386 Reports and Proceedings, 



Discussion. — 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 Eocks 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 de- 

 scribed the Physical Geography of the district and the Cretaceous 

 beds below the Chalk, comparing them with their English equivalents. 



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 fossiliferous 

 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 fauna 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 

 partly to the Folkestone beds (or highest division of the Lower 

 Greensand) and partly to the Wealden — the intermediate stages 

 being absent, although well developed where last seen on the Kentish 

 coast. The ferruginous sands, with variegated clays and iron-ore, 

 which cap the hills in the interior of the Bas-Boulonnais, were re- 

 ferred by the author to the Wealden series, as were also the pebble- 

 beds of St. Etienne and elsewhere, hitherto regarded as " drift." 



The Wealden beds were shown to rest upon the Portlandian around 

 Boulogne, and upon lower members of the Oolites in the west and 

 north; while in the north-west corner they fill "pipes" in Palaeo- 

 zoic limestones. The Wealden beds, thus proved to be unconform- 

 able to those below them, were shown to underlie conformably the 

 remaining Cretaceous beds above, thinning away, however, against 

 the old ridge, where, by overlapping, the Lower Greensand and 

 finally the Gault, rest immediately upon the Palaeozoic rocks. 



The paper was illustrated by a map, showing the probable out- 

 crop of the Cretaceous rocks beneath the English Channel. 



Discussion. — Sir Koderick Murchison, without doubting the cor- 

 rectness of the author's views, wished that fossil evidence had been 



