OF THE PARIS BASIN. 



15 



in detached crystals of considerable size. Fluor-spar, or " spath- 

 fluor" is also found in veins, in small cubes, perfectly distinct, 

 and of a pure fawn-colour.* Translucent gypsum or alabaster is 

 also well developed in some districts. 



In addition to the lithological characters, fossil zones have 

 been to some extent defined as indicating certain horizons : but it 

 has been noticed in many cases that the characteristic fossil is 

 absent, although the physical characters are clear, or that the 

 particular species selected as the zone fossil passes into another 

 bed. Thus Nummnlites kevigatus is very abundant in the Lower 

 Calcaire drossier, but it does not always exist in the lower beds, 

 and is again met with in the Middle Calcaire drossier ; while 

 Orbitolites cotnplanatus, so plentiful in the last mentioned horizon, 

 passes into the Upper. t 



It is advisable, therefore, not to insist too strongly upon the 

 value of distinctive fossils as indicating definite horizons when 

 taken alone, but when they are considered in conjunction with 

 the lithological characters the relation of the various beds in the 

 Paris basin can be readily and accurately determined. 



In common with all series of rocks the Calcaire drossier has 

 been divided into groups in different ways by various authors. 

 Here we are only concerned with the most generally accepted and 

 latest divisions and sub-divisions employed. 



The classification adopted by M. Michelot X is followed by 

 many authors, and is appended ; four horizons are recognised 

 in his tabulation. 



Classification of the Calcaire Grossier [after Michelot) 

 fCaillasses without shells (marl 

 <{ Nanterre) .... 



l^Caillasses with shells (Rochette) , 

 I'Roche (de Paris) 

 I Bancs-francs (de Paris) 

 -] Clicquart {i-oches-dii-haut of the Aisne) 

 I Banc Vert (and accessory beds) . 

 i Saint Nom (j-oc/ies-du-bas of the Aisne) 



J Banc Royal .... 

 ) Vergel^s (Lambourdes) 



Caillasses of the 

 Calcaire Grossier, 



Upper Calcaire 



Grossier, with 



Cerithium. 



Middle Calcaire 

 Grossier, with 



Milwla. 



Lower Calcaire 



Grossier, with 



NummuHtes. 



L 



f Bancs a Verrains {Cerithium gigantetiin) 

 <j Saint Leu (Roche des Forgets) . 

 l^Bancs a Nitmmulites {N. Icevigatus) 



The classification subsequently proposed by M. C. Dollfus § 

 was more detailed, and it remains the most complete yet pub- 

 lished. In this classification the Caillasses are included in the 

 Upper Calcaire Cxrossier, the latter being sub-divided into three 

 groups. 



* Stanislas Meunier, Geol. des Env. de Paris. Paris (1875), p. 196. 

 \ G. Dollfus, Bull Soc. Geol. Fr., 30. s^r., vol. vi. (1878), p. 261. 

 X Michelot, Bull. Soc. Geol. Fr., i-e. s^r., vol. xii. (1855), p. 1345. 



§ Dollfus, Couf-e Geol. de Cheiii. de Fer de Mery-sur-Oise ; Bull. Soc. Geol. Fr., 36. scr., 

 vol. vi. ( 1S7S;, p. 271. 



