Cycles of Sedimentation in the Eocene. 149 
regions of Upper Landenian fluviatile or lacustrine beds (e.g. mottled 
clays) the mixed fauna of the Sables de Sinceny does not occur, and 
the fossils from the base of the Ypresian are entirely marine. 
Apart from these basal beds the Ypresian is represented in the 
Paris Basin by a series of sands—the Sables de Cuise (sensu lato). 
It is characterized by the occurrence of Nummulites planulatus d’ Orb. 
—elegans Sow.! The change from the disturbed conditions which 
prevailed during the deposition of the Sables de Sinceny to the more 
tranquil conditions of the Sables de Cuise is marked by the existence 
in many localities of a thin basal bed to the last-mentioned sands. 
In exactly the same way the London Clay of the London Basin retains 
its own basement bed even when resting on the Blackheath Beds. 
The Sables de Cuise are glauconitic sands, sometimes coarse, 
especially near the base, but on the whole remarkably fine-grained. 
The Cuise Sands are succeeded by presumed continental deposits— 
a bed of greenish clay without fossils (Argile de Laon or de Saint 
Gobain),. or by sands with fluviatile fossils (Sables & Unios 
et Térédines). 
Lutetian—The Lutetian is the famous Calcaire grossier of the 
Paris Basin. It generally commences with a coarse glauconitic 
sand, containing pebbles or rolled fossils at the base. The marine 
Lutetian consists of varied calcareous beds, of which the best-known 
is the shelly, foraminiferal limestone, so prized for building. Sandy 
limestones and calcareous sands are of common occurrence. 
Although characterized throughout by the presence of Nummulites 
levigatus Lamk.—Lamarcki @’ Arc., this fossil is ‘especially abundant 
at one horizon. Leriche has shown that this marine Lutetian is 
divisible into four zones :—® 
4. Zone of Cerithium giganteum. 
3. Zone of Ditrupa strangulata. 
2. Zone of Nummulites levigatus. 
1. Zone of Maretia Omaliusi. 
The zone of Nummulites levigatus constitutes a bed a few metres 
thick, consisting almost entirely of the zone-fossil. It is known as 
the ** Pierre a liards”’, and is a very easily recognized horizon. The 
geographical distribution of the zones demonstrates beautifully 
the successive overlap; the first zone only just reaches the Paris 
Basin, while the higher zones have successively wider distribution. 
The succeeding continental beds are the so-called Calcaire grossier 
supérieur, and comprise thin-bedded limestones with estuarine 
fossils (especially Cerithium). Towards the periphery of the basin 
these pass into unfossiliferous mottled clays and mazls. 
* In most cases the megalospheric and microspheric forms of each species - 
of Nummulites have been described under different names. In this paper the 
double name is given on the first occasion of reference to the species, but, for 
the sake of brevity, the more usual name is generally used. 
® Leriche, op. cit., 1912, p. 700 (with references). 
3 Leriche, op. cit., 1912, pl. xxv. 
