interval we catch it again in the west of Asia, on the southern borders of the Caspian Sea, whence it may be traced at the Greek Islands, Vesuvius, and the Italian Islands, to the Azores, Canaries, and Cape Verde Islands.

Besides these main lines, however, scattered volcanoes occur on other distant islands or on the edges of the continents. In the North Atlantic and Arctic Oceans lie the active craters of Iceland and Jan Mayen. On the west side of the basin of the Indian Ocean we find small volcanoes on the Red Sea and in the Isle of Bourbon. The line of volcanoes in Terra del Fuego at the southern apex of America seems to be continued in the chain of the South Shetland Islands, and to extend even into the supposed Antarctic continent, where, amid the vast snow-fields of that region, Sir James Ross in 1841 discovered an active volcanic cone 12,369 feet high.

But besides these active volcanoes there is a still larger number which are either dormant or extinct. It would seem that few large tracts of land exist where evidence may not be obtained of former volcanic action. Lavastreams and consolidated beds of volcanic dust may be found in almost all countries. Sometimes, indeed, as in Central France, the cones are still as fresh as if they had been thrown up only recently; and yet no record remains that they have ever been in eruption within the times of human history. Hence, if to the present long list of active volcanoes we add those which are now extinct, we shall find the whole surface of the land to be studded over with points of volcanic eruption.

When we consider that each of these points marks an orifice at which highly-heated materials have been poured forth from the interior, and that they are so widely distributed over the earth's surface, we see how important is their evidence as to the high internal temperature of the earth.

While the interior of the earth is probably solid as a whole, each portion of it, beyond a depth of a few miles, is probably at the melting-point, and ready to pass into a liquid condition when any diminution of the pressure takes place. The ridges on the surface of the earth, formed, as they have been, during the contraction and consequent general subsidence of the outer parts of the planet, have doubtless by their uprise relieved the pressure upon the parts underneath them. This relief has probably allowed portions of the interior to pass into the state of fusion. You observe how the active volcanoes of the globe are mostly arranged along such lines of elevation, whether on a continent as in South America, or in chains of islands as in the western and northern sides of the North Pacific Ocean. This arrangement can hardly be accident. It helps to connect the elevation of the land and the phenomena of volcanoes by showing how we should expect large spaces of melted rock to lie under those very regions where active volcanoes occur. Volcanoes do not pierce every mountain-chain, however, though in some cases they can be shown to have once existed but to have been long extinct.

The reservoirs of molten rock may exist underneath

without giving rise to actual volcanic explosions so long as no passage is opened to the surface. When water derived from rain, rivers, lakes, or the sea, filters through the upper rocks and eventually reaches these deep, intensely hot regions, it is raised to a very high temperature, indeed to the white heat of the molten rock with which it comes in contact. When portions of this superheated water succeed in effecting their escape, their removal relieves the pressure on the mingled mass of molten rock and water below, which is then forced upwards, and, where possible, finds an exit to the surface. It is these subterranean movements which give rise to the explosions, ashes, stones, and lava-streams of an active volcano. ARCHIBALD GEIKIE.

a

રી

forge. From Lat. fabrica,
workshop; " from faber,
workman," from facere, "to
make or do."
ĕrupt-eruption. Lat. e, "out,"
and ruptum, "to break, or
burst."
ĕmit-ěmission. Lat. e, "out,"
and mitto, missum, " to send."
dormant. French, pres. part.
of dormir (Lat. dormire), “
"to
sleep."
orifice, a small opening. Lat.
orificium (lit., "the making
of a mouth "), from os (oris),

saturated

consolidated

"the mouth," and -fic- (for facere), "to make." cráter, the cup-like, hollow opening of a volcano. Grk. and Lat. crater, "a large bowl (in which things were mixed together)." Connected with Grk. kerannumi, "I mix."

debris (dèbrě). The French débris (rubbish, fragments, ruins) adopted. Old French, desbriser, "to rive asunder," from des (Lat. dis), and briser, "to break."

["The accompanying drawing represents one of the streets of Pompeii, as it now appears after the volcanic deposit under which the city lay buried for sixteen centuries (A.D. 79 to 1711) has been cleared off. At the further end of the street, where the excavations have stopped, the dark layer on the top of the walls, and on which the pine tree is growing, represents the thickness of the general covering of volcanic ashes."-PROF. ARCHIBALD GEIKIE.

"In some places thirty feet in thickness."-PROF. HUXLEY.]

THE awful night preceding the fierce joy of the amphitheatre rolled drearily away, and greyly broke forth the dawn of THE LAST DAY OF POMPEII! The air

was uncommonly calm and sultry-a thin and dull mist gathered over the valleys and hollows of the broad Campanian fields. But yet it was remarked with surprise by the early fishermen that, despite the exceeding stillness of the atmosphere, the waves of the sea were agitated, and seemed, as it were, to run distractedly back from the shore; while along the blue and stately Sarnus, whose ancient breadth of channel the traveller now vainly seeks to discover, there crept a hoarse and sullen murmur, as it glided by the laughing plains and the gaudy villas of the wealthy citizens. Clear above the low mist rose the time-worn towers of the immemorial town, the red-tiled roofs of the bright streets, the solemn columns of many temples, and the statue-crowned portals of the Forum and the Arch of Triumph. Far in the distance the outline of the circling hills soared above the vapours, and mingled with the changeful hues of the morning sky. The cloud that had rested over the crest of Vesuvius had suddenly vanished, and its rugged and haughty brow looked without a frown over the beautiful scenes below.

Despite the earliness of the hour, the gates of the city were already opened. Horsemen upon horsemen, vehicle after vehicle, poured rapidly in; and the voices of the numerous pedestrian groups, clad in holiday attire, rose high in joyous and excited merriment; the streets were crowded with citizens and strangers from the populous neighbourhood of Pompeii, and noisily, fast, confusedly swept the many streams of life towards the fatal show.