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The next division of the paper treats of the veined or laminar 

 structure of glacier ice, which Prof. J. D. Forbes, in his earlier 

 writings, compared to slaty cleavage. His theory of the structure 

 is perhaps the only one which has made any profound impression, 

 and it may be briefly stated as follows. Owing to the quicker 

 flow of the centre of a glacier, a sliding of the particles of ice past 

 each other takes place ; in consequence of this sliding, fissures are 

 produced, which, when filled with water and frozen in winter, pro- 

 duce the blue veins of the glacier. To account for the obliquity of 

 the veins to the sides of the glacier, a drag towards the centre is 

 supposed to take place, producing a differential motion which results 

 in the formation of fissures. But at the centre of the glacier this 

 drag towards it cannot be supposed to exist ; and to account for the 

 veined or laminated structure of the centre, which, under normal 

 conditions, is transverse to the length of the glacier, it is supposed 

 that the thrust behind meeting an enormous resistance in front, pro- 

 duces a differential motion in a direction approximating to the verti- 

 cal, and that in consequence of this motion fissures are produced, 

 which, when filled and frozen, produce, as in the other cases, the 

 blue veins. In the present paper it is observed that the only fact 

 connected with this theory, is that of differential motion in the direc- 

 tion of the length of the glacier. Beyond this, all is conjecture. It 



refers to an observation which might be made on a fine day in summer, and 

 which would show the air within the glacier ice escaping from its surface. M. 

 Agassiz supposes the ice to be diathermanous, and that thus the sun-beams get 

 through it and heat the air-bubbles which it encloses, causing the air to expand, 

 rupture the ice, and escape in the manner observed. The observation is an 

 interesting one, whatever difficulty we may find in the explanation. An experi- 

 ment made to-day (January 31) appears to me to account for the observation in a 

 satisfactory manner. Snow having fallen, I was early at work compressing it ; 

 and on removing a plate of it from the press, I noticed, as the surface melted, a 

 sparkling motion produced by the escape of the air enclosed within the mass. 

 To imitate the action of the sun upon the glacier, an iron spatula was heated, 

 and on bringing it near the surface of the compressed snow, the jumping of the 

 surface, caused by the issue of air through the film of water which covered it, 

 was greatly augmented. On removing the spatula the motion subsided. To a 

 similar action on the part of the sun melting the surface of the glacier, and thus 

 liberating by degrees the air-bubbles with which the ice is filled, the observation 

 of M. Agassiz is in all probability to be referred. J. T. 



