ON THE LAND. 221 



is atmospheric moisture sufficient to produce continuous 

 snows their great geological function is to round and 

 smooth down all rocky asperities, to round off projections, 

 and produce roches-moutonnees as they are termed, to en- 

 large and deepen rock-basins, and to grind out and furrow 

 the mountain glens down which they descend. And this 

 descent, though obstructed by inequalities of surface, or re- 

 tarded by the frosts of winter, never ceases. Cracked and 

 crevassed as the ice-mass may be by the thaw of summer, 

 hard and snow-clad as it is during the frosts of winter, it is 

 still on the move, as persistent as gravitation itself, and as 

 continuous as the snowfall by which it is created. This 

 characteristic motion is thus summed up by Principal Forbes 

 in his truly philosophical work * On the Theory of Gla- 

 ciers : ' 1. That the downward motion of the ice from the 

 mountains towards the valleys is a continuous and regular 

 motion, going on day and night without starts or stops. 

 2. That it occurs in winter as well as in summer, though 

 less in amount. 3. That it varies at all times with the 

 temperature, being less in cold than in hot weather. 4. 

 That rain and melting snow tend to accelerate the glacier 

 motion. 5. That the centre of the glacier moves faster 

 than the sides, as in the case of a river. 6. That the sur- 

 face of the glacier moves faster than the bottom, also as in 

 a river. 7. The glacier moves fastest (other things being 

 supposed alike) on steep inclinations. 8. The motion of a 

 glacier is not prevented, nor its continuity hindered, by 

 contractions of the rocky channel in which it moves, nor 

 by the inequalities of its bed. 9. The crevasses are for 

 the most part formed anew annually, the old ones disap- 

 pearing by the collapse of the ice during and after the hot 

 season. 



In the mountains of Norway, the Himalaya, and the Alps, 

 the glacier winds its way down the glens and hollows till it 



