Herculaneum was destroyed by fragments of pumice stone and ashes, scarcely distinguishable from those which one may see raked away from the half-uncovered walls of some new house at Pompeii. With this storm of falling cinders--how dense and thick one may picture dimly by remembering once more that all the seaward wall of the vast old crater was being blown away--with this crushing, choking shower, came torrents of rain, enough to turn the falling ashes to a sort of mud, which hardened into tufa. Indeed, just as the yellow tufa of Posilipo is composed of volcanic ash ejected underneath the sea, and is thus formed of ash and water, such precisely is the crust which hardened over Herculaneum, and holds the city in its clutch unto this hour. Perhaps the mud formed on the mountain slopes, and came rolling down upon the town. Professor Phillips thought it formed within the crater. Some obvious warning of great peril there must have been, and that quite early on the fatal 24th of August; for it was not long past noon when a message reached Pliny at Misenum, begging for his ships, since escape was even then impossible except by sea. Already Pliny, looking from Misenum, saw the mountain topped by that vast and awful cloud shaped like a pine tree, out of which ashes were raining down on the three cities. His ships, approaching the coast towards evening, ran into a hail of pumice stone. The ashes fell hotter and hotter on the decks, and in continually larger masses. The sea ebbed suddenly. Ruins were tumbling from the mountain. There was no possibility of giving help to the doomed city, and Pliny gave orders to steer off the coast. No eye has seen Herculaneum from that day to this. What became of the citizens is not known. Comparatively few bodies have been found; but the excavations were too imperfect to prove that somewhere in the city bounds they do not lie in heaps. Such was the end of Herculaneum, by ashes, not by lava. It is true that lava beds lie above the city now. Probably the lava of 1631 passed over it. Sir William Hamilton distinguished the débris of no less than six eruptions besides that which destroyed it. Sir Charles Lyell also thought that a large part of the covering of the city was subsequent to its first destruction.