1852.] LYELL BELGIAN TERTIARY FORMATIONS. 3'S'd 



Scalaria spirata, and Nummulites variolariiis. The fossils obtained 

 from the same beds by Captain Le Hon amount to the number of 7^, 

 and are enumerated in the column " Upper Brussels," Table XIII. 

 p. 351. The following twenty species are among the more common, 

 and the numbers appended, as furnished by Captain Le Hon, express 

 their relative abundance. 



Operculina Orbignyi 



Dactylopora cylindracea ? 



Corbula rugosa ? 



pisum 



Crassatella trigonata 



Lucina Galeottiana 



Venus nitidula ? 



Astarte Nystiana 



Cardium semigranulatum 

 Cardita elegans 



Pectunculus pulvinatus , 



Stalagmium Nystii , 



Pecten imbricatus ? , 



corneus 



Dentalium substriatum 



Vermetus (Solarium) Nystii 



Turritella granulosa 



Bulla lignaria 



Natica glaucinoides 



Scalaria spirata 



From these data Professor E. Forbes infers that the deposit took 

 place either in the lowest part of the perilittoral zone or the upper 

 division of the median zone, perhaps in 20 fathoms water. 



The strata of greenish and yellowish sands from which these shells 

 were derived are from 10 to 15 feet thick, where I saw them exposed. 

 At other points near Dileghem, nodular sandstone occurs, containing 

 casts of shells, some of which were collected by M. Deby many years 

 ago in pits no longer open- The specimens which he presented to 

 me contained Nummulites variolarius, together with casts of Lucina 

 glohosa and Pectunculus pulvinatus. 



What I had seen at Cassel before my arrival at Brussels, and an 

 examination of the section between Lille and Mons-en-Pevelle, which 

 I shall mention in the sequel, had led me to conclude that the strata 

 intervening between the Limburg series and the " London Clay 

 proper" might be conveniently divided into three groups, distin- 

 guished among other characters by three diiferent species of Nvm- 

 midites, — N. variolarius, N. IcBvigatus, and N. planulatus. When 

 I adopted this classification, I was not aware, or had forgotten, that 

 the superposition of these three species in the order here assigned had 

 been already recognized in the North of France, in 1842, by M. 

 d'Archiac in his paper on the Department of the Aisne (Mem. de 

 la Soc. Geol. de France, tom. v.). After my return from Belgium, 

 when visiting Cuisse-Lamotte near Compiegne in France, I saw the 

 shelly sands called ^^ sables inferieurs^' with Nummulites planulatus, 

 surmounted by a nummulitic limestone, full of N. IcEvigatus and N. 

 scaber, which is used as a building-stone at Mont Ganelon near Com- 

 piegne and other neighbouring places. Again, at Auvers, near Pon- 

 toise, north of Paris, I saw the lower calcaire grossier (or glauconie 

 grossiere), containing Nummulites Icevigatus, and overlaid by sands 

 {sables moyens or gres de Beauchamp) abounding in N. variolarius^ . 



* Since my return from Brussels, M. d'Arcbiac has shown me, in a collection of 

 fossOs from Jette, a Nummulite which he could not distinguish from N. planulatus, 

 mixed with N. variolarius. If the former species should be found to have endured 

 down to the period of the " Laeken beds," its occurrence in them still appears to 

 be an exception to the rule. 



I must here take the opportunity of making a few remarks on the distribution 

 of the three species of Nummulites, which are noticed in the text, in the English 



z 



