[io MIDDLE ALBIAN STRATIGRAPHY 



With the completion of the description of the individual sections in England to- 

 gether with a brief review of those in France, it is now possible to consider in detail 

 the Zonal and Subzonal scheme of the Middle Albian. It is instructive and sobering 

 to examine also the history of the development of this particular scheme, not atypical 

 of many zonal schemes. There are workers who would insist that zonal schemes 

 should be fixed for all time with little regard to future detailed work, or whether the 

 scheme is based upon firm foundations. 



IV. DEFINITION OF THE MIDDLE ALBIAN SUBSTAGE AND ITS 

 ZONAL SCHEME IN THE ANGLO-PARIS BASIN 



A. Historical background 



The Formation name Gault was accepted in much the same sense by English and 

 French geologists within the first half of the 19th Century. The history of its use in 

 England was given by Jukes-Browne (1900 ; 14-31). D'Orbigny took William 

 Smith's concept, that individual formations could be determined by their fossil con- 

 tent, a major step forward when he recognised that fossils characteristic of one litho- 

 logical unit occurred in different lithologies and that these, although deposited at 

 different localities, were formed at the same time. He erected, therefore, a series of 

 chronostratigraphic stages to include these diverse lithologies. Apart from the 

 localities mentioned by d'Orbigny (1842 ; 404-5) in his definition of the Albien stage 

 (latinized to Albian), he recorded others in 1849 {^ n Geinitz 1849 ; 6-7). Pictet & 

 Campiche adopted d'Orbigny 's stage name when they commenced their description 

 of the Cretaceous fauna of Ste Croix, Vaud, Switzerland, subdividing it into Albien 

 inferiur, moyen and superieur (1858 ; table facing p. 27). 



De Ranee (1868 ; 163-171) was the first worker to describe the Gault section at 

 Folkestone in detail. He accepted d'Orbigny's term Albian and divided it into lower 

 and upper divisions drawing the boundary between them at what is now known as 

 the junction between Beds VIII and IX. The lower division corresponds approx- 

 imately, therefore, to Pictet & Campiche's Albien moyen. He recognised eleven beds 

 in the Folkestone Gault and referred each to a zone based on its characteristic fossil ; 

 employing essentially the characteristic ammonite. Later Price (1874 ; 342-368) 

 revised De Ranee's description but neither of these workers on these occasions 

 attempted to apply their zonal scheme to sections other than at Folkestone. 



Barrois (1875b ; 707-714) was the first geologist to formally define a zonal scheme 

 for the Albian of the Anglo-Paris Basin in the sense that we use today. This idea 

 of the application of an index fossil denoting a segment of time and represented by 

 different types of sediment, or none at all, differed from that of De Ranee & Price who 

 used them merely in a local sense for an actual lithological unit. However, the idea 

 crystallised by Barrois for the Albian is implicit in the writings of earlier French 

 workers including d'Orbigny. Barrois recognised a tripartite division into : — - 



Zone a Ammonites inflatus 

 Zone a Ammonites interruptus 

 Zone a Ammonites mammillare 



Of these only the lower two zones were included in the Albian, the Zone a Ammon- 



