1846.] GRADATIONS OF DISCONTINUITY IN GLACIERS. 163 



4. In very wide glaciers, moving with feeble velocities, the 

 veined structure is slightly developed, except near the sides, 

 simply because the twist being small the ice is hardly bruised. 

 Nor can we wonder to find the structure at the distance of 

 many hundred yards from the sides of a vast slow-moving 

 glacier of this description, if developed at all, to be complex 

 and irregular, exhibiting twists such as I have figured in my 

 Travels, p. 164, and which are peculiarly conspicuous in the 

 magnificent glacier of Aletsch. This circumstance finds a pre- 

 cise analogue in the case of a great river, such as the Rhine, 

 or indeed in any river moving with a very slight inclination ; 

 the excess of velocity of the central above the lateral parts, 

 not very great at any rate, is distributed over such a space 

 that the slightest casual disturbance of the current, from an 

 irregularity in the bottom or sinuosities of the course, pro- 

 duces local differences of velocity, occasioning ripples and eddies 

 in various parts of the breadth. If these ripples and eddies, 

 in other words, differential motions of adjacent particles, could 

 be visibly represented by using differently coloured fluids, they 

 would undoubtedly afford sections exhibiting undulations and 

 contortions exactly like those which the ice presents in the 

 cases mentioned above. We claim therefore the apparent 

 exception as a real proof of our general rule. 



5. In the neve proper, no true veined structure is developed ; 

 first, Because, whilst the mass is snowy, its powdery nature 

 yields without admitting of a fracture or bruise ; secondly, 

 Because the true neve has rarely any lateral compression worth 

 mentioning, being widely spread, and not contained between 

 steep barriers ; thirdly, Because its motion is altogether very 

 small; lastly, Because its extreme dryness does not afford water 

 enough to percolate its substance and there to be frozen ; * 

 when it does so, it ceases to be neve. 



On these grounds I hope that the theory of the veined 



* [Or, according to the view which 1 first adopted on a renewed examination of 

 the glacier in 1846 (a few months after these pages were written), because moisture 

 and pressure, combined with internal friction, had not moulded the granules of the 

 snow into a uniform consistence. See Letter Thirteenth, below.] 



