STATEMENT BY M. ofZANNB. 343 



one upon another in the same region, A final agitation gave to the 

 different chains of these the existing elevation; it elevated the 

 summit and opened up deep fissures or divisions, which have become 

 the valleys of the present time. From the time this occurred the 

 waters began to fashion the thalwegs, following the line which best 

 suited them; wearing down outlets and filling up basins. It is 

 necessary to admit, or to assume, that the depth or thickness of the 

 alluvial deposits in the bottom of certain valleys — for instance, those 

 of the Isere in the Graisivaudau, or of the Rhine in Alsace, — is to be 

 reckoned by hundreds, and perhaps by thousands, of metres or yards ; 

 for even yet certain lakes existing in depressions of the Alps have 

 their bottom below the level of the sea. 



" After a long series of ages the mountains assumed the leading 

 features which they now exhibit, when, the climate changing, great 

 glaciers carried on actively the work of erosion ; these have planed 

 away escarpments, and fashioned into something like horizontal lines 

 the rocky belts of the valleys. 



" Dehddes, or inundations, from the escape of the waters of pent-up 

 lakes, and deluges resulting from the tremendous rains of summers on 

 the extensive fields of ice, have carried away and deposited in the 

 principal valleys in certain favourable places, but more especially at 

 the debouches of lateral gorges, the masses of loess which have 

 formed cones in the higher plains, and in which the water-courses 

 have subsequently dug out the secondary valleys, 



" At a later period, after the melting away of those glaciers, the 

 torrents seized upon the bared mountains ; and without restraint 

 they have dug out their basins, and have again taken up the materials 

 disintegrated by the glaciers, and deposited these in the gigantic 

 cones which give to certain regions a physiognomy peculiarly their 

 own 



" But after a time the forests, spreading by degrees, stifled the 

 waters under a mantle of verdure ; the torrents became extinct, — an 

 era of peace and of compai'ative quiet supervened in the mountains ; 

 then the tribes of men, who during the glacial period rambled over 

 the low-lying plains, in company with the reindeer, the aurochs, and 

 the bears, began to spread themselves in the high-lying valleys. The 

 most ancient settlements were made at the gorges of the torrents, 

 towards the summit of the cone ; in point of fact, there are to be 

 found in the mountain valleys very few of these gorges in which we 

 do nut meet either with an existing village or with an ancient ruin. 



" Ju this location, which was then one favourable to their pursuits, 



