222 COSMOS. 



be taken as a synonymous name "for Maar, as small lakes 

 have been found by Abich and myself on the summits of the 

 highest volcanoes, on true cones of elevation in extinguished 

 craters ; for example, on the Mexican volcano of Toluca at 

 an elevation of 12,246 feet, and on the Caucasian Elburuz 

 at 19,717 feet. In the volcanoes of the Eifel we must care- 

 fully distinguish from each other two kinds of volcanic ac- 

 tivity of very unequal age the true volcanoes emitting 

 streams of lava, and the weaker eruptive phenomena of the 

 Maars. To the former belong the basaltic stream of lava, 

 rich in olivin, and cleft into upright columns, in the valley 

 of Uesbach, near Bert-rich ;* the volcano of Gerolstein, which 

 is seated in a limestone containing dolomite, deposited in the 

 form of a basin in the Devonian gray wacke schists ; and the 

 long ridge of the Mosenberg (1753 feet above the sea), not 

 far from Bettenfeld, to the west of Manderscheid. The last- 

 named volcano has three craters, of which the first and sec- 

 ond, those furthest to the north, are perfectly round, and 

 covered with peat mosses ; while from the third and most 

 southern! crater there flows down a vast, reddish brown, 

 deep stream of lava, separated into a columnar form, toward 

 the valley of the little Kyll. It is a remarkable phenome- 

 non, foreign to lava-producing volcanoes in general, that nei- 

 ther on the Mosenberg nor on the Gerolstein, nor in other 

 true volcanoes of the Eifel, are the lava eruptions visibly sur- 

 rounded at their origin by a trachytic rock, but, as far as 

 they are accessible to observation, proceed directly from the 

 Devonian strata. The surface of the Mosenberg does not at 

 all prove what is hidden in its depths. The scoriae contain- 

 ing augite, which by cohesion pass into basaltic streams, 

 contain small, calcined fragments of slate, but no trace of 

 inclosed trachyte. Nor is the latter to be found inclosed in 

 the crater of the Rodderberg, notwithstanding that it lies 

 in the immediate vicinity of the Siebengebirge, the greatest 

 trachytic mass of the Rhine district. 



"The Maars appear," as the mining surveyor Von De. 



* H. von Dechen, Geognost. Uelersicht der Umgegend von Bad Ber^ 

 tricli, 1847, s. 11-51. 



t Stengel, in Noggerath, das Gebirge von Rhetnland tmd Westphalen, 

 bd. i., s. 79, taf. iii. See also C. von Oeynhausen's admirable expla- 

 nations of his geognostic Map of the Lake of Laach, 1847, p. 34, 39, 

 and 42, including the Eifel and the basin of Neuwied. Upon th 

 Maars, see Steininger, Geognostische Beschreibung der Eifel, 1853, s. 

 113. His earliest meritorious work, "Die erloschenen Vulkane in der 

 Eifel tmd am Nieder-Rhein," belongs to the year 1820. 



