MAARS. 237 



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 leit bank of the Rhine. From the friability 

 of the material the place of eruption may have disappeared 

 without leaving any ti-aces, 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 M aars the 

 small fragments of felspathic 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 for- 

 mations decidedly extend to a more recent period than the 

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

 therefore, to be regarded younger than the trachyte. In 

 the present declivities \,f the valley of the Rhine many 

 basaltic groups (the quarry of Unkel, Rolandseck, Godes- 

 berg), were only laid bare by the opening. of the valley, 

 as up to that time they were probably enclosed in the Devo- 

 nian grauwacke 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 

 most brilliant discoveries of our time, have their principal 

 seat in the volcanic Eifel, in the Rapilli, Trass-strata, and 

 pumice-conglomerates. Organisms with silicious shields fill 

 the valley of Brohl and the eruptive matters of Hochsim- 

 mer ; sometimes, in the Trass, they are mixed with uncar- 

 bonised twigs of coniferae. According to Ehrenberg, the 



