Formations on the Left Bank of' the Rhine. 151 - 



Brohl, strongly impregnated with the same gas, which is usu- 

 ally the latest product of an otherwise extinct volcano. 



At some distance from Laach, towards the south-west, and 

 between the villages of Bell and Mayen, rises another group 

 of cones, containing two or three irregular crateriform basins, 

 from which different mud streams appear to have flowed, co- 

 vering the slate plateau in their neighbourhood with their de- 

 posits. These volcanic vents differ, however, from that of 

 Laach, in having produced leucitic lavas, and, consequently, 

 their conglomerates are of a different character, resembling 

 exactly the peperinoof Monte Albano. Such is the rock quar- 

 ried near Bell, and called bak'Of en-stein. It is in request for 

 lining ovens, from its capacity of resistance to fire, which it 

 owes to its being almost wholly composed of leucite in a frag- 

 mentary state. It encloses many small white farinaceous leu- 

 cites, fragments and blocks of leucitic lava, of burnt clay-slate, 

 and large broken plates of mica. 



The leucitic phonolite spoken of by Keferstein, as existing in 

 massive beds near Beiden and Meyr, I presume to derive from 

 this system of vents. 



Further to the south, and near the village of Kruft, rise 

 three other smaller cones, covered with vegetation, and with 

 faint traces only of craters. Other cones, and some of a large 

 size, are visible to the westward of Olburg, but my time did 

 not permit me to examine them in detail. On the whole, the 

 volcanic products of Andernach, and the Upper Eiffel, seem- 

 ed to me to bear the greatest analogy to those of Italy, par- 

 ticularly of the Campagna di Boma. The points on which they 

 differ, are the result of the former volcanos having broke forth 

 on a high and dry slate plateau, the latter from a submarine 

 alluvial shore. In both these districts, as well as in the Cam- 

 pi Phlegraei, it is remarkable that the same, or at least very 

 neighbouring vents, have produced trachytic, leucitic, and ba- 

 saltic lavas. 



2. District of the Lower Eiffel. 



The groupe of volcanic vents which occupies this district, 

 is in immediate contact with that of Laach and the Upper Eiffel, 

 though the points on which eruptions have taken place are 

 rather more thickly sown towards the western limit, particu- 



