566 STRATIGEAPHICAL GEOLOGY 



of white marls with beds of siliceous limestone which have been used 

 for making millstones (meulieres) ; total thickness about 100 feet. 

 Stampian. This part of the series consists chiefly of sands 

 which were formerly known as the " Sables de Fontainebleau," 

 but being more fossiliferous near Etampes to the south of Paris 

 are now named after that village. The lowest bed is a marl 

 containing marine fossils, Ostrea cyathula, 0. longirostris, and 

 Corbula subpisum. The overlying sands of Morigny and of 

 Ormoy yield many fossils, including Pectunculus obovatus, Lucina 

 Thierensi, Valuta Rathieri, Tritonium flandricum, and Potamides 

 plicatus, a fauna which correlates them with the Rupelian of 

 Belgium. At the top is a lacustrine limestone with Helix Ramondi 

 and Cyclostoma antiquum, formerly known as the " Calcaire de la 

 Beauce inferieur," but now termed the Calcaire d'Etampes. The 

 thickness of the Stampian Group near Paris is about 250 feet. 



5. Central France 



Extensive lakes were also formed in Central France during the 

 Sannoisian epoch, and continued to exist through the Rupelian (or 

 Stampian) and the greater part of Miocene time, leaving their 

 records in the lacustrine deposits of the Auvergne, Cantal, and 

 Velay. French geologists believe that there were three separate 

 lakes, the largest and most northern occupying the valley plain of 

 the Allier known as the Limagne d' Auvergne, the second being 

 in Velay, and the third in the Cantal ; but the latter is now for the 

 most part buried below the volcanic mass of that district. 24 



The deposits of the Limagne are the most complete and 

 accessible ; this plain has an average breadth of 20 miles, and its 

 length from Nevers to Brionde is nearly 100 miles. It consists of 

 nearly horizontal strata of sandstones, marls, and limestones, 

 which often rise into low hills capped by fragments of ancient 

 lava-streams. This tract is bounded both on the east and the 

 west by lofty hills of granite and gneiss which rise to a height of 

 1600 feet above the plain and 3000 feet above the sea; and the 

 western plateau supports a chain of extinct volcanoes from which 

 in Miocene and Pliocene times lava-streams flowed into the valley 

 below. The succession of the Oligocene portion of these deposits is 



as follows (see Fig. 194) : 



Feet. 



( Limestones and marls with Helix Ramondi .... 200 



St.-! Marls with Cyprisfaba and Limncea pachygaster ... 60 



{ Limestones with Potamides Lamarcki ..... 160 



[Sands and clays with marly partings and a limestone at the 



Sa. | base, Melania, Limncea, and Cyrena semistriata . . . 200 



( Sandy clays and coarse sands (arkoses) ..... 150 



