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GEOLOGICAL MEMOIRS. 



banks the smaller Molluscs and the Radiata are abundant ; in the 

 larger circle of the atolls and lagoons exist numbers of Fish and Crus- 

 taceans ; and on the shores Reptiles, Insects, and freshwater animals. 

 In no other Period does the climate undergo so great a change ; — in 

 no other Period do so many new species appear upon the Earth ; and 

 no other Period possesses so much importance with respect to the 

 history of our planet, as that of the " Jura." 



"With this I conclude the comparison of the " Jura " in the countries 

 mentioned. Each has its peculiar predominating formations, sur- 

 passing the other members of the Jurassic series. In the North of 

 England there are generally great sandstone-formations, that throw 

 the clays and limestones into the background ; in the South of En- 

 gland and in the West of France it is oolite, in the East of France 

 and in Switzerland limestones, and in Swabia it is the clays that pre- 

 dominate. A formation, capable of being identified by geological 

 succession and by organic remains, may appear in different countries 

 sometimes as sand or clay, sometimes as a limestone or an oolite. 

 Still there are not merely differences in the characters of identical 

 strata, but there are strata geognostically distinct from others. This 

 is the case with the Great Oolite, which is so important in the Eng- 

 lish and French " Jura," but entirely wanting in Swabia and Fran- 

 conia. This important group, often developed more extensively than 

 the whole of the other accompanying Jurassic Formations, supplies 

 the "Jura" with an additional link in its chain, and influences its 

 geological division. Of the four principal Divisions of the " Jura," — 

 Lias, Oolite, Oxfordian, and Corallian, — or Lias, Lower, Middle, and 

 Upper Oolite, the Great Oolite and the beds above it as far as the 

 Coral-rag have been taken together to form the third Division ; the 

 Coral-rag and the superincumbent beds constituting the fourth or 

 last part. In the German " Jura" the relative proportions are quite 

 different : here, where the Great Oolite is wanting, we must make two 

 groups of our " Brown Jura ;" viz. Oolite and Oxfordian, which can 

 bear no proportion in development to the " Black " and the " White 

 Jura." The other principal difference arises from this, — that the 

 clays and limestones of the Lower and Middle "White Jura" and 

 the Sponffites-heds 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 members of the Lower and Middle " White Jura," that are 

 so important 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-heds and the Coral-reefs of the an- 

 cient 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" commences with the Coral-rag. Thus then, in 

 the north-west of Europe it is chiefly the "Oolite" formations which 

 characterize the "Jura" ; whilst in Germany the " White Jura" (the 

 Spongites-heds) is characteristic. The " White Jura " might, per- 

 haps, be extended much further to the Alpine limestones of Provence, 

 Italy, and Austria. Victor Thiolliere, through Quenstedt's " Flotz- 



