1821.] and adjoining Farts of the Continent, 461 



composed of fragments of serpentine ; and in Hmigary also in 

 an analogous breccia composed of fragments of volcanic rocks. 



Although no trap rocks occur between the central Alpine 

 Ridge and great Valley of the Danube, yet small portions of it 

 occur on the north border of this valley at Hoent Wyl, near 

 Schaffhausen, and again at Urach, in the Rouh Alp, on the 

 north-west of Ulm. 



Its extent a little further north in Saxony and Bohemia is too 

 notorious to require mention. 



Jura Chain. 



The general history of the Jura Chain may be stated more 

 briefly than that of the Alps, from which it is separated only by 

 the great valley of Switzerland, extending from Geneva to Con- 

 stance ; and being in fact only the continuation of the upper 

 extremity of the Valley of the Danube, and like it composed 

 almost exclusively of strata of tertiary formation. 



The Jura Chain runs in a line parallel to that of the Alps, and 

 of this great valley from Nantua, on the NE of Lyons, to Neuf- 

 chatel and Schaffhausen ^ from whence its prolongation through 

 the Rouh Alp on the south of Swabia connects it with Nuremburg, 

 and the great calcareous masses of the centre of Germany. 



Its dip is toward the Alps, plunging under the molasse and 

 nagelflue of the great valley above-mentioned. Its escarpment 

 rises NW towards the primitive and transition rocks of the 

 Black Forest, and the Vosges. Its component formationsr are, 

 beginning with the lowest, new red sandstone, magnesian lime- 

 stone, lias, and several varieties of oolite ; on these latter are 

 dispersed some irregular patches of freshwater formation and 

 lignite. Its most obvious and most abundant rocks are beds of 

 oolite, resembling that of the CotswoldHills aud neighbourhood of 

 Bath ; and the term Jura limestone has been applied most 

 usually, and with most propriety, to this variety of its comyjonent 

 rocks, particularly in the case of the oolites of France. But in 

 Germany, many rocks which belong to the magnesian limestone 

 formation have been confounded with the true oolite from the 

 circumstance of their analogues having been observed in the 

 Jura, and the Jura being erroneously considered to contain but 

 one formation. The upper beds of the Jura Chain lying above 

 its oolite assume the ordinary compact form of younger Alpine 

 limestone, as may be seen at Schaffhausen ; and confirm the 

 opinion that the oolite formation is a component portion of the 

 younger Alpine limestone. 



Three Great Valleys bordering on the Alps. 



], Valley of Switzerland, 



The position of the Great Valley of Switzerland between: the 

 Alps and Jura Chain, and parallel to both of them, has beea 



