PRESTWICH BRITISH AND FOREIGN TERTIARIES. 20/ 



between the latter deposit and the Calcaire grossier* — a conclusion 

 confirmed and rendered more definite by subsequent observations — 

 and having established the relation which the Tertiaries of London 

 bear to those of Hampshire, the comparison between the main 

 divisions of the London, Hampshire, and Paris groups becomes 

 comparatively easy. At the same time, owing to the absence or 

 obscurity of several intermediate links in the Hampshire group, the 

 exact correlation of each varied member of the more distant groups 

 of Paris and London would not be perfectly clear without the addi- 

 tional assistance of the Belgian Tertiaries, which, as they aiford a 

 type in many respects more closely allied than the Hampshire series 

 to the Paris Tertiaries, serve to complete the chain of evidence. This 

 comparison of the Belgian Tertiaries was, as far as the Lower divisions 

 are concerned, not practicable until the clear and exact order of 

 superposition established by M. Dumontf , chiefly upon very accurate 

 physical evidence, and confirmed by the important palaeontological 

 evidence recently brought forward by Sir Charles Lyell;};, settled the 

 true grouping of these strata §. The lists of fossils from the Lower 

 tertiary beds of Belgium, previous to those drawn up by Sir Charles, 

 and those more recently published by M. Omalius d'HalloyH, ^^^^ 

 either too erroneous or too incomplete to allow geologists to correlate 

 satisfactorily, upon such grounds, this series with that of France and 

 of England^. 



In this part of the paper I shall confine my observations to those 

 Tertiary beds, which, commencing immediately above the Chalk, are in 

 England limited above by the Bracklesham SandSy in France Jjy the 

 Calcaire grossier, and in Belgium by the Systeme Bruxellien of Du- 

 mont. My object will be to show the more exact correlation of the 

 strata beneath that zone, and to claim for the London Tertiaries, as 

 a group, a distinct and independent position under that of that Paris 



* Quart. Journ. Geol. Soc. vol. iii. p. 378. 



t Trans, of the Acad. Roy. de Bruxelles, vols. vi. xvi. xviii. 1839-1851. 



X Quart. Journ. Geol. Soc. vol. viii. p. 277, 1852. 



§ The Tertiary palaeontology of Belgium had nevertheless received some very 

 valuable contributions in several papers by M. De Koninck, and the larger mono- 

 graph of M. Nyst ; whilst the general geology had been partially illustrated by M. 

 Galeotti and M. Omalius D'Halloy. Sketches of local sections and a few good 

 general sections are much wanted, however, to facilitate the study of the Belgian 

 tertiaries. 



II Abrege de Geologie, 1853. 



\ One instance occurring at the onset — in the lowest Tertiary beds of Belgium 

 — affected the bearing of the whole sequence ; for, by some mistake, in previous 

 works on Belgian Geology, amongst the fossils of the " Tufeau de Lincent," or 

 " Landenien inferieur," a number of Calcaire grossier species, including the Num- 

 mulites Icevigatus, had been introduced ; this is now proved to be an error. 

 M. D'Archiac, who has given two most excellent sketches of the relation of the 

 Belgian strata with those of France, had very properly overruled this anomaly, 

 and fixed, with his usual discrimination, the correlation of all the more important 

 and leading middle divisions (Bull. Soc. Geol. de France, vol. x. p. 168, and 

 Hist, des Prog, de la Geol. vol. ii. p. 500). Another step has also recently been 

 made in correlating the higher beds by the evidence brought forward by 

 M. Hebert proving the close relation of the fauna of the Limbourg beds with 

 that of the Gres de Fontainbleau (Bull. Soc. Geol. de France, 2nd ser. vol. vi. 

 p. 459). 



