110 M. do 13oa\imont on lite Glacier T/icoiy. 



by tlie slight inclination of the lino. Although the amount is 

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

 inclined ; and this limit is foi-nicd 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 l>c'(l of Procrustes, in which all the theories that may be pro- 

 pounded on the suliject must necessarily be tested. 



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

 height of the upper level of the ti'aces of the ei'ratic 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 dedviced. 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 :— 



Helfjlit of the Upi)cr Limit of the Erratic Zone. 



jri'tros. 



Nc.ir the Col du Grimsel (about), .... 2.300 



Near yErncn (Valais) (Cliarpcntier), .... 1813 



In the basin of Brieg, ...... 1520 



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



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



At the Mountain of Plan-y-beuf(Cliarpentier), . . 17G9 



Above Monthey, ..... . 1157 



At the rocks of jNIimlsse, . . . . . 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 tlic rochesi moutoniv'uft), . . 2924 



Grimtcl (the Col itsdf), ...... 2200 



Brunig (the CoO» • • • • .1103 



