t a stone.

"It is the same," he said, "that Mishter Sprowl pumped his head against.
I thought I should find some use for it; and now let's see."

He dropped it into the well. It sunk without a sound, the noise of its
distant fall being lost in the solemn and profound murmur of the
descending water.

"What make de cave, anyhow?" asked Cudjo.

"The wery question I vas going to ask," said Carl.

"It will take but a few words to tell you all I know about it," said
Penn. "Water containing carbonic acid gas has the quality of dissolving
such rock as this part of the mountain is made of. It is limestone; and
the water, working its way through it, dissolves it as it would sugar,
only very slowly. Do you understand?"

"O, yes, massa! de carbunkum asses tote it away!"

Penn smiled, and continued his explanation, addressing himself to Carl.

"So, little by little, the interior of the rock is worn, until these
great cavities are formed."

"But what comes o' de rock?" cried Cudjo; "dat's de question!"

"What becomes of the sugar that dissolves in your coffee?"

"Soaks up, I reckon; so ye can't see it widout it settles."

"Just so with the limestone, Cudjo. It _soaks up_, as you say. And
see!--I will show you where a little of it has settled. Notice this long
white spear hanging from the roof."

"Dat? Dat ar a stun icicle. Me broke de pint off oncet, but 'pears like
it growed agin. Times de water draps from it right smart."

"A good idea--a stone icicle! It grew as an icicle grows downward from
the eaves. It was formed by the particles of lime in the water, which
have collected there and hardened into what is called _stalactite_.
These curious smooth white folds of stone under it, which look so much
like a cushion, were formed by the water as it dropped. This is called
_stalagmite_."

"Heap o' dem 'ar sticktights furder 'long hyar," observed Cudjo, anxious
to be showing the wonders.

They came into a vast chamber, from the floor of which rose against the
darkness columns resembling a grove of petrified forest trees. The
flaming torches, raised aloft in the midst of them, revealed, supported
by them, a wonderful gothic roof, with cornice, and frieze, and groined
arches, like the interior of a cathedral. A very distinct fresco could
also be seen, formed by mineral incrustations, on the ceiling and walls.
On a cloudy background could be traced forms of men and beasts, of
forests and flowers, armies, castles, and ship