176 M. Agassiz on the Erratic Blocks of the Jura. 



facilities of observation peculiarly advantageous, and a disposi- 

 tion to take advantage of these facilities to advance the know- 

 ledge of this interesting subject. For a number of years I 

 have resided in the immediate neighbourhood of some of the 

 best spawning streams of the river Nith, and during the spawn- 

 ing season I have devoted more attention to the operations of the 

 salmon than most men under any circumstances have an oppor- 

 tunity of doing. Finally, I may state, that I shall continue to 

 take specimens of the young salmon from my ponds, at stated 

 periods, until they assume their migratory dress, when I shall 

 embody my observations in another paper on the subject. 



1. On the Erratic Blocks of the Jura. By M. Agassiz. — 2. 

 Oa the Production of Crystals of Insoluble Substances by 

 Artificial Means. By M. Gaudin. — 3. On the Operation 

 of the Earths in the process of Vegetation.'-'^. Oti the Alg<e 

 which communicated a Red Colour to the Waters of some 

 Salt Marshes. By M. F. Ddnal. 



1. On the Erratic Blocks of the Jura. By M. Agassiz. 



Last year I spent several months in the neighbourhood of 

 the Alps, for the purpose of studying the glaciers, and of ex- 

 amining the observations of MM. Venetz and Charpentier on 

 the great moraines, which are found at distances more or less 

 considerable from the existing glaciers ; and I have convinced 

 myself of the accuracy of the facts adduced by these ob- 

 servers. 



I have not been less struck by the polished appearance pre- 

 sented by the rocks on which the glaciers have moved, an ap- 

 pearance which is still to be remarked in all the valleys, whose 

 flanks are covered by ancient moraines^ at whatever distance 

 they may occui- from the existing glaciers. Thus the flanks 

 of the valley of the Rhone are entirely polished, even to the 

 banks of the lake of Geneva, more than a day's journey from 

 the glaciers, wherever the rock has been sufficiently hard to 

 withstand the action of the weather. At the sight of this phe- 

 nomenon, evidently produced by the glaciers which extended 

 to the plains of Switzerland, and which, when they retired, 



