G. W. Lainplugh — Belemnites of Faring don Sponge-gravels. 33 



different size aud density have been rudely assorted by the currents, 

 the heavier preponderating in one place, the lighter in another ; and 

 where the pebbles are largest, there also are the largest Belemnites 

 found. 



From the character of the deposit it has long been recognized that 

 only a small proportion of its organisms can have actually lived 

 where they occur. The case of the Belemnites is not therefore 

 different from that of the majority of the fossils, except that, owing 

 to their weight, brittleness and shape, they have suffered greater 

 attrition than the shells during transport. The presence of 

 numerous pebbles derived from older rocks, as large and larger 

 than the Belemnites, does indeed show that there is no inherent 

 impossibility in the view that these also might be derivative ; but the 

 determination of the fossils as representing only a single species, 

 and moreover, one which is not of Jurassic age, is strong evidence 

 against this view. It cannot, indeed, be proved that the specimens 

 are exactly of the age of the deposit, but I think it is certain that 

 they cannot be much older ; and that at any rate they were lying on 

 the sea-floor along with other organisms which were swept together 

 to form the bank. 



We will now consider what indication these Belemnites give as to 

 the age of the ' Sponge-gravels.' Bel. Speetonensis at Speeton and 

 in Lincolnshire occurs only in the 'zone of Bel. Brunsvicensis,' 

 and therefore in beds comparatively high in the Lower Cretaceous 

 Series. The uppermost portion of this zone contains Amm. 

 {Hoplites) DesJiayesi and other characteristic fossils of the Atherfield 

 Clay and lowest part of the Lower Greensand of Kent and the Isle 

 of Wight ; and although the zonal Belemnite has not yet been 

 observed to occur in these beds in the south of England, the 

 correlation of the Atherfield Clay with the upper part of the ' zone 

 of Bel. Brunsvicensis ' of Speeton appears to be well established. 

 Whether the Faringdon Belemnites are actually contemporaneous 

 with or somewhat older than their matrix, the 'Sponge-gravels' 

 cannot represent a lower horizon than the upper part of the ' zone 

 of Bel. Brunsvicensis.'' 



In the Hythe Beds of Kent and at a corresponding horizon in the 

 Isle of Wight there is occasionally found a form of Belemnites which 

 is the same as a species occurring at Speeton,^ above the 'zone 

 of Bel. Brunsvicensis ' and below the ' marls with Bel. minimus.'' 

 The nomenclature of this species has been greatly confused, and 

 stands in need of careful elucidation ; in some lists it appears as 

 Bel. jaculum and as Belemnitella plena, from both of which, however, 

 it is quite distinct ; it is probably the form known on the Continent 

 as Bel. fusiformis, Voltz. I did not find any trace of this species at 

 Faringdon, and its apparent absence suggests that the ' Sponge- 

 gravels ' may be older than the beds containing this fossil in Kent 

 and at Speeton, though its rarity anywhere in the south of England 



' See my paper " On the Speeton Series in Yorkshire and Lincolnshire," Quart. 

 Journ. Geol. Soc, vol. Hi (1896), p. 181 ; and notes on the Hythe Beds in Annual 

 Summary of Progress of Geol. Survey for 1897, p. 129. 



DECADE IV. VOL. X. — NO. I. 3 



