OF THE PARIS BASIN. 37 



The Strata are well exhibited in a section to the north of the farm 

 of Vintue, as well as in front of the Chateau of Brunehaut, both 

 near Etrechy; whilst they are also found at Sannois, Montmartre, 

 Pantin, Noisy-le-Sec, Villeparisis and La Ferte-sous-Jouarre. The 

 limestone is essentially lacustrine in character, but fossils are rare. 

 The principal are Limncea cornea, Planorbis cornu, and hithinia 

 Duchasteli. 



M. Uouville has shown* the close affinity existing between 

 these beds and the reddish and grey limestones, which, near 

 Fontainebleau pass to the " Cakaire de ChdteaH-Lando?i." 



3. OSTREA-MARLS AND MOLASSE OF ETRECHY. 



This bed, well represented on the hills in the northern part of the 

 Oligocene area, is of regular occurrence, from 130 feet to 195 feet 

 in thickness, and composed of marls and white and yellow quartzose, 

 slightlymicaceoussands. Inthenorth-west,atNeuilly-en-Vexin,near 

 Chars, M.M. Hebert and Renevier foundf Potamides trochlearis 

 and P. plicatus. In the Parisian area the marls contain an 

 abundance of Ostrea cyathula and O. longirostris, with Corhula 

 subpisum. The bed is well represented in the classic locality of 

 Montmartre, where an intercalated calcareous stratum with 

 Cyrena, Cerithium, &c., exhibited lacustrine characters. J This 

 same lacustrine bed has also been found in a cutting at Ville 

 d'Avray on the St. Cloud railway, and at Sannois. M. G. Dollfus 

 is of opinion§ that the small fauna indicates close affinities with 

 that of the Brie limestone. The lower horizon of the Ostrea- 

 marls is particularly interesting at Sceaux, Massy and Palaiseau. 



On going south of Paris these marls change their character 

 and thin out near Etrechy, where the last vestiges become more 

 split up by beds of friable, yellowish, sandy and marly limestones, 

 and M. Lambert gave|| the whole the name of '•' Molasse 

 d'J^trechy." At that place this bed is vefy fossiliferous with a 

 marine fauna, but the fossils are difficult to extract entire, 

 being mostly casts and imprints. Here and there thin bands 

 may be found where the shells are silicified. Amongst the 

 Mollusca recorded as occurring in the formation we may cite 

 Bayania seinidecussata, Potamides plicatus, Bittium subliina, 

 Brachyirema Boblayei, Trochus subincrassatiis, Meretrix incrassata 

 and Perna Heberti. 



Speaking in general terms the Molasse of Etrechy is about 

 6 ft. 6 in. in thickness round Etampes. It is seen at Vintue, at 

 Gillevoisin near Chamarande, also at Jeurre (p. 38) underneath 

 the bed with AmpnI/ina crassatina, along the Orleans railway, 

 near Brunehaut and other places. 



* Douvill^, Bull. Soc. Orel. Fr., 2e. s^r., t. xxviii. (1871), p. 52. 



t Hebert and Renevier, Desc. Foss. iert. Num. sup. des env. dc Ga/>. Grenoble (1854), 

 PP- 35. 38, 39- 



t La Jonkaire, Bitll. Soc. Gcol. Fr., le. str., t. i. (1831), p. 223. 

 § Dollfus, Bull. Soc. Geol. Fr., 36. s6r., t. vi. (1S78), p. 298. 

 !1 Lambert, Bull Soc. Gcol. Fr., 36. str., t. iv. (1876), p. 501. 



