42 THE OLIGOCENE BEDS 



of our visit to the district, we were informed that this ex- 

 posure was closed ; but it will no doubt be opened from time to 

 time as the neighbouring farmers require to make use of the 

 valuable deposit for their lands. Messrs. Cossmann and Lambert 

 give * the following section : — 



Section at Pia-i-efitie. 



ft. in. 

 Vegetable earth ......... i 6 



I Loess with (/(V;;-/? from the Beauce limestone . 3 o 



Drift ■; Gravels and diluvium sands with large 



( blocks of nieuliere . . . . 3 ft. to 9 6 



Falun 1 Falun, fossiliferous sands . , . 3 ft. to 6 6 



of I Pebble bed ...... 03 



Pierrefitte ( Fine sands without fossils ... 5 o 



The most characteristic fossil of this falun, not only at Pierre- 

 fitte, but elsewhere, is Corlmlomya iriangula. The beds contain a 

 decidedly marine fauna although Fotajuides Laviarcki, Planorbis 

 iiiflpinatiis, and other brackish and fresh-water forms occur. In 

 some sections the teeth of Lainna are also found. 



The Pierrefitte formation is also well in evidence at Moulin- 

 veau, and along the valley of the Chalouette at Saint-Hilaire and 

 Moulin de Voujouan, and at Cote-St.-Martin. Other exposures 

 are near Vauvert and Vauroux (p. 41), and in the wood of Vandou- 

 leurs (near Morigny). At the last-mentioned locality a friable 

 sandstone is found with Aximva obovata and Meretrix suba?-ata. 



9. PEBBLY SANDS OF SACLAS. 



Thls horizon, which is met with to the south of Etampes is 

 littoral in origin ; the sands are of lilac, yellow and grey tints, fine, 

 quartzose, occasionally finely stratified, and alternating with beds 

 of pebbles. 7 he formation is best seen in the vicinity of Chalo- 

 Saint-Mars, but it is also exposed at Boissy-la-Riviere, Saclas, 

 Mereville, Petit-Saint-Mars and Ormoy, all of which are no great 

 distance from the convenient Oligocene centre — Etampes. The 

 only fossils found in the beds are rolled teeth of La/iunx, which 

 are probably remanies. 



10. SANDS OF ORMOY. 



This characteristic and important horizon is rarely more than 

 thirteen feet in thickness, but is very useful for correlating 

 purposes, x^s we have previously mentioned (p. 40), it is regarded 

 as the equivalent of the Fontainebleau sandstone. The quartzose 

 white Ormoy sands frequently become compacted into a hard 

 sandstone with a calcareous matrix, which is used for building 

 purposes ; and Ijy resisting erosion is often seen playing the I'lVe 

 of a protecting shield on the tops of the hills round the typical 



* Coshinann and Lambert, c/. cit., p. 23. 



