JURASSIC OF THE PARIS BASIN. 



565 



doggers, often becoming continuous, which develop to a considerable 

 thickness at Chatillon, are worked there and at Mont Lambert, and 

 constitute the base of Gris Nez. These are capped by the great 

 ripple-marked conglomerate, distinguished everywhere by the abun- 

 dance of Exogyra virgula, Trigonia Pellati, and T. Munieri, which 

 becomes, however, a mass of false-bedded sand with hard doggers 

 at Gris Nez. These are so associated with the sands below, that 

 the natural subdivision would seem to be made above them, where 

 Ex. virgula ceases to be a common fossil ; and these two parts, 

 N 1? N 2 of M. Pellat, 23-25 of M. Hebert, may form the zone of 

 Ammonites gigas, which certainly occurs throughout. 



The next zone is the chief fossiliferous one. It consists, at the 

 base, of soft marly sands with hard bands, of M. Pellat, charac- 

 terized by Perna Boucliardi ; next, of some hard grits in more than 

 one bed (N 4 ), with Cyprina Brongniarti, Pterocera oceani ?, Natica 

 Marcousana, and Hemicidaris purbeckensis ; and, finally, of earthy 

 beds and sands more or less ferruginous and consolidated, with 

 rolled pebbles and local unconformities. The whole of this does 

 not occupy more than 20 feet at La Creche. At Portel the middle 

 portion is nodular, and the whole is thicker. At the quarry of 

 Mt. Lambert, nearest Boulogne, the whole appears as massive sand- 

 stones ; but at Gris JSTez the most instructive section occurs. On the 

 east of that point the marly beds are crowded withPer?ia Bouchardi 

 and many other fossils ; over these come the hard grits with Cyprina 

 Brongniarti, forming a well-marked feature ; and above is a local 

 band of green earth, followed by a conglomeratic sandstone and 

 sand, which in the cliff on the south appear to thicken out to nearly 

 30 feet. The whole in the first locality is overlain by the shales of 

 the " Middle Portland," not previously noticed here. The nodular 

 character of these upper sandstones is noted by M. Hebert in his 

 No. 17' of La Creche. With regard to the fossils, Trigonia Pellati 

 extends to the top at Gris Nez, and so does Ammonites gigas at La 

 Creche, according to M. Hebert; the others noted areMerita transversa, 

 Orthostoma Bvvignieri, Corbida autissiodorensis, Corbicella Bayani, 

 Mytilus Morrisii, Pecten suprajurensis, Corbida ferruginea, from 

 the Perna-be&s; and from the grits and sands, Turritella Sosmanni, 

 Acteonina Bavidsoni, Palceomya autissiodorensis ?, and Ostrea rugosa 

 in addition. 



The succeeding series, constituting the " Middle Portlandian " of 

 M. Pellat, is very well marked. It commences at the base with 

 some 30 feet of black, almost paper, shales, very similar to those of 

 Hen-cliff and of the Upper Kimmeridge of Lincolnshire. These are 

 followed by several cement-stone bands, two being especially con- 

 spicuous ; and then more shales, with a lumachelle of Ostrea dubi- 

 ensis at the top, making a total of about 50 feet. The fossils are, as 

 usual, flattened in the shales, and in places are innumerable. The 

 most important species noticed were Alaria cingulata, Astarte 

 scalaria, Cardium morinicum, Lucina minuscula, Mytilus autissiodo- 

 rensis, Anomia suprajurensis, Biscina latissima, and Avicula oetavia 



