MIDDLE CHALK—NORTH OF FRANCE. 
493 
stratigraphidSl relations of these dieves ai*e most clearly seen in the 
Aisne and Nord, where they are divisible into a lower zone, very 
argillaceous, but poor in fossils, and an upper zone, less argil¬ 
laceous, and containing an abundance of Terebratulina gracilis. ” 
“ Not only are these zones distinguishable by their fossils and their 
lithological composition, but they are separated from one another 
by a bone-bed containing fish-teeth and pliosphatised fossils rolled 
broken (at Foigny and It ornery). The upper division represents 
the zone of Ter. gracilis; the lower division, lying between it and the 
marl with Bel. plenus, corresponds with the zone of Inoc. labiatus.” 
In continuation he remarks that he had not previously been able 
to recognise the same sub-division of the dieves in the Ardennes, 
but that during a second exploration he had found fossils in the 
lower beds which included some special forms not found either in 
the beds above nor in the normal facies of the zone. Hence he 
concludes that these beds constitute a littoral facies of the zone, 
and that the nodular chalk was formed in deeper water. 
These Turonian marls form the lower slopes of the hills which 
border the district of Champagne, and the following remarks (with 
Fig. 86) are quoted from Professor de Lapparent’s well-known 
Manual of Geology (third edition, p. 1162): — “ Near Valmy the zone 
of Inoc. labiatus is quite a marly chalk, and the zone of Ter. gracilis 
is a white marl of no great thickness, overlain by the nodular white 
chalk containing Micraster breviporus and Hoi aster planus ” 
Their respective thicknesses in this district are about 80 feet and 
about 20 feet. 
Bionne 
8 . 
Fig. 86. —Section t 
Craie a Micrasters. 
7. Marnes a Ter. gracilis. 
6. Craie marneiise a I. labiates. 
5. Marnes cenomaniennes. 
4. Glauconie A P. asper. 
3. Marnes au dessus de la Gaize 
2. Gaize de l’Argonne. 
1. Gault. 
In the north of the Ardennes, near Coucy and Doux, Professor 
Barrois records exposures from which he obtained fossils, and 
from these it would appear that the thickness of the I. labiatus 
zone is there about 12 metres (40 feet), and that of the T. gracilis 
zone only about 3 metres (10 feet). Further north, near Vervins, 
the lower marls are over 60 feet thick, but the T. gracilis marl 
not more than 6 feet. 
In the department of the Nord, these marls crop out in the valley 
of the Sambre, and in the Forest of Mormal, where their thickness 
is from 70 to 100 feet. To the north-west they have been identified 
in many of the deep borings, as at Valenciennes, Carvin, Guesnain, 
Orchies and Lille, with a thickness varying from 60 to 140 feet. 
