MIDDLE CHALK—NORTH OF FRANCE. 
491 
CHAPTER XLIL 
THE EQUIVALENTS OF THE MIDDLE CHALK IN 
THE NORTH OF FRANCE. 
The Middle Chalk of England corresponds exactly with the 
Turonien of d’Orbigny and with the “ craie marneuse ” and the 
“ craie a Inoceramus lahiatus ” of Hebert. 
Hebert afterwards included in it the zone of Belemnites plenus 
and divided it into three parts or zones thus* :— 
Upper Zone.—Marly chalk with Rhynchonella Cuvieri , Hpiaster 
cor avium , and Inoceramus Brongniarti. 
Middle zone.—Nodular chalk with Ammonites nodosoides , Am. rusticus 
and Am. catinus. 
Lower Zone.—Argillaceous chalk with Belemnites plenus. 
In 1871 he included the overlying chalk with Holaster planus 
in his Turonienf, and subsequently Professor C. Barrois showed 
reason for excluding the zone of Belemnites plenus , and for dividing 
the “ craie marneuse ” of eastern France into two zones—that of 
Inoceramus lahiatus (restricted), and that of Terebratulina gracilis , 
the latter being the equivalent of Hebert’s upper zone. J 
More recently still, higher beds (the zones of Micraster breviporus 
and Micraster cortestudinarium ) have been referred to theTuronian 
by Professor Barrois and other French geologists, so that their 
Turonian now includes much more than that of d’Orbigny, 
which did not comprise any beds containing Echinocorys scutatus 
and its varieties. Such beds he referred to the Senonian, and so 
did Hebert up to the year 1870. 
It is clear, therefore, that the French equivalent of our Middle 
Chalk is the restricted Turonian of d’Orbigny, and we shall see that 
in the cliffs of Normandy this division has the Melbourn Rock at its 
base, and the Chalk Rock above it, exactly as in so many parts of 
England. 
To give anything like a complete account of the Turonian Chalk 
of the Paris basin would be quite beyond the scope of this memoir, 
and it must suffice if we confine our notice to those regions in north¬ 
ern France where the chalk of this stage exhibits such lithological 
changes as seem to indicate the neighbourhood of land. These re¬ 
gions are, of course, at the extreme north-eastern and at the extreme 
western borders of the area which it occupies. For a description of the 
former region, we shall rely chiefly on the publications of Professor 
*See Comptes-rendus Acad. Sci., 1864 and 1866, and Bui. Soc. Geol. de 
France, Ser. 3, Tom. ii. p. 416. 
t See Bull. Soc. Sciences de l’Yonne for 1876. p. 15. 
+ Ann. Soc. Geol. du Nord, Vol. ii. p. 146. 
