STRATIGRAPHICAL GEOLOGY. 51 1 



Peninsula, and Russia, were comparatively late in being 

 examined and surveyed, and it seemed scarcely possible to 

 determine the parallelism of the facies in these areas with the 

 Jurassic deposits of North-Western and Central Europe. In 

 the Swiss Alps, geologists have identified the age of the larger 

 Jurassic groups, but have not attempted a detailed comparison 

 with the extra-Alpine zones. In the Bavarian, Austrian, and 

 Italian Alps, as well as in the Apennines and the Carpathians, 

 the Alpine facies is also fundamentally different from the extra- 

 Alpine, but it has been possible to identify locally some of 

 Oppel's zones. Alpine geologists invariably try to recognise in 

 the Alpine Trias the equivalents of Oppel's chief groups, Lias, 

 Dogger, and Malm. 



No serious attempt has ever been made to apply Oppel's 

 zonal nomenclature in Alpine geology. It has been customary, 

 especially in Austria, to designate the various sub-divisions 

 with the names of localities (Adneth limestone, Gresten, Hier- 

 latz, Allgau, Vils, Stramberg strata, etc.). 



After the controversy regarding the proper systematic 

 position of the Avicula contorta zone or Rhsetic group had 

 been brought to a fairly satisfactory conclusion (p. 479), con- 

 siderable discussion began to be raised about the proper limit 

 between the Jurassic and the Cretaceous formations. In 

 France, South Germany, and in the Swiss Jura there was no 

 difficulty, as the uppermost numbers of the Jurassic system 

 (Portland and Purbeck strata) are well defined both petro- 

 graphically and palaeontologically, and the limit between these 

 horizons and the Cretaceous formations can be readily deter- 

 mined. On the other hand, in the south of England, North 

 Germany, and Belgium, a fresh-water formation (Weald clay 

 and Hastings sand) is interposed between the uppermost 

 Jurassic and the Cretaceous horizons, and creates a difficulty 

 in determining the precise limit of the two formations. Man- 

 tell united the fresh-water formation with the Cretaceous 

 Greensand ; Webster and Fitton combined them with the Pur- 

 beck strata, and regarded the group as independent. Sir Richard 

 Owen and Robertson drew attention to the similarity of 

 the Purbeck and Wealden faunas with that of the Stonesfield 

 slate, and placed the Wealden in the Upper Jurassic division. 

 Elie de Beaumont supported the other view, that the Wealden 

 formation was an equivalent of the " Neocomien," and 

 Forbes, Lyell, Topley, the Geological Survey, and most of 



