150 L. Dudley Stamp— 
Ledian (Auversian).—The lagoon areas of the Upper Calcaire 
grossier were invaded by the sea, which deposited the Sables de 
Beauchamp. These beds are characterized by the occurrence of 
Nummulites variolarius Sow.—Heberti @ Arc. In the Paris Basin 
they generally consist of clean sands (sometimes calcareous), but 
appear to have been formed in shallower water than was the case 
with the earlier marine invasions. In places, therefore, they are 
more markedly false-bedded and frequently coarse. The succeeding 
continental deposit 1s a well-marked fresh-water limestone—the 
Calcaire de Saint Ouen—with Limneea (L. longiscata) and Planorbis. 
Bartonian.—When considering the highest beds of the Hocene 
strata in the Paris region, it 1s necessary to bear constantly in mind 
the more specialized conditions which prevailed during their 
formation. The marine invasion of the Ledian is very distinct, but 
the fauna has a shallow-water aspect. In other words the basin was 
becoming silted up. This is still more apparent in the succeeding 
stage—the Bartonian. One has all the phenomena of the partial 
drying-up of an enclosed sea, culminating in the deposition of 
enormous masses of gypsum. Interstratified with the latter one 
finds beds of marl with marine fossils (Ludian or Marne 4 Pholadomya 
ludensis). The fossils differ slightly from those found in the lower 
part of the stage, but the differences are such as one would expect 
to result from local evolution 7 situ in response to unfavourable 
conditions. It is not difficult to see why the highest series of the 
Eocene beds has been much discussed and numerous correlations 
proposed. 
It is far better, therefore, to take as the type of the highest part 
of the Kocene the Hampshire sequence. There one has a perfectly 
natural cycle of sedimentation, commencing with the marine 
invasion of the Barton Clay (horizon of Nuwmmulites Orbignyi Gal. 
—wemmelensis De la Harpe, = N. prestwichianus Rupert Jones, = 
NV. elegans Sow. var. Prestwichii Rupert Jones), passing upwards 
into the shallower-water conditions of the Barton Sands (Long Mead 
End Beds), which, in turn, fade gradually into the continental 
conditions of the Lower Headon Beds. The stage is very clearly 
defined by the abrupt change at the base of the next marine invasion, 
that of the Middle Headon Beds. 
Briefly, in the Paris Basin there is a lower series of marine sands— 
the Sables de Marines—the fauna of which differs but slightly from 
that of the Ledian, but in which Nuwmmulites variolarius does not 
occur. These are succeeded by a series of marls and gypseous beds. 
Amongst the marls there is a thin, but constant, bed of marl or 
limestone—the Marne & Pholadomyw ludensis or the Caleaire de 
Ludes—with marine fossils. The existence of this limestone has 
caused it to be said that there are two cycles in the highest Hocene 
of the Paris Basin, a lower or Marinesian (sensu stricto) and an upper 
or Ludian. If one examines the Calcaire de Ludes in the field, 
however, as at Verzenay (near the type locality of Ludes), one finds 
