STRATIGRAPHICAL GEOLOGY. 499 



caire de Valognes) between the Lower Lias and the Trias, 

 which afterwards proved to be in part an equivalent of the 

 Rhoetic series. 



While it was comparatively easy to determine the parallelism 

 between the succession of Oolite deposits in the North of 

 France and the succession in England, it was a much more 

 difficult matter to compare the German and Swiss deposits 

 of the same age' with the English types. In 1795, when 

 Humboldt travelled through Bavaria and Switzerland on his 

 way to Upper Italy, he described a thick series of limestones 

 " between the old Gypsum (of the Zechstein formation) and the 

 newer sandstone (Bunter sandstone)," both in the Franconian 

 Alps and the Swiss Jura Chain, and he applied the name of "Jura 

 Limestone" to this massive development. Ami Bou^ in 1829 

 denned the stratigraphical position of the "Jura Limestone" 

 more accurately ; he limited the term to the limestone above 

 the Lias and below the Wealden formation. In the same year 

 Brongniart had selected the term Terrain Jurassique for the 

 sedimentary deposits comprised within almost the same limits. 

 Rengger, also in the same year, contributed a memoir on 

 the "Aargau Jura," under which name he comprised all the 

 rocks between the Bunter Sandstone and the Molasse 

 practically all the Mesozoic rocks and the older Tertiary. 

 Rengger's section through the Aargau Jura shows that he 

 never understood the repetition of strata caused by tectonic 

 disturbances, and he assigned each recurrence of the typical 

 limestones to a younger geological epoch. 



Similar views were shared by Merian when he first wrote 

 on the Swiss Jura mountains ; but as his investigations 

 continued, he explained the repetitions of certain strata as a 

 result of the curvature of the crust. An important work by 

 E. Thirria on the Jura of the Haute Saone showed that in 

 the French Jura Chain the Lias was succeeded by a richly 

 diversified complex of strata, which Thirria, in accordance with 

 Brongniart's suggestion, called "Terrain Jurassique" and 

 arranged in a number of sub-divisions. These were compared 

 with the English sub-divisions on the basis of the identification 

 of the fossils by Voltz. The literature, however, was not yet 

 sufficient for an exact comparison of the fossils, and although the 

 attempt was well planned, there were several palaeontological 

 blunders. The four chief divisions of Thirria were as 

 follows : - 



