part 1] GAULT AND LOWEE GREEXSAJSTD NEAR LEIGHTON. 59» 



difference exists between the ' Mammillatus ' nodules and those at 

 the base of the Upper Gault. 



Prof. Barrois's comments ^ on the manner of occurrence of the 

 nodules are also very apposite. Keferring to the segregated, 

 nodules at the top of the Mammillatus Beds, he writes : — 



' Les lits qu'ils forment aujourd'hui dans ces sables ne sont pas d'origine 

 premiere ; ces nodules ont pris naissance isolement dans le depot des sables, 

 puis des affouillements locaux et sous-marins ont dcchausse en divers points 

 ces nodules, ont enlevo le sable qui les empatait et laisse sur place sans les 

 rouler les nodules et les fossiles trop lourds pour etre enleves. En un mot, je 

 crois les lits de nodules de phosphate de chaux (coquins de sable),, 

 remanies sur place, et independamment les uns des autres -. ' [and, after- 

 fig-uring- and describing examples, he adds] ' on doit croire ici a un remanie- 

 ment sur place ; c'est-a-dire, a I'enlevement des parties tenues argilo-sableuses 

 et a I'accumulation consoquente des nodules plus lourds.' 



The same conclusion with res^ard to the mode of accumulation' 

 of the Cretaceous phosphatic nodule-beds has been expressed by 

 many English investigators.^ Yet, in spite of all, one often still 

 finds that such nodules are postulated to be ' derivative ' or ' derived 

 pebbles ' as a matter of course, particularly if their fossil-contents 

 happen not to agree with palseontological preconceptions. The- 

 possibility of the nodules becoming derivative pebbles is obvious,, 

 though their material is not of a kind to sustain much hard wear ; 

 but the weight of existing evidence demands that they should be- 

 assumed to be in place, or, at least, 'remanies sur place,' unless 

 the contrary can be proved; and not vice versa. 



It has long been recognized that phosphatic nodules are indica- 

 tive of slow sedimentation (see ante, p. 9) ; and if there has 

 been, in addition, a repeated washing-awa}^ of their matrix, with 

 resultant concentration of the nodules, we may expect to find, as 

 we generally do find, that the organic relics contained within 

 narrow bounds represent a condensed fauna which elsewhere may 

 tenant a great thickness of sediments of another type. The nodule- 

 bearing Mammillatus Beds of the North of France are represented 

 in North Germany by a fuller sequence which is capable of sub- 

 division, and the later German investigators, on the strength of 

 this, have thrown aside the French classification, and have adopted 

 a new scheme of zones. In their general scheme our Upper and 

 Lower Gault become 'Upper Gault'; our Mammillatus Beds 

 become the upper part of the ' Middle Gault,' with a lower part not 

 yet recognized in this countr}^ ; and most of our Lower Greensand 



1 Ann. Soc. Geol. Nord, vol. v (1878) p. 278. 



" As, for example, F. G. H. Price, ' The Gault ' 1879, p. 9 ; and ' Probable 

 Depth of the Gault Sea ' Proc. Geol. Assoc, vol. iv (1875) p. 269. A. J. Jukes- 

 Browne, 'The Cambridge Gault & Greensand' Q. J. G. S. vol. xxxi (1875) 

 p. 282 ; (with W. Hill) ' The Lower Part of the Upper Cretaceous Series in 

 West Suffolk, &c.' Ibid, vol. xliii (1887) p. 572; and 'The Gault & Upper 

 Greensand ' Mem. Geol. Surv. 1900, p. 428. G. W. Lamplugh, ' On .... the 

 Speeton Clay' Q. J. G. S. vol. xlv (1889) pp. 584, 588; 'The Speeton Series 

 in Yorkshire & Lincolnshire ' Ihid. vol. lii (1896) pp. 195-99 ; ' Lower 

 Cretaceous Phosphatic Beds, &c.' Geol. Mag. 1904, p. 551, and Eep. Brit. 

 Assoc. 1904, p. 548. 



