1854.] PRESTWICH LOWER TERTIARIES. 455 



grassier ', and in Belgium, by the Systeme Bruxellien of M. Dumont; 

 and he endeavoured to show the exact correlation of the several divi- 

 sions of these lower tertiaries, and claimed for the " London Ter- 

 tiaries," as a group, a distinct and separate position beneath that of 

 the Paris group, of which latter the Calcaire ffrossier may be taken 

 as the centre and type. The chief points of importance are — that the 

 Lower Bagshots are the equivalents of the Lits coquilliers ; and that 

 the well-known Sable de Bracheux, with its marine fossils, corre- 

 sponds with the lower part of the Woolwich series. 



The author first pointed out that the known equivalents among 

 the Tertiary beds in question are — 



1 . Calcaire grossier, France = Bracklesham Sands, England = 

 Systeme Bruxellien, Belgium. 



2. Lits coquilliers, France = Syst. Ypresien superieur, Belgium. 

 (The zone of Nummulites planulatus.) 



3. Lignites of the Soissonnais = Fluviatile beds of Woolwich and 

 Lewisham. 



Mr. Prestwich then described in detail the grouping of the tertiary 

 strata in France, Belgium, and England respectively ; and, having 

 pointed out the local differences and peculiarities exhibited by these 

 deposits, he entered upon a detailed comparison of the different 

 divisions of the tertiaries of the several districts. 



Beginning with the lowest tertiaries, Mr. Prestwich dwelt upon the 

 correlation of the Thanet Sands of the South-east of England with 

 the Lower Landenian of Belgium, and showed that this series is 

 wanting in the Paris Basin. The Woolwich and Reading series of 

 England is the Upper Landenian of M. Dumont in Belgium ; and 

 its lower, middle, and upper divisions are, according to the author, 

 the equivalents, respectively, of the Glauconie inferieure et Sables 

 inferieurs, lignites et argiles plastiques, and the gres et pou- 

 dingues of the Soissonnais ; whilst at Paris the middle division only, 

 the argile plastique, is represented, and lies immediately on the 

 Chalk. 



The series next in ascending order is the London Clay, which 

 Mr. Prestwich regards as a clearly defined group, with well-marked 

 testaceous types. This, in Belgium, forms the Lower Ypresian of 

 M. Dumont ; and has recently been found by the author near Dieppe, 

 but is wanting in the Paris and Soissonnais districts. In fact, the 

 London Clay dies out southward towards Lille, thus indicating the 

 limits of this old sea on the shore of a southern continent. 



This area having been subsequently depressed, the whole region 

 was occupied by the sea in which the Bagshot series was deposited. 

 The lower portion of this group is represented — by the sands below 

 the Bracklesham beds in Hants, — by the Lower Bagshots of the 

 London district, — the Upjier Ypresian and the Panisilian combined, 

 in Belgium, — and by the Lits coquilliers (which the author here 

 defined), in the Soissonnais district. The middle portion is repre- 

 sented by the Bracklesham beds in Hants, — the middle Bagshots in 

 the London district, — the Systeme Bruxellien of M. Dumont, — and 

 the Calcaire grossier of the Soissonnais and Paris. In the last-named 



VOL. X. — PART I. 2 I 



