168 BOA.RD OF AGRICULTURE. 



materials underneath, but yet carried forward down into the 

 valley ; and how far they have travelled can be ascertained by 

 tracking the varieties of rocks to their origin. You will find in 

 these walls a combination of granitic materials mixed with black 

 slate, and wherever there is any particular rock there is no diffi- 

 culty in tracking it to its place. In the glacier of the Aar I 

 have tracked some of these rocks from the point where they 

 broke loose to a distance of seventeen miles upon the sides of 

 the glacier. To that extent the evidence of the precipitation of 

 this loose mass by the glacier was as direct as could be. 



But it is not at the lower end of the glacier that these loose 

 materials stop. We find them further out. You will find tliis 

 same black slate down the bank of the Aar, at Meyringen, 

 which is about twenty miles from the end of the glacier ; so that 

 we have here evidence that these loose materials have been car- 

 ried thirty-eight miles, to Meyringen, by the agency of ice ; for 

 through the whole length of the valley you may track these pol- 

 ished, grooved and scratched surfaces to the very place to which 

 I have just alluded. 



One word more about the glacier itself. At a certain level, 

 where the atmospheric currents are so warm as to counterbal- 

 ance the onward movement of the ice, it melts away, so that the 

 glacier begins as snow, that snow is transformed into loose ice, 

 is finally transformed into solid ice, and at a certain level it 

 melts as water and forms a stream, which flows further on ; so 

 that in the glacier we have three stages — the snow stage, the ice 

 stage and the water stage. Now the water, when it begins to 

 flow, acts upon the loose materials which have been ground by 

 the ice, and the manner in which those materials may be rolled 

 tends to lessen the distinctive marks which had been impressed 

 upon them by the glacier, so that at some distance the amount 

 of pebbles that are polished and scratched is greatly less ; and 

 when these materials have been worn by the current for a long 

 time they cease to have, to the same extent, that uniform char- 

 acter, showing plainly that the current is not the cause of the 

 appearances which we observe on the loose materials higher up, 

 since the action of the current is to efface those marks. 



Besides these walls of loose materials on the side of the gla- 

 cier, we have still another appearance. Suppose that we have 

 two glaciers, coming from two mountains, and uniting into one. 



