492 
THE CRETACEOUS ROCKS OF BRITAIN. 
Ch. Barrois, and for the western area on those of Messrs. Hebert, 
Lennier, and P. Bizet. 
1. The North-east of France. 
Near Calais and around the Boulonnais, the two zones which 
constitute the Middle Chalk present the same lithological facies, and 
contain the same assemblages of fossils as they do in the south-east 
of England. They are well exposed in the cliff at and east of Cap 
Blanc Nez, as shown in Fig. 85, which is based on a section drawn 
by Professor Barrois. * He describes the two divisions as follows : — 
Compact thick-bedded white chalk, with Terebratulina feet. 
gracilis , Echinoconus subrotundus , Spondylus spinosus, 
Inoceramus Brongniarti , etc. Some flints in its higher 
part --------- 120 
Hard gritty nodular chalk, greenish or yellowish, containing 
many fragments of Jnocerami , Inoc. labiatus , Ammonites 
nodosoides, Am. rusticus , Rkynch. Cuvieri, Cardiaster 
pygmceus - - 66 
186 
Fig. 85. —Section from Sangette to Cap Blanc Nez. 
Horizontal scale 1 inch = 1 mile. Vertical scale 400 feet to 1 inch. 
4. Zone of Holaster planus. 2. Zone of Rkynch. Cuvieri. 
3. Zone of Terebratulina gracilis. 1. Lower Chalk. 
Again in the southern part of the Paris Basin, in the departments 
of the Yonne and the Aube, they present similar characters, and 
have a combined thickness of from 350 to 400 feet.j 
Between these two regions, however, there is another in which 
the beds gradually assume a different facies. Writing of the zone 
of InoceramAis labiatus Professor Barrois says :1 “ In the south of the 
department of la Marne this zone consists, as in the Aube, of hard 
nodular chalk containing Ammonites and the usual fauna. To¬ 
wards the north it becomes more homogeneous, and I have only 
found Bivalves and Brachiopods in it. Still farther north, on the 
border of the department, it is still a .hard chalk, but its thickness is 
reduced to a few inches. It is overlain and gradually replaced by 
an argillaceous marl, containing sometimes as much as 70 per cent, 
of clay, and dug for brickmaking. This argillaceous marl can ho 
followed through the departments of the Ardennes, the Aisne, and 
the Nord, where the workmen give it the name of dieves. The 
* Proc. Geol. Assoc., Vol. vi. p. 26 (1879). 
t See Hebert (Bull. Soc. Sc. Yonne, 1876) and Barrois (Ann. Soc. Geol. 
Nord, T. ii. p. 146, 1875). 
X Terrain Cretace des Ardennes, Ann. Soc. Geol. Nord, T. v. p. 381 (1878). 
