Cycles of Sedimentation in the Eocene. 155 
are three pebble-beds which permit of a triple division of the clay. 
Kach division commences with a layer of pebbles, followed by stiff 
clay, which becomes sandy in the upper part, passing into a sand. 
White ! emphasizes these variations in lithology and points out that 
they indicate a change from comparatively deep water to shallower- 
water conditions—or “* shoaling’’—and he actually refers to them as 
““eycles of deposition”’. At the same time White points out that 
these pebble-beds are constant neither in number nor in position. 
It is interesting to note that they imcrease in number as one 
approaches the area of the Wealden Dome, and there can be little 
doubt that that was the source of the pebbles, and that gentle 
movements of uplift during Ypresian times were responsible for the 
changes in lithology. It must be emphasized that these slight 
variations in the mass of the clay do not constitute cycles of 
deposition. 
Lutetian.—No apology is needed for dividing the Bracklesham 
Beds into two divisions. Previous observers have already made 
this separation, and Leriche,? White,* and others have correlated 
the two divisions with the French succession of Lutetian and Ledian 
(Auversian). The first-mentioned beds are characterized by the 
presence of Nummutlites levigatus, the second by the presence of 
N. variolarius. These two species never occur together. The 
Lutetian invasion is marked by a basal pebble-bed or pebbly 
glauconitic sand at Bracklesham and Whitecliff Bays, and is very 
distinct. Remembering the enormous amount of sediment which 
was being being brought from the west and being deposited as the 
Bagshot Sands in the neighbourhood of Bournemouth, it is not 
surprising that the marine sediments of the encroaching sea should 
be mixed with, and partly masked by, the continental deposits. 
Even as far east as Whitecliff Bay one finds the basal glauconitic 
bed of the Lutetian succeeded by “ green sand and laminated clays 
with seams of lignite ” “(Fisher’s Bed IT), and passing further west 
the separation ‘of the marine beds becomes more difficult. As 
mentioned above, the representatives of the marine Lutetian have 
not been clearly distinguished in Alum Bay. Passing across to 
Bournemouth Bay, the Bournemouth Marine Beds evidently mark 
the Lutetian marine invasion, but are at almost the western end of 
the sea, or, as White puts it, the beds represent “ the seaward facies 
of a deltaic formation such as the Freshwater Series ”’.° 
1 White, loc. inti, Jo, JUL 
4 Leriche, “ Observations sur la Géologie de l’Hle de Wight’: Ann. Soc. 
géol. Nord, vol. xxxiv, 1905, p. 16. 
3 White, loc. cit., p. 20. 
4 Fisher, SaOn the Bracklesham Beds of the Isle of Wight Basin’’: Quart. 
Journ. Geol. Soe., vol. xviii, 1862, p. 65. 
> White, “ Geology of the Country around Bournemouth,” 2nd ed. (Mem. 
Geol. Surv. ), 1917, p. 29. The Bournemouth Freshwater Series is situated in 
the upper part of the Ba gshot Sands. 
