OF THE PARIS BASIN. 33 



extended and constant horizon of the series. It is of great 

 economic value, being the principal mass of gypsum which 

 furnishes the celebrated " plaster of Paris." From this bed at 

 Montmartre the renowned Cuvier obtained Palceotherium ?nag- 

 nuvi, P. medium, P. minus, Anoplotherium commutie, Xiphodon 

 gracilis, &c. The gypsum itself is so homogeneous that it is diffi- 

 cult to recognise any divisions, but its junction with the beds both 

 above and below is uneven. 



(d.) Supra-gypseous marls. — These important marls are of 

 considerable thickness and as they are found at many points and 

 in several gypsum quarries can be easily studied. They are 

 divided into two parts as before stated : — (i) The lower blue marls, 

 with but few fossils, including Planorbis infiatus and Bithinia 

 Duchasteli, well developed at Frepillon ; and (2) The upper white 

 marls with Limncea strigosa, Cham Tourtioueri, &c., seen typically 

 at Romainville, Villeparisis, Essonnes, Mery-sur-Oise and Montfort- 

 I'Amaury. 



The similarity of certain of the " supra-gypseous " beds to 

 the Oligocene green marls above, together with their variability, 

 have led to much confusion in the classification of this portion of 

 the Parisian Tertiaries ; but the careful manner in which they have 

 now been worked out by MM. Dollfus, Carez, A'asseur, and other 

 French geologists, leaves but little to be desired. 



Limestone of Champigny. — At Champigny-sur-Marne and 

 district, the gypsum and marls of the environs of Paris undergo a 

 sudden transformation into a travertine. M. Hebert * has proved 

 that this bed, which is largely quarried in the manufacture of lime, 

 and is twenty-nine feet in thickness, comes between the Pholadomya- 

 iudensis-heds of the gypseous series and the " Cydostovia- 

 truficatum "-marls, thus demonstrating its contemporaneity with 

 the Paris gypsum series. The limestone of Champigny is also 

 developed at Chateau Thierry, in the valley of the Essonne, 

 J nine, Orge, &c. 



To this formation the limestone or '''' travei-fin supcrieur" 

 of Provins and the marls of Tardenois belong. 



* HObert, Bull. Sac. Ceol. Fr., 2e. ser., t. xvii. (i860), p. 800. 



Note to Fig. ii. 



a pholographic view of this magnificent section, and detailed measurements nf all the 

 minor sub-divisions of the beds, are given in' the Vertical Sections of Sheet 48, C'ar/i; Ci'ol. 

 del. dc France, pi. i. 



In a quarry near tlie railway, close by. the 3rd and 4th masses of Gyi)siiri are seen, and 

 below the latter a green sand in contact with the .St. Ouen Limestone. 



