STRATIGRAPHICAL GEOLOGY. 515 



Jurassic rocks in Central and North-Western Europe, and in 

 Great Britain. 



In Germany, Charpentier in 1778 distinguished Planer 

 limestone and Quader sandstone in his geological map of 

 Saxony. Werner and his pupils placed these formations 

 amongst the younger " Flotz " series. William Smith had 

 recognised in England four strata between the London clay 

 and the Portland stone : 



4. White Chalk. 



3. Lower or Grey Chalk. 



2. Greensand. 



i. Micaceous Clay (Brick earth). 



In Cambridgeshire, dark plastic clays occur below the Green- 

 sand, and Michell had in 1788 designated these as Gault or 

 Gait ; W. Smith called them Blue Marl. Conybeare and 

 Phillips sub-divided the series into two groups : 



2. The Chalk. 



'(if.) Chalk Marl. 

 (<r.) Greensand. 

 fo) Weald Clay. 

 .) Ferruginous Sand. 



The White Chalk was early described, and the similarity of 

 its lithological and palaeontological features established in the 

 south-east of England, the north of France, Belgium, Denmark, 

 Sweden, North Germany, and Poland. D'Omalius d'Halloy 

 traced the formations of the Paris basin into Belgium, dis- 

 tinguished four groups of deposit in ascending order, (a) grey 

 clay, (^) sand and sandstone (Tourtia), (c) chalk marl, (d) chalk 

 and flint, and comprised these in one formation, which he 

 named "Terrain cretace." In the same year, 1822, Brongniart 

 and Cuvier published a detailed description of the deposits of 

 the Paris basin in the second edition of their work, Recherches 

 sur les ossements fossiles. After a careful comparison of the 

 French Cretaceous formations with the English, Belgian, and 

 Scandinavian, Brongniart added a description of the chloritic 

 Cretaceous deposits of the Savoy and of the Perte du Rhone, 

 near Bellegarde, together with an enumeration of the fossils 

 occurring in them. 



Another work of that year which considerably advanced the 

 knowledge of Cretaceous rocks was that of Gideon Mantell on 



