1 12 Mr Oscar Fraas' Observations on the Effects , 



groups of our " brown Jura," viz., oolite and Oxfordian, which 

 can bear no proportion in development to the " black" and 

 the " w^hite Jura.*" The other principal difference arises from 

 this — that the clays and limestones of the lower and middle 

 " white Jura," and the spongites beds, are entirely wanting 

 in the Jurassic series of France and England. In Swabia, 

 " oolite" is wanting ; instead of it, there is the " white Jura." 

 In France and England *' oolite" is present, but those mem- 

 bers of the low^er and middle " white Jura,-' that are so im- 

 portant in Germany, are absent ; for in England and the west 

 of France the coral-rag lies immediately above the ornati, or 

 Oxford clays. In Swabia the spongites beds, and the coral 

 reefs of the ancient German Sea, form the centrum^ to which 

 the rest of the " white Jura" is subordinate. They form the 

 summits, and, for the most part, the mass of the Alps ; whilst 

 in England and the north of France the "white Jura" com- 

 mences with the coral-rag. Thus, then, in the north-west of 

 Europe it is chiefly the " oolite" formations which charac- 

 terise the " Jura ;" whilst in Germany the " white Jura'' (^the 

 spongites beds) is characteristic. The "white Jura'' might, 

 perhaps, be extended much further to the alpine limestones 

 of Provence, Italy, and Austria. Victor ThioUiere, through 

 Quenstedt's *' Flotz-gebirge and Petrefakten Deutschlands," 

 has drawn attention to and studied the Provencal Alps ; and 

 and in the before-mentioned work, " Sur les Terrains Juras- 

 siques de la Partie Meridionale du Basson 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 equiva- 

 lents of the Swabian Scypfdce 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 characterise the " Jura" in the Mediterranean district 

 {lejurassique Mediierraneen)^ 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. 

 hecticuSf Belem. hastatus^ Aptychus imbricatus, Terebrat. iacu- 



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



