290 Messrs Murchison and Lyell on the Tertiary 



By penetrating still further tlirough marls and marlstones, to 

 the depth of from thirty to forty feet, a second mass of gypsum 

 is found, which, although of excellent quality, is less worked 

 than the upper zone just described, as being less accessible. 

 Fish of various sizes, and in great abundance, are also found in 

 this part of the series. A third range of gypsum occasionally 

 crops out on the denuded and fissured sides of the hills, but is 

 said to be of inferior quality, and, from its ordinary deep-seated 

 position, is rarely worked. 



These ranges of gypsum and marl graduate downwards into 

 a flesh-coloured limestone, highly charged with potamides {Ce- 

 rithium of Lamarck), and two species of Cyclades, one of which 

 is the Cyclas gihbosa above mentioned, and the other is a large 

 and also a new species, and has been named Cyclas AqucB Sextice. 

 The limestone is, in some parts, highly contorted, passing into 

 a sandy calcareous grit, in other localities into a red sandstone 

 ('molasse)^ and still lower into a calcareous breccia, very com- 

 pact, the beds of which are separated by wayboards of argilla- 

 ceous marl, the whole terminating in a coarse conglomerate of 

 rounded pebbles (nagelflue.) In all the parts of this lower sys- 

 tem which we examined, we found the beds much contorted, or 

 inclined from 25° to SO"" to the N. N. E., and hence they are ra- 

 pidly lost under the marls and gypsums *. 



The accompanying sketch (Plate V.) will give a general idea 

 of the relations of this vast fresh water formation, shewing that, 

 since the epoch of its deposite, all the deep valley in which the 

 town of Aix stands, has been formed f. 



We have briefly described the strata forming the escai-pment 



• In an interesting article in the .second number of the London Review 

 (from the pen, we believe of Dr Daiibeny), the frequent verticality and vio- 

 lent disturbance of the strata in the immediate proximity of hot-springs is 

 pointed out. The contiguity of the baths of Aix lo great dislocations of the 

 strata, afford a good example in corroboration of his views. 



-|- Upon the fresh water beds in the bottom of the valley are seen, in the 

 immediate environs of Aix, a small deposite of marine sand, containing large 

 oj'sters. These strata, iS well as some insulated patches resting on the jura 

 limestone, near Aix, must be reftiTed to a formation posterior to tlie fresh 

 water series described. To determine, with accuracy, the geological relations 

 of these more recent strata, would require a more extensive investigation of 

 this and the neighbouring districts, than our time enabled us to accomplish. 



