PRESTWICH — BRITISH AND FOREIGN TERTIARIES. 



133 



indications of the withdrawal of the sea, and of the presence of 

 bodies of fresh water in the upper part of the Calcaire grossier. 

 These, however, are displaced for a time, and the sea of the Sables 

 moyens covers the whole of the French, English, and probably the 

 Belgian areas ; but at the point where we now leave off, the sea begins 

 to shift its bed from over the greater part * of this more extended 

 area and for a much longer and more settled period. Fresh and 

 brackish water conditions of singular variety and interest set in, and 

 are continued with few breaks (sufficient, however, to show the prox- 

 imity of the sea and of a marine fauna but little changed) up to an- 

 other and more general change, and the introduction of a fauna, 

 both marine and freshwater, in greater part new and distinct. 



Of these changes, and of the correlations prevailing in the three 

 areas under review, during the further continuance of this Eocene 

 period, I hope to treat on a future occasion, having confined the in- 

 quiry at present to that part of the Barton series represented by the 

 clay-beds at Barton and forming its lower division. 



Table of Synchronous Strata of that jportion of the Paris Tertiary 

 Group treated of in this Paper. 



English Area. 



Belgian Area. 



French Area. 



Barton Clay. 



Systeme Laekenien. ? 



Sables Moyens — lower zone. 



Bracklesham 

 Sands 



Upper. 

 Middle. 

 Lower. 



Systeme Bruxellien. 



Calcaire 



grossier & 

 Glauconie 

 grossiere. 



■ Freshwater marls. 



Upper flags. 



Freestone. 

 _ Greenish sands. 



Lower Bagiliot Sands. 



Systeme Ypresien 

 superiem-. 



Lits Coquilliers and Glauconie 

 Moyenne. 



The subdivisions of the Bracklesham Sands here introduced are merely no- 

 minal, as they present no marked or permanent limits ; the middle of the series 

 is, however, distinguished by the greater abundance of fossils at White Chflf Bay 

 (see p. 99). To the sands underlying the Bracklesham series, and forming pos- 

 sibly a lower division tliereof, I think it more convenient to restrict the term 

 of Lower Bagshot Sands, although both in the Isle of Wight and on the Hamp- 

 shire coast they seem, in structure, to form part of one like series of strata. 



The Glauconie grossiere includes the Glauconie superieure of M. Graves. With 

 the Lits coquilliers of D'Archiac, I include the Glaisesf and Sables divers, i. e. 

 I take his upper three divisions of his group of Sables Inferieurs together. The 

 Glauconie Moyenne I take as defined by M. Graves. 



* Partially only frcm off the Belgian area. 



t This with a doubt. 



