ON ITS EXTERIOE. VOLCANOES. 221 



may be regarded in the light of " fumeroles " connected 

 with extinct volcanoes, more particularly as springs of 

 carbonic acid gas are a characteristic of one of the latest 

 stages of such volcanoes, others, on the other hand, as 

 naphtha-springs, appear to be wholly independent of 

 genuine lava-erupting volcanoes. They follow (as Abich 

 has already shown in the Caucasus) definite directions over 

 extensive spaces, breaking forth from fissures, on the plain, 

 and even in the deep basin of the Caspian, as well as on 

 mountain heights of nearly 8000 feet. Like volcanoes 

 proper, their apparently slumbering activity sometimes 

 suddenly displays itself by the bursting forth of columns 

 of flame, which spread terror afar. They show the 

 same successive stages in both continents, at parts of the 

 earth very remote from each other ; but hitherto expe- 

 rience has not authorised us to regard them as foreshow- 

 ing the rise of true volcanoes erupting lavas and scoriae. 

 Their activity is of another kind ; perhaps originating at 

 lesser depths, and dependent on other chemical pro- 

 cesses. 



d. Volcanoes, according to their Diversity in Shape 

 and Activity Action through Fissures and Maars 

 Encircling Ridges round Craters of Elevation 

 Volcanic, conical, and dome-shaped Mountains, 

 with open or unopened Summits Diversity of 

 Rocks through which Volcanoes act. 



(Enlargement of the Picture of Nature in Cosmos, 

 Vol.I. p. 213235.) 



Among the manifold kinds of manifestation of force in 

 the reaction of the interior of our planet against its 



