ut at some one or other of the vents in the bottom of the crater.
If the heating goes on, the lava comes out hotter and hotter from the
opening, and by melting away the sides of it and blowing it out, it
gradually enlarges it. The lava that is blown out, too, falls down all
around the hole, and gradually builds up a mound around it, like a
little dome, while the successive blasts keep the outlet open all the
time at the top. This small cone, rising up gradually thus, in the
bottom of the crater formed by the sinking in of the mountain before,
and the chimney opening up through the centre of it, gives vent to all
the steam from below, while a great many of the other orifices are
stopped up by the lava which comes up out of the great opening falling
into them. After a time, the lava that is thrown out spreads over the
whole floor of the crater in a mass of black, corrugated slag, with the
small cone rising from the centre of it, and the opening at the top
glowing like the mouth of a fiery furnace, and bursting out every now
and then, with explosions of steam, and red-hot stones, and melted
lava.

This was precisely the condition of Vesuvius at the time that Rollo
visited it. The top of the mountain had fallen in, in two places, some
time before, on account of the cooling below, and two great craters had
been formed. Now, the furnace had been for some time heating up again,
and in each crater a black cone, with a fiery mouth open at the apex of
it, was gradually growing up, and covering the whole floor of the crater
with the black and molten matter which it was ejecting.

It was to the edge of one of these craters that the party now advanced,
and the engraving will give you some idea of the view which it
presented.

[Illustration: VIEW OF THE CRATER.]

There were several persons, both ladies and gentlemen, standing on the
margin of the crater when our party arrived. Mr. George led Rosie to the
place, and looked down with her into the abyss. The sides of it were
formed of precipitous cliffs of rocks and sand, all beautifully colored,
in every shade of red and yellow, by the deposits of sulphur which had
accumulated upon them from the fumes of the volcano. The floor of the
crater was black as jet, being covered by the molten lava, which had
gradually spread over it. The surface of this lava lay in wave-like
corrugations, like the hide of a rhinoceros, showing that it was or had
been semi-fluid. In the centre rose a great