ON ITS EXTERIOR. VOLCANOES. 407 



or fifty less, because prepared on different principles. 

 I have here restricted myself to volcanoes which either 

 still emit vapours, or which have had historically assured 

 eruptions within the nineteenth or the latter half of 

 the eighteenth century. There have indeed been in- 

 tervals between successive eruptions of the same volcano 

 extending over four centuries and upwards; but such 

 cases are very rare. We know the slow succession of 

 great eruptions of Vesuvius, in the years 79, 203, 512, 

 652, 983, 1138, and 1500. Previous to the great 

 eruption of Epomeo in Ischia in 1302, we know only 

 of those of the years 36 and 45 B.C., therefore fifty- 

 five years before the breaking out of Vesuvius. 



Strabo, who died under Tiberius at the age of ninety, 

 (ninety-nine years after Spartacus had intrenched him- 

 self on Vesuvius), and who had no historic knowledge 

 of an older eruption, declares Vesuvius to be an 

 ancient volcano which had long ago burnt out and 

 become extinct. He says : " Above those places " 

 (Herculaneum and Pompeii) " lies Mount Vesuios, 

 encompassed by the finest cultivated fields, except on 

 its summit. This is, indeed, mostly a plain surface, 

 but unfruitful, and has an ashy appearance. It shows 

 cleft hollows of sooty-looking rock, appearing as if it 

 had been eaten into by the action of fire, so that we 

 may conjecture that at some former time there burnt in 

 these orifices a fire which has now become extinct, the 

 fuel which supported it having been consumed." (Strabo, 

 lib. v. page 247, Casaub.) This description does not 

 indicate either a cone of ashes or a crater-like depres- 

 sion ( 557 ) of the ancient summit, the encircling ridge of 



