PRESTWICH BRITISH AND FOREIGN TERTIARIES. 117 



clays also exhibit 31 species in common with the Laeken beds, and 

 32 with the Brussels bed. 



There are, however, in the Laeken beds some of the characteristic 

 shells of the upper French and English zone, as the 



Avicula fragilis, Defr. Cypricardia pectinifera, Sow. 



Bulla eonstricta, Sow. Lucina ambigua, Defr. 



Sowerbyi, Nyst. saxorum, Lam. 



Cardium turgidum, Brand. Ostrea gigantea. Brand. 



Corbula umbonella, Desk. Turritella brevis, Sow. 



pisum. Sow. Venerupis striatula. Desk. 



Crassatella plicata. Sow. 



The Nummulites variolarius, which in France characterizes the 

 zone of the Sables moyens, appears, in Belgium, to have lived in the 

 upper beds of the Bruxellian System, as there is some reason to 

 believe that it did in the upper part of the Bracklesham series in 

 England. At the same time, if the Belgian divisions are rightly 

 drawn, many species peculiar to the underlying zone in France and 

 England appear in Belgium to have reached on to the Laeken period. 

 Amongst them especially the Belgian geologists give the Cerithium 

 giganteum, Scalaria crispa, Carditu imhricata^ Crassatella compressa, 

 Pecteu imbricatus, and some others. The paucity oi PleurotomcE and 

 Cerithia in both divisions in the Belgian area, contrasts strongly with 

 their abundance in France and England. On the whole, the affinities 

 of the Laeken beds are rather greater with the Barton clays and the 

 Sables moyens than with the other zones; still I consider the question 

 an open one. It is possible that the Laeken beds may be the marine 

 equivalents of the upper Calcaire grossier, like the Bramshaw beds ; 

 or it is possible that the apparent confusion may be caused by an 

 intermixture of the fossils of some of the lower beds, — the equivalents 

 of the Lits Coquilliers, or of those of the upper divisions. 



The following is a list of the organic remains found in the Barton 

 Clay. Three sets of columns are added, — the first showing the 

 range of the Barton species in the other underlying English Ter- 

 tiaries, the second in the contemporaneous and underlying French 

 Tertiaries, and the third in the contemporaneous and next under- 

 lying Belgian series. For the Paris area my authorities are M. Des- 

 hayes, M. Graves, and M. D'Archiac, and my own collection ; and for 

 the Belgian area Sir Charles Lyell and M. Omalius D'Halloy *. 



* Mr. Edwards and Mr. Morris have kindly examined and corrected this list ; 

 and to Mr. Rupert Jones I am indebted for the addition of the various species of 

 microscopic Crustacea. Feb. 1857. 



