completely, both above and at the sides, with a solid crust, within which, as in a tunnel, it continues to flow slowly as long as it is supplied from the source, here and there breaking through the crust which, as continually, reforms in front. Thus the terrible, inexorable river of fire slowly descends, destroying everything in its course.
The stone, ashes, and mud ejected during eruptions are even more destructive than the rivers of lava. In 1851 Tomboro, a volcano on the island of Sumbava, cost more lives than fell in the battle of Waterloo. The earthquake of Lisbon in 1755 destroyed 60,000 persons. During the earthquake of Riobamba and the mud eruption of Tunguragua, and again in that of Krakatoa, it is estimated that the number who perished was between 30,000 and 40,000. At the earthquake of Antioch in 526, no less than 200,000 persons are said to have lost their lives.
Vesuvius and Somma.
Perhaps the most destructive eruption of modern times has been that on Cosequina. For twenty-five miles it covered the ground with muddy water sixteen feet in depth. The dust and ashes formed a dense cloud extending over many miles, some of it being carried twenty degrees to the west. The total mass ejected has been estimated at fifty milliards of square metres.
Though long extinct, volcanoes once existed in the English Isles: Arthur's Seat, near Edinburgh, for instance, appears to be the funnel of a small volcano, belonging to the carboniferous period.
The summit of the mountain is often entirely blown away. Between my two first visits to Vesuvius 200 feet of the mountain had been thus blown up. Vesuvius itself stands in the ancient crater, part of which still remains and is now known as Somma, the greater part having disappeared in the great eruption of 79, when the mountain, waking from its long sleep, destroyed Herculaneum and Pompeii.
As regards the origin of volcanoes there have been two main theories. Impressed by the magnitude and grandeur of the phenomena, enhanced as they are by their destructive character, many have been disposed to regard the craters of volcanoes as gigantic chimneys, passing right through the solid crust of the globe, and communicating with the central fire. Recent researches, however, have indicated that, grand and imposing as they are, volcanoes must yet be regarded as due mainly to local and superficial causes.
A glance at the map shows that volcanoes are almost always situated on, or near, the sea coast. From the interiors of continents they are entirely wanting. The number of active volcanoes in the Andes contrasted with their absence in the Alps and Ourals, the Himalayas and Central Asian chains, is very striking. Indeed, the Pacific Ocean is encircled, as Ritter pointed out, by a ring of fire. It seems probable that the friction and pressure which have led to the formation of mountain chains had given rise to areas of excessively high temperature, and that where water has access to such regions volcanoes are produced by the explosions.
Yet though we cannot connect volcanic action with the central heat of the earth, but must regard it as a minor and local manifestation of force, volcanoes still remain among the grandest, most awful, and at the same time most magnificent spectacles which the earth can afford.
