126 



EARTH FEATURES AND THEIR MEANING 



pimpled with great numbers of parasitic cinder cones, each the 

 monument to some earlier eruption (Fig. 125). 



It is generally the case that a single 

 eruption makes 'but a relatively small 

 contribution to the bulk of the mountain. 

 From each new cone or bocca there pro- 

 ceeds a stream of lava spread in a rela- 

 tively narrow stream extending down the 

 slopes (Fig. 126). 



The caldera of composite cones. 

 Because of the varied episodes in the 

 FIG. 126. Sketch map of history of composite cones, they lack the 

 Etna, showing the indi- regu i ar ii nes characteristic of the two 



t d t a S :k rf ) aC a e nd Ta the e rfl simpler types. The larger number of the 



covered surf ace (stippled), more important composite cones have 



been built up within an outer crater of 



relatively large diameter, the Somma cone or caldera, which 

 surrounds them like a gigantic ruff or collar. This caldera is 

 clearly in most cases at least the relic of an earlier explosive 

 crater, after which successive eruptions of lesser violence have 

 built a more sharply conical structure. This can only be inter- 

 preted to mean that most larger and long-active volcanoes have 



FIG. 127. Panum crater, showing the caldera and the later interior cones 

 (after Russell). 



been born in the grandest throes of their life history, and that a 

 larger or smaller lateral migration of the vent has been responsible 

 for the partial destruction of the explosion crater. Upon Vesu- 



