sometimes of vast depth. Some volcanoes consist of a crater alone,
with scarcely any mountain at all; but in the majority of cases the
crater is situated on the top of a mountain, which in some
instances towers to an enormous height. The part of the mountain
which terminates in the principal crater is usually of a conical
form--much like a glass-house chimney, and is therefore named the
cone. It is generally composed of loose ashes and cinders, with
here and there masses of stone, which have been tossed into the air
by the volcanic forces. In some mountains the cone rises out of a
hollow at a considerable height from the base. A hollow of this
kind is generally regarded as having been a former crater, which
had become extinct before the existing cone was raised. There are
sometimes formed lower down the mountain subordinate craters,
smaller than that which occupies the summit of the cone. Within the
crater itself there are frequently numerous little cones, from
which vapours are continually issuing, with occasional volleys of
ashes and stones.

One of the largest and most perfect of the volcanic cones in the
world is that of the Peak of Teneriffe, of which you have here a
representation. It conveys a good idea of the general form of the
cone, and has long been a conspicuous and useful landmark to
mariners. It is upwards of twelve thousand feet in height, and is
said to be visible in very clear weather at a distance of a hundred
miles.

The most interesting products of an active volcano are the streams
of lava which it pours forth--sometimes from the principal crater
on the summit--sometimes from the smaller craters lower down. This
lava consists of melted stone. When it issues from the mountain its