England and the " Red Chalk " of the Eastern Counties. 199 



lower strata are not seen westward of mid-Dorset ; towards the 

 north they do not extend beyond West Dereham. Indeed, these 

 most Avesterly and northerly occurrences may only be isolated 

 patches. Both at Okeford Fitzpaine and at West Dereham the Lower 

 Gault has been denuded down almost to its base. At Okeford 

 Fitzpaine these beds are far removed from their nearest outcrop ; 

 to the south of West Dereham, they are absent in places and the 

 surface of ])ost-i)iferruptus denudation is situated almost at the base 

 of the Lower Greensand. Whilst there is evidence that a certain 

 degree of tilting and general pla nation of the Lower Gault and 

 older strata took place before Upper Gault deposition began, the 

 facts just mentioned seem to suggest that some shallow folding of 

 the beds may have taken place before the transgression and that, 

 here and there, remnants of the Lower Gault in the synclinals have 

 escaped total removal. 



While these considerations arising out of the present study may 

 throw^ light on the irregular occurrence of the mammillatus-zone 

 in this country, which has frequently been the subject of comment, 

 the extensive erosioi: accompanying this transgression at the close 

 of Middle Albian time introduces a factor to be reckoned with 

 in any comprehensive study of the Lower Greensand. The 

 uncertainty in correlating the sandy strata which, in different 

 localities, appear to form the top of the'Aptian Series has always been 

 great, owing to the sparsely fossiliferous nature of these deposits. 

 The difficulty is increased by the knowledge that erosion of these 

 beds had taken place here and there with great local inequality 

 before the deposition of the Upper Gault. To mention one example, 

 the true position of the Carstone of the Hunstanton district has 

 never been ascertained ; possibly the best clue is to be sought in a 

 study and correlation of the fauna of the Snettisham Clay, a 

 desirable subject for investigation. The so-called " Carstone " of 

 SandoAvn Bay, Isle of Wight, is probably on a much higher horizon. 

 A transgression of the mammillatus-zone must also have 

 produced its local effects on the imderlying sands. At Okeford 

 Fitzpaine that zone rests almost directly upon Kimmeridge Clay, 

 wbile we have recently obtained evidence of a corresponding un- 

 conformity of ])re-mammillatus date in Bedfordshire and in Norfolk. 



Of the movements that gave rise to transgressions during 

 Cretaceous time in this country, that which produced the Ujiper 

 Gault overlap has left the most conspicuous effects. It was one of 

 the several widespread movements which brought about the 

 remarkable extensions of Upper Albian and Lower Cenomaniaa 

 deposits in many parts of the world. 



Our examination of the '"' Eed Chalk " of Norfolk has led us to 

 correlate its lower three-quarters with the Upper Gault, its upper- 

 most quarter with the Iiower Chalk, perhaps including the Pecten 

 apser zone. We regard these beds as a much condensed continuous 

 aeries. At Speeton we have found the Upper Gault to be repre- 



