MAARS, 233 



southern 98 crater, theie flows down a vast, reddish brown, 

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

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

 menon, foreign to lava-producing volcanoes in general, that 

 neither on the Mosenberg nor on the Gerolstein, nor in 

 other true volcanoes of the Eifel are the lava-eruptions 

 visibly surrounded 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 containing augite, which by cohesion pass into 

 basaltic streams, contain small, calcined fragments of slate, 

 but no trace of enclosed trachyte. Nor is the latter to be 

 found enclosed in the crater of the Rodderberg, notwith- 

 standing that it lies in the immediate vicinity of the Sieben- 

 gebirge, the greatest trachytic mass of the Rhine district. 



"The Maars appear," as the mining surveyor Von Dechen has 

 ingeniously observed, " to belong in their formation to about 

 the same epoch as the eruption of the lava-streams of the 

 true volcanoes. Both are situated in the vicinity of deeply 

 cut valleys. The lava-producing volcanoes were decidedly 

 active at a time when the valleys had already attained very 

 nearly their present form ; and we also see the most ancient 

 lava-streams of this district pouring down into the valleys." 

 The Maars are surrounded by fragments of Devonian slates 

 and by heaps of gray sand and tufa-margins. The Laacher 

 lake, wh ether it be regarded as a large Maar, or, with my 

 old friend C. von Oeynhausen, as part of a large cauldron- 

 like valley in the clay slate (like the basin of Wehr), ex- 

 hibits some volcanic eruptions of scoriae upon the ridge sur- 

 rounding it, as is the case on the Krufter Ofen, the Yeitskopf 

 and Laacher Kopf. It is not, however, merely the entire want 

 of lava-streams, such as are to be observed on the Canary 

 Islands upon the outer margin of true craters of elevation 

 and in their immediate vicinity, it is not the inconsiderable 



92 Stengel, in Ndggerath, das Gebirye von Rheinland und Westphalen, 

 Bd. i, s. 79, Taf. iii. See also C. von Oeynhauseii's admirable explana- 

 tions of his geognostic Map of the Lake of Laach, 1847, pp. 34, 39, and 

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

 see Steininger, Geognostische Beschreibung der Eifel, 1853, s. 113. Hip 

 earliest meritorious work, " Die erloschenen Vulkane in der Eifel und 

 am Niedcr-RItein," belongs to the year 1820. 



