On the Agency of Water in Volcanic Eruptions. 127 



continue often for some time with immense and scarcely diminished 

 energy." Vesuvius " has often continued in eruption for periods of 

 several months, discharging moderate jets of scoriae, lapilli, and sand, 

 from temporary orifices at the summit or flank of the cone, or at the 

 bottom of its crater, when there was a crater ; while streams of lava 

 welled out, sometimes almost with the tranquillity of a water-spring 

 from the same or from contiguous openings."* 



Professor Palmierif says of Vesuvius, that on some occasions the 

 eruptions commence with explosions and detonations of greater or 

 lesser violence, ending with a great eruption and a copious flow of 

 lava ; and that at other times great eruptions have taken place with- 

 out any precursory signs. 



Professor Phillips observes of the great eruption of Vesuvius of 

 1794, which was characterised by the flow of some of the largest lava 

 currents ever erupted from this mountain, that " for nearly a month 

 after the eruption (of lava), vast quantities of fine white ashes mixed 

 with volumes of steam were thrown out from the crater. "J 



M. Ch. St. Claire Deville§ states that the great eruption of Vesu- 

 vius in 1855 was one of the most tranquil. The projections only lasted 

 a few days, and the detonations soon ceased. The lava continued to 

 flow for twenty-eight days, and formed the largest current which has 

 passed out in the north-west direction. || This eruption was in great 

 contrast with that of 1850, which was one of the most violent and par- 

 oxysmal, when the mountain was changed in form, the central cone 

 reduced, and the crater enlarged to 2 miles in circumference, yet the 

 flow of lava was comparatively small. 



The eruption of Etna of 1852 was one of unusual magnitude, and 

 the flow of lava greater than ever witnessed, except probably in 1669. 

 It commenced in August with violent explosions and ejection of 

 scorise. The lava then began to flow from several openings, and 

 flooded the country for a length of 6 miles and a breadth, in places, 

 of 2 miles. The ejections of scoriae continued during sixteen days, 

 but after that time they almost ceased, except in a few smaller craters, 

 though dense volumes of steam were occasionally discharged from the 

 central crater, but the flow of lava continued with little interruption 

 through September, October, November, and December, and did not 

 entirely cease until May, 1853. \ 



An eruption, which seems of itself almost sufficient to prove the 



* Op. cit., p. 17. The italics here and in the following pages of this chapter are 

 mine. — J. P. 



f " Eruption of Vesuvius of 1871-2." Mallet's Translation, pp. 94, 99-100. 

 X " Vesuvius," pp. 92-4. 



§ " Bull. Soc. G-eol. de France," 2nd Ser., vol. xii, p. 1065. 

 || " Vesuvius," p. 107. 

 % Lyell, " Phil. Trans.," vol. 148, p. 18. 



