288 Messrs Murchison and Lyell on the Terliary 



of M. Elie de Beaumont, we shall confine ourselves to such a 

 Kne of section as may illustrate the objects above alluded to. 



The oldest and fundamental rock of this district, is a se- 

 condary limestone, comtaining Belemnites, Gryphites and Te- 

 rebratulae, which, in highly inclined and contorted strata, rises 

 to the lofty and peaked summits of Mont St Victoire. This 

 rock is referable to some member of the Jura limestone, and un- 

 conformably deposited thereon is the vast fresh-water formation 

 we are about to describe. 



The town of Aix is situated in the lowest part of a deep val- 

 ley, running from E. to W., the immediate flanks of which are 

 composed of this overlying deposit. On the northern side of 

 the valley the strata rise to the height of many hundred feet 

 above the town ; and the high road from Paris descends over a 

 denuded escarpment of strata, which may, for our present pui'- 

 pose, be grouped together in the following manner : — 



Upper Beds. White calcareous marls and marlstone, passing occasionally 



into a calcareo-silicious grit, used as millstones, with a band of resinous 

 flint. This system contains a small and undescribed species of Cyclas, 

 named gibbosa by Mr Sowerby, Potamides Lamarckii, BuKmus terebra, 

 B. pygmeus, and a new species of Cypris. Below these beds, which form 

 the cap of the range, are marls, both argillaceous and calcareous, con- 

 taining many species of fossil plants, some of which, together with seve- 

 ral others occurring in the inferior gypseous beds, have been examined 

 by Mr Lindley, whose account of them will be found at the end of 

 this memoir. 



The amount of thickness of these overlying beds is at least 

 150 feet. Here the subjacent strata run out horizontally into 

 a terrace, in which is placed the upper zone of gypsum, and 

 which is reached by a highly inclined flight of steps sunk 

 through beds of marlstone and marl. These gypsum quarries 

 had long been celebrated for their prodigious number of fossil 

 iish and plants, but the discovery of insects is of very recent 

 date ; and their occurrence was first made known to the scienti- 

 fic world by M. Marcel de Serres *. In our examination of 

 the exact position of these remains we descended about 260 

 steps, through marls and marlstones, abounding in plants, fish, 

 and an occasional shell ; and, on reaching the gypsum gallery, 

 we observed the following order :— 



* Bvilletin des Sciences, vol. viii. p. 181. (No. 15.) 



