298 Geological Socie/j/. 



your attention to the enormous thickness of a regular succession of 

 deposits described by these gentlemen in a section extending from the 

 hills above Aix to the coal works of Fuveau. We have at the base of 

 the section a great system of alternating beds of limestone and shale 

 containing many seams of coal, some of which are worked by perpen- 

 dicular sliafts 500 feet in depth. Over this succession of beds, come 

 vast groups of strata forming ranges of hills composed of limestone, 

 shale and sandstone. These are surmounted by tiiick deposits of red 

 marl and fibrous gypsum, and by vast masses of conglomerate. Fi- 

 nally, over the conglomerate comes a series of beds conforming to 

 the more ordinary tertiary type ; remarkable for the regularity of 

 their deposition, and for the beautiful preservation of the shells, the 

 fishes, and ^ven tlie insects contained in them. Such are the mincra- 

 logical characters of the lower members of this great series, that they 

 have been referred (even by expert naturalists, who had not sufficiently 

 examined the organic remains) to the old coal formation and the new 

 red sandstone ; but from top to bottom their fossils are exclusively 

 tertiary and lacustrine. At the same time we attempt in vain, by 

 joining in imagination the prominent elevations of the older rocks in 

 the neighbouring regions, to restore the former barriers once con- 

 taining that great body of water within which these deposits had their 

 origin. 



The Paper on the Cantal brought before us a series of facts no 

 less striking and impressive. In this high region are the escarp- 

 ments of an old lacustrine formation, nearly 500 feet in thickness, 

 full of freshwater shells, many specifically identical with fossils of 

 the basins of Paris and of the Isle of Wight : but here, as in 

 the former case, there are no barriers to mark the limits of the 

 lake within which this deposit was once confined. The same region 

 also bears the impress of another succession of phenomena ; for 

 within the area of this ancient lake, and after the solidification of 

 the beds of marl formed in its waters, burst forth one of those great 

 trachytic eruptions which mark all the neighbouring parts of France. 

 So that we now find beds of basalt, trachytic breccia, and other old 

 volcanic rocks, overtopping, on the side of one valley, by more than 

 800 feet, the highest lacustrine rocks through which they have 

 breached a passage to the surface of the earth : and in the neigh- 

 bouring region the same old volcanic rocks have risen to several 

 times that elevation. 



When we examine the upper rock marl of the Isle of Wight, we 

 see a deposit separated from us and the things about us, only by a 

 few feet of transported gravel. The outline of the country might 

 have been remodified, and the gravel formed by some transient 

 inundation. We have therefore no measure of the time which may 

 have elapsed since the first existence of the phenomena before us. 

 If, however, we examine the shells in the rock marl, we find that 

 few, if any, belong to species existing in our lakes or rivers. We 

 cannot believe that there is so great a violation of continuity in 

 the forms of animated nature, except in subordination to nature's 

 laws ; and we feel almost forced to seek for a solution of our dif- 

 ficulties amidst the ideal revolutions of former ages. 



But 



