Beport of the Besearches of M. Agamz. 157 



that, as to accuracy of execution, it may safely be placed by the 

 side of the most beautiful specimens of mapping of our age. 

 Not only are all the features of the glacier, which the scale 

 permits, indicated with the greatest precision, but what will 

 render it peculiarly valuable to all the observers of glaciers, 

 M. Wild has thereon determined the position of quite a net- 

 work of the blocks distributed on the surface of the glacier. 

 These blocks, to the number of eighteen, are all associated 

 with fixed points in the valley, so that, in time coming, every 

 one may, by examining these points, ascertain how much any 

 part of the glacier has advanced within a given period. 



In addition to the general map, M. Agassiz has also caused 

 to be represented, a transversal band, 500 feet in width, 

 across the glacier, in a locality where it is very much crevassed. 

 This band, which has been measured and levelled by M. Wild 

 with the greatest accuracy, has been prepared on a very large 

 scale, amounting to one two-thousandth part, so as to exhibit 

 the most minute details. Not only are all the crevasses in- 

 dicated upon it, but their relative form and dimensions are ac- 

 curately measured, so that it may be easily ascertained, in the 

 ensuing summer, what changes they have undergone, if they 

 advance vi^ith the entire mass, or if they arrange themselves 

 anew, or finally, if new ones occupy their place. Should this 

 last alternative be the case, it would be demonstrated that the 

 form of the crevasses depends essentially upon the windings and 

 irregularities of the valley. This, in fact, has for long been the 

 general supposition, though nothing like a demonstration has 

 been supplied. Accordingly, it seems quite natural that Pro- 

 fessor Forbes should have adopted this opinion, but we have 

 been astonished that this philosopher, who very properly looks 

 for exactitude in every thing, has propounded this opinion as a 

 fact, since, having made only one sojourn on the Merde Glace, 

 it is impossible he could have obtained positive results from 

 observations which require to be verified for a succession of 

 years. 



This same band, 500 feet wide, may be made subservient 

 to the supply of positive information, respecting another and 

 not less remarkable particular, namely, concerning the me- 



