362 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 19, 



Fig. 10. — Section near Tour nay. 



Loess 



TGlauconite 5 " 

 Lower Landenians 



LGreymarl 4 



Chalk-marl 



Tourtia 



Carboniferous Limestone 1 



beds of a green sandy glauconite (5) 10 feet thick, in the upper part 

 of which layers of cherty stone from 6 to 8 inches thick abound, with 

 casts of shells. In this glauconite the same Ostrea lateralis and 

 Terehratula striatula occur which are met with in the grey marl 

 (4), so that it seemed to me impossible to draw a line between 

 the beds "4" and "5," or to consider "4'* as cretaceous and 

 "5" tertiary. The other fossils which I found in "5" con- 

 sisted of a Pholadomya (P. Koninckii ?), Cucullcea, Pinna, Turri- 

 telluy Fusus, Natica, &c., chiefly casts, and these in too unsatis- 

 factory a state to admit of being specifically distinguished. A gigantic 

 Pleurotomaria, sometimes retaining its shell, is not uncommon in 

 these beds, and is very unlike any fossil occurring in the Lower Ter- 

 tiaries of England or France. It resembles rather the P. gig ant ea 

 of the Lower Greensand. One species, and as yet one only, of this 

 genus, is known in the Calcaire grossier, — P. concava of Deshayes 

 (' Coq. Foss. de Paris,' vol. ii. pi. 32. fig. 1, 2, 3), much smaller 

 in size, though somewhat analogous in form. According to Baron 

 Ryckholt, who possesses the finest collection of shells from the glau- 

 conite of Tournay, all the species which have been referred to ter- 

 tiary shells are distinct. Not a few of them he considers identical 

 with fossils of the Faxoe, Maestricht, and other cretaceous formations. 

 The difficulty of defining the specific characters in the genera Phola- 

 domya, Scalaria, My a, and Pinna, without having a full and perfect 

 series of the individuals for comparison, is such that I cannnot pre- 

 tend, without better specimens than I brought from Tournay and 

 Angres, to offer a positive opinion on this point. I believe neverthe- 

 less that Baron Ryckholt, when he publishes a full account of his 

 valuable cqllection, will succeed in proving the beds in question to be 

 older than any fossiliferous strata above the Chalk in England. 



