116 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



shells appear so equal in this and the underlying formation ; hut 

 still the number of Calcaire grossier species is very much less*. If 

 we treat this question as we have done the previous one respecting 

 Barton, and take the proportion of species common in the two suc- 

 cessive periods in each area, we obtain the following result : — 



Sir C. Lyell gives 58 species of Molluscs from the Laeken beds, 

 andM.D'Halloy 84. 



Common in England to the Common in France to the 



Total number of 

 species of the 



Lond, 



Brack- 



Barton 



Lits 



Calc. 



Sables 



Laeken beds. 



clay. 



lesham. 



clay. 



coq. 



gross. 



moyens. 



95 



8 



o^ 



31 



28 



45 



32 



If we consider the actual magnitude of each fauna in the several 

 typical provinces, and take the number of Molluscs in the Calcaire 

 grossier, Bracklesham Sands, Sables moyens, and Barton Clay to be 

 respectively 651, 368, 377, and 252, then of each of these faunas 

 there are in the Laeken beds the following per-centage : — 



Bracklesham 9'5 Barton 12* or as 3 : 4 nearly. 



Calcaire grossier 6'7 Sables moyens 8*5 or as 3 : 4 nearly. 



showing a difference considerably less than that which is exhibited 

 by the equivalent deposits in the French and English areas, though 

 still somewhat in favour of affinities between the Laeken beds and 

 the Sables moyens. 



If we apply the per-centage test to note the actual difference 

 between the two deposits in the Belgian area, we find also some 

 anomaly ; for their distinctiveness is greater than between the equi- 

 valent French and English beds. Thus the above-named lists show 

 only 29 species common to the Brussels and Laeken beds. This 

 gives the projjortion of shells ranging from the lower to the upper 

 deposits as — 



Laeken beds 27 



Brussels beds 100 



a proportion I cannot reconcile with the other facts. The Barton 



* As I cannot help feeling some doubt in the correlation suggested by Sir 

 C. Lyell of the upper beds at Cassel (/and g, figs. 4 and 5, op. cit.) with the 

 Barton Clay and Sables moyens, I have excluded the upper Cassel list from the 

 following calculations, and confined myself to his Brussels and lower Cassel list. 

 Although it is true that the Nummulifes variolarius occurs in the Cassel beds, and 

 is considered peculiar to the Sables moyens, yet it is not limited to that zone in 

 England, as it is apparently found with A'^. l<2vigatus in the Bracklesham Sands of 

 the Isle of Wight (Q. J. G. S. vol. viii. p. 334, note). We have also to note the oc- 

 currence of the Cerithium g'ujanteiim, which is found associated with the N. vario- 

 larius at Cassel, and which fossil both in France and England is confined to the 

 Calcaire grossier zone. Further, >.\ith the exception of the Natica ambulacrum, 

 Cardium turgidum, and Pecten reconditus, all the other foreign species belong to 

 the Calcaire grossier and Bracklaeham Sands ; the larger number in fact appear- 

 ing to me to be the fossils of that zone, to which group I sliould be inclined to 

 refer these Cassel beds. I will not, however, say that the Sables moyens are alto- 

 gether wanting at Cassel. Some of the higher beds may prove to be of that age. 

 My own examination of that hill has not been sufficiently detailed to speak from 

 personal knowledge. 



