1852.] 



LYELL — BELGIAN TERTIARY FORMATIONS. 



307 



Fossils ofb, Table VIII., or Yellowish Sands of Kleyn Spawen, in 

 the collection of M. Bosquet. 



^anopaea Hebertiana, Bosq. 

 Corbulomya complanata, Nyst, 



triangula, Nyst. 



Corbula pisum, Sow. 

 Erycina neglecta, Nyst. 

 Psammobia rudis, LamJc. 

 Tellina Hebertiana, Bosq. 

 Lucina Thierensii, Heb. 



tenuistria, Heb. 



striatula, Nyst. 



Cyrena semistriata, Besh. 

 Venus Kickxii, Nyst. 



incrassatoides, Nyst. 



Limopsis Goldfussii, Bosq. 

 Pectunculus terebratularis, Lamk. 

 Mytilus fragilis, Nyst. 



Faujasii, Al. Brong. 



Trocbus striatellus, Bosq. 

 Paludestrina Draparnaudii, Bosq. (1) 



Paludestrina pupa, Bosq. 

 Rissoina Nystii, Bosq. (1) 

 Rissoa ? Chastelii, Bosq. (1) 



plicata. Desk. (1) 



Turbonilla Isevissima, Bosq. 

 Pyramidella cancellata, Nyst. 

 Nerita concava. Sow. 

 Natica glaucinoides ?, Sow. 

 Pleurotoma costellaria, Duchast. 

 Cerithium elegans, Desh. (3) 



subcostellatum, Schlt. (6) 



C. pUcatum, Lamk. 



iucrassatum, Merian. 



lima, Desh. 



Buccinum Gossardii, Nyst. 



suturosum, Nyst. 



Cytheridea MuUeri, Bosq. (1) 



Williamsoniana, Bosq. 



Cythere Jurinei, Munster. 



It will be seen that the only abundant shells in 5, Table VIII., are 

 fresh or brackish water species, and that Cerithium subcostellatum is 

 the most frequent. According to Professor Forbes, this bed was 

 formed in a shallow part of the perilittoral zone. 



Next in the descending order are the green marls and clays, c, Table 

 VIII., the Upper Tongrian of Dumont, which occur below the yel- 

 lowish sands (b of the same Table). Their thickness at Lethen, 

 Vieux Jonc, Henis, and other localities which I visited is considerable 

 (not less than 36 feet at Lethen), and they appear to indicate many- 

 oscillations of the water from a fresh to a brackish state. Sometimes, 

 for example, a thin bed occurs almost exclusively characterized by 

 Venus incrassatoides and Lucina Thierensii, then a layer with Cyrena 

 semistriata, then another with Cerithia. I found occasionally at 

 Lethen a well-rounded flint-pebble in the midst of these green clays 

 and marls. 



In the following list of seventeen species belonging to this subdi- 

 vision, the relative abundance of the fourteen commonest species is 

 expressed by numbers supplied by M. Bosquet. Prof. Forbes infers 

 from them and the fossils generally that these clays were deposited 

 in his perilittoral zone, in the neighbourhood of the influx of fresh 

 water. 



Fossils of the Green Marls, c. Table VIII. (part of the Middle or 

 Fluvio-marine Limburg Beds) . 



Rissoa plicata 



? Chastelii 1 



Rissoina Nystii 2 



Pyramidella cancellata 



Natica glaucinoides 1 



Cerithium subcostellatum 5 



elegans 3 



Cytheridea Mulleri 6 



Corbula pisum 2 



complanata 1 



Corbulomya triangula 2 



Cyrena semistriata 4 



Lucina Thierensii 2 



Tellina Hebertiana 1 



Venus incrassatoides 5 



Trochus striatellus 



Paludestrina Draparnaudii 2 



