Mr. J. Ball on the Veined Structure of Glaciers. 367^ 



\fith alternations of maxima and minima. All that I contend 

 for is, that the subject is one important and interesting enough 

 to deserve still further illustration and experiment. With this 

 objectj I would suggest that ordinary snow, neve, and glacier 

 ice should each be subjected to powerful compression in chests 

 containing about a cubic yard, of which the sides should be 

 elastic to allow of some lateral expansion. The effects of greater 

 compression, applied for a short time, might be compared with 

 those of a lesser pressure, continued for months, or even a longer 

 time. 



It appears probable that a very considerable amount of pres- 

 sure must be necessary to produce the structure, as otherwise 

 we should more frequently find it disposed horizontally, deve- 

 loped by the pressure of the upper on the lower parts of a 

 glacier. 



To make this clear, let AB be a glacier formed by the con- 

 fluence at A of two smaller glaciers, from the mutual thrust of 

 which the veined structure will be developed in vertical planes 

 parallel to the medial moraine. At C, where the glacier lies in 

 a uniform bed with a moderate slope, that thrust will have 

 ceased to operate ; but the veined structure once created remains 

 visible, and is ]io less visible at D, a point a mile lower down 

 the glacier. But if the average rate of advance be 200 feet in 

 the year, and the average annual ablation, or removal of the 

 surface by melting, be 4 feet — both reasonable estimates — the 

 ice which we see on the surface at D must have been 104 feet 

 deep when it was under the point C. The absence of all trace 

 of horizontal structure in such positions, leads to the inference 

 that the mere pressure of the ice upon its own lower beds is not 

 in general capable of developing the veined structure. 



The same diagram will serve to suggest an explanation of a 

 difficulty felt by some observers, and which, I suspect, led even 

 Professor Forbes into a slight error. Let XY represent an ice- 

 cataract, E a point at its base, F a point further down the glacier 

 — say one mile distant from E. At E, for the reason explained 

 by I'rofcssorTyndall, the veined structure is developed across the 

 glacier, parallel to XY; but lower down, at F, it is seen in the 

 old position, parallel to the medial moraine. It is inferred that 



T2 



