saturated material. 



On the other hand, in the winter months, that part of the 

 glacier at the foot of the upper slopes, or ice- cascades, will 

 be less saturated, as the surface of the whole glacier is then in 

 a state of comparative rest, in consequence of the diminished 

 effect of the sun's rays in thawing the surface of the neve. 

 At this time, also, the glacier moves with far less rapidity ; 

 and so the quantity of glacier in a less saturated state thus 

 moving on, will be considerably less than that advancing 

 during the summer. In consequence, also, of its being less 

 saturated with water, it will, after consolidation, be less com- 

 pact than that which moved forward during the summer. 

 Viewed in this light, the foot of the upper slopes, or ice-cas- 

 cades, may be considered as a kind of laboratory for the ma- 

 nufacture of alternate bands of compact and porous ice, — the 

 former made during the summer, and the latter in the winter 

 months. Thus, if my theory be correct, a wide band of com- 

 paratively compact ice, and a narrow band of porous ice, will 

 be annually formed and added to the glacier. 



If these alternate bands be considered as identical with the 

 porous and compact bands to which the dirt-bands belong, it 

 follows, that the porous bands, during the progress down the 

 glacier, become apparent by the absorption of the drift, which 

 is washed over the surface, and their distinctness increases 

 with the length of time during which they have been sub- 

 jected to the drift. 



Thus the wide compact band answers to the interval be- 

 tween the " dirt-bands,'' and the narrow porous band to the 

 " dirt- band" itself. The one owes its formation to the sum- 

 mer, the other to the winter. 



