Baron Humboldt on Volcanoes. 289 



has laboured incessantly, at least since the times of the Ho- 

 meric traditions, and serves as a light-house to the Tyrrhenian 

 Sea, guiding the seaman with its fiery signal on his course, the 

 more lofty volcanoes are characterized by lengthened periods 

 of repose. The eruptions of the greater number of the colossal 

 volcanoes that crown the Andes, occur at intervals almost of a 

 century apart : where exceptions to this rule have been ob- 

 served, — and I long ago directed attention to them, — they may 

 probably be connected with the circumstance, that the com- 

 munication between the volcanic focus and the crater of erup- 

 tion is not, and cannot be conceived to be, equally or perma- 

 nently free in every volcano at all times. In the less elevated 

 volcanoes the channel of communication may be closed for a 

 season ; so that their eruptions become rarer, without their 

 being, on this account, any nearer to extinction. 



With the consideration of the relation between the absolute 

 height of volcanoes, and the frequency of their activity, in so 

 far as this is externally visible, the place at which the lava 

 flows out is closely connected. Eruptions from the crater are 

 extremely rare in the case of many volcanoes ; they generally 

 proceed from the lateral fissures (as noticed by the celebrated 

 historian Bembo, in the 16th century, whilst yet a youth), at 

 places Avhere the flanks of the uplifted mountain, in conse- 

 quence of their shape and position, off"er the least amount 

 of resistance. Upon these fissures cones of eruption are occa- 

 sionally raised. The larger of these are of such dimensions 

 that they are often erroneously designated by the title of new 

 volcanoes. Ranked side by side, they shew the direction of a 

 fissure which has again become closed : the smaller ones fre- 

 quently occur in groups, closely set together, and cover whole 

 districts, as it were, Avith bell-shaped, or beehive-like, eleva- 

 tions. To the latter class belong the hornitos of Jorullo, and 

 the cone of the eruption of Vesuvius of October 1822, of the 

 volcano of Awatscha, according to Postels, and of the lava field 

 near the Baidare moimtains, in the peninsula of Kamtschatka, 

 according to Erman. 



When volcanoes do not rise free and isolated from a plain, 

 when, on the contrary, they are surrounded by table-lands 

 VOL. XXXIX. NO. LXXVIII. — OCTOBER 1845. T 



