S68 M. Agassiz on Glaciers, Moraines, and Erratic Blocks. 



which may be observed not less distinctly in all the valleys the 

 flanks of which are crowned with ancient moraines, at whatso- 

 ever distance they may now be from the existing glaciers. In 

 fact the whole sides of the valley of the Rhone are thus polish- 

 ed, to the very shores of the Lake of Geneva, more than a day's 

 journey from the glaciers, and in all places where the rocks are 

 so hard as to have resisted the influence of the atmosphere. 



The explanatioji which M. de Charpentier has given of these 

 facts, viz. that they are clearly produced by great masses of ice 

 which, at a former time, had filled the bottom of all the Alpine 

 valleys, does not appear to embrace the whole question, and the 

 Jura exhibits a series of phenomena which lead to additional 

 conclusions. 



That I may more satisfactorily discuss what I mean to ad- 

 vance on this subject, I shall first make some remarks on those 

 polished surfaces which are to be found over the whole of the 

 southern slope of the Jura, and which are designated laves by 

 our mountaineers, as we are informed by M. Leopold de Buch, 

 the individual who, of all geologists, was the first deeply to study 

 the Neuchatel Jura, and who has most successfully investigated 

 tlie subject which now engages our attention. 



The southern slope of the Jura, which fronts the Alps, ex- 

 hibits these laves to its very summits, from the shores of the 

 lake Bienne even to beyond Orbe, limits within which I have 

 myself ascertained their existence.* They are polished surfaces 

 completely independent of the stratification of the beds and of 

 the direction of the mountain-chain of the Jura ; they extend 

 over the whole surface, following its undulations, and are equal- 

 ly marked upon the Neocomian and the Jurassic rocks ; they 

 penetrate into the depressions which form the little valleys, and 

 elevate themselves on the most isolated ridges, presenting a po- 

 lish not less uniform than that of a mirror, especially where the 

 rocks have been recently exposed, that is to say, cleared of the 

 eaith, gravel, and sand which generally cover them. These 

 surfaces are sometimes plane, sometimes undulated, and often 

 even traversed by furrows more or less deep and tortuous, or 

 with longitudinal very rounded elevations, but which never fol- 



• They extend much further, as we learn by a letter from M. Schimper, 

 received July 25, and inserted in the Transactions of the Society, p. 38. 



