of Local Influences upon the Formation of Strata. Ill 



shale, Alum shale, Whitby shale). B. Brown Jura or Oolite. 

 — This subdivided into — 1. Lower brown Jura (inferior oolite, 

 Northampton sandstone, Cheltenham Freestone, Ferruginous 

 beds). 2. Middle brown Jura (inferior oolite, lower coal, 

 calcaire a entroques. Great oolite, Bath oolite, Bradford clay, 

 Forest marble). 3. Upper brown oolite (Oxford clay). C. 

 White Jura — subdivided into — 1. Lower white Jura (Maries 

 Oxfordiennes superieures). 2. Middle white Jura (Scyphia- 

 limestones and Lacunosa beds). 3. Upper white Jura (Coral- 

 rag, Saccharoid limestone, Marble, Dolomite). 



After a detailed and valuable account of the deposits just 

 enumerated, Mr Fraas thus finishes his memoir : — " With 

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

 mentioned. Each has its peculiar predominating formations, 

 surpassing the other members of the Jurassic series. In the 

 north of England there are generally great sandstone forma- 

 tions, that throw the clays and limestones into the back- 

 ground ; in the south of England and in the west of France 

 it is oolite ; in the east of France and in Switzerland, lime- 

 stones ; and in Swabia it is the clays that predominate. A 

 formation, capable of being identified by geological succes- 

 sion and by organic remains, may appear in diff^erent coun- 

 tries 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 geognos- 

 tically distinct from others. This is the case with the great 

 oolite, which is so important in the English and French 

 " Jura," but entirely wanting in Swabia and Franconia. This 

 important group, often developed more extensively than the 

 whole of the 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 superincum- 

 bent beds constituting the fourth or last part. In the Ger- 

 man " Jura," the relative proportions are quite different : 

 here, where the great oolite is wanting, we must make two 



