﻿FRAAS ON THE JURA FORMATION. 



77 



Gebirge " and " Petrefakten Deutschlands," has drawn attention to 

 and studied the Provencal Alps ; and in the hefore-mentioned work 

 " Sur les terrains jurassiques de la partie meridionale du bassin du 

 Rhone*," he has defended the opinion that the Alpine limestones with 

 Terebrat. diphya and Am. Tatricus, and, further on, the red marble- 

 like limestone of Italy, are nothing but the equivalents of the Swabian 

 Scyphice-limestones. T. diphya and Am. Tatricus, he observes, are 

 found in the Lias, in the Oxford -group (i.e. the Middle " White 

 Jura"), and in the Neocomian ; they characterize the "Jura" in 

 the Mediterranean district (le jurassique mediterraneen), but not 

 any single formations. 



The above-mentioned limestones, called also the Crussol- and Porte 

 la France-limestones, more especially contain Am. polygyratus, Am. 

 polyplocus, Am. biplex, Am. flexuosus, Am. hecticus, Belem. hasta- 

 tus, Aptychus imbricatus, Terebrat. lacunosa, and T. nucleataf, all 

 characteristic of the " White Jura." Even if the Sponge-corals are 

 wanting in the Alps, this must not mislead us. Corals can never be 

 characteristic of Formations ; they appear, rather, everywhere if cli- 

 matal conditions have been favourable ; and the Sponyit es-\imestones 

 of Germany were only another Facies of the sea which in the South 

 of Europe has formed the Alpine limestone. With this view the 

 stratigraphical order of the other Jurassic Formations agrees ; for in 

 Provence below the Alpine limestone the ornati-dajs with Am. Par- 

 kinsoni occur ; lower down the opalinus-cl&ys and the Lias. This 

 Jurassic group extends in France from the Mediterranean, along the 

 Cevennes and the Alps, to Mont d'Or Lyonnais and in the north of 

 the Isere-Departement, where the Form of the English-French 

 "Jura" commences. If now, in the latter Jurassic range "Oolite" 

 is pre-eminently developed, and in the North of Europe (Russia) the 

 "Brown Jura" predominates, it seems that the German "Jura" 

 forms the transition from the " Jura " of the North to that of the 

 South, where the " White Jura " has its chief development. The 

 English-French Gulf of the Jurassic sea, in the middle of which we 

 now find the Paris and London basin, constitutes with its " Oolite " 

 formations an isolated group analogous to that of the Northern "Jura" 

 with its masses of " Brown Jura." The Fauna of the North exhibits 

 but slight differences ; but the contrary obtains with the formations 

 and inhabitants of the Southern Jurassic sea, stretching over Italy 

 and Greece, towards Africa and Asia. In the middle, between 

 North and South Europe, lies the German " Jura," separated from 

 that of the North-west by the absence of the " Great Oolite," but 

 generally containing in itself the substances of the Northern and the 

 Southern " Jura," and at all events forming by its coral-banks the 

 north edge of the southern Jurassic sea. 



The following Tables afford a general survey of the contempo- 

 raneous Formations of the " Jura" in descending order in Franconia, 

 Swabia, France, and England ; and the vertical development of the 

 respective Formations is in a general way typographically expressed. 



* Bullet, de la Soc. Geol. de France, Seance 8 Nov. 1847. 

 t Quenstedt, Petref. Deutsch. p. 264. 



