see little miniature deltas being formed there, though the sea
generally washes them away again in a few hours, unless the
place is well sheltered.

This, then, is what becomes of the earth carried down by rivers.
Either on plains, or in lakes, or in the sea, it falls down to
form new land. But what becomes of the dissolved chalk and other
substances? We have seen that a great deal of it is used by river
and sea animals to build their shells and skeletons, and some of
it is left on the surface of the ground by springs when the water
evaporates. It is this carbonate of lime which forms a hard crust
over anything upon which it may happen to be deposited, and then
these things are called "petrified."

But it is in the caves and hollows of the earth that this
dissolved matter is built up into the most beautiful forms. If
you have ever been to Buxton in Derbyshire, you will probably
have visited a cavern called Poole's Cavern, not far from there,
which when you enter it looks as if it were built up entirely of
rods of beautiful transparent white glass, hanging from the
ceiling, from the walls, or rising up from the floor. In this
cavern, and many others like it,*(See the picture at the head of
the lecture.) water comes dripping through the roof, and as it
falls carbonate of lime forms itself into a thin, white film on
the roof, often making a complete circle, and then, as the water
drips from it day by day, it goes on growing and growing till it
forms a long needle-shaped or tube-shaped rod, hanging like an
icicle. These rods are called stalactites, and they are so
beautiful, as their minute crystals glisten when a light is
taken into the cavern, that one of them near Tenby is called the