﻿Mr. W.Topley on the Cretaceous Rocks of the Bas-Boulonnais. 149 



in the Society's Library, he had described and referred to the age 

 of the Bagshot sands. Premising that there could be no mistake as 

 to the beds under discussion, as Mr. Hughes and the author had 

 found their lines of the Middle Glacial gravel (termed " gravel of 

 the lower plain" by the former geologist) to coincide, Mr. Wood 

 described the distribution of the gravels which he regarded as of Bag- 

 shot age, and gave an account of the physical phenomena which he 

 conceived had led to their deposition and subsequent denudation. 

 He objected to Mr. Hughes's view, that the pebble-bed termed 

 " gravel of the higher plain " by Mr. Hughes belongs to a period 

 anterior to the gravel of the lower plain, as it involves the admission 

 that there has been a period intermediate between that of the Bag- 

 shot pebble-beds and the Glacial, during which the sea occupied 

 these counties and deposited the gravel of the higher plain — an ad- 

 mission which would be fatal to his view of the Bagshot age of the 

 pebble-beds described in this paper. 



Mr. Prestwich was inclined to regard some of the beds referred 

 by the author to the Bagshot series rather as local drifts derived 

 mainly from those beds than as the beds themselves. 



Mr. Whitaker saw a difficulty in classing the pebble-beds at 

 Brentwood and elsewhere among the Bagshot beds, as in the London 

 district, at all events, no such pebble-beds occur in the Bagshot 

 series. 



Mr. Evans pointed out the difficulty in supposing that the 

 gravels at the high level could have been deposited at a later period 

 than those of the low level without, at the same time, overlying the 

 latter. 



Mr. Searles Wood considered that there was not that broad 

 line of distinction to be drawn between the gravels of the higher 

 and lower level ; he maintained that the pebble-beds when truly in 

 situ were free from Quartzite, and truly of the Bagshot age. 



3. " On the Cretaceous Rocks of the Bas-Boulonnais." By 

 William Topley, Esq., F.G.S., of the Geological Survey of England 

 and Wales. 



After a resume of previous notices on the subject, the author 

 described the Physical Geography of the district and the Cretaceous 

 beds below the chalk, comparing them with their English equi- 

 valents. 



Each great division of the Kentish series was stated to be repre- 

 sented in the Boulonnais, although, in every case, in diminished 

 thickness. The Upper Greensand and Gault were shown to sur- 

 round the district at the base of the chalk hills ; and a fcssiliferous 

 phosphatic bed was described at the bottom of the Gault, as in Kent. 

 This bed was regarded by the author as a passage between Gault 

 and Lower Greensand, as nodules with fossils often occur in the 

 sands below ; and it was shown to be frequently impossible in 

 sections to mark off accurately the Lower Greensand from the Gault. 

 The marked change in the faunse of these formations was regarded 

 by the author as due to the complete change in the conditions of 

 deposit. 



The sands which occur below the Gault were shown to belong 



