150 FORESTRY OF NORWAY. 



But it is not thus that these rock lakes have been formed. 

 Of the theory of Professor Ramsay the following illustra- 

 tion is supplied by Professor Geikie : ' A river of ice is 

 not bound by the same restraints as those which determine 

 the action of a river of water. When a glacier is, as it 

 were, choked by the narrowing of its valley, the ice 

 actually rises. In such places there is necessarily an 

 enormous amount of pressure, the ice is broken into 

 yawning crevices, and the solid rocks suffer a propor- 

 tionate abrasion. The increased thickness of the mass of 

 ice at these points must augment the vertical pressure, 

 and give rise to a greater scooping of the bed of the 

 glacier. If this state of things lasts, it is plain that a 

 hollow or basin will be here ground out of the rock, and 

 that once formed, there will always be a tendency to pre- 

 serve it during the general lowering of the bottom 

 of the valley. On the retreat of the ice, owing to 

 climatal changes, this hollow, unless previously choked up 

 with sand and stones, will be filled with water, and form a 

 lake. It will be a true rock basin, with ice-worn surfaces 

 around its lip, and over its sides and bottom. 



' And such is the appearance presented by many a lake 

 and tarn in the Highlands of Scotland. One of the largest 

 and noblest of the whole Loch Awe may be taken as 

 an illustrative example.' 



Nor is it only the formation of single lakes which can be thus 

 accounted for; a continuous succession of lakes in the direc- 

 tion of the movement of the glacier may be thus produced. 

 As popular illustrations of the mode of operation I may 

 cite the following: Young boys, and girls too, amuse them- 

 selves making what they call ' ducks and drakes ' by 

 throwing flat stones across a placid sheet of water, as 

 nearly parallel to the surface of it as they can, causing 

 them to skim along and above the water, touching and 

 rising again and again, rebounding in ever-diminishing 

 bounds till they sink. The same phenomenon may be 

 seen on a larger scale in the recochetting of a cannon ball 



