
826 STRATIGRAPHICAL GEOLOGY. [Book VI. 
adjacent areas of deposit than that which meets the eye of the traveller 
who crosses from the basin of the Seine to those of the Loire and Garonne. _ 
In the north of France and Belgium soft white chalk covers wide tracts _ 
presenting the same lithological and scenic characters as in England. 
In the centre and south of France the soft chalk is replaced by hard 
limestone, with comparatively few sandy or clayey beds. This mass of 
limestone attains its greatest development in the southern part of the 
department of the Dordogne, where it is said to be about 800 feet thick. 
The lithological differences, however, are not greater than those of the 
fossils. In the north of France, Belgium, and England, the singular mol- 
lusean family of the Hippuritide or Rudistes appears only occasionally and 
sporadically in the Cretaceous rocks, as if a stray individual had from 
time to time found its way into the region, but without being able to esta- 
blish a colony there. In the south of France, however, the hippurites 
occur in prodigious quantity, often mainly composing the limestones, hence ~ 
called hippurite limestone (Rudisten-Kalk). They attained a great size, 
and seem to have grown on immense banks like our modern oyster. They 
appear in successive species on the different stages of the Cretaceous 
system, and can be used for marking paleontological horizons, as the 
cephalopods are employed elsewhere. But while these lamellibranchs 
played so important a part throughout the Cretaceous period in the south 
of France, the numerous ammonites and belemnites, so characteristic of 
the Chalk in England, were comparatively rate there. The very dis- 
tinctive type of hippurite limestone has so much wider an extension 
than the northern or Chalk type of the upper Cretaceous system that it 
should be regarded as really the normal development. It ranges through 
the Alps into Dalmatia, and round the great Mediterranean basin far 
into Asia. 
Cenomanian (Craie glauconieuse).—According to the classification of 
M. Hébert this formation is composed of two groups: 1st, Lower or 
touen chalk, equivalent to the upper greensand and grey chalk of 
England. In the northern region of France and Belgium it consists of 
the following subdivisions: a. a lower group or assise of glauconitic beds 
like the English upper greensand, containing Ammonites inflatus below 
and Pecten asper above; b. Middle glauconitic chalk with Turvrilites tuber- 
culatus, Holaster carinatus, &c., probably equivalent to the English 
Chloritic Marl and Chalk Marl; c. Upper hard, somewhat argillaceous, 
grey chalk with Holaster subglobosus; the threefold subdivision of this 
assise already given is well developed in the north of France; d. Calea- 
reous marls with Belemnites plenus. 2nd. Upper or marine sandstone ; 
according to M. Hébert this group is wanting in the northern region of 
France, England, and Belgium. In the old province of Maine it con- 
sists of sands and marls with Anorthopygus orbicularis, Hxogyra ( Ostrea) 
columba, Trigonia, and Ostrea. Further south these strata are replaced 
by limestones with hippurites (Caprina adversa), which extend up into 
the Pyrenees and eastwards across the Rhine into Provence.! 
Turonian (Craie Marneuse ).—-This formation presents a very different 
facies according to the part of the country where it is examined. In the 
northern basin, according to M. Hébert, only its lower portions occur, 
separated by a notable hiatus from the base of the Senonian series, _ 
1 See a memoir on the Upper Cretaceous rocks of the basin of Uchaux (Provence) by 
Hébert and Toucas, Ann. Sciences Géol. vi, (1875), 
