341 The Oligocene OF THE Southern United States 31 



At Chalo-Saint-Mars this marine fauna occurs above a thin 

 lignitic bed with Potamidcs Laviarcki and Pahidcstrina Dubiiis- 

 soni, thus foreshadowing the deposition of the Beauce limestone, 

 and showing the close connection between the latter and the 

 sandstone. 



Beauce limestone. A photograph, taken in 1900 in the quarry 

 at Orsa5^ is shown on the opposite page. It shows an interesting 

 contact between the marine Fontainebleau sandstone and the 

 freshwater Beauce limestone. The sandstone, which is being 

 quarried for building purposes, is stained with manganese. Di- 

 redlly upon its upper surface, rests the limestone. The latter rock, 

 which is in part silicified and resistant, and in part disintegrated 

 by chemical action, is extremely irregular and cavernous in its 

 strucfture. No fossils were obtained at Orsay, but Potamides La- 

 marcki an^ Cyclostoma aiitiqinctn were collec^led at other localities 

 in this limestone. At Montmorency the Beauce limestone has 

 undergone silicification to such an extent that millstones occur 

 locally. 



The Stampieyi period. M. Cossmann and M. Lambert have 

 proposed the name Stampien* for the period between the deposi- 

 tion of the sands of ifetrechy and those of Ormoy. 



The lower sands of Fontainebleau fall under the Rupelian. 

 The Tongrian is represented by the Brie limestone and the clays 

 and, perhaps, the gypsum. 



Oligocene in Brittajiy. Although nearly all of the peninsula 

 of Brittany is of igneous rock, several very local Oligocene de- 

 posits occur. These are most important in the vicinity of Rennes. 

 Near that city is a coarse-grained limestone which was correlated 

 by Desnoyers, in i83i,t with the Eocene limestone (calcaire gros- 

 sier) of the Paris basin. 



Limestone of Rennes charaSlerized by Archiadna. Tournouer , 



* From the Latin name for Etampes where these beds are typical. Mim. 

 Soc. Geol. de Fr., 3eme ser., t. 3, pt. i, 1884. 



t Note sur les terrains tertiaires du nord-ouest de la France, autres que 

 la formation des faluns de la Loire, Bull. Soc. Gi'ol. de France, ire s^rie, 

 t. IL p. 414, 4 juin, 1831. 



