180 BOARD OF AGRICULTURE. 



to explain, that the northern ice-fields move southward, not 

 because they are resting on a surface inclining from the north 

 southward, but owing to the fact that it is colder further jiorth 

 than further south. Further north there is more snow accu- 

 mulating, further south there is more ice forming, in conse- 

 quence of the frequent thawing and freezing, and these alter- 

 nations of thawing and freezing. That is, from the north 

 southwards, we have all the conditions which we have very 

 high up and down in an Alpine valley. There is one fact 

 to show us that this is unquestionably so. Every year the 

 Atlantic is covered by icebergs. Now, these icebergs are not 

 frozen sea-water ; they are masses of arctic land ice, which 

 advance to the ocean by their own periodical movement, and 

 which, when pushed over into the ocean, having no further 

 support, break off from the land ice, and are floated south. 

 That is the origin of icebergs. The fact has been observed 

 by all Arctic travellers. It has been satisfactorily observed 

 off Spitzbergen by a friend of mine, who knew the glaciers 

 before going there, and who saw these glacier icebergs break 

 off from the land ice, which had its own movement, similar to 

 the movement of the glaciers of the Alps. 



Now, what is such a mass of ice doing in the way of mechan- 

 ical work, while it moves in that manner ? What is the 

 mechanical work done annually by the glaciers of the Alps in 

 their descent from the higher mountains to the lower valleys in 

 which they terminate. Mount Blanc, fifteen thousand feet high, 

 is on all sides covered at the summit with snow ; further down, 

 with glaciers which terminate in the valley of Chamouni. In 

 the valleys on the southern side, we find glaciers, the lower 

 ends of which are only three thousand feet above the level of 

 the sea. They are masses of ice which have come down eleven 

 or twelve thousand feet, from the summit of the mountain down 

 to the valley. You find the glacier of the Grindelwald, and all 

 the other glaciers of Switzerland, commencing at heights vary- 

 ing from twelve to fifteen thousand feet, and terminating in the 

 valley, at heights of five, four, or three thousand feet above the 

 level of the sea. 



Now, these glaciers, when they come down, are all the time 

 rubbing over the surface of the rocks, and rubbing, bruising, 

 crushing, polishing, and grinding, in a very efficient manner, 



