THE 'DERIVED' FOSSILS. 37 



large Cardium suUiillanum from the Upware dark grit fragments, 

 for both of these are found in the Lower Neocomian sands of 

 Donnington, in Lincolnshire. At this place, scattered through 

 the lower green-coloured sands (Lower Neocomian of Judd), 

 are large masses of hard- cemented greensand-rock, whose litholo- 

 gical characters are similar to the various boulders we have been 

 describing. And we have seen that they contain some of the same 

 fossil species, I conclude therefore (1) that the various blocks of 

 greenish grit with Terebratula ovoides are of the same age as the 

 derived fragments of dark grit in the Nodule bed at Upware, Potton, 

 and Hunstanton; and (2) that they are all of Neocomian age, 

 having been derived from a deposit closely connected with that of 

 the Lower Neocomian sands of Lincolnshire, whose loose sandy 

 materials being removed, the harder masses were left ; some of them, 

 perhaps, like 'sarsen stones,' never having been far removed from 

 the place of their original construction, while others have been 

 carried as 'drift' to greater distances. I believe, then, that the 

 original home of Terebratula ovoides and T. ovoides var. rex was in 

 the Neocomian seas, and not in the upper oolite. 



GENERAL CONCLUSIONS AS TO THE 'DERIVED' NEOCOMIAN 

 FOSSILS. 



The presence of these 'derived' Neocomian fossils has had 

 curiously different influences upon different observers, according to 

 the different aspects in which they have been regarded. The 

 Rev. T. Wiltshire, looking upon them as indigenous fossils, came 

 to the conclusion that the Hunstanton carstone and ironsands 

 were of the age of the Atherfield clay; Mr Teall, seeing that 

 they were derived fossils, was, it would seem, thereby influenced 

 to consider the Upware and Potton beds of later date than the 

 horizon to which I believe they truly belong ; whilst Mr Godwin 

 Austen and Mr Seeley, recognising them as Neocomian species, 

 and believing them to be indigenous, and seeing also their 

 close correspondence in appearance and preservation to the 

 Jurassic species (Am. biplex, &c.), concluded that these latter 

 likewise were " denizens of the old sea-bed." As proceeding from 

 this belief we have their theories of the cretaceo-oolitic age of the 

 Farringdon and Potton series. 



