38 MIDDLE ALBIAN STRATIGRAPHY 



A much more diverse fauna appears in 2 (iv). A thin bedding plane 4 inches 

 (o-ioi m.) above the base, sometimes washed out, has yielded one of the best pre- 

 served ammonite faunas yet known from the lyelli Subzone. The fossils are part- 

 phosphatised and part pyritised. Some ammonites are in a ' death rest ' position ; 

 that is, they are vertically orientated resting on the venter. The amount of distortion 

 permits the compaction ratio of the clay to be deduced. The fauna includes : 



P. (P.) nodoneum.P. (P.) barrense, Pseudhelicoceras argonnensis (Buvignier), P. sp., 

 Beudanticeras laevigatum, B. albense Breistroffer, B. sanctaecrucis Bonarelli, Hoplites 

 (H.) baylei Spath, Hoplites (H.) spp. Douvilleiceras sp. juv., Oxytropidoceras evansi 

 (Spath), 0. sp., Lyelliceras lyelli (d'Orbigny), L. gevreyi (Jacob), L. sp., Brancoceras 

 senequieri (d'Orbigny), B. versicostatum (Michelin non d'Orbigny nee Douville) B. 

 spp., Inoceramus concentricus, Semisolarium moniliferum (Michelin). ' Auricula ' 

 acuminata Deshayes. Hemiaster sp. 



This list shows a preponderance of lyelliceratid ammonites over the hoplitids which 

 are greatly subordinate in actual numbers. The fossils are mainly crushed flat in the 

 remainder of 2 (iv) and (v) but there is no significant difference in the fauna. Large 

 uncrushed or partly crushed fossils occur in 2 (vi) and include : 



P. (P.) barrense, Beudanticeras sanctaecrucis, H. (H.) benettianus (J. Sowerby), H. 

 (H.) spp., Lyelliceras lyelli, Brancoceras spp. Eutrephoceras sp. 



At this level Hoplites occurs in roughly equal numbers to the non-hoplitid genera 

 combined. Some of the ammonites are also in a vertical 'death rest ' position and 

 these, like those in 2 (iv), have a common orientation indicating a current direction 

 coming from what is now 210 Magnetic. 



spathi Subzone 



Divisions 3 and 4 are classified with this Subzone. There is a sharp change in the 

 ammonite fauna at the base of Division 3, the ammonites consisting essentially of 

 Hoplites (H.) spp. At the commencement of the spathi Subzone, deposition of 

 sediments increased rapidly and the bulk of the remainder of the Lower Gault, 

 although very fossiliferous, yields little but crushed material except at a few horizons. 

 Sedimentation during the spathi Subzone was particularly thick. At least 56 feet 9 

 inches (19-812 m.) of clays have been observed and the gap in the sequence between 

 the northern field and the main workings is probably only a few feet. 



Division 3 (i) contains numerous I. concentricus and crushed Hoplites (H.) the 

 bulk of which possess dentatus-like ribbing : a few pyritic nuclei occur. Protanisoceras 

 (P.) spp. have been obtained from Division 4 (i) but otherwise the heteromorph 

 ammonites are almost exclusively species of Hamites. A beautifully-preserved 

 fauna occurs in 3 (ii)-(iv) consisting mainly of ammonites and almost entirely of 

 species of Hoplites (H.) identical to that of the well preserved element in the dentatus 

 nodule bed at Folkestone (p. 13). Some specimens reach a diameter of 9 inches 

 (0-228 m.). A loose block certainly from either 3 (ii) or (iv) contains an example of 

 Mojsisovicsia delaruei (d'Orbigny). Division 4 (i) has a fauna closely comparable to 

 that of 3 below. However 4 (ii) contains species of Hoplites (H). transitional from 

 those seen below to those characteristic of the upper part of the spathi Subzone. 

 They are of the grade well represented condensed in Division A of the Maidstone 



