20 The Ignigenous Bocks near Montbrison. [Jan.? 



vicinity of the city of Yienne, but also that the nearest indications 

 of igneous action to be met with occur about Issoire, in the neigh- 

 bouring department of the Puy-de-D6me, a town situated in a 

 straight line at a distance from Yienne of about eighty English 

 miles, or else near Puy-en-Yelay, which is not less than, sixty from 

 the same locality. 



It has, however, since been suggested to me, that I had over- 

 looked a little group of volcanos situated round about Montbrison, 

 the capital of the department of the Loire, a town which lies con- 

 siderably nearer to Yienne than either of the places to which my 

 attention had been directed, being in fact not more in a straight line 

 than about thirty-five miles distant from the city of Yienne, and 

 that it was possible, therefore, that the convulsions of nature to 

 which Sidonius and Alcimus refer might find their explanation in 

 certain eruptions of which this neighbourhood had still retained the 

 impress. 



I was, therefore, glad to avail myself of the opportunity of 

 visiting, in company with my friend, Mr. Corfield, a Fellow 

 of Pembroke College, Oxford, the above locality on our way to 

 Switzerland this autumn, and I am now ^prepared to say that, 

 without pretending to have surveyed the entire district, I saw 

 enough to convince me, that no volcanic disturbance which had 

 occurred within this area at so late a period as that alluded to 

 could have escaped our notice, and that every indication of igneous 

 action which presents itself throughout the country bears marks of 

 a much greater antiquity. 



Thus much at least I can venture to affirm, namely, that 

 neither craters, streams of lava, scoriae, nor even cellular trap, are to 

 be met with anywhere within the limits of this district. On the 

 contrary, the only igneous rocks which came under our observation 

 consisted of a compact basalt, containing nests of olivine, a material 

 which could only have been elaborated by the aid of great pressure, 

 and under a different configuration of the surface from that now 

 existing. 



To descend to particulars — the granitic formation, which occupies 

 a large portion of central France, may be seen extending to the west 

 of Montbrison, but the valley of the Loire, in which this town is 

 itself situated, consists of tertiary fresh-water beds, covered over in 

 many places by thick deposits of alluvial matter. 



On the right bank of the Loire, however, the granite is again 

 seen, and stretches as far as the Khone valley, in which Lyons is 

 situated. 



Farther to the south, however, occurs the Coal formation of 

 St. Etienne, which consequently intervenes between the valley of the 

 Loire, in which Montbrison stands, and the city of Yienne, situated 

 on the banks of the Ehone, which also is built upon a granitic rock. 



