234- COSMOS. 



elevation of the ridge surrounding the Maar, that distin- 

 guishes this from craters of elevation ; the margins of the 

 Maars are destitute of a regular stratification of the rock, 

 falling, in consequence of the upheaval, constantly outwards. 

 The Maars sunk in the Devonian slate, appear, as has already 

 been observed, like the craters of mines, into which, after 

 the violent explosion of hot gases and vapours, the looser 

 ejected masses (Bapillt), have for the most part fallen 

 back. As examples I shall only mention here the Immera- 

 ther, the Pulverinaar, and theMeerfelder Maar. In the centre 

 of the first mentioned, the dry bottom of which, at a depth 

 of two hundred feet, is cultivated, are situated the two 

 villages of Ober- and Unter-Immerath. Here, in the vol- 

 canic tufa of the vicinity, exactly as on the Laacher lake, 

 mixtures of felspar and augite occur in spheroids, in which 

 particles of black and green glass are scattered. Similar 

 spheroids of mica, hornblende and augite, full of vitrified 

 portions are also contained in the tufa veins of the Pulver- 

 maar near Gillenfeld, which, however, is entirely converted 

 into a deep lake. The regularly circular Meerfelder Maar, 

 covered partly with water and partly with peat, is character- 

 ized geognostically by the proximity of the three craters of 

 the groat Mosenberg, the most southern of which has fur- 

 nished a stream of lava. The Maar, however, is situated 

 639 feet below the long ridge of the volcano, and at its 

 northern extremity, not in the axis of the series of craters, 

 but more to the north-west. The average elevation of the 

 Maars of the Eifel above the surface of the sea falls be- 

 tween 922 feet (Laacher lake ?) and 1588 feet (Mosbrucher 

 Maar). 



As this is peculiarly the place in which to call attention 

 to the uniformity and agreement exhibited by volcanic 

 activity in its production of material results, in the 

 most different forms of the outer framework (as Maars, 

 as circuinvallated craters of elevation, or cones opened 

 at the summit), I may mention the remarkable abun- 

 dance of crystallized minerals which have been thrown 

 out by .the Maars in their first explosion, and which still 

 in part lie buried in the tufas. In the environs of the 

 Laacher lake this abundance is certainly greatest, but; other 

 Maars also, for example the Immerather, and the Meerfelder 



