Their height is not uniform, however.

We passed through one a hundred feet long, which leads through a spur of the hill and opens out well up in the sheer wall of a precipice whose foot rests in the waves of the sea.

It is a commodious tunnel, except that there are occasional places in it where one must stoop to pass under.

The roof is lava, of course, and is thickly studded with little lava-pointed icicles an inch long, which hardened as they dripped.

They project as closely together as the iron teeth of a corn-sheller, and if one will stand up straight and walk any distance there, he can get his hair combed free of charge..