SECOND VISIT TO THE GLACIER. 727 



or feet. Any investigation from the upper 

 surface would, therefore, require special ap- 

 paratus, and much more time than Agassiz 

 and his party could give. Neither was an ap- 

 proach from the side very easy. The glacier 

 arches so much in the centre, and slopes away 

 so steeply, that when one is in the lateral 

 depression between it and the mountain, one 

 faces an almost perpendicular wall of ice, 

 which blocks the vision completely. M. de 

 Pourtales measured one of the crevasses in 

 this wall, and found that it had a depth of 

 some seventy feet. Judging from the re- 

 markable convexity of the glacier, it can 

 hardly be less in the centre than two or three 

 times its thickness on the edges, — something 

 over two hundred feet, therefore. Probably 

 none of these glaciers of the Strait of Magel- 

 lan are as thick as those of Switzerland, 

 though they are often much broader. The 

 mountains are not so high, the valleys not so 

 deep, as in the Alps ; the ice is consequently 

 not packed into such confined troughs. By 

 some of the party an attempt was made to as- 

 certain the rate of movement, signals having 

 been adjusted the day before for its measure- 

 ment. During the middle of the day, it ad- 

 vanced at the rate of ten inches and a fraction 



