in the Erratic Basin of the lihone. 257 



and Berne, and extend to the environs of Zoffingen and Av- 

 bourg, wliei'e measurable blocks of clilorites may be consi- 

 dered the last representatives of the Pennine rocks, and mark 

 the extreme limit of the extension of the basin of the Rhone. 



Still further, these rocks are the only ones which pene- 

 trate into the interior of the high valleys of the Jura. Be- 

 yond the superior limit of the erratic formation, indicated in 

 the Jura of Neuchatel and Vaudois by large blocks of gra- 

 nite and the existence of polished surfaces, beyond the two 

 or three first chains, and still further, we encounter in the 

 bottom of the high valleys, at a height of more than 3500 

 feet, an erratic formation, composed of fragments and blocks, 

 the largest of which scarcely measure a metre, accompanied 

 with numerous quartz pebbles. 



These fragments are usually very angular, yet have an in- 

 describable appearance of great age ; the rock seems greatly 

 altered. They appear to have been buried for a longer or 

 shorter time under the earth, where they are still found for 

 the most part. Yet the rocks composing this erratic forma- 

 tion, which may well be called insulated and distinct from the 

 rest of the basin, are still exclusively the Pennine rocks. 

 Not one granite from Mont Blanc, nor one pudding-stone of 

 the Yalorsine, penetrates into this inclosm'e, defended by the 

 high chains of the Jura. The valleys open towards the plain, 

 such as those of Yallorbe, Yal de Travers, Yal de Ruz, are 

 the only ones of the Jura into which the latter penetrate. 

 The quartz only, in numerous pebbles of all sizes, accompa- 

 nies the Pennine rocks into the interior of the Jura, and thus 

 become, along with them, the last and most distant repre- 

 sentatives of the Alpine rocks over the whole of this extre- 

 mity. 



But although these three species of rocks thus act a com- 

 mon part, we can, nevertheless, remark a diiferenco in their 

 distribution, which confirms the law indicated above. 



The granular chlorites, which come in greatest abundance 

 from the lower part of the valley of the PJione, have a ten- 

 dency to preserve their exterior position along the left bank 

 of the basin. They are found in greatest plenty, and in 

 bloclvs of tlie largest size, in the western part of tlie basin. 



\itl,. xr,IV. NO. LXXXVIII. — APRITi 1848. It 



