550 STRATIGKAPHICAL GEOLOGY 



The name Montian is taken from Mons in Belgium, Thanetian 

 from our Isle of Thanet, Sparnacian from Eparnay (Sparnacum), 

 Ypresian from Ypres in Belgium, Lutetian from Lutetia the 

 Roman name of Paris, and Wemmelian from Wemmel in Belgium. 



From the above table it will be seen that deposition began 

 earlier both in Belgium and France than in the English area, the 

 Montian Beds forming a kind of link between the Cretaceous and 

 Eocene Series. 



1. Belgium 



Montian. The beds referred to this stage have a thickness 

 of from 200 to 300 feet, and the Geological Survey of Belgium 

 now recognises three subdivisions which in descending order are : 



3. Freshwater beds with Physa montensis. 



2. The limestone of Mons (and Upper Tuffeau of Ciply). 



1. The Cerithium limestone and basal conglomerate. 



The basal conglomerate lies unconformably on the higher 

 Cretaceous strata, and the Cerithium limestone is so called from 

 containing a large Cerithium (C. Cornell). The Mons limestone is 

 a rough yellowish friable rock composed mainly of shell-fragments, 

 Foraminifera, and calcareous algae. It contains a large fauna, 

 consisting mainly of Gastropoda, with a fair number of Lamelli- 

 branchs and a few Echinoderms ; Cerithium montense, Cer. in- 

 opinatum, Turritella montensis, Mitra Dewalquei, Pseudoliva robusta, 

 Cidaris distincta, Cassidulus elongatus, and Echinanthus Corneti are 

 characteristic species, and there are a number of freshwater and 

 terrestrial shells which have been washed into the deposit from 

 neighbouring land. No Ammonites or true Belemnites occur, but 

 the latter are represented by two species of Beloptera. 



The Heersian or Lower Landeniaii of Mourlon consists of 

 glauconitic sands passing laterally into soft sandstone or sandy 

 marl. Its fauna is marine and like that of our Thanet Beds, but 

 near Gelinden the sands include a band of white marl containing 

 the remains of an early Eocene flora (Osmunda eocenica, Laurus 

 Omalii, Cinnamomum Sezannense, etc.). The total thickness of the 

 Heersian is about 60 feet. 



Landenian. This group is of freshwater origin and resembles 

 our Woolwich Beds, consisting of sands and marls with beds of 

 shaly lignite. The thickness is only from 30 to 50 feet. 



Ypresian. This stage falls naturally into two parts, of which 

 the lower (Argile de Flandres) is a continuation of the London 

 Clay. In a boring at Ostende its thickness was found to be 460 

 feet, but it thins eastward just as the London Clay thins westward. 

 Fossils are scarce in this clay, but it is overlain by sands and 



