148 'Report of the Researches of M, Agassiz. 



formation of crevasses, which propagate themselves with ex- 

 treme rapidity over an immense extent, appears to be a strong 

 objection against the theory of semi-fluidity. How, in fact, 

 is it possible to conceive a tension and rigidity, such as the 

 circumstances require, if we once admit that the glacier is 

 a semi-fluid body, moving after the manner of torrents of 

 lava % Mr Forbes attempts no explanation on this point, and 

 puts the difficulty aside. 



I have elsewhere insisted* upon the differences which exist 

 between those crevasses which are found in the middle and 

 lower parts of a glacier, and those which are encountered 

 upon the plains of the loftier snows. These latter are much 

 broader, and are generally of an elliptical shape, wide in the 

 middle, and contracted towards the extremities. They have 

 usually also a tendency to close over at the top, and are often 

 even covered over with a coating of snow. 



There is another kind of cavity which has not hitherto 

 been noticed, and whose formation is not less remarkable 

 than that of the crevasses ; I allude to those which may be 

 called the Meridian cavities. 



When we traverse a glacier, which is uniform, and but 

 little inclined, as, for example, the two glaciers of the Aar 

 and the glacier of Aletsch in their upper and middle parts, the 

 glacier of Zermatt, that of Zmutt, and many others, we en- 

 counter on their surface a number of small cavities or holes, 

 the bottoms of which are covered with gravel, and which are 

 usually from half a foot to a foot deep, with a corresponding 

 breadth, and a length extending from a foot to a foot and a 

 half, and sometimes to two feet. With these cavities we 

 were quite familiar, from having encountered many, but 

 we had never bestowed any particular attention upon them. 

 Our friend, M. F. Keller, was the first who was struck with 

 the uniformity of their shape. He remarked, that they 

 were all semicircular, and had their arc turned to the 

 north, and the chord of the arc to the south. He also 

 remarked, that to the south of each cavity, there was a heap 

 or hillock of ice, and that the greatest depth of each cavity 



* Bibl. Univ. Nov. 1841., (vol. xxxvi). Ascension de la Jungfrau. Also 

 Jameson's Journal, vol. 32. 



