YOLCANOES. 237 



eruption, distributed almost regularly in all directions ; under 

 the second, those lying at some little distance from one another, 

 forming, as it were, chimneys or vents along an extended fissure. 

 Linear volcanoes again admit of further subdivision ; namely, 

 those which rise like separate conical islands from the bottom 

 of the sea, being generally parallel with a chain of primitive 

 mountains whose foot they appear to indicate, and those vol- 

 canic chains which are elevated on the highest ridges of these 

 mountain chains, of which they form the summits.* The 

 Peak of Teneriffe, for instance, is a central volcano, being the 

 central point of the volcanic group to which the eruption of 

 Palma and Lancerote may be referred. The long rampart- 

 like chain of the Andes, which is sometimes single, and some- 

 times divided into two or three parallel branches, connected 

 by various transverse ridges, presents, from the soutii of Chili 

 to the north-west coast of America, one of the grandest in- 

 stances of a continental volcanic chain. The proximity of 

 active volcanoes is always manifested in the chain of the 

 Andes, by the appearance of certain rocks (as dolerite, mela- 

 phyre, trachyte, andesite, and dioritic porphyry), which divide 

 the so-called primitive rocks, the transition slates and sand- 

 stones, and the stratified formations. The constant recurrence 

 of this phenomenon convinced me long since that these spo- 

 radic rocks were the seat of volcanic phenomena, and were 

 connected with volcanic eruptions. At the foot of the grand 

 Tunguragua, near Penipe, on the banks of the Rio Puela, I 

 first distinctly observed mica slate resting on granite, broken 

 through by a volcanic rock. 



In the volcanic chain of the new r continent, the separate 

 volcanoes are occasionally, when near together, in mutual de- 

 pendence upon one another ; and it is even seen that the 

 volcanic activity for centuries together has moved 011 in one 



* Leopold von Buck, Pliysikal. Besclireib. der Canarisclien Inseln, 

 s. 326-407. I doubt if we can agree with the ingenious Charles Darwin 

 (Geological Observations on Volcanic Islands. 1844, p. 127) in regard- 

 ing central volcanoes in general as volcanic chains of small extent on 

 parallel fissures. Friedrich Hoffman believes that in the group of the 

 Lipari Islands, which he has so admirably described, and in which two 

 eruption fissures intersect near Panaria, he has found tin intermediate 

 link between the two principal modes in which volcanoes appear, namoly, 

 the central volcanoes and volcanic chains of Von Buch (Poggendorff, 

 Annalen der Physik, bd. xxvi. s. 81-88.) 



