very black, even compared with the sort of twilight at the bottom
of the tower; it grew larger because the children kept pulling off
the stones and throwing them down into another heap. The stones
must have been there a very long time, for they were covered with
moss, and some of them were stuck together by it. So it was fairly
hard work, as Robert pointed out.

When the hole reached to about halfway between the top of the arch
and the tower, Robert and Cyril let themselves down cautiously on
the inside, and lit matches. How thankful they felt then that they
had a sensible father, who did not forbid them to carry matches, as
some boys' fathers do. The father of Robert and Cyril only
insisted on the matches being of the kind that strike only on the
box.

'It's not a door, it's a sort of tunnel,' Robert cried to the
girls, after the first match had flared up, flickered, and gone
out. 'Stand off--we'll push some more stones down!'

They did, amid deep excitement. And now the stone heap was almost
gone--and before them the girls saw the dark archway leading to
unknown things. All doubts and fears as to getting home were
forgotten in this thrilling moment. It was like Monte Cristo--it
was like--

'I say,' cried Anthea, suddenly, 'come out! There's always bad air
in places that have been shut up. It makes your torches go out,
and then you die. It's called fire-damp, I believe. Come out, I
tell you.'