MAARS. 221 



and Martins encamped for several days, is a closed amphi- 

 theatre with a nearly flat bottom, at an elevation of nearly 

 12,811 feet; from the midst of which the colossal pyramid 

 of the summit rises.* The same upheaving forces produce 

 similar forms, although modilied by the composition of the 

 different rocks. The annular and caldron-like valleys (val- 

 leys of elevation) described by Hoffman, Buckland, Murchi- 

 son, and Thurmann, in the sedimentary rocks of the north 

 of Germany, in Herefordshire, and the Jura mountains of 

 Porrentruy, arc also connected with the phenomena here de- 

 scribed, as well as, although with a less degree of analogy, 

 some elevated plains of the Cordilleras inclosed on all sides 

 by mountain masses, in which are situated the towns of 

 Caxamarca (9362 feet), Bogota (8729 feet), and Mexico 

 (7469 feet), and in the Himalayas the caldron-like valley of 

 Caschmir (5819 feet). 



Less related to the craters of elevation than to the above 

 described simplest form of volcanic activity (the action from 

 mere fissures) are the numerous Maars among the extinct 

 volcanoes of the Eifel — caldron-like depressions in non-vol- 

 canic rock (Devonian slate), and surrounded by slightly ele- 

 vated margins, formed by themselves. "These are, as it 

 were, the funnels of mines, indications of mine-like erup- 

 tions," resembling the remarkable phenomenon described by 

 me of the human bones scattered upon the hill of La Culcaf 

 during the earthquake of Riobamba (4th February, 1797). 

 When single Maars, not situated at any great height, in the 

 Eifel, in Auvergne, or in Java, are filled with water, such 

 former craters of explosion may in this state be denominated 

 crateres-lacs ; but it seems to me that this term should not 



* Bravais and Martins, Observ. /kites au Sommet et au Grand Pla- 

 teau du Mont Blanc, in the Annuaire Meteorol. de la France pour 1850, 

 p. 131. 



t Cosmos, vol. v., p. 173. I have twice visited the volcanoes of the 

 Eifel, when geognosy was in very different states of development, in 

 the autumn of 1794, and in August, 1845 ; the first time in the vicin- 

 ity of the Lake of Laach and the monastery there, which was then 

 still inhabited by monks ; the second time in the neighborhood of 

 Bertrich, the Mosenberg, and the adjacent Maars, but never for more 

 than a few days. As in the latter excursion I had the good fortune 

 to be able to accompany my intimate friend, the mining surveyor, 

 Von Dechen, I have been enabled by many years' correspondence, 

 and the communication of important manuscript memoirs, to make 

 free use of the observations of this acute geognosist. I have often in- 

 dicated by quotation marks, as is my wont, what I have borrowed, 

 word for word, from his communications. 



