152 M. Studer on the Geological Structiire of the Alps» 



the gneiss, we see in reality the wedges of limestone which 

 penetrate the gneiss, adhering to and incorporated with the 

 main mass of the limestone. 



The determination of the age of the sedimentary beds, si- 

 tuated to the north of the iVlps, presents great difficulties, but 

 nevertheless these difficulties belong rather to the details than 

 to the general features. We know that in Switzerland, at 

 least, the most ancient sedimentary deposits contain belem- 

 nites, particular species of ammonites, and pentacrinites, and 

 that therefore they cannot be of more ancient date than the 

 lias. We know, moreover, that the upper masses of our 

 sedimentary masses belong to the chalk, and frequently the 

 limit between the cretaceous strata and the Jurassic formation 

 can be traced with perfect certainty. 



Mixed Formation. — Immediately above the gneissitic quartz- 

 ite we generally find a series of peculiar rocks, which we pro- 

 pose to term the Mixed Formation {terrain mixte). The 

 thickness of this series is frequently not greater than a few 

 fathoms, but in other localities it amounts to several hundred 

 and even several thousand feet. Amongst these beds we often 

 meet with quartzites which it is very difficult to distinguish 

 from the gneissitic quartzites, if indeed they are really dif- 

 ferent ; but they have one peculiarity, that they dip to the 

 north like all the other rocks of this formation. Dolomitic 

 limestones, which are either compact or cellular, also occur, 

 and these are identical with the carnieule {Rauchwacke) which 

 accompanies our gypsums, and have a yellowish tint passing 

 into red and brown. Red argillaceous slates likewise present 

 themselves, with which are associated argillaceous or talcose 

 conglomerates. The latter sometimes constitute entire moun- 

 tains. Finally, above these last we find red or blackish green 

 ferruginous oolites, containing magnetic iron ore, iron glance, 

 and pyrites. In general, this whole formation is very fcrru- 

 ginous ; there are no conglomerates which do not contain iron, 

 and several spots are shewn where it was formerly attempted 

 to carry on mining operations. The oolitic bed affords many 

 petrifactions, especially ammonites and belemnites. 



Limestone of the High Alps and Black Slate. — A very thick 

 and uniform limestone formation, the limcbtone of the higli 



