208 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



group, of which latter the Calcaire grossier may be taken as the centre 

 and the type*. (See Table.) 



In France the Calcaire grossier forms so well-marked and definite 

 an horizon, that no difference of opinion exists with reference to its 

 range and characters. The Bracklesham Sands in this country, and 

 the Systeme Bruxellien in Belgium, are the equivalents of this portion 

 of the French series, and afford a base-line equally well-defined. 

 Between this geological level and the Chalk the strata are very 

 variable. Their relative position in the mass is, however, perfectly 

 apparent ; but yet there is in this portion of the French and English 

 tertiary series one division only of which the exact synchronism 

 stands recognized on sufficient combined physical and palseontological 

 evidence, viz. that division formed by the lignites of the Soissonnais 

 and the fluviatile beds of Woolwich and Lewishamf . In France and 

 Belgium, the zone of the Nummulites planulatus in the upper part 

 of the Soissonnais Sands and of the Ypresian series forms the only 

 other well-established zoological horizon in these lower beds. On 

 stratigraphical grounds the Ypresian Clay of Belgium had also been 

 referred by M. Dumont to the London Clay. 



§ 2. Grouping of the Lower Tertiary strata in France ^ Belffium, 

 and England. (See Table.) 



In the Paris district the strata beneath the Calcaire grossier have 

 been variously grouped. By M. D'Archiac J, in his very able classi- 

 fication of the French series, they have been all (with the exception 

 of th§ Glauconie grossiere) included in one group — that of his 

 "Sables Infe'rieurs," or Lower Tertiary Sands — consisting of six 

 members, which in his latest work, the " Histoire des Progres de la 

 Ge'ologie," (vol. ii. p. 598) stand as under, commencing with the 

 uppermost di\dsion : — 



Group of the '^ Sables Inferieurs^' (jyArchiac). 



ler Etage. Glaises et sables glauconieux (Clays and glauconiferous sands). 



2 „ Lits coquilliers (Shell beds). 



3 ,, Sables divers ou Glauconie moyenne (Varied Sands or middle Glau- 



conite). 



4 „ Gres, poudingues, et sables coquilliers (Sandstones, puddingstones, 



and shelly sands). 



5 „ Glaises sableuses, Bancs d'Huitres, etc., marnes lacustres, lignite, 



argile plastique (Sandy clays, oyster beds, lacustrine marls, lignite, 

 plastic clay). 



6 „ Glauconie inferieure, Calcaire lacustre inferieur, poudingues et argiles 



du sud-est du bassin (Lower Glauconite, lower lacustrine limestone, 

 conglomerates and clays of the south-east of the basin). 



This series is only fully exhibited in the more northern part of 

 the Paris tertiary district. This, however, is the area with which, 

 as it is the nearest to England, we must first establish our relations. 



* See also Sir Charles Lyell's and M. Dumont's tables in Quart. Journ. Geol. 

 Soc. vol. viii. pp. 279 and 370, 1852. 



f With which, as suggested by M. Dumont, the Upper Landenian is syn- 

 chronous. 



+ 1839, Bull. Soc. Geol. vol. x. p. 172 ; 1840, Mem. Soc. Ge'ol. de France, 

 2nd ser. vol. v. p. 263 ; 1848, Hist, des Prog, de la Geol. vol. ii. p. 598. 



