Formation on the Left Bank of' the Rhine. 161 



sion, and out of place, for which I am bound duly to apolo- 



gize. 



Having now given a brief sketch of the principal volcanic 

 products of the Eiffel, I need not prolong this paper, already, 

 I fear, swelled beyond its proper limits. There occur a few 

 other vents in the vicinity of Ulmen, Kellberg, Adenau, and 

 Boos, which form the connecting links between this district 

 and that of Andernach. Some of these I did not visit, but 

 from those which I saw, as well as from Steinenger's account 

 of the others, they appear to be mere repetitions of the least 

 interesting of the cones and maare already mentioned. 



Upon the whole, though the vestiges of volcanic phenome- 

 na to be observed in the Prussian provinces on this side of the 

 Rhine, offer, without doubt, a highly interesting field of study 

 to the geologist, yet they cannot be recommended as types of 

 volcanic formations to those who, without visiting; other more 

 distant vents of subterranean energy, either active or extinct, 

 might seek, in the short tour between Spa and Cdblentz, to 

 acquire a general knowledge of the effects of this class of natu- 

 ral agents. In this view, as in every other, they are far less 

 instructive than the analogous formations of Auvergne, the 

 Velay,andVivarais, where almost every possible modification of 

 the volcanic phenomena is to be clearly traced, and on a much 

 larger scale. In the Rhine districts, there is a comparative little- 

 ness, and an appearance as if the volcanic energy had been damp- 

 ed and impeded by the mass of transition and secondary stra- 

 ta which it had to pierce, and still more so perhaps by the fra- 

 gile nature of the greywacke slate, which, shattered and pul- 

 verized by the first few aeriform explosions of every eruption, 

 would accumulate in prodigious volumes above and within 

 the vent, and speedily stifle its further activity. The same 

 circumstance will account both for the general paucity of lava 

 produced by these volcanos, and for the numerous deep and 

 wide craters, the formation of which, by the rapid and explo- 

 sive discharge of subterranean vapour, will, it is evident, have 

 been facilitated in proportion to the fragility and incoherence 

 of the superficial rock. 



VOL. v. NO. I. JULY 1826. l 



