444 G. W. Lamplugh — Age of English Wealden Series. 



since it is universally acknowledged that the fresh-water conditions 

 did not set in until the closing stages of the Jurassic period, it seems 

 inevitable from this consideration alone that such conditions per- 

 sisted into Lower Cretaceous times. 



Again, nearly all the ' Wealden ' fossils in which Jurassic affinities 

 have been observed have been obtained from the lower part of the 

 Wealden Series, i.e. from the Hastings Beds, and very little is known 

 respecting the corresponding fossils from the Weald Clay, which 

 probably represents the major portion of the Wealden period. 



Moreover, the argument from the Jurassic affinities of the land 

 and fresh-water fossils alone inspires no confidence, since if we 

 eliminate the Lower Wealden fossils from the Lower Cretaceous 

 lists our knowledge is practically limited to the marine life of this 

 period ; and it may be legitimately asked whether the land and 

 fresh-water fossils of the Hastings Beds are not, after all, of the 

 character proper to the lowermost part of the Cretaceous, wherein 

 a close relationship to the immediately preceding period seems quite 

 appropriate. 



It is from the stratigraphical evidence, however, that the Lower 

 Cretaceous age of at least the greater portion of the English 

 Wealden Series can be most satisfactorily established by its relation 

 to the marine sequence which must form the ultimate basis of the 

 classification. The marine beds directly overlying the Weald Clay 

 in the South of England represent only the latest stage (Aptien) of 

 the Lower Cretaceous period ; and although there is a sharp line 

 of demarcation at their base, this seems to denote a rapid change of 

 conditions and not a lengthy time-interval, since the incoming of 

 marine or brackish-water shells near the top of the Wealden strata 

 in Dorset, Hampshire, and Surrey, foreshadowing the termination of 

 the fresh-water episode, indicates that the series is practically com- 

 plete, and had undergone little, if any, erosion in these parts before 

 the deposition of the overlying marine strata. Such erosion may, 

 however, have taken place locally towards the easterly and westerly 

 terminations of the basin of deposition, where the topmost beds of 

 the Wealden Series are not found. 



In the Speeton Clay, where the Lower Cretaceous marine sequence 

 is fully represented, the equivalents of the Lower Greensand and 

 Atherfield Clay of the South of England are comprised within 

 a relatively narrow compass in the sparingly fossiliferous upper 

 part of the sequence ; ^ and therefore, by far the greater portion of 

 the Lower Cretaceous period, if represented at all in the South of 

 England, must be represented in the Wealden Series. The portion of 

 the Speeton Clay unrepresented by marine sediments in the south 

 includes the lower part of the zone of Belemnites Brunsvicensis and 

 the whole of the zone of Bel. jaculum, both undoubtedly Lower 

 Cretaceous (Barremien, Hauler ivien, and Valanginien), together with 

 the whole of the zone of Bel. lateralis, the fauna of which shows 

 Jurassic affinities. Furthermore, in tracing this marine series south- 

 ward from Yorkshire, through Lincolnshire into Norfolk, the author 



1 See Summary of Progress of the Geological Survey for 1897, p. 129. 



