LOWER CHALK—NORTH-EAST OF FRANCE. 
241 
constant and continuous throughout the east of France, but that 
the beds which correspond to our Chalk Marl and Grey Chalk thin 
out and disappear as they pass toward the Palaeozoic ridge. 
Such a stratigraphical arrangement is certainly possible, but it 
is not that which would a priori be most probable. The epoch of the 
Cenomanian in the Anglo-Parisian basin is admitted by all geolo¬ 
gists to have been one of gradual and continued subsidence, which 
permitted the waters of the Cretaceous sea to spread farther and 
farther over the surrounding land. Dr. Barrois offers no evidence 
for the idea of any local interruption of this subsidence in the middle 
of the Cenomanian epoch; and if there was no such interruption, 
the mode of thinning would most probably be by overlap. 
As the Department du Nord presents a special attenuated and 
evidently shallow water type of the Cenomanian, and as the zones 
of the deep water English and Boulonnais type cannot be traced 
continuously into the Ardennes, we think that the relations of the 
Tourtias will be better understood if they are approached from the 
south. We shall therefore first give the succession to be found in 
the Departments of the Yonne and the Aube, where a deep-water 
facies presents itself, very similar to that of southern England. 
From this region the stratigraphical changes can be traced north¬ 
ward along the outcrop which runs through the Departments 
of the Marne, Ardennes, and Aisne. 
It must be understood that in the following account we have 
taken Professor Barrois’ memoirs* as our chief guide for the strati¬ 
graphical facts, but shall assume that the zonal correlation of the 
beds is open to revision and correction. On this some remarks 
will be made in the sequel. 
Departments of Yonne, Aube, Marne, and Aisne. —Commencing, 
therefore, in the Yonne we find the Cenomanian presenting a fair 
thickness (about 100 feet), and lying between well-defined limits ; 
for its basement bed rests on the marly clays of the zone of Ammo¬ 
nites in flatus (Upper Gault), while above it is the hard nodular 
chalk which forms the zone of Inoceram.us labiatus (Turonian). 
The succession is well exposed near Saully, and is given by Pro¬ 
fessor Barrois as follows :— 
ft. 
Compact greyish-white chalk with grey flints, Am. 
[. Acanth .] rotomagensis .60 
Grey sandy marl with some fossils .16 
Thin layer of sandy glauconitic marl, with phosphatic 
nodules (a few inches). 
Gault. —Black marly clay with septaria (zone of Am. injlaius). 
Professor Barrois did not find fossils in the nodule bed above 
the Gault, and there is therefore no ground for identifying it with 
any particular zone : it is simply the basement bed of the Chalk, 
like that at Burham in Kent. The overlying marl contains Pecten 
as per, -Rhynchonella grasiana, and Micrabacia coronula, and is 
referable to the lower part of our Chalk Marl (zone of Am. various). 
* La Zone a Belemnites plenus, Ann. Soc. Geol. du Nord, T. ii. p. 147 
(1875); and Le Terrain Cretace des Ardennes, Ibid., Tom. v. p. 227 (1878). 
