16 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



which he wrongly equated with the " Tuffeau de Ciply " and the limestone of 

 ' Folx-les-Caves " in Belgium, and correlated with the " calcaire pisolithique " of 

 the Paris Basin, which Desor had previously correlated with his Danian. 



A year later, d'Orbigny (1850) described the characteristic fauna of his Senonian, 

 including the Maestrichtian of Dumont as the upper part of this stage. 



D'Orbigny (1852) recognised seven stages in the Cretaceous system, all of which 

 except the first and last, were established by him. They are, from the base upwards : 

 Neocomian, Aptian, Albian, Cenomanian, Turanian, Senonian, and Danian. These 

 stages have since been generally accepted by most stratigraphers, in spite of disagree- 

 ments and controversies regarding their limits. 



While d'Orbigny regarded the Senonian as comprising the succession of strata 

 between the uppermost Turanian and the basal Danian, Hebert (1875) excluded the 

 Maestrichtian of Dumont, considering it to range into the Danian, and Haug (1908- 

 n) included the Danian of Desor within the Senonian. 



Coquand (1857) divided the Senonian into four substages which he named from 

 the base upwards : Coniacian, Santonian, Campanian and Dordonian. However, 

 de Grossouvre (1897, 1901) considered the Dordonian to be a junior synonym of the 

 Maestrichtian of Dumont (1849) and included the latter within the Campanian as its 

 uppermost part. He also subdivided the Campanian (in his sense), on the basis 

 of ammonifies, into four successive zones which he named from the base upwards : 

 the Placenticeras bidorsatum Zone, the Taxanites delawarense Zone, the Hoplito- 

 placenticeras vari Zone and the Pachydiscus neubergicus Zone. On the other hand, 

 Arnaud (1897) showed that the ammonite fauna of the type Dordonian (the Pachy- 

 discus neubergicus Zone of de Grossouvre) is quite distinct from that of the Campan- 

 ian, and should be considered separately. However, in agreement with de Gross- 

 ouvre, he regarded the Dordonian as a junior synonym of the Maestrichtian thus 

 considering the Senonian stage to include the four substages : Coniacian, Santonian, 

 Campanian and Maestrichtian. This classification was followed by most authors, 

 although the limits between the various substages, especially those of the Campanian 

 and the Maestrichtian, have been largely disputed and mostly unsettled. This has 

 been mainly explained by the fact that the original definition of the Maestrichtian 

 by Dumont (1849) was rather vague and ambiguous and thus its lower limit has been 

 always chosen arbitrarily by the different authors. Again, while in fact no definite 

 Maestrichtian deposits have yet been described in the Paris Basin, Dumont wrongly 

 correlated the Maestricht chalk tuff with the so-called " pisolitic limestone " of 

 Laversines and Vigny, which further complicated the problem. Moreover, de 

 Grossouvre (1897, 1901) on the one hand, included the Maestrichtian within the 

 Campanian as its uppermost part, and Haug (1908, 1911) on the other, extended the 

 Maestrichtian downwards in the succession to include the uppermost part of the 

 Campanian at its base. As a result, Haug attached the chalk with Belemnitella 

 mucronata to the Maestrichtian, and thus considered the Meudon Chalk of the Paris 

 Basin, and the " chalk of d'Obourg ", the " Nouvelles chalk ", the " Spiennes 



