394 Mr. Weaver on M. Alcide d'Orbigny's View 



senting a zone well characterized by the abundance of Num- 

 mulina, of which we have not found the analogue in the creta- 

 ceous beds of the North of France. 



2. That in the North the succession is far from taking place 

 in the same manner; and that the Foraminifers, in much 

 greater numbers, present a larger suite in superposition, with 

 facts not less curious. The genus Citharina, which consti- 

 tutes the greatest portion of the species in the oolite forma- 

 tion, ceases with the green sand of Mans, being found no 

 further in the cretaceous beds. In the chalk marl of the banks 

 of the Loire we meet for the first time with the genus Lituola 

 with the Dentalina; but all at once, in the white chalk, we 

 observe a great number of species, among which, with all the 

 genera and even some analogous species of the green sand of 

 Mans, there appear for the first time on the globe the genera 

 Nodosaria, Marginulina, Valvulina, JRolalina, Rosalina, Trun- 

 catulina, Uvigerma, Verneuilina^ Gaudryina, Globigerina, Py- 

 rulina^ Sagrina, Flabellina, and Frondicularia. These genera 

 contain a considerable number of species; but with the white 

 chalk the genus Flabellina ceases, which had continued hitherto 

 from the green sand, and the genera Verneuilina and Gau- 

 dryina^ which first appear in the white chalk, also terminate 

 with it; while in its interior the Frondicularia abound, as well 

 as species whose cells form a pile on a single line. 



The white chalk of Ciply, although contemporaneous with 

 that of the Paris basin, since it also contains Flabellina, does 

 not present the same species, and may perhaps be a little 

 higher in the series, but we have not as yet sufficient data to 

 enable us to affirm this fact. 



In the beds which we consider higher in the series than 

 the white chalk of Paris, namely, in the coral chalk of Tours, 

 of Chayagne, and of Vendome, we meet for the first time 

 with the genera Polystomella, Polymorphina and Globulina, 

 yet accompanied with the same genera as those of the white 

 chalk, with the exception of those whose discontinuance we 

 have noticed ; again, in the upper chalk of Maestricht and 

 Fauquemont we have, with the three genera just mentioned, 

 also the genera Nonionina, Faujasina, and Helerostegina. 

 All are found living at present, or at least occurring in ter- 

 tiary tracts ; but we arrive at the last beds of the cretaceous 

 group without having seen a single species of the Miliola of 

 Lamarck (our order of Agathistegues), which, as we ascer- 

 tained in 1825, only commences with the tertiary beds, and 

 may be considered as the most certain sign of a change of 

 formation. 



This rapid survey shows that in ascending from the lower 



