ESCHER VORARLBERG. 19 



of the granite and porphyry so plentiful in the Swiss Nagelfluh. The 

 Nagelfluh alternates with the sandstones and marls of the Molasse ; 

 thus proving, contrary to M. von Bueh's opinion, the contempora- 

 neity of the two groups, — the Nagelfluh being merely a coarse- 

 grained sandstone. 



Having described these more modern formations, M. Escher 

 reverts to the rocks below the Lias ; commencing with No. 13, the 

 limestone with the Megalodon scutafAis, Schaf., which is known also 

 as the " Dachstein-bi valve." This large shell has been wrongly identi- 

 fied with the Cardium triquetrum of Wulfen. It occurs in a whitish 

 granular limestone in association with Corals, 



The next is the St. Cassian group, No. 14, which has a thickness 

 of from 30 to 200 feet, and abounds with fossils ; such as 



Bactryllium striolatum, Heer. Cardita crenata, Gold/. 



B. deplanatum, Heer. Cardium Rhseticum, Mer. 



Spirifer uncinatus, Schaf. Avicula speciosa, Mer. 



Ostrea. A. Escheri, Mer. 



Spondylus obliquus, Munst. Gervillia inflata, Schaf. 



Pecten Falgeri, Mer. Natica alpina, Mer. 



P. Lugdunensis, Mich. ? Oliva alpina, Klipst, 



It is difficult, however, to determine as yet whether this group is 

 a marine equivalent of the Upper Keuper of Germany, or whether 

 the Keuper is incomplete in Germany, not possessing these deposits 

 which in the Alps occur between the Keuper and the Lower Lias. 

 The same may be said of the Megalodon-limestone. 



Beneath the above-mentioned rocks is Dolomite, No. 15, having a 

 thickness of 1500 feet. This forms the bare and sterile mountain- 

 tops of the Vorarlberg. 



From the analyses made by M. Landolt (tables of which are given 

 by M. Escher), it appears that, with regard to the magnesia, this 

 rock presents many varieties. At one extreme we find 



12-23 Garb, of magnesia 1 , , othpr J"^^'^'' ^^^^- of magnesia 

 84-47 Garb, of lime / ^^"^ ^^ ^^^ ^^^^^ \ 49-89 Garb, of lime, 



as the constituent proportions. The analyses made with respect to 

 the stratigraphical position of the specimens seem to show that the 

 lower part of the dolomite is more highly charged with magnesia than 

 the upper portion. 



M. Escher is of opinion that there is more than one dolomitic 

 series ; since the St. Cassian group in the Vorarlberg is underlaid by 

 dolomite, whilst the same group at St. Cassian itself is overlaid by 

 dolomite. There also occur great bands of dolomite in the groups 

 Nos. 16 and 1/. Hence it is evident that the succession of the 

 groups beneath the Lias is less precise than that of those above. 



In the Rells Valley, at the Triesnerkulm, and the Col de Virgloria, 

 the dolomite rests on a red sandstone and a quartzose conglomerate, 

 which have long been classed with the Grauwacke, but are now in 

 the map of Switzerland* recognized as Verrucano. At other places 

 the dolomite rests on Nos. 16 and 17, which evidently belong to the 

 Trias. 

 * Carte geologiqne de la Suisse; by MM. Studer and Escher v. d. Linth, 1853. 



