of the White Chalk of the Paris Basin. 393 



Group of the North of France and of Group of the West and South of 



Belgium. France. 



Upper chalk of Maestricht and Fau- 



quemont (Belgium). 

 Coral chalk of Valognes and Nehou. 

 Coral chalk of the basin of the Loire, 

 at Vendome (Loir and Cher), at 

 Chavagne ( Maine and Loire), at 

 Tours (Indre and Loire). 

 White chalk of Ciply (Belgium). 

 White chalk of Paris, of the depart- 

 ments of Yonne and Aube, and of 

 England. 



Nummulite chalk of Royan (Charente 

 Inferieure), of Saint Martory (Haute 

 Garonne), of Saint Gaudens, &c. 

 Coral chalk of Saintes (Charente Inferi- 

 eure), 

 Chalk marl of the Loire, with Gryph<Ba Ammonite chalk of Martrous, near 

 columba, Rochefort (with Gryphcea columba). 



Caprine chalk of the Isle of Aix, of the 

 Corbieres (Aude). 

 Green sand of Mans (Sarthe). Green sand of Fouras, of the Isle of 



Aix, and Corbieres. 

 Gault of the environs of Troyes (Aube). 

 Neocomian tract of Aube. 



To establish zoologically what we have advanced, let us 

 pass in review the succession of the genera, and endeavour to 

 convey an idea of the modifications which have taken place in 

 the Foraminifers of the cretaceous system, in the ascending 

 order of the beds. 



At the epoch of the Neocomian formation we have hitherto 

 found only the genus Textularia. 



The green sand presents, as we have said, two series of 

 genera nearly distinct. That of the mouth of the Charente 

 contains the genera Dentalina, Cristellaria, Lituola, Alveolina, 

 Chrysalidina, and Cuneollna ; that of Mans, the genera Den- 

 talina, Citharina, Frondicularia^ Fiabellina, Cristellaria^ Bu~ 

 limina, and Guttulina. Hence we see, that, with the excep- 

 tion of two genera common to both localities, all the rest are 

 different in each of them. 



If we follow our examination of the succession of genera in 

 the cretaceous groups of the South and the North, we shall 

 find— 



1. That in the South the same genera of the green sand 

 are reproduced in the Caprine chalk. By degrees they pre- 

 vail at length in the upper beds, and are reduced to the Cris- 

 tellaria alone in the environs of Saintes ; but near the mouth 

 of the Gironde (at Royan) they are accompanied by the 

 genera Nummulina and Guttulina, as well as on the whole 

 line of the foot of the Pyrenees, at Saint Martory, at Saint 

 Gaudens, extending into the department of Aude; thus pre- 



