348 DISTRIBUTION OF BOULDER STONES. 



in the same heap, and single, large, and small, blocks on 

 mountain summits, and in the bottoms of valleys. The 

 smaller blocks are more or less rounded, but seldom so 

 much so as the boulders of rivers, which have been ex- 

 posed to long continued friction. The larger blocks are 

 indeed angular, but not sharp edged. But in examin- 

 ing this relation, we must carefully distinguish whether 

 or not the angles or edges are original, or have been pro- 

 duced by subsequent, natural, or artificial causes. Very 

 often masses of this description are blasted with gun- 

 powder, either with the view of clearing the fields, or 

 of obtaining stones for building; and these, if left on 

 the ground, may lead into error. 



These blocks vary in their nature, some being of the 

 primitive class, while others belong to those of the tran- 

 sition and secondary classes. In general, they appertain 

 to rock formations, situated nearer to the central alpine 

 chains than those of the places where they are found. 

 Thus, no rocks of the transition class occur in gneiss val- 

 leys ; no alpine limestone in transition valleys ; and, in 

 general, nowhere but in Jura, do blocks of Jura lime- 

 stone make their appearance. Therefore, all the loose 

 blocks of rocks between the Jura and the Alps, belong to 

 the strata of the high chains of the Alps. 



But these blocks have different characters in different 

 districts. The loose blocks which occur in the river ba- 

 sin of the Rhone, and the Lake of Geneva, are quite dif- 

 ferent from those which lie strewed about in the river 

 basin of the Rhine. These, again, are equally different 

 from the loose blocks of the river basin of the Aare, as 

 those of the Aare are from the blocks of the Lake of 



