226 



COSMOS. 



duckstein itself. Notwithstanding some analogies "which 

 the Cordilleras appear to present, I have always doubted 

 whether the Trass can be ascribed to eruptions of mud from 

 the lava-producing volcanoes of the Eifel. I rather suppose, 

 with H. von Dechen, that the pumice-stone was thrown out 

 dry, andthat the Trass was formed in the same way as oth- 

 er congWnerates. " Pumice-stone is foreign to the Sieben- 

 gebirge ; and the great pumice eruption of the Eifel, the 

 principal mass of which still lies above the loess (Trass) and 

 alternates therewith in particular parts, may, in accordance 

 with the presumption to which the local conditions lead, 

 have taken place in the valley of the Rhine, above Neuwied, 

 in the great Neuwied basin, perhaps near Urmits, on the left 

 bank of the Rhine. From the friability of the material, the 

 place of eruption may have disappeared without leaving any 

 traces by the subsequent action of the current of the Rhine. 

 In the entire tract of the Maars of the Eifel, as in that of 

 its volcanoes from Bertrich to Ormond, no pumice-stone is 

 found. That of the Laacher lake is limited to the rocks 

 upon its margin ; and on the other Maars the small frag- 

 ments of feldspathic rock, which lie in the volcanic sand and 

 tuff, do not pass into pumice." 



We have already touched upon the relative antiquity of the 

 Maars and of the eruptions of the lava streams, which differ so 

 much from them, compared with that of the formation of the 

 valleys. " The trachyte of the Siebengebirge appears to be 

 much older than the valley formation, and even older than the 

 Rhenish brown coal. Its appearance has been independent 

 of the cutting of the valley of the Rhine, even if we should 

 ascribe this valley to the formation of a fissure. The forma- 

 tion of the valleys is more recent than the Rhenish brown 

 coal, and more recent than the Rhenish basalt ; but older 

 than the volcanic eruptions with lava streams, and older than 

 the great pumice eruption and the Trass. Basalt formations 

 decidedly extend to a more recent period than the formation 

 of trachyte, and the principal mass of the basalt is, therefore, 

 to be regarded as younger than the trachyte. In the pres- 

 ent declivities of the valley of the Rhine many basaltic groups 

 (the quarry of Unkel, Rolandseck, Godesberg) were only laid 

 bare by the opening of the valley, as up to that time they were 

 probably inclosed in the Devonian graywacke rocks." 



The infusoria, whose universal diffusion, demonstrated by 

 Ehrenberg, upon the continents, in the greatest depths of the 

 sea, and in the upper strata of the atmosphere, is one of the 



