64 EIGHTH LETTER ON GLACIERS. [1844. 



where the ice is extremely flat and compact for a space of about 

 seventy yards in width, and several hundred yards in length, 

 which is wholly devoid of open crevasses, and where I expected 

 to find the variation of velocity from the side towards the centre 

 very sensible, because the veined structure is there more per- 

 fectly developed than in any other part of the glacier. In this 

 anticipation I was not disappointed. The ice in question is 

 separated from the western moraine of the glacier by a space 

 deeply crevassed 50 or 60 yards wide. The entire breadth of 

 the glacier is here at least 800 yards. The central part has 

 great transversal crevasses due to the rapid descent of the 

 glacier where it sweeps round the promontory of Trelaporte 

 immediately above. There is no trace of longitudinal fissures 

 of any kind, except the true blue veined or ribboned structure, 

 which, as already mentioned, is here exceedingly developed ; 

 giving to the even part of the glacier already specified the 

 appearance of exquisite veined chalcedony of an aqua-marine 

 colour ; and the vertical plates of ice thus subdivided are so 

 distinct as to produce a true cleavage when the ice is broken by 

 a hammer or cut with an axe. When the glacier is wet, the 

 blade of a knife may be introduced to a depth of some inches 

 between the laminae, which are commonly not more than a 

 quarter of an inch apart. 



I fixed in a line transverse to the axis of the glacier six 

 stations. Over the first of these the theodolite was regularly 

 centred, in order to observe the relative motions of the others, 

 which were respectively 30, 60, 90, 120, and 180 feet distant. 

 Finding that, even in the course of a single day, the accelera- 

 tion of the more central parts was evident, and the six points 

 in question formed a portion of a continuous curve, I subdi- 

 vided the first 90 feet from the theodolite into 45 spaces of 2 

 feet, each of which was marked by a perforation in the ice 

 into which short pins could be accurately fitted, and the de- 

 formation of this straight line of 90 feet in length was carefully 

 observed at short intervals. The errors of the original places 

 of the marks were determined by a simple but nice process, and 



