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is by no means established tbat the cold of winter can reach to 

 depths sufficient to produce the blue veins, which are affirmed to be a 

 portion " of the inmost structure" of the glacier. Again, the lamina- 

 tion in some cases presents itself in the form of transparent lenticular 

 masses, imbedded in the general substance of the white ice. The 

 differential motion referred to would be mechanically inadequate to 

 produce detached cavities corresponding to these masses, which 

 vary greatly in size, and in some cases accurately resemble the 

 greenish spots seen in slate rock when a section perpendicular to the 

 cleavage is exposed. Further, as the fissures are produced by the 

 motion of the glacier, and as this motion takes place both in summer 

 and winter, it is to be inferred that they are formed at both seasons 

 of the year. But if formed in winter, they cannot be filled and 

 frozen that season for want of water ; and, if formed in summer, 

 they cannot be frozen while summer continues for want of cold. 

 Hence, at the end of each summer there ought, if the above theory 

 be correct, to be a whole year's unfrozen fissures in the ice. Such 

 fissures could not possibly escape observation if they existed ; but 

 they never have been observed, hence it is inferred that they have 

 no existence. With regard to the drag towards the centre of the 

 glacier, it is observed, that if such a drag existed, the centre would 

 ultimately absorb the sides, unless the loss were made good by a 

 motion in some part of the glacier, from the centre towards the 

 sides, which would be in opposition to the theory. Experiments 

 are described which prove that no such drag exists, and the actual 

 motion observed is reduced to its elementary mechanical principles. 

 "With regard to the transverse lamination at the centre of the glacier, 

 the hypothesis involves, among others, the difficulty of supposing 

 that fissures can be formed in a mass assumed to be viscous, at right 

 angles to the direction of an enormous pressure to which the mass is 

 subjected. 



An attempt is next made to apply the theory of slaty cleavage, 

 propounded by one of the authors, to the laminated structure of 

 glacier ice. It is shown that this lamination, like that of slate rock, 

 is always approximately at right angles to the direction of maximum 

 pressure ; that local circumstances which give rise to a violent 

 thrust, produce at the same time a highly developed lamination. 

 "When two confluent glaciers unite to form a single trunk, the effect 



