62 MK. G. W. LAMPLTJGH ON THE JTJXCTIOX OF [vol. Ixxviii, 



breccia at its base, banked around the crags and upon the slopes of 

 the ]'eef. It has been argued that the sand here is Upper Greensand 

 in an inverted position, but every feature of the section tells against 

 the supposition. The peculiar breccia, so unlike any other deposit 

 ".known in the district, is unquestionably linked with that of 

 'Chamberlain Barn, known to lie at the bottom, of fossiliferous 

 Mammillatus beds ; and the difference in the composition of the 

 beds above it is no more than these inherently variable beds display 

 from place to place in other sections. In this particular instance 

 the reason for the difference is not far to seek, as the section shows 

 that the sand was accumulated among the crags on the side of the 

 reef, and presumably was thus sheltered from the full sweep of 

 the currents. The calcareous particles mixed with the sand denote 

 -the wastage of the neighbouring shell-bank, probably already 

 ■partl}^ consolidated. It is possible that some of the sand at this 

 ispot may be equivalent in time to some of the lowest Grault clays 

 ■of the deeper- water areas, but it is certainly older than the clays 

 of the immediate neighbourhood, and may be placed most con- 

 "veiiiently, as a whole, in the Mammillatus Zone. 



In the Grarside's-pit section we reach the margin of the area in 

 which the fossiliferous limestone occurs, and the beds of the Grove- 

 bury type are wanting or found only in hollows and pockets. 

 'The description of the limestone and its concomitants in our 

 jjrevious paper has stood the test of all my later observations, and 

 needs no modification in any essential. The conclusions as to its 

 stratigraphical position and mode of origin have been strengthened 

 by the new evidence, and it w^ill be shoMai (in § V) that the 

 Tecently- urged palaeontological argument for a hypothetical in- 

 version of the beds in relation to the Gault has no foundation in 

 fact. The discovery of 'Ammonites regularis' and 'A. cf. beudanti' 

 in the limestone (p. 47) along with some other fossils, has afforded 

 ;a palaeontological link with the Grovebury type of Basement beds, 

 while its stratigraphical association with the same beds is now 

 ■ established by the new Chamberlain Barn section and that at 

 :Southcott. In our previous discussion we suggested that the 

 Shenlev fauna mio-ht be somewhat older than that of the Mammil- 

 latus Bed of Folkestone. It is now apparent, however, that the bed 

 ■at Folkestone does not represent the whole Zone ; and the Shenley 

 limestone should fall within the Mammillatus Zone in the broader 

 sense. I p^ave reason, in the same discussion, for holding that the 

 English Mammillatus beds should be retained in the Lower 

 Greensand, their original classification, on the grounds of priority 

 and of stratigraphical convenience^ ; but, as then stated, I regard 

 these matters of conventional classification as of secondary con- 



^ It will be noticed that, iu his account of the Long Crendon section (quoted 

 ■on p. 41), Jukes-Browne classed the thin ferruginous beds below the Gault 

 as ' Lower Greensand,' on stratigraphical grounds ; but, if he had been aware 

 that they contained fossils linking them with the Mammillatus beds, he 

 would have united them with the Gault as ' Upper Cretaceous,' since he 

 .adhered to the French classification of the Mammillatus Zone. 



