lie M. do Beaumont on the Glacier Thco'y. 



by the slight inclination of the lino. Althongh the amount is 

 but little, yet the upper limit of the erratic zone is sensibly 

 inclined ; and this limit is formed by a surface which gradually 

 sinks from the centre of the mountainous region towards its 

 edges, cutting the flanks of the mountains in lines very dif- 

 ferent from horizontal ones. 



The knowledge of the inclination of the upper limit of the 

 erratic zone, is one of the most essential elements of the pro- 

 blem to which the erratic phenomena have given rise. It is 

 a bed of Procrustes, in which all the theories that may be pro- 

 pounded on the subject must necessarily be tested. 



We are now in possession of many data as to the absolute 

 height of the upper level of the traces of the erratic pheno- 

 mena ; but these heights have rarely been combined with the 

 horizontal distances of the points to which they refer, so as to 

 admit of the inclination of the surface-limit being deduced. I 

 have made this calculation for the valley of the Rhone from 

 the Grimsel to the Lake of Geneva ; for the valley of the 

 Drance from the Saint-Bernard to Martigny ; and for the por- 

 tion of the basin of Lower Switzerland over which the erratic 

 phenomenon of the Valais extends. I have also made it for 

 some parts of the valley of the Aar. Perhaps the publication 

 of these numerical results may cause the publication of ana- 

 logous calculations for the other valleys of the Alps, and for 

 those of the Pyrenees, the Vosges, &c. The following is the 

 table :— 



Height of the Upper Limit of the Erratic Zone. 



Mot res. 



Near the Col du Grimsel (about), .... 2300 



Near iErncn (Valais) (Charpcnticr), .... 1813 



In tlic basin of Brieg, ...... 1520 



In the vicinity of Martigny, ..... 1450 



Near the Great Saint-Bernard (about), .... 2500 



At the Mountain of Plan-y-beuf (Charpentier), . . 17C9 



Above Monthey, ..... . 1157 



At the rocks of Mimisse, . . . . . 1025 



At the huts of Playau, ...... 1222 



On the slope of Chasscron (Jura), .... 1050 



Gi.'neva (the Lake), ...... 375 



Neve of Ober-Aar (limit of the roches montonnees), . . 2924 



Grimsel (the Col itself), ...... 2200 



Biunig (the CoOj • • • • . 11G3 



