52P6 



GEOLOGICAL OBSERVATIONS IN FRANCE. 



From Geneva 

 along the 

 course of the 

 Rhone. 



Lakes Syant 

 andNantaa. 



Extremity of 

 the Jura. 



the two stations* : neither were they made witli such strict 

 attention to accuracy, as to be considered as absolutely de- 

 termined. 



It wouhl be diflficiilt to add any thinji^ to what Mr. von 

 Saussure says of the road from Geneva to Lyons in his Tours 

 to the Alps: I shall only* enlarge a little more than he has 

 done on some places where pebbles or blocks of primitive 

 rocks occur. Following more or less closely the course of 

 the Rhone from Geneva, we meet with some at the villages 

 of Coniigoon and petite Grave, where they rest on a bed of 

 soft gritstone; at Chancy, where we found on the banks of 

 the Rhone a granite with' reddish feldtspar ; and in the bed 

 of the Loudon, a small river that comes from mount Jura, 

 and falls into the Rhone, where there are several pebbles of 

 serpentine, including^ tolerably large garnets. But in a 

 marshy bottom situate below the village of Fougny a large 

 quantity of primitive compound rocks are seen^ some with 

 a base of diallage [sraarag'dite of Saussure] and jade, others 

 of almost pure jade, or compact petrosilex. Not far from 

 the loss of the Rhone, near the village of Vanchy, primi- 

 tive pebbles are still perceptible; afterward toward Chatil- 

 lon they become more rare ; yet I have seen blocks of gneiss 

 on this road, about a mile from the little lake of Syant or 

 Sylant, which no doubt formerly made but one with that of 

 Nantua, about 120 yards below it. Every thing leads us 

 to believe, as Mr. Saussnre remarks, that the latter ex- 

 tended much farther to the south-west, covering the large 

 flat meadows observed in that quarter, the soil of which 

 is composed of rounded pebbles for tlie inoit part calca- 

 reous. 



From this place to the extremity of the Jura, between 

 Poncin and Pont-d'Ain, scarcely any primitive pebbles oc- 

 cur. There we begin to meet with pebbles of quartz in 

 considerable quantity, and some blocks of gneiss in the en- 



♦ "Though the correction for temperature, with respect to the dilation 

 -of the air, is indispensable in nieasunr.g differences o( level in the same 

 cpuntry and at the same time j it is not quite certain, that it ought to bs 

 emj)loyed when we comt>are countries very distant from each other, and 

 take the mean of a great number of observalions." J. B. Biot's Phy- 

 sical Astronomy, vol. 1, p. 145, 



virons 



