﻿FRAAS ON THE JURA FORMATION. 



59 



viz. those of sandstone formations in localities bordering on older 

 sandstone monntains, such as the Peak, the Vosges, and the Black 

 Forest. Far from such mountains, upon the open sea, these con- 

 ditions were wanting, and consequently these deposits are also want- 

 ing, or are represented only by unimportant limestone beds. 



II. Middle Brown Jura, y. and o. 

 Inferior Oolite. Etage bajocien (D'Orb.). 



y. Lower Coal. Calcaire a Entroques. Calcaire Icedonien. Cal- 

 caire a Polypiers. 



Z. Oolite inferieure. Oolite de Bayeux. 



Manxes vesuliennes. Marnes a foulon. 



Fuller's Earth. 



Hard blue limestones with Pecten demissus passing upwards into 

 brown marls, with Myacites depressus and spines of Cidarites, con- 

 stitute the transition to a system of clays and calcareous marls — $, 

 which, sometimes of a lighter, sometimes of a darker colour, are 

 distinguished by an abundance of fossils. Am. coronatus, Am. Hurn- 

 phriesianus, Ostrea crista-galli, O. pectiniformis, a legion of Tere- 

 bratulce, and Donax Alduini, are characteristic of this series. Above 

 these succeed dark-coloured cIsljs with Belemnites giganteus. So also 

 in Swabia and Switzerland. In the latter district above the sandy 

 clay beds, with Am. Murchisonce and a Gryphcea with a large ear 

 (which is also frequent in the south-west of Swabia), lies a red 

 ferruginous oolite, containing the shells of £, Terebratulce, Am. 

 coronatus, Ostrea, and Bel. gig aniens. In Mont Jura, as well as 

 in Swabia, this is separated into beds of hard limestones and clays, 

 the former surpassing in bulk the superincumbent clay, contrary 

 to what takes place in Swabia. The limestone which is very 

 constant, and passes through the whole of Burgundy, is greyish 

 blue, hard, and brittle, containing numerous stems and arms of 

 Encrinites. Hence it derives its name, Calcaire a entroques ; an- 

 other name is Calcaire Icedonien, from Lsedo, Lons le Saunier (Dep. 

 Mont Jura), where these limestones attain their greatest develop- 

 ment. Above it repose thick limestones with corals, the Calcaire 

 a Polypiers, which occupies a considerable tract in the east of France. 

 These limestones, then, pass from Mont Jura, along the Vosges, over 

 Besancon, Vesoul, and Nancy, to Metz. Agaricia, Pavonia, Astrcea, 

 Anthophyllum, Lithodendron, in company with Terebratulce, Myce, 

 and spines of Cidarites, characterize this formation, which in many 

 places has so great a proportion of silica, that the shells of the Myce and 

 Terebratulce are well-preserved in quartz. The similarity between 

 this and the Coral-rag is very remarkable. These coral-limestones 

 must be looked upon as peculiarly a French formation ; for its equal 

 is nowhere to be found either in Switzerland or in Germany. I am 

 inclined, however, to regard our blue limestones as a synchronous 

 deposit, the lower portions of which, the real, hard, blue limestones, 

 which are poor in fossils, answer at all events to the Calcaire a en- 

 troques, and the French coral-limestones might then be compared 



