518 HISTORY OF GEOLOGY AND PAL/EONTOLOGY. 



the lower Cretaceous formations of the south-eastern part of 

 the Paris basin. Cornuel described deposits in the Haute- 

 Marne which he identified partly as Gault (Marnes a Plica- 

 tules), partly as lower Greensand, partly as Neocomian. The 

 localities Bassy and St. Dizier have been regarded since that 

 time as types of the lower Cretaceous development in the 

 north-east of France. 



Leymerie's memoir on the Cretaceous deposits of the Aube 

 Department was published by the French Geological Society 

 in 1841. It still ranks as a classic in the geological literature 

 of the Paris basin. Leymerie distinguished three sub-divisions 

 in the Cretaceous system : Neocomian, Greensand and Brick- 

 clays, White Chalk. Each horizon was accurately described, 

 and the distribution of the fossils was indicated with scrupulous 

 care and detail. According to Leymerie, the horizon of the 

 White Chalk contains the same organic remains as the Upper 

 and Lower Chalk and the Chalk Marl of England. The 

 Brick-days (Argile teguline) and Greensand group comprises 

 two sub-groups, the younger of which corresponds to the 

 Gault, the older contains fossils which are known to occur in 

 the Upper and Lower Greensand as well as in the Gault of 

 the English area; this is the group which D'Orbigny afterwards 

 called Aptien. 



The Neocomian reposes upon the Upper Jurassic rocks, and 

 consists of three sub-groups : Marls with variegated sandy 

 deposits; Marls and limestones with Exogyra subplicata, harpa^ 

 etc. ; Spatangus limestone (the name being given on account 

 of the abundant occurrence of tests of Echtnospatangus cordi- 

 formis). An accurate comparison of the Neocomian in the 

 north of France with the Lower Cretaceous formations of 

 England led Leymerie to the conclusion that the French 

 Neocomian was not the equivalent of the Lower Greensand 

 of England, but, as had already been said by D'Archiac, it 

 represented the Wealden formation of England. The palae- 

 ontological part of Leymerie's work appeared in 1843, and 

 included a description of one hundred and thirteen new species 

 from the Neocomian horizon. 



In 1842, a mineralogical and geological description and a 

 geological map of the Ardennes Department was published by 

 C. Sauvage and A. Buvignier. The two authors demonstrated 

 that the Cretaceous system was here represented by the White 

 Chalk, the Greensand or the Chalk Marl (Gaize), highly 



