Excavation of Valleys. 39 



marls enclosing lymnei and planorbes. These dip to N.W. ge- 

 nerally at a considerable angle. On the road from Monton to 

 Vayres, their inclination is 25 degrees. 



If we now compare the localities last described with those al- 

 luded to in other parts of the present communication, they may 

 perhaps be found mutually to elucidate each other.; and although, 

 considered singly and without relation to other volcanic pheno- 

 mena in Central France, the deposites of Mount Perrin may 

 seem inexplicable, and due to some preternatural causes, yet, 

 when more closely examined, they will appear the simple results 

 of some of the most ordinary operations. 



The various sections of Perrier, Monton, St Maurice, and 

 that of the new valley of the Sioule, above the Etang de Fung, 

 all concur in testifying that many ancient valleys in Auvergne, 

 have at certain remote periods been filled up with transported 

 matter of different kinds, after which they have been re-excavated, 

 and generally to a depth much below their original level. 



Now, among the effects of the last series of volanic eruptions 

 in Auvergne, we observe the frequent damming up of rivers by 

 currents of lava, whereby ancient valleys have been converted 

 into lakes, and are at present slowly filling up with alluvial mat- 

 ter, such as the Lac d'Aidat, and the Lac de Chambon. The 

 Etang de Fung had a similar origin, but was drained partly by 

 nature, and in part by man, before the alluvial accumulations 

 had time to become considerable. 



In the Vivarais, also, as we have before stated, a modern lava 

 current barred the course of the Fontauher, whereby the valley 

 above appears to have become filled with alluvium and volcanic 

 sand, some of which still remains, as at Mont Perrier, at a higher 

 elevation than the present river. 



We have stated our reasons for embracing the opinion that 

 Auvergne has experienced, throughout several successive pe- 

 riods, the effects of volcanic action. It is reasonable therefore 

 to conclude, that the lavas of every age gave rise to similar local 

 accidents, and that many of them dammed up pre-existing val- 

 leys, wherein transported matter was gradually deposited, and 

 which, in the course of ages, was again removed, wholly or in 

 part, together with the volcanic barriers. And as the ancient 

 lava* of Auvergne were infinitely more copious than the mo» 



