WHAT IS A GLACIER? H 



away. It is largely owing to this that a true terminal 

 moraine is made up of knolls and bowl-shaped depressions 

 called kettle-holes, and of short tortuous ridges of bowlders 

 and gravel. 



Another result connected with the decay of a glacier is 

 the production of kames — this being the Scotch word for 

 sharp, narrow ridges of gravel, corresponding to what are 

 called osars in Sweden and eskers in Ireland. The trend of 

 these ridges is the same as that of the motion of the glacier, 

 and is at right angles to the terminal moraine. Their for- 

 mation can be witnessed on a large scale near the front of 

 the Muir Glacier in Alaska. In certain localities a great 

 amount of sand, gravel, and bowlders becomes spread out 

 over the surface of the ice at a considerable elevation. 

 Through some changes in the subglacial drainage a stream 

 wears a long tunnel in the ice underneath this deposit, 

 which at length proceeds so far that the roof caves in, and 

 the earthy debris is gradually precipitated to the bottom 

 of the tunnel, thus forming one class of kames. In other 

 places, evidently, water- worn channels in the ice have been 

 silted up by the stream, and then the line of drainage 

 changed, so that, when the supporting walls of ice melted 

 away, another class of kames, with what is called " anticli- 

 nal " stratification, is produced. 



It should be mentioned also that, after the analogy of a 

 river, a glacier shoves sand and gravel and bowlders under- 

 neath it along its bed ; from which it can easily be seen that 

 a glacier is a powerful eroding agency, rasping down the 

 surface over which it moves, and by the firm grasp in which 

 it holds the sand, gravel, and bowlders underneath it, pro- 

 ducing grooves and scratches and polished surfaces on the 

 rocks below, while these stones themselves will in turn be 

 scratched and polished in a peculiar manner. Wherever the 

 glaciers have receded, so that their bed can be examined, 

 these phenomena, which we reason from the nature of the 

 case must have been produced, are found actually to occur, 

 and a terminal moraine is sure to contain many pebbles and 



