IN THE ANGLO-PARIS BASIN 35 



(1924 ; 27-8), and the current sections have been described in part by Milbourne 

 (1961 ; 135-7), Casey (1961a ; 558), and Owen (1963a ; 46). It shows the thickest 

 sequence yet known in the Lower Gault of England, and is undoubtedly the most 

 important. The clays contain finely disseminated pyrite, and their silty nature 

 allows the deep penetration of weathering agents ; this obscures the bedding for at 

 least 12-14 feet (3-658-4-267 m.) from the surface, but fortunately there is a dip of 

 8° S. present. In the fresh condition, the clays are seen to be fairly uniform through- 

 out, and the Divisions adopted here are based upon cycles of sedimentation. Each 

 cycle commences with relatively rapid sedimentation and terminates with partly 

 arrested deposition indicated by marly seams and cementstone nodules. Individual 

 units display an alternation of dark-grey and more fawn-grey bands. That this is an 

 original feature is occasionally shown by the fauna ; there being often a more diverse 

 benthos in the fawn-grey bands. 



Casey has described the boreholes drilled over the area of the northern field 

 situated to the E. of Horton Wood (1961a ; 558). The subsequent excavation of this 

 field commenced in 1964 at the northern boundary, and the sequence is now being cut 

 down dip. There is unfortunately a small gap in the observed sequence as shown in 

 text-fig. 14, between this new field and the older workings. 



Eodentatus & basal lyelli Subzones 



About 13 feet (3-962 m.) of glauconitic sandy clay and loam (1 (i) & (ii) ) classified 

 with these Subzones occurs below the lowest level seen in the excavations (Casey 

 1961a ; 558). 



lyelli Subzone 



Divisions 1 (ii) to the top of 2 (vi) are classified with this Subzone. As this is the 

 first time that such a faunal sequence has been described in England, it is discussed 

 in detail. The top 3 feet 8 inches (1-117 m -) °f x (^) * s seen m the excavations, but 

 only the upper foot is fossiliferous and this has yielded Hoplites (H.) spp. and the 

 ubiquitous Inoceramus concentricus, among other fossils. The shell seam that marks 

 the base of 2 (i) has yielded the following : — 



Protanisoceras (Protanisoceras) nodoneum (Buvignier). P. (P.) barrense (Buvignier), 

 P. (P.) alternotuberculatum (Leymerie), Beudanticeras laevigatum (J. de C. Sowerby), 

 B. albense Breistroffer, Hoplites (H.) spp., Lyelliceras aff. lyelli (d'Orbigny), Branco- 

 ceras (Brancoceras) sp., Neohibolites minimus (Miller), /. concentricus Parkinson, 

 Acila (Truncacila) bivirgata (J. de C. Sowerby), Natica sp. 



A comparable fauna occurs throughout the remainder of 2 (i). In 2 (ii) the 

 benthonic element of the fauna increases in importance and one of the characteristic 

 fossils is a solitary caryophyUid coral. The ammonites consist essentially of species 

 of Hoplites (H.) and Protanisoceras (P. barrense & P. nodoneum) ; Lyelliceras is not 

 common. The benthonic element is much reduced and the nekton to a lesser extent 

 in 2 (iii) . The ammonites include the following : 



H. (H.) dentatus (J. Sowerby), H. (H.) spp. common ; P. (P.) barrense, Lyelliceras 

 lyelli (d'Orbigny) the lowest definite occurrence of the typical form, Beudanticeras 

 sp., accompanied by I. concentricus. 



