1852.] PRESTWICH ON THE THANET SANDS. 255 



de Beaumont '^. He particularly notices the chloritic sands in the 

 north of France as constantly reposing upon the chalk and forming 

 numerous detached outliers, and discusses their relations to the lig- 

 nites of the Soissonnais and to the Calcaire grossier. M. D'Archiac 

 has. since distinguished these sands under the designation of the 

 " Glauconie inferieure," constituting the sixth or lowest division of his 

 " Sables inferieurs," which include all the beds between the Calcaire 

 grossier and the Chalk f. It is with this group that the Thanet Sands 

 appear to me to bear the closest resemblance, although there are some 

 anomalies in the evidence afforded by organic remains. The only 

 fossils quoted by M. D'Archiac from these sands are casts of the 

 Cyprina Scutellaria^ a Serpula, a species of Sponge, bones of Emydes 

 and of a small carnivore {Falceocion primcevus, Blainv.) ; whereas 

 amongst the shells which he mentions as characterizing his fourth 

 division of the "Sables inferieurs" (Gres et Sables coquilliers) are 

 the Cucullcea crassatina and Corhula longirostris, the former one of 

 the most characteristic species of the Thanet sands. With them are 

 associated the Ostrea Bellovacina, two species of Venericardia, Nu- 

 cula fragilis, Cyprina Scutellaria, &c. These two divisions are sepa- 

 rated by the " Lignites and Argile plastique." 



Some marine beds, far more fossihferous than the above, have been 

 described by M. Melleville J and M. Hebert § in the departments of 

 the Aisne and the Marne . M. Hebert considers that this deposit is syn- 

 chronous with the sands of Bracheux and Abbecourt, and that they 

 both underlie the lignites and repose immediately upon the chalk, 

 except where the "Sables de Billy" and the " Calcaire pisolitique" 

 intervene. M. d' Archiac on the contrary is of opinion that these beds, 

 equally with those of Bracheux, &c., are higher in the series, and 

 above the "Lignites and Argile plastique 1|." 



In this uncertainty, and pending a fuller description of the fossils 

 of these lower marine tertiaries in France, it would be premature to 

 conclude with which one or more of these beds the " Thanet Sands " 

 are the exact equivalent, although I have no doubt of its including 

 the " Glauconie inferieure " of the more northern parts of France, 

 but where unfortunately this stratum is comparativelyunfossiliferous^. 



Neither the " Glauconie inferieure " nor the lower marine sands 

 range to the south of the parallel of Paris. 



* " Sur I'Etendue du Systeme Tertiaire inferieur dans le Nord de la France," 

 Mem. Soc. Geol. de France, vol. i. p. 107, 1833. 



t BuU. Soc. G^ol. de France, vol. vi. p. 240, 1835 ; Ibid. vol. x. p. 173, 1839 ; 

 and Hist, des Progres de la Geologie, vol. ii. p. 599, 1848. 



X BuU. Soc. Geol. de France, vol. ix. p. 214, 1838. Ann. des Sciences Geol. 

 vol. ii. p. 7, 1845. 



§ Bull. Soc. Geol., 2nd series, vol. v. p. 388, 1848 ; vol. vi. p. 695 et seq., 1849 ; 

 and vol. vii. p. 338, 1850. 



II Hist, des Progres de la Geol. vol. ii. p. 607. 



^ Several other local w^orks may be consulted with advantage on this subject ; 

 amongst them are those of M. Buteux on the Department of the Somme, and 

 M. Graves on the Department of the Oise. 



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