174 ELEVENTH LETTER ON GLACIERS. [1840. 



mass was exceedingly compact and uniform. The terminal face 

 of compact ice was inclined, at the point selected for experi- 

 ment, at an angle of about 40 to the horizon, and the three 

 stations (1), (2), (3), were selected one above the other in a 

 vertical plane passing through this face in a direction which 

 was judged to be nearly that of the progressive motion of the 

 ice. Any variation in the motion of these three points could 

 only be imputed to the effect of the friction of the soil, for by 

 the progress of the glacier each would pass in succession verti- 

 cally over the same spot. The position was also unexcep- 

 tionable in this respect, that the glacier is here subject to no 

 extraordinary constraint. The sides are free, and the base 

 rests on a bed of rubbish and debris nearly flat, therefore 

 offering no fixed barrier to the forward motion of the ice ; the 

 retardation, if it exist, can only, therefore, be due to the legiti- 

 mate effect of friction. The glacier, too, is here seen from top 

 to bottom, for the contact with the soil is only concealed by 

 the trifling mound of rubbish not many feet in height, shewn 

 at M in fig. 4, which it presses before it ; the gravel between 

 M and X being flat, and untouched by the glacier for many 

 years. The lowest mark (1) was estimated at not less than 4 

 feet, and not exceeding 12 feet from the real base or soil of 

 the glacier. The mark (2) was 46 feet vertically above (1), 

 and No. (3) was 89 feet vertically above No. (2). From the 

 analogy of the lateral friction of glaciers, and from the phe- 

 nomena of rivers, it was anticipated that the retardation of (1) 

 upon (2), and of (2) upon (3), would be sensible, but that the 

 former would be greatest, which the results confirm. 



The progress of each point, as well in direction as in 

 amount, was rigorously determined by a trigonometrical pro- 

 cess, reference being had to two fixed stations, one of which 

 X, seen in fig. 4, was in the original plane of the points ob- 

 served, the other was 75*525 feet distant to the right hand 

 [in] fig. 3. The choice of stations was limited by the peculiar 

 local circumstances, and was not otherwise the most desirable. 

 The continual fall of blocks which bounded with great velocity 



