320 M. A. Guyot on (he 



which was to search for the prhnitive situations of the erratic 

 blocks of the basin of the Rhone. 



He first remarked that the portion of the Alps comprised 

 between Mont Blanc and Mont Rosa, or rather between 

 Col du St Bernard and that of the Simplon, constituted the 

 most elevated, most continuous, and most gigantic masses of 

 the Hautes Alps. Its enormous breadth of base, the mean 

 elevation of its cols and ridges, the height and number of its 

 pics and aiguilles, surpass any thing of the same kind to be 

 found in the celebrated masses of the Bernese Oberland, the 

 Orteler, Oetzthaler-Fernei*, and of Mont Blanc itself. 



The group of Mont Rosa in particular, composed of the three 

 chains of Mont Rosa, the Saasgrat, and the "Weisshorn, -in the 

 centre of which lies the valley of Zermatt, brings together in 

 a limited space from twenty to thirty peaks, all of which mea- 

 sure from 12,000 to 14,000 feet high. The ridge itself of this 

 part of the Alps presents only immense fields of snow whence 

 numerous glaciers descend ; it is with difficulty accessible, 

 and the wild valleys that lead to it are so uninviting to the 

 traveller, that these regions, although situate in the very 

 centre of Europe, have hitherto remained almost unknown. 

 The best maps of Switzerland which we possess, although 

 corrected of late years in some particulars, still present us 

 with a very rough, and often altogether inaccurate, represen- 

 tation of these regions. 



After ascending the valley of Salvan, and again observing in 

 this classical region the montonneed rocks, and furrowed and 

 striated rocks, which indicate the passage of ancient glaciers, 

 M. Guyot, ascending the Col de Balme, again collected the 

 diverse varieties of granite which descend from the numerous 

 aiguilles of Mont Blanc, by the glaciers of Tour, Argentiere, 

 and Des Bois. 



The complete identity of these varieties with those that 

 compose the majority of the blocks scattered on the sides of 

 the Jiu"a, fully convinced him of the truth of what he had for- 

 merly advanced, namely, that it is from the western declivity of 

 the Mont Blanc chain that the greater part of the Jura blocks 

 are derived, while the varieties less talcose, and with a more 

 equal granular structure, come principally from the Val Fer- 



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