DISTRIBUTION OF BOULDER STONES. 351 



which are most remote from the places opposite the 

 mouths of the alpine valleys, the blocks seldom reach at 

 a height of 2000 feet above the level of the sea. 



In those places where the Jura chain branches into the 

 great valley between the Jura and the Alps, loose blocks 

 are found in the valleys behind the projecting chains. 

 The Jura range is sometimes intersected in places oppo- 

 site to the Alps ; and it is remarked, that loose blocks are 

 met with in the valleys behind these intersected portions 

 of the range ; and that, when loose blocks occur in the 

 Jura range, at a distance from the Alps, it is only in such 

 places as are directly opposite to the intersected portions 

 of the chain opposite to the Alps. 



The circumstance of the non-occurrence of these blocks 

 in the sandstone, marl, and nagelfluh, which occupy 

 the great valley between the Alps and the Jura, proves 

 that that revolution of our globe, by which these were 

 dispersed, took place after the formation of these rocks, 

 and may therefore have belonged to one of the latest 

 changes which have contributed to the present form of 

 the earth's surface. 



When we compare the relations of the alluvium of the 

 rivers in valleys with those of the loose blocks, their simi- 

 larity must strike every one. Thus, rolled masses are sel- 

 dom deposited in those places where a river forces its way 

 through a narrow passage ; but where an expansion takes 

 place, owing to the distance of the banks increasing, the 

 rolled masses are sometimes accumulated in whole banks. 

 The same loose blocks seldom occur in the narrow 

 passages of the transverse valleys in the Alps ; but as 

 soon as widenings of the valleys take place below these 

 narrowings, the blocks occur in abundance. 



