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ance is due to a series of thin plates or layers which lie 

 like a series of troughs, one within the other, in a direction 

 almost parallel to the enclosing walls and end of the glacier. 

 They are of such thinness that it is not uncommon to find three 

 or four of them in the width of an inch. This structure is not 

 due to the cause which produces the transverse loops, or any 

 mechanical cause, but in Prof. Rogers's opinion, to a true mo- 

 lecular action in the substance of the ice. He said that he had 

 before advanced the opinion that all cleavage in rocks is parallel 

 to the planes of the highest temperature. He had been greatly 

 interested in finding a precisely similar structure in glaciers under 

 the same conditions. Prof. Rogers, with a view to an explana- 

 tion of the phenomenon in question, stated a fact observed in ice 

 held for a long- time at a point just below melting. A block of 

 clear ice kept for some time at this degree of temperature loses 

 its transparency and cohesiveness, and on being struck falls to 

 pieces in a number of perpendicular, thin, columnar fragments. 

 The shape of these pieces is not due, he said, to the enlarging 

 and running together of a number of air bubbles, but it is a true 

 acicular, crystalline structure. The opacity of the ice he con- 

 sidered evidence of a change in the arrangement of its particles. 

 He thought it possible that the laminated structure of the glacier 

 of which he was speaking might arise from a similar cause. 



Dr. Jackson said he was inclined to attribute the appearances 

 in question to the action of air bubbles. Water he said, contains 

 two and one half per cent, of atmospheric air. Its presence 

 renders ice vesicular. He had never found a piece of ice with- 

 out air-bubbles, and it can only be obtained for experiments by 

 exhausting the air from the water by boiling, and rapidly freezing 

 it. As to the first looped structure spoken of by Prof. Rogers, 

 he could not understand it if Agassiz's theory were true, namely, 

 that glaciers move by the alternate freezing and thawing of water 

 in their interstices. If such were the case, then the thin glaciers 

 would move fastest, other things being equal. As the freezing 

 and thawing are the greatest on the edges, then the motion must 

 necessarily be the greatest on the edges, which is not the case. 

 The thickest are found to move the fastest, even on very slightly 

 inclined surfaces, because there is less resistance on the sides in 

 proportion to the mass. Mr. Forbes had found that glaciers 



