220 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This shows a total of twenty-six out of the forty-two species of 

 our English species as common in the lignites or in the lower sands 

 of the French series. Of the other sixteen, ten are new and rare 

 species, which have not yet been made the object of research and 

 comparison in the French beds*. 



Taking therefore the fact of the recurrence of marine fossils above 

 similar to those beneath the lignites and fluviatile clays, and seeing 

 the alternation of the mottled clays with the fossiliferous beds, I 

 think that we should place them all in one group, identical as a 

 whole, howsoever variable at places, in mineral and palseontological 

 characters ; and that even in all the subdivisions of this portion of 

 the French and English series, there is a far closer correlation than 

 could at first sight have been anticipated. As a whole, the total 

 number of mollusks belonging to the Woolwich series, including 

 the marine beds of East Kent, amounts to fifty-three species, thirty- 

 four of which are common also to the lignites of the Soissonnais and 

 associated fossiliferous sands. 



In French Flanders and Belgium, all this series presents, as it 

 were, a sort of neutral ground. Neither the great mass of the 

 mottled clays nor the fluviatile shelly clays exist f, but the sands of 

 East Kent and the north of France, in their unfossiliferous condition, 

 prevail exclusively ; the only organic remains mentioned by M. 

 Dumont and M. Meugy (and they under the circumstances are not 

 unimportant) being a few traces of lignite. Still the general cha- 

 racter of these sands, and their superposition on the lower Landenian 

 or the Thanet sands, leave but little doubt of their correlation with 

 the Woolwich and Readmg series. (See PI. VIII., Diagram, str. i,j.) 



§ 6. The Pebble beds ; Gres, PoudingueSy and Sables {ly Archiac). 



We now come to a point where more obscurity prevails in the 

 correlation of the French and English series. The sections of the 

 Lower Tertiaries forming the connecting links between the Paris and 

 London Tertiary districts are chiefly met with in mere isolated patches 

 and detached outliers on the extensive chalk plains of Picardy. Con- 

 sequently, as the series is very variable, and the sections are not con- 

 tinuous, great dissimilarity in the smaller details exists between the 

 several sections, and the correlation of their various subdivisions is 

 frequently far from apparent. Thus, on some of the hills in this 

 extensively denuded district, there are large outlying masses of mottled 



* The greater and more distinctive development in the Paris basin of both the 

 marine and freshwater series has given to each a far larger fauna than we possess 

 in this country; for, besides the species named above as common to the Lignites and 

 Plastic Clay, there are twenty-seven other species not found here, whilst in the 

 lower sands of Rheims and Bracheux there are also about eighty species unknown 

 in the Woolwich and Reading Series. We can only compare, however, the 

 known forms, and refer the greater profusion of life at that period in the French 

 area to the more exclusive and fuller prevalence of marine and freshwater con- 

 ditions respectively. Those s[)ecies which are common to the two countries are, 

 however, generally speaking, amongst the most characteristic in each. 



t It is possible that some rudiments of these are to be traced. (For some 

 sections of this series, see further on, p. 243.) 



