LECTURES. 57 



they are composed of ice crystals, the ice becoming 

 more and more compact as you go downwards; until 

 the bottom is clear, solid ice. Snow when re- 

 solved into fine granules is called neve: where this 

 changes to ice is called 'the limit of perpetual snow.' 

 Physical geographies are incorrect in their state- 

 ments of the snow-level on the Straits of Magellan 

 and many other places. Similar conditions are found 

 at the same line of perpetual snow; they are also 

 similar in the same number of degrees distant in dif- 

 ferent localities. Glacial ice differs from common 

 ice, the first is composed of ice crystals melted to- 

 gether and can be reduced to powder, the latter is 

 formed in layers. Glaciers possess a motion in them- 

 selves which is both an upward and a downward mo- 

 tion; it is greatest in the middle, and least upon the 

 edges. Moving ice, therefore, exerts a great power. 

 As the glacier moves, it collects a large quantity of 

 loose materials which it carries along with it. Part 

 of this material over-crowds itself and forms a low 

 line of rocks on either side of the glacier: these lines 

 are called lateral moraines. When two glaciers or 

 two arms of the same glacier unite, they continue as 

 one, while their lateral moraines unite and form a 

 medial moraine. The bottoms of glaciers, then, be- 

 ing covered with rocks, act like an immense rasp. 

 In passing over walls of rocks, or open faces of ex- 

 posed ledges, both the upper faces of the under 

 rocks, and the under faces of the upper rocks, which 

 are in the glacier, are scratched and scarred alike. 

 Yet the rocks which are in the glacier will still be an- 

 gular above where only the ice covers them. Now 

 the continual motion of the ice pushes forward the 

 larger rocks, and at the same time all the loose ma- 

 terial is ground still finer; and each pebble rounded 

 in a manner which is never produced by water. 

 Thus the moraines are ground more and more as 

 they advance, so that, whatever their shape may at 

 first be they come out, at the end of the glacier, 

 rounded material; and when the glacier begins to 



