THE 



EDINBURGH NEW 

 PHILOSOPHICAL JOURNAL. 



Fourth Letter on the Glacier Theory, to Professor Jameson. 

 By Professor Forbes, 



Geneva, hth October 1842. 



My Dear Sir, — Since my last letter from Zermatt, I have 

 had an opportunity of examining the glaciers on different sides 

 of Monte Rosa, particularly those of Lys and Macugnaga, and 

 those near the Valley of Saas ; and on my return to Cha- 

 mouni early in September, I devoted a day to each of the glaciers 

 of Trient and Argentiere, before resuming my station at the 

 Montanvert, where I remained until almost the last days of 

 the month. 



What I think it most interesting now to add as supplemen- 

 tary to my former statements, is not a description of these 

 various glaciers, but, with particular reference to the Mer de 

 Glace, to mention what the extended period of examination 

 which I have been able to give to it, has enabled me to con- 

 clude beyond what is contained in my previous letters, re- 

 specting the Theory of glacier-movement generally. Having 

 accurately observed the condition and motions of this glacier 

 throughout by far the greater part of the season at which it, 



VOr,. XXIV. NO. T.XVII. JAMUARY 1843. A 



