64 ME. G. AV. LAMPLUGH OX THE JUXCTIOX OF [vol. Ixxviii^ 



evidence of scouring and abrasion, to be noted on the upper surface 

 of the top pan wherever it has remained unbroken, also shows that 

 this la3'er was in existence as a hard bed before the covering strata 

 Avere deposited. Most of these points Avere duly noted in our 

 previous communication, and all have been contirmed by later 

 obserA^ations. That there maA" have been further seo-reo'ation of 

 ii'on resulting from the Aveathering of the deposits in comparatiA^ely 

 recent times also receiA^ed early consideration (L. W., p. 240), and 

 more Avas then assigned to it than the later eA'idence indicates as 

 probable. The main effect of recent weathering appears to have 

 tended toAvards the decomposition of all except the more stable coiu- 

 ponents of the breccia, and not to the induration of any part of it. 

 Some of the patchy ferruginous discoloration of the highly porous 

 Silver Sand probably marks the com*se of the iron-solutions per- 

 colating from decomposing breccia in late times. 



It is remarkable that this condition of iron-concentration is 

 exhibited in almost all the shalloAV-Avater deposits accumulated in 

 this country towards the end of LoAver Cretaceous times and during 

 the early stages of the Uj)per Cretaceous transgression. Thus, in 

 the Isle of Wight, A\^e find at this horizon the Carstone or Fer- 

 ruginous Sands ^ ; in West Sussex, the crimson grit — a thin band 

 of hard ferricrete ~ ; in the Yale of AVardour and other parts of 

 Wiltshire, gritty ferruginous beds ^ ; in Oxfordshire, the Hurst- 

 Hill and Boar's- Hill Sands ^; in Norfolk and Lincolnshire, the 

 Carstone ^ ; in Yorkshire, at the Avestern edge of the Chalk Wolds, 

 patches of ferruginous sand, and, AA^here these are absent, an iron- 

 stone breccia in the attenuated Bed Chalk. ^ It has been obserA^ed 

 in all these cases that the ferruginous beds hang in stratigraphical 

 continuity with the overlying Upper Ci'etaceous rocks, but have 

 usually a sharp and sometimes transgressive basement."^ Like the 

 Tourtias of Flanders, they are evidently not strictly synchronous in 

 separate districts, but mark a condition of the encroaching shallow 

 sea, Avhen the land Avas only in part submerged and still yielded 

 much Avaste to the current-swept channels and straits which were 

 gradually expanding around its remnants. In some cases the 

 present aspect of the beds may be due to the decomposition of 

 original sjlauconite long after theu' accumulation ; but often it can 



The following' references migtit be greatly expanded, but Tvill serve as 

 g'eneral indications to the literature : — 



i ' Geology of tbe Isle of Wight ' Mem. Geol. Surv. 2nd ed. (1889) pp. 52-59. 



2 'Geology of the Country near Chichester' Ibid. 1903, pp. 12, 16. 



3 'Cretaceous Rocks, &c. vol. i — Gatilt & Upper Greensand' Ibid. 1900, 

 p. 228 : and ' Geology of the Country South & East of Devizes ' Ibid. 1905, 

 pp. 8-12. 



•* ' Geology of the Country around Oxford' Ibid. 1908, pp. 75-78. 



° A. Strahan, 'On the Lincolnshire Carstone' Q. J. G. S. voL xlii (1886) 

 pp. 486-92. 



^ ' Geology of the Country North-East of York & South of Malton ' Mem. 

 Geol. Surv. 1884, pp. 25-26 ; and ' Special Reports on Mineral Resources, &c. 

 Tol. xii: Iron Ores (contd.)— Bedded Ores, &c ' Ibid. 1920, pp. 207, 208. 



'' A. Strahan, op. supra cit. pp. 489-90, and ' Geology of the Isle of Wig-ht' 

 op. supra cit. p. 53. 



