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GEOLOGICAL MEMOIRS. 



merable fragments of plants (twenty species of Monocotyledons and 

 some Dicotyledons) between the grey limestone and cornbrash. And 

 thus here, as in Swabia, the extensive Jura-sandstone formations 

 have taken the place of the Great Oolite (Haupt-Rogenstein) . 



III. Upper Brown Jura, e. and £. 



C 1 . The clays of e. Cornhrash limestone. Assise supcrieur de 

 ^ J Vetage bathonien. Dalle nacrce, Thurm. 



I 2. The ferruginous oolite of e. Kelloways rock. Callovien. 

 L Oxfordien inferieur, D'Orb. 

 £. Oxford clay. Oxfordien moyen, D'Orb. Argiles de Dives. 

 Marnes oxfordiennes. 



Above the greyish blue marly limestones with Am. coronatus, and 

 the clays with Belemnites giganteus, there often appear in Swabia 

 strongly developed black clays. They contain silicified Ammonites, — 

 Am. Parkinsoni, Am. hecticus, Hamites bifurcatus, Ostrea costata ; 

 small Bivalves, Trigonia costata, Pleurotomaria decorata, Trochus 

 monilitectus, Turritella echinata ; a small Anthophyllum, DentaUum, 

 &c. Above these lie hard limestones, generally with a number of 

 Terebr. varians ; and upon these a few feet of reddish brown 

 oolitic beds, with Am. macrocephalus, Am. triplicatus, Am. sub- 

 Icevis, Am. bullatus, Am. microstoma, Galerites depressus, Belem. 

 latisulcatus, and B. canaliculars. The same is the case in the 

 north-west of Swabia, for instance on the Lochen, where these beds 

 are more particularly developed ; but even at other places in Swabia 

 we always find, between the coronati- and macrocephali-be&s, that 

 with Am. Parkinsoni, Am. bifurcatus, Pholadomya Murchisoni } 

 and Trigonia costata. I believe that the black Parkinsoni-cl&ys are 

 best represented by the English Cornbrash, which may likewise partly 

 represent the bed with Am. coronatus ; because the Cornbrash con- 

 tains greyish blue limestones and clays with Pholadomya Murchi- 

 soni, Ostrea Marshii, Mya V-scripta, numbers of Terebratulce, and 

 perhaps even Am. Herveyi. The fossils certainly do not correspond 

 here, but only the position of the clay-bed directly underneath the 

 Kelloways rock ; but we see by the formation of this bed in dif- 

 ferent countries how the e. of Swabia passes gradually over into the 

 Cornbrash. The French Cornbrash has quite a middle position, 

 which by no means accords with that of England ; but on account 

 of its contemporaneity the French have given it the English name. 

 I did not find this formation in the west of France, but in the eastern 

 parts, especially in Mont Jura. Here it consists of sometimes finely 

 oolitic limestones, sometimes dark clays with small Corals and Bi- 

 valves, which, however, are found both in the upper and the lower 

 portions, in consequence of which we cannot point out true typical 

 shells. In Aargau and Basle first appear as characteristic forms 

 Am. Parkinsoni and Pleurotomaria decorata, and also Am. macro- 

 cephalus, Am. athleta, and Am. triplicatus. On account of the frag- 

 ments in the Shell-breccia partly retaining their natural lustre, Thur- 

 mann* calls it Dalle nacrce. These beds in Switzerland lastly make 

 * Essai sur les souleveraens jurassiques du Porrentruy. 



