208 NEOZOIC TIME. [CHAP. XI. 



pass up into the brackish and freshwater beds of the 

 overlying Oligocene series. 



Whether the Barton Beds ever reached northward into 

 the area of the London basin we cannot tell, because of 

 the uncertainty that hangs over the correlation of the 

 Bagshot Beds ; it seems probable, however, that the Barton 

 Clay was a formation of much more limited extent than 

 the London Clay. 



In the Paris basin the Bracklesham Beds are represented 

 by the Calcaire G-rossier, a limestone group about 100 

 feet thick, and containing numerous fossils. At the base 

 there is a layer of pebbles overlain by glauconitic sands 

 and limestones, and these by shelly and foraminiferal 

 limestones, which must have formed in clear water at a 

 considerable distance from land. The thickness of the 

 group is only about 100 feet, but they evidently correspond 

 to the whole of the Bracklesham and Bournemouth Beds, 

 for such limestones would be accumulated much more 

 slowly than deposits near the mouth of a large river. The 

 Calcaire G-rossier is succeeded by sands and sandstones, 

 with marine fossils of Bartonian type. 



The French series, therefore, differs from ours chiefly 

 in the absence of the two great clay formations, the London 

 and Barton Clays, which are such conspicuous members of 

 our series. The former is consequently much thinner 

 than ours, and all the beds, except the Calcaire Grossier, 

 would seem to have been formed near a shore-line. The 

 Calcaire Grossier stands out among these shallow-water 

 beds, and marks the occurrence of an extensive subsidence, 

 while its fauna proves that this subsidence opened the- 

 way for the immigration of a new and more tropical or 

 southern fauna. 



The only other region it is necessary to notice is that of 

 northern Ireland and western Scotland, where a very 

 different set of rocks was being accumulated. These dis- 



