Se 
goed 
S48 STRATIGRAPHICAL GEOLOGY.  [Boox VI. 
beds in one region by marine beds in another, together with occasional 
gaps in the record, show us some of the geographical conditions and 
oscillations during the time of deposition. “4 
Lower.—In the Paris basin the Sables de Bracheux form an excel- — 
lent horizon, which corresponds to the Thanet sand of England and 
Dumont’s ‘‘ systéme landenien” in Belgium. Below this horizon there 
occurs in the Franco-Belgian region a lower series of deposits than is 
found in England. In the Paris basin these strata present a variable 
and local character, but, according to Hébert, may be grouped as under 
in descending order : 

Marl of Dormans (Physa gigantea). 
Conglomerate of Meudon with fresh-water shells=Marine Heersian marl of 
Belgium. 
Rilly limestone (fresh-water) and strontianiferous marls of Meudon, correspond- 
ing to the upper Heersian sands. 
Hyaline sands of Rilly, corresponding to the lower part of the hyaline sands of 
Heers. 
Marine conglomerate of Rilly and conglomerates of Nemours (marine fossils), cor- 
responding to the denudation between the Mons limestone and the Heersian 
beds. 
Mons limestone, not represented in Paris basin." 
The Sables de Bracheux, traceable as a definite platform through 
the Anglo-French and Belgian area, contain among their characteristic 
fossils Pholadomya cuneata, P. Konincku, Cyprina Morrisii, Cucullea 
crassatina, Pecten breveauritus, Psammobia Edwardsii, Corbula regulbiensis, » 
Turritella bellovacina, Natica deshayesiana. 'The lignites of the Soissonnais 
are intercalated among beds of sand and clay, containing the same 
molluscan fauna as the Woolwich and Reading beds. But a break 
seems to occur in the series at this point; for in the Paris basin no 
representative of the London Clay is found. The lignites of the Soisson- 
nais are covered by sands (Sables de Cuise) containing, among other 
abundant marine organisms, Nummulites planulata, Turritella edita, 
T. hybrida, Crassatella propinqua, Lucina squamula ; they are regarded as 
- the equivalent of the lower part of the English Bagshot sand, and form 
the highest member of the Lower Hocene of the Paris basin. 
In the Belgian area some differences are presented in the succession 
of sediments. The strata of that district have been grouped by Dumont 
into a series of “‘systemes.” The most ancient Tertiary deposit of the 
west of Europe appears to be the limestone of Mons (Syst¢me Montien). 
This rock lies in a denuded hollow of the Chalk, and has been found by 
boring to be more than 300 feet thick. It consists of friable and compact 
limestone, charged with a remarkable series of organic remains. Upwards 
of 400 species of fossils have been obtained from it, including marine, 
fresh-water, and terrestrial shells. Among them are about 200 species 
of gasteropods, about 125 lamellibranchs, and fifty polyzoa, besides 
numerous foraminifers (Quinqueloculina), and calcareous alge (Dactylo- 
pora, Acicularia, &c.). 'Two conspicuous features in this deposit are the 
extraordinary proportion of its new and peculiar species, and the resem- 
blance of its fauna, especially its numerous Cerithiums and Turritellas, 
to that of the middle Kocene beds of Belgium and the Paris basin rather 
1 Hébert, Ann, Sciences Géol. iv, (1873), Art. iv. p. 14. 
