LAMINATION DUE TO DIFFERENTIAL MOTION. 257 



the quasi-fluid character of the motion impressed upon it. 

 That it is so is evident not only from the direction of the 

 lamine, but from their becoming distinct exactly in proportion 

 to their nearness to the point where the bruise is necessarily 

 strongest.* 



This observation sufficiently illustrates the general fact, 

 that the veined structure appears most vividly in a direction 

 parallel to the sides of glaciers, being caused by the friction of 

 the rocky shore compelling a forced molecular separation of the 

 middle parts from the side parts of the glacier. 



But we have seen (p. 246) that the direction of the hori- 

 zontal section of these laminae gradually inclines inwards, so as 

 to form loops on the surface of the glacier. The portion of 

 these loops next to the shore, which is at first parallel to the 

 shore, but which gradually inclines towards the axis or middle 

 of the glacier, is conceived to be owing to the differential 

 motion of the parts retarded by lateral friction, as in the case 

 of the Glacier of La Brenva just mentioned. But, moreover, 

 the opposing resistance of the shore-ice immediately in front 

 will give a tendency to molecular dislocation in a direction 

 sloping towards the middle of the glacier, where the current 

 moves fastest, in consequence of the friction being less. When 

 we arrive at a distance from the shore comparable to the depth 

 of the ice, then the friction due to the led of the glacier com- 

 municated through its plastic layers to the surface combines 

 with the lateral friction in determining the lamination in a 

 direction at once upwards and towards the middle ; and when 

 we reach the middle region of the ice, the lamination takes 

 place entirely in the vertical plane, completing the spoon-shaped 

 arrangement of those surfaces of dislocation, of which the form 

 has already been illustrated at p. 247. The particles are 

 supposed to be acted on by a force partaking of the nature of 



* Twelfth Letter on Glaciers. Edinburgh Philosophical Journal, 1847, where 

 the details of the observation are illustrated by a figure. [Reprinted in this 

 volume, p. 182.] 



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