Inverted Mass of Upper Cretaceous Strata. 53 



A similar but less complete section of tlie beds overlying the 

 Lower Greensand is to be seen at the eastern end of the sand-pit 

 on the north side of the level-crossing (No. 2). 



The following are some of the fossils collected by us from the 

 tardefurcata bed of these two pits : all, with the exception of a single 

 specimen of the Desmoceras, found half-way up in the bed, were 

 encased in the rough-coated nodules. 



Terebratula sp. Desmoceras aff. beudanti (Brongn.). 



Exogyra conica ? (J. Sow.). Douvilleiceras mammillatum (Schloth.). 



Panopea sp. Leymeriella regularis (Brug.). 



Pecten {Syncyclonema) orbicularis L. tardefurcata (d'Orb.). 



J. Sow. Sonneratia dutenipleana (d'Orb.). 

 P. (Neithia) sp. 



The most significant of these fossils are the species of Leymeriella 

 and Sonneratia, which have hitherto not been recorded from any 

 locality in this country. These or other species of the Leymeriella- 

 fauna ^ mark a definite zonal subdivision in certain districts on the 

 Continent (Ardennes, South-Eastern France, and Brunswick),^ 

 occurring in association with Douvilleiceras mammillatum, but 

 marking a time-period prior to the introduction of the interrwptus- 

 fauna. The mammillatus bed at Folkestone, as in the neighbouring 

 part of France, contains elements of the interruptus-faxinsi, but no 

 specimen of Leymeriella has been recorded from it. It therefore 

 seems highly probable that the zonal representation is imperfect 

 in that region, and we may conclude that the passage from Lower 

 Greensand to Gault is more clearly demonstrated at Leighton 

 Buzzard than at any exposure in England hitherto described. 

 We think it not unlikely that the sandy basement-bed of the Gault 

 at West Dereham, Norfolk,^ would also yield the tardefurcata-isiuna, 

 if it were thoroughly searched. Jukes-Browne's description of the 

 lowest Gault at Clophill,^ east of Ampthill, conveys the same 

 suggestion. 



It should be noted that no specimen of Belemnites minimus 

 or of any ammonite of the interruptus-tjjpe was found in the 

 tardefurcata bed, while in the higher part of the section not one of 



^ For figures and descriptions see C. Jacob, " Etude sur quelques Ammonites 

 du Cretace Moyen " : Mem. Soc. Geol. France, Paleontologie, No. 38, 1907, 

 pp. 53-8, pis. vii, viii. 



^ C. Jacob, " Etudes Paleontologiques et Stratigraphiques sur la Partie 

 Moyenne des Terrains Cretaces dans les Alpes Fran9aises et les Regions 

 voisines " : Trav. Laboratoire de Geologie de la Faculte des Sciences de 

 rUniversite de Grenoble, vol. viii, fasc. ii, 1908, pp. 296-7. W. Kilian, 

 Lethea Geognostica, II. Das Mesozoicum, Bd. iii, Abth. i, " Unterkreide," 

 Lief, i, 1907, p. 62. G. Miiller, " Beitrag zur Kenntniss der Unteren Kreide 

 im Herzogthum Braunschweig " : Jahrb. k. preuss. geol. Landesanst. fiir 1895, 

 vol. xvi, p. 110, Berlin, 1896. 



^ J. J. H. Teall, " The Potton and Wicken Phosj^hatic Deposits " (Sedgwick 

 Prize Essay), 1875, pp. 20-2. A. J. Jukes-Browne, The Cretaceous Rocks of 

 Britain, vol. i, "The Gault and Upper Greensand of England" (Mem. Geol. 

 Surv.), 1900, p. 297. 



* Op. cit., p. 285. 



