228 COSMOS. 



nisable, even in scattered detritus, on many of the largest 

 and most active volcanoes. 



It is a great merit of modern times not only to have more 

 accurately investigated the peculiar conditions of the forma- 

 tion of volcanoes by a careful comparison of those which are 

 widely separated from each other, but also to have intro- 

 duced more definite expressions into language, by which the 

 heterogeneous features of the general outline, as well as 

 the manifestations of volcanic activity are distinguished. 

 If we are not decidedly disinclined to all classifications, 

 because in the endeavour after generalization these always 

 rest only upon imperfect indications, we may conceive the 

 bursting forth of fused masses and solid matter, vapours and 

 gases, in four different ways. Proceeding from the simple 

 to the complex phenomena, we may first mention eruptions 

 from fissures, not forming separate series of cones, but pro- 

 ducing volcanic rocks superlying each other, in a fused 

 and viscid state ; secondly, eruptions through heaped up 

 cones, without any circumvallation, and yet emitting streams 

 of lava, as was the case for five years during the destruction 

 of the Island of Lancerote, in the first half of the last 

 century ; thirdly, craters of elevation, with up-heaved strata, 

 but without central cones, emitting streams of lava only on 

 the outside of the circumvallation, never from the interior, 

 which is soon closed up with detritus ; fourthly, closed bell- 

 shaped mountains or cones of elevation, open at the summit, 

 either enclosed by a circular wall, which is at least partially 

 retained, as on the Pic of Teneriffe, in Fogo, and Rocca 

 Monfina ; or entirely without circumvallation or crater of 

 elevation, as in Iceland, 85 in the Cordilleras of Quito, and 

 the central parts of Mexico. The open cones of elevation of 

 this fourth class maintain a permanent connection between 

 the fiery interior of the earth and the atmosphere, which is 

 more or less effective at undetermined intervals of time. 

 Of the dome-shaped and bell-shaped trachytic and doleritic 

 mountains which have remained closed at the summit, there 

 appear, according to my observations, to be more than of 

 the open cones whether active or extinct, and far more 

 than of the true volcanoes. Dome-shaped and bell-shaped 



85 Sartorius von Waltershausen, Physisch-geographische Slcizze vor 

 Island, 1847, s. 107. 



