ETNA AND VESUVIl'S 271 



sliauseii/''-^ oJ' tlie central crater at diilereiit times between 1804 and 1816 

 show two vents which are in fixed positions during these 13 years. The 

 only change which they undergo is the gradual building np of a small 

 cone about each. ISTeither of these appears to correspond to the vent 

 shown by Eicco or either of those of 1914:. 



At Yesuvins there is still less evidence afforded by the plans and 

 sketches ; but some of the plans indicate the presence, fifty and more years 

 ago, of a vent which corresponds in position approximately to that of 

 1914.^0 



What is probably another example of persistence of location of vents is 

 furnished by the gigantic volcano of Tejigger in Java. Here in the floor 

 of the crater (about 25 kilometers in circumference), which resembles 

 that of Kilauea, rise five cones, each a volcano in itself, which by their 

 very size testify to the persistence in location of their conduits through a 

 long period of time. 



General Discussion 



That a vent can maintain its position on a crater floor for a very con- 

 siderable period of years is at variance with some of our accepted ideas of 

 an active volcano. Because of the profound alteration in the size, form, 

 and depth of the crater and in the altitude and topography of the crater 

 floor, which are so often brought about by central eruptions, we are accus- 

 tomed to associate the idea of constant change rather than that of perma- 

 nence with most active volcanoes, and to assume that the location of an 

 active vent at the time of a new eruption is variable and fortuitous, 

 though the general position of the crater may not shift. 



That the foci of activity do shift position in successive eruptions is 

 unquestionably true of those Avhich take place on the flanks of volcanoes, 

 as at Etna and Vesuvius. But the evidence presented in preceding pages 

 seems to be conclusive, as far as it is available in point of time and ac- 

 curacy of location, that ivitliin the main crater, both at Stromboli and 

 Kilauea, and possibly at other volcanoes, a focus of activity or vent of 

 small size may remain localized for a century or more. 



That general volcanic activity may shift along a line, presumably that 

 of a fracture in the earth's "crust,'' is well known, and is exemplified on 

 a large scale l)y the row of volcanoes of western Italy from Bolsena to 

 Vesuvius^^ and bv the row of volcanic Hawaiian Islands.*- With this 



39 Sai-torius von Waltershausen : Der Etna. Leipzig, 1880, vol. ii, pp. 304, 305. These 

 are reproduced by Daly, Igneous rocks, p. 143. 



^ Wasliington and Day : Bull. Geol. See. Am., vol. 26, 1915, p. 379. 



A. Malladra : Boll. Soc. Geog. Ital., 1914, p. 45 ; Rend. Ace. Sci. Nap., 1914, p. 10. 

 ^^H. S. Washington : The Iloman comagmatic region. Carnegie Publ. no. 57, 1906, p. 176. 

 *2 W. Cross : U. S. Geol. Surv., P. P. 88, 1915, p. 8. 



XIX— -Bull. Geol. Soc. Am., Vol. 28, 1916 



