THE POLAR GLACIERS. 37 



to produce such an arrangement and diversity of soils and such 

 a peculiar outline of country as no other agency could ever have 

 brought about. So different is the nature and work of the great 

 polar glacier from anything with which we are familiar at the 

 present day, that it has seemed to me to require a few words of 

 more particular description. 



As is well known, the glacier is an accumulation of many win- 

 ters' snows, consolidated by pressure into a clear blue ice. In this 

 condition it manifests the peculiar property of viscous bodies 

 it is in continual slow motion in the direction of least resistance. 

 Whether it is by the expansion produced by the repeated thaw- 

 ing and freezing of water in its interstices, as Agassiz claimed, or 

 whether by the pressure of the mass and glacial regelation, which 

 is the constant freezing together of ice-surfaces in contact, after 

 breaking under unequal pressures, or crushing against obstacles, 

 which is the theory of Prof. Tyndall, or whether by both causes 

 combined, certain it is that large bodies of ice not only flow like 

 a heavy lava-stream, conforming themselves to all inequalities of 

 the surface, but they also scrape along in solid mass, as if pushed 

 by some irresistible force from behind. Mountain-glaciers show 

 both motions. But the great polar glacier, extending over com- 

 paratively level surfaces, seems to have been pushed bodily out- 

 ward from its fixed polar base, and to have moved almost entirely 

 under the mighty impulse of expansion. The parallel scratches 

 and furrows which, in our hemisphere, mount straight up the 

 north sides of mountains; the worn and rounded appearance of 

 those sides and of the summits, as compared with the rough, un- 

 smoothed southern slopes ; the erratic blocks, or some peculiar 

 specimens like the native copper of Lake Superior, carried almost 

 directly south for scores or hundreds of miles, over heights, and 

 even over arms of the sea all show conclusively that the great 

 glacier pushed its meridional course over all obstacles and to long 

 distances. 



Imbedding in its under surface the grit and gravel on which it 

 froze, the mountain grindstone grated and ground the solid rocks 

 over which it passed into the various materials of soil. Sand and 

 gravel were the products from granitic rocks and sandstones, clay 



