TRA.VSACTIONS OF SEOTION C. 767 



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 overlyino- 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 demarca- 

 tion at their base, this seems to denote a rapid change of conditions and not a 

 lengthy tune-interval, since the incoming of marine or brackish-water shells near 

 the top of the Wealden strata in Dorset, Hampshire, and Surrey, foreshadowino- 

 the termination of the fresh-water episode, indicates that the series is practically 

 complete, and has 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 fullv 

 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 o-reater 

 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 (Barremteti, Hauterivieii, and Valcmginien) 

 together with the whole of the Zone of Bel. lateralis, the fauna of which shows 

 J urassic affinities. Furthermore, in tracing this marine series southward from York- 

 shire through Lincolnshire into Norfolk, the author has found that in the latter 

 county the lower zones are apparently absent, and the remainino- portion represent- 

 ing probably the lower part of the Zone of Bel. brunsvicensis^ia chara'ctensed by 

 the presence among the marine fossils of plant remains, chiefly frao'ments of a 

 Wealden fern, Weichselia (Mantel^), and by other indications of flu'viatile influ- 

 ence, suggesting the beginning of a lateral change into Wealden conditions - 



With the well-recognised gradual development of fresh-water conditions in 

 the Turbeck beds of the Wealden area towards the close of the Jurassic period 

 and indications of the reversal of this process in the top of the Weald Clay durin^^ 

 the later stages of the Lower Cretaceous, and with evidence for a lateral passao-e o'f 

 part of the Lower Cretaceous marine sediments of the North of Enn-land "into 

 estuarine deposits further south, there seems every reason to believe that in the 

 fresh-water or estuarine strata of the English Wealden the whole of the time- 

 interval between the Portlandian and Aptien stages is represented, and that it 

 would be equally erroneous to classify the series entirely with the Jurassic 

 system and entirely with the Cretaceous, if the hitherto recognised boundary of these 

 systems m the marine deposits of other areas is to be maintained. 



The deposits classed as Wealden in Belgium, Germany, and France appear to 

 be much more restricted in vertical ran^e than the English series, and to represent 

 different parts of the period in different places, but nowhere to imply the same 

 long continuance of fresh-water conditions in a single area. 



' ^e.e. Summary of Progress of the Geological Survey f.iT l^':)! p 1''9 

 = See Survey Mem. Borders of the Wash (sheet 69 O.S)., pp. '21I25. ' 



Report on the Irish Elk Remains in the Isle of Man. 

 See Reports, p. 319. 



