Cycles of Sedimentation v1 the Hocene. 195 
Lutetian.—The beds above the Ypresian in the London Basin occur 
in a somewhat limited area—the Bagshot District of Surrey and 
Berkshire. The marine Lutetian is rep resented by glauconitic clayey 
sands, etc., in which Nummulites levigatus has been found. These 
are the Bracklesham Beds of the Survey and recent authors. The 
Lutetian thickens eastwards from about 30 feet near Ascot to about 
100 feet on St. George’s Hill, near Weybridge. The upper part 
indicates shallower-water conditions. __ 
Ledian or Bartonian.—The “‘ Upper Bagshot Sands ”’ (now usually 
called Barton Sands) of the London Basin comprise a series of 
sands over 200 feet in thickness with a very persistent and well- 
defined pebble-bed at the base. Marine fossils poorly preserved are 
found locally, and the fauna is generally considered as indicating 
a Lower Barton age. If that is so the Ledian is absent from 
the London Basin. Although “ Nummulites elegans” (?=N. 
Prestwichit) was recorded by Prestwich himself in 18471 he seems 
to have favoured the correlation of these “‘ Upper Bagshot Sands ”’ 
with the Upper Bracklesham or Ledian.2 A careful search for 
Nummulites in the ironstones should settle this question.® 
D. Tue Berean “ BAstIn’’. 
In many ways the Hocene strata in Belgium and North France 
differ from those in other parts of the Basin. Above the Landenian 
the succession is almost, if not entirely, marine. This is due, 
doubtless, to the absence of rivers bringing sediment from the east. 
At the same time the Paleozoic floor in Belgium is found at no great 
depth, and parts of it projected to form islands or rocky submerged 
shoals in the Eocene sea. This is particularly noticeable in the case 
of the Diorite masses of Quenast, etc., round which one finds con- 
glomeratic beds of Landenian or Ypresian age. It is well to bear 
this fact in mind in considering the distribution of the deposits 
known as “ Paniselian ”’ 
The beds can be grouped in the same six cycles as in other parts 
of the Basin. The succession has naturally often been compared 
with that in the Paris region, and the correlation is now well 
established. For that reason the diagram (Fig. 4) has been drawn 
to show the connexion with the London Basin. 
Montian.—As in the Paris Basin, the Montian deposits are of 
restricted occurrence, being found principally in the “ Bassin de 
Mons”. The “ Bassin de Mons”? is a synclinal region running from 
west to east. It is partly an original basin of deposition, and must 
have formed a gulf-like inlet from the west. The Eocene rocks now 
form a very pronounced syncline due to later folding. The marine 
Montian consists of the famous Calcaire grossier de Mons—a very 
fossiliferous soft limestone—which, unfortunately, is rarely visible. 
1 Prestwich, Quart. Journ. Geol. Soc., vol, ii, 1847, p. 393. 
2 Prestwich (in discussion), ibid., vol. xxxix, 1883, p. 354. 
3 White records NV. variolarius, op. cit., 1917, p. 270 (Handb. Reg. Geol.). 
