472 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 3, 



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

 niainlj 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 j^ebble-beds occur in the Bagshot 

 series. 



Mr. Eyan"s pointed out the extreme improbability of the gravels 

 at the high level having been deposited at a later period than 

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

 latter. 



Mr. Seaeles 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 referred by him to 

 the Bagshot series, when truly in situ, were free from Quartzite. 



3. On the Lower Cretaceous Beds of the Bas-Bottloistj-ais, with notes 

 on their English Eqitiyalents. By William Topley, Esq., F.G.S., 

 of the Geological Survey of England and Wales. 



(Abridged.) 



Contents. 



I. G-eneral description of the district. 

 II. Description of the beds. 



1. Upper Grreensand and G-ault. 



2. Junction beds. 



3. Lower G-reensand. 



4. Neocomian (?). 



5. Wealden. 



6. Purbeck. 

 III. Conclusion. 



The following notes are the result of an excursion made, with my 

 colleague Mr. ^Tiitaker, in the summer of 1866, supplemented by 

 two hasty visits by myself later in the same year. 



To Mr. Whitaker and to M. E. Eigaux, of Boulogne, I am in- 

 debted for much assistance. 



I. General Description of the District. 



The Bas-Boulonnais forms the easterly continuation of the English 

 Wealden area, both being bounded alike by a well-defined escarp- 

 ment of Chalk. The lowest beds exposed in the Weald have 

 been doubtfully referred to the Purbeck formation ; but none of 

 undoubted precretaceous age occur therein on the English side of 

 the Channel. 



In the Bas Boulonnais the major part of the surface is occupied by 

 Lower Secondary and Palaeozoic beds, the Lower Cretaceous rocks 

 occupying only a narrow border at the foot of the Chalk escarpment, 

 and capping the hills in the interior. The Chalk falls away from 

 the escarpment with a gentle slope. The Gault generally occupies 

 a slight depression at the base of the Chalk hills ; but, from its di- 

 minished thickness, the valley thus formed is far less striking than 



