195 



In this way it has been shown that the enormous lacustrine depo- 

 sits of Aix in Provence, of the Cantal, of the Limagne d'Auvergne, and 

 of other districts in the south of France, belong to the period of the 

 great tertiary system of the Paris basin. I have no time even to allude 

 to the important works connected with these subjects, which we owe 

 to the naturalists of France : and the two Memoirs of Messrs. Lyell 

 and Murchison," On the tertiary deposit of the Cantal," and " On 

 the freshwater formations of Aix in Provence," have been already 

 published *. I am not, therefore, called upon to give any regular 

 analysis of their contents. I may, however, be permitted to recall 

 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 shafts 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 thick 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 3 remarkable for the regularity of 

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

 fishes, and even the insects contained in them. Such are the minera- 

 logical characters of the lower members of this great series, that t hey 

 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 pheenomena ; 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- 



* See Edinburgh New Phi!. Journal, Oct. 1829; and Annates des 

 Sciences Naturelles, torn, xviii. p. 172. 



