224 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



in a subordinate position: but with regard to the "Lits CoquiUiers," 

 the fossils are most numerous and characteristic, and furnish us with 

 an horizon perfectly to be depended upon. 



The independent character of the fauna itself of the lower beds of 

 sand was, however, pointed out by M. d'Archiac in 1839*, subse- 

 quently by M. Melleville in 1843t, and by M. Grares in 184 7^. 

 The lists of fossils respectively found in the several districts which 

 these authors described give the following results : — 



Total number of Species ranging Number of 



species in the into the Lits species peculiar to 



Beauvais and CoquiUiers or the beds of Beau- 



Rheims Sands. beds above. vais and Rheiras. 



D'Archiac ... 49 11§ 38,— or 77 per cent. 



Melleville ...119 60 59,— or 50 1| per cent. 



Graves 94 48 46, — or 49 11 per cent. 



These results differ materially. This may arise partly from the 

 circumstance that M. d'Archiac takes a general view of these beds 

 in their whole range, and treats only of the fossils determined 

 in 1839 ; that M. Melleville gives a joint list of the Rheims and 

 Beauvais fauna, adding a number of new species from the neigh- 

 bourhood of Rheims ; whilst M. Graves's list is confined to the 

 neighbourhood of Beauvais, and he describes no additional new 

 species. If we separate from M. Melleville' s list the Beauvais 

 shells, which have since been more accurately determined by M. 

 Graves, and confine ourselves to the list he furnishes of the mollusks 

 of the Rheims sands only, the numbers vdll stand thus : — 



Melleville 43 11 32,— or 70 per cent. 



M. Hebert^ has since added 25 species to M. Melleville's list. 

 Of these I infer that 10 are new species, or species peculiar to the 

 Lower beds, whilst he names 8 species which have a higher range. 

 Of the other 7 specimens he only gives the name of the genus. 



As the fossils of these beds are generally so friable and often so 

 indifferently preserved, while at the same time there yet evidently 

 are many undescribed species, these lists are, no doubt, far from 

 complete ; and as also the determinations have been made chiefly 

 upon comparisons with the better studied and far more perfect and 



* Bull. Soc. Geol. France, vol. x. p. 174. As before-mentioned, M. d'Archiac 

 has since considered that some of these beds may be higher in the series than he 

 believed at that time ; still they would underlie the " Lits CoquiUiers," and our 

 argument would not therefore be affected. 



t Mem. sur les Sables Tert. Inferieurs, p. 78, 



t Top. Geog. de I'Oise, p. 196. 



§ M. d'Archiac makes the numbers 12 and 37 instead of 11 and 38; the 

 Pectunculus terebratularis, however, which was then thought to be identical with 

 the Gres de Fontainebleau species, has since been found to be different, and to be 

 peculiar to these lower sands. 



II The similarity of these results is more apparent than real, for in M. Melleville's 

 enumeratian of the Beauvais shells there are 21 Lits CoquiUiers and Calcaire 

 grossier species not found in M. Graves's later list. Against this there are 23 

 new species described for the first time by M. Melleville, and mostly peculiar to the 

 Rheiras district. There are also a few species given by M. Melleville as peculiar 

 to the lower sands, which M. Graves gives also from the " Lits CoquiUiers." 



^ Bull. Soc. Geol. France, 1849, 2nd ser. vol. vi. p. 730. 



