126 Ml DOLE ALBI AN STRATIGRAPHY 



(iii) THE POSITION OF THE SUBZONE OF DIPOLOCERAS 



CRISTATUM 



The junction of the Lower with the Upper Gault at Folkestone is marked by two 

 seams of phosphatic nodules separated by a few inches of clay (p. 15). This junction 

 bed (Bed IV of De Ranee 1868, and Bed VIII of Price 1879, 1880, Jukes-Browne 1900 

 and subsequent workers) has always been included in the Lower Gault. However, it 

 has long been recognised that the fauna is a transitional one containing elements 

 characteristic of the beds below and above. The bed formed the zone of Ammonites 

 beudantii of De Ranee, and that of Ammonites cristatus of Price. Jukes-Browne 

 (1900 ; 45) did not include the time span represented by Bed VIII in his zone of 

 Ammonites lautus. Spath, however, placed his cristatum ' zone ' in the Middle 

 Albian (1923a, b) and later relegated it to subzonal rank and included it in the lautus 

 Zone in his sense (1926b ; 425). This classification has been followed by later Eng- 

 lish workers (e.g. in Hancock 1965 ; 245, 246). Breistroffer (1947 ; 48, 68) included 

 the Subzone in the Upper Albian where it stood in isolation. The author stated that 

 more research would have to be carried out before a final decision could be made on 

 the position of the cristatum Subzone (1958 ; 164). However, in the meantime, 

 Breistroffer's recommendation (see also 1965 ; table) has been accepted by other 

 workers such as Collignon (1963 ; 2) for the sequence in the Malagasy Republic, and 

 Young (1966 ; 15) for the succession in Texas, and in England by Melville (in Smart 

 et ah, 1964 ; 7). 



Although Bed VIII contains a fauna which on balance links it with the Upper 

 Albian, its lower nodule bed includes an important Middle Albian element derived 

 from sediments of daviesi Subzone age. One of the principle objections to placing 

 the cristatum Subzone in the Upper Albian is that hitherto it has meant placing the 

 Middle-Upper Albian junction at a level of erosion. However, it is now known that 

 the basal part of the cristatum Subzone is represented in an uncondensed sequence in 

 Bed 12 (v) near Wissant. This fact removes any objection that the writer might 

 formerly have held against placing the Subzone in the Upper Albian, and I now 

 recommend that it be included in the Upper Albian to form the basal Subzone of the 

 inflatum Zone. 



In Bed 12 (v) at Wissant we can see the incoming of a basal Upper Albian fauna in 

 an uncondensed sequence (p. 85) . The change in Inoceramus from a concentricus to a 

 sulcatus form has already been mentioned. Beudanticeras beudanti appears together 

 with D. bouchardianum. These forms are all known from Bed VIII (i) at Folkestone. 

 Bed 13 at Wissant contains en melee material derived from the equivalent of Bed VIII 

 (ii) & (iii) at Folkestone together with the lower part of Bed IX up to and including 

 the horizon of Euhoplites inornatus. In truth Bed 13 at Wissant forms the base of 

 the Upper Gault in our sense as well as that of our French colleagues. However, they 

 consider it to be the direct equivalent of Bed VIII, whereas it is in fact the product 

 of one period of erosion which occurred at Wissant later in the cristatum Subzone, 

 while at Folkestone there were essentially two phases of erosion at earlier dates 

 within this Subzone. It has been, up to now, the view of our French colleagues that 



