Now we can understand why earthquakes should be most common round volcanos; and we can understand, too, why they would be worst before a volcano breaks out, because then the steam is trying to escape; and we can understand, too, why people who live near volcanos are glad to see them blazing and spouting, because then they have hope that the steam has found its way out, and will not make earthquakes any more for a while.  But still that is merely foolish speculation on chance.  Volcanos can never be trusted.  No one knows when one will break out, or what it will do; and those who live close to them—­as the city of Naples is close to Mount Vesuvius—­must not be astonished if they are blown up or swallowed up, as that great and beautiful city of Naples may be without a warning, any day.

For what happened to that same Mount Vesuvius nearly 1800 years ago, in the old Roman times?  For ages and ages it had been lying quiet, like any other hill.  Beautiful cities were built at its foot, filled with people who were as handsome, and as comfortable, and (I am afraid) as wicked, as people ever were on earth.  Fair gardens, vineyards, olive-yards, covered the mountain slopes.  It was held to be one of the Paradises of the world.  As for the mountain’s being a burning mountain, who ever thought of that?  To be sure, on the top of it was a great round crater, or cup, a mile or more across, and a few hundred yards deep.  But that was all overgrown with bushes and wild vines, full of boars and deer.  What sign of fire was there in that?  To be sure, also, there was an ugly place below by the sea-shore, called the Phlegraen fields, where smoke and brimstone came out of the ground, and a lake called Avernus over which poisonous gases hung, and which (old stories told) was one of the mouths of the Nether Pit.  But what of that?  It had never harmed any one, and how could it harm them?

So they all lived on, merrily and happily enough, till, in the year A.D. 79 (that was eight years, you know, after the Emperor Titus destroyed Jerusalem), there was stationed in the Bay of Naples a Roman admiral, called Pliny, who was also a very studious and learned man, and author of a famous old book on natural history.  He was staying on shore with his sister; and as he sat in his study she called him out to see a strange cloud which had been hanging for some time over the top of Mount Vesuvius.  It was in shape just like a pine-tree; not, of course, like one of our branching Scotch firs here, but like an Italian stone pine, with a long straight stem and a flat parasol-shaped top.  Sometimes it was blackish, sometimes spotted; and the good Admiral Pliny, who was always curious about natural science, ordered his cutter and went away across the bay to see what it could be.  Earthquake shocks had been very common for the last few days; but I do not suppose that Pliny had any notion that the earthquakes and the cloud had aught to do with each other.  However, he soon found