t too,' he said. 'I was wondering whether I was
developing hallucinations like Thora. Notice, by the way, that the
blocks beside it are quite warm beneath the sun.'

"We examined the slab eagerly. Its edges were cut as though by an
engraver of jewels. They fitted against the neighbouring blocks in
almost a hair-line. Its base was slightly curved, and fitted as
closely as top and sides upon the huge stones on which it rested. And
then we noted that these stones had been hollowed to follow the line
of the grey stone's foot. There was a semicircular depression running
from one side of the slab to the other. It was as though the grey rock
stood in the centre of a shallow cup--revealing half, covering half.
Something about this hollow attracted me. I reached down and felt it.
Goodwin, although the balance of the stones that formed it, like all
the stones of the courtyard, were rough and age-worn--this was as
smooth, as even surfaced as though it had just left the hands of the
polisher.

"'It's a door!' exclaimed Stanton. 'It swings around in that little
cup. That's what makes the hollow so smooth.'

"'Maybe you're right,' I replied. 'But how the devil can we open it?'

"We went over the slab again--pressing upon its edges, thrusting
against its sides. During one of those efforts I happened to look
up--and cried out. A foot above and on each side of the corner of the
grey rock's lintel was a slight convexity, visible only from the angle
at which my gaze struck it.

"We carried with us a small scaling-ladder and up this I went. The
bosses were apparently nothing more than chiseled curvatures in the
stone. I laid my hand on the one I was examining, and drew it back
sharply. In my palm, at the base of my thumb, I had felt the same
shock that I had in touching the slab below. I put my hand back. The
impression came from a spot not more than an inch wide. I went
carefully over the entire convexity, and six times more the chill ran
through my arm. There were seven circles an inch wide in the curved
place, each of which communicated the precise sensation I have
described. The convexity on the opposite side of the slab gave exactly
the same results. But no amount of touching or of pressing these spots
singly or in any combination gave the slightest promise of motion to
the slab itself.

"'And yet--they're what open it,' said Stanton positively.

"'Why do you say that?' I asked.

"'I--don't know,' he answered hesitating