CHAP. XV. THEIR GREAT EXTENT. 291 



plains adjoining them, those appearances which have been 

 80 often alhided to, as distinguishing or accompanying the 

 drift, between the 50th and 70th parallels of north latitude, 

 suddenly reappear and assume, in a southern region, a truly 

 arctic development. Where the Alps are highest, the lai-gest 

 erratic blocks have been sent forth ; as, for example, from 

 the regions of Mont Blanc and Monte Eosa, into the adjoin- 

 ing parts of Switzerland and Italy ; while in districts where 

 the great chain sinks in altitude, as in Carinthia, Carniola, 

 and elsewhere, no such rocky fragments, or a few only and 

 of smaller bulk, have been detached and transported to a 

 distance. 



In the year 1821, M. Venetz first announced his opinion 

 that the Alpine glaciers must formerl}^ have extended far 

 beyond their present limits, and the proofs appealed to by 

 him in confirmation of this doctrine were afterwards ac- 

 knowledged by M. Charpentier, who strengthened them by 

 new observations and arguments, and declared, in 1836, his 

 conviction that the glaciers of the Alps must once have 

 reached as far as the Jura, and have carried thither their 

 moraines across the great valley of Switzerland. M. Agassiz, 

 after several excursions in the Alps with M. Charj)entier, 

 and after devoting himself some years to the study of glaciers, 

 published, in 1840, an admirable description of them and of 

 the marks which attest the former action of great masses of 

 ice over the entire surfoce of the AIjds and the surrounding- 

 country.* He pointed out that the surface of every large 

 glacier is strewed over with gravel and stones detached from 

 the surrounding precipices b}^ frost, rain, lightning, or ava- 

 lanches. And he described more carefully than preceding- 

 writers the long lines of these stones, which settle on the 

 sides of the glacier, and iire called the lateral moraines ; those 



* Agassiz, Etudes sur les Glaciers et Systeme Glaciaire. 



