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GEOLOGICAL MEMOIRS. 



with limestone beds, rises from the a7*ietes-beds up to the posido- 

 nomy ^-schists ; the order however of the fossils remains the same. 

 Undermost in the clays are Am. bifer and Am. oxynotus ; in the 

 limestones Pholadomya ambigua, Mactromya gibbosa, and Am. rari- 

 costatus ; further upwards succeed Am. planicosta, Am. natrix, Am. 

 lineatus, silicified in the clays and calcareous in the limestone ; and 

 after these come the Belemnite-heds with Am. Davcei. Above this 

 again are found Am. Amaltheus (margaritatus, d'Orb.) and Am. 

 costatus {spinatus, Brug.) impregnated with quartz ; an immense 

 number of Plicatula spinosa and Belemnites paocillosus mark the 

 termination ; the latter, however, not in such beauty and numbers 

 as in Swabia. This last stratum is called by the geologists of the 

 Jura, Manxes a Plicatules. 



In Burgundy, the numism,alis-c\ays do not differ from those of 

 Swabia ; on the other hand, the amaltheus-cl&ys (3.) have a develop- 

 ment not to be seen in the latter country. They are no longer the clays 

 that form 3, but greyish blue limestones of considerable development, 

 in which, together with the gigantic Am. Amaltheus and Am. cos- 

 tatus, occur Gryphcea gigantea, Goldf. (a variety of G. cymbium ?), 

 Terebratula acuta, T. digona, T. lagenalis, T. vicinalis, Pecten 

 cequwalvis, P. glaber, Pholadomyce, Myce, and Spiriferi, in great 

 quantity and mostly also of great size. The environs of Avallon, 

 Vassy especially, is a normal district of this middle Lias. The 

 amaltheus-limestones here form whole rocks of a greyish yellow 

 colour, and filled with the fossils enumerated. Clays with silicified 

 shells are entirely wanting ; the bed appears only in a calcareous form, 

 and together with the character of its organic forms, has reference 

 evidently to deep-sea conditions. It appears that this great deve- 

 lopment of the Amaltheus-strsitum does not exist anywhere except 

 in Burgundy ; for in the Cher-Department or the Isere it is much 

 decreased ; at the latter place it contains a great deal of iron, like 

 our Wasseralfing limestone ; Am. Amaltheus and Am. heterophyllus 

 are frequently present in it. Further towards the south and also 

 towards the west this stratum disappears ; and it re-appears at Cal- 

 vados near Bayeux, Curcy, Croisille, &c. But here the character of 

 the formation has become very different, chiefly in reference to the 

 organic remains, the light yellow calcareous marls of y. containing, 

 together with Am. Jamesoni, Am. Davcei, and a host of very beautiful 

 and rare Terebratulee and Spiriferi, a number of Corals, Cidaris- 

 spines, and very rare Gasteropoda, — Euomphalus and Conus. The 

 following are very conspicuous : — Terebratula quadrifida, T. JDes- 

 longchampsi (quite new, and having a general resemblance, except as 

 regards the central perforation, to T. diphyd), T. lagenalis, T. vici- 

 nalis (of a remarkable size), Euomphalus cadomensis, a great quan- 

 tity of Turbo, Trochus, and Pleurotomaria, and towards the top, 

 Am. Amaltheus and A. spinatus, the Gryphcea gigantea of Bur- 

 gundy, Pecten cequwalms, and P. glaber. The light-yellow coloured 

 beds in which the above-mentioned fossils are found are scarcely three 

 feet thick. Clays are here entirely wanting, but appear nevertheless 

 at some places ; for instance at Vieuxpont, where Am. Amaltheus, 



