The Keuper stage of this system is represented by the variegated marls of the Vosges and Moselle; these are clayey marls of strongly contrasted colours, in which red and green predominate.
In France, in the liasic system, are found the Bayeux clays which are used in the manufacture of fired china, and reach a height of 15 to 20 metres. In England the Bradford clays belong to the mediojurassic series, and to the suprajurassic, Oxford clay, which is tenacious, of a dark blue colour, sometimes bituminous, and reaches a thickness of 150 to 200 metres. The clay is also found in the Calvados, in France, where, mingled with fine sand, it serves as support to the rich pasturage of the Auge country. At Honfleur it is 20 metres thick. At Villequier (Seine-Inf*rieure) an excavation to a depth of 40 metres brings to light the so-called Kimeridgian clay situated a little higher, which is worked for brick and tile manufacture.
I, lower clays (upper Kimeridge); 2, lithographic limestone; 3, upper clays (upper Kimeridge); 4, sand, sandstone, and limestone marls; 5, clay (Portland); 6, sandstone; 7, lower cretaceous earth; 8, chalk; F, excavation.
The Bray country possesses clays, little worked, however, belonging to the suprajurassic system (Portland and Kimeridge stages) and arranged as in Fig. 2.
The neocomian stage of the same infracretaceous series includes considerable deposits of clay which are of great industrial importance.
In England is found the blue or brown Weald clay, whose thickness reaches 300 metres.
In France, the very interesting clays of the Bray country belong to the same stage, but have very different properties according to the position they occupy. The section in Fig. 3 shows their arrangement.
In the middle neocomian are found the stone clays, called in the Bray district terre *¦ pots or terre *¦ grÅ s, which have been worked from time immemorial at la Chapelle-aux-Pots (Oise), Saint-Germain-la-Poterie, Savignies (Oise), for the manufacture of stoneware articles, chimney-pots, fountains, bonbonnes, ink bottles, etc. They are extracted from open pits or by means of shafts.
Fig- 3 - Transverse Section (1 in 10,000) from the Northern Outskirts of Bray, near Glatigny. 1, lower Portland and Kimeridge; 2, upper Portland; 3, white sands and refractory-clays ; 4, ferruginous sandstone and potter's clays; 5, streaked clay; 6, green sands; 7, gault and gaize; 8, cenomanian chalk ; 9, turonian chalk; 10, senonian chalk; F, excavation.
The refractory clays, found in the Bray country from Forges to Gournay, belong to the lower neocomian. They are more or less mixed with white sand, and are especially abundant in the neighbourhood of Forges. The best variety is of a bluish silver-grey, which whitens on exposure to air. The seams are very irregular, and the products of different pits are extremely diverse. The masses of clay, in the midst of sand, take often the shape of isolated balls. At Forges these masses are large and numerous, while at Serqueux, only two kilometres distant, the sand contains hardly any clay.
The upper neocomian presents, also in the Bray district, a considerable outcrop of streaked loam, or marbled pink clay, worked for the manufacture of tiles, pipes, and paving squares. This is also an ingredient of the mixtures used for the manufacture of stoneware.
The most important pits are on the road from Auneuil to Beauvais and on that from Forges to Rouen.
At Desvres (Pas-de-Calais) is also found a layer of clays 20 metres thick, some grey and violet, others streaked with red and grey, which are often refractory, and appear to correspond to the English Weald deposit.
To the albian stage of the lower cretacian series belong 30 or 40 metres of green sand found in the Bray district, and worked for brick-making.