But we kept on top—­most of the time—­and fought our way forward by inches.  The black walls frowning at us from either side appeared to me to remain exactly the same, stationary, after a long and desperate struggle; but when I gave a quick glance behind I saw that we had pulled so far away from the raft that it was no longer in sight.  That gave me renewed strength, and, shouting assurance to Harry and Desiree, I redoubled my efforts.  Desiree was by now almost able to hold her own, but we still supported her.

Every stroke made the next one easier, carrying us away from the whirlpool, and soon we swam smoothly.  Less and less strong became the resistance of the current, until finally it was possible to float easily on our backs and rest.

“How far is it to the cavern?” Harry panted.

“Somewhere between one and ten miles,” was my answer.  “How the deuce should I know?  But we’ll make it now, I think.  Can you hold out, Desiree?”

“Easily,” she answered.  “If only I could get some air!  Just one good, long breath.”

There was the danger, and on that account no time was to be lost.  Again we struck out into the blackness ahead.  I felt myself no longer fresh, and began to doubt seriously if we should reach our goal.

But we reached it.  No need to recount our struggles, which toward the end were inspired by suffering amounting to agony as we choked and gasped for sufficient air to keep us up.

Another hundred yards would have been too much for us; but it is enough that finally we staggered onto the bank at the entrance to the cavern in which we had previously rested, panting, dizzy, and completely exhausted.

But an hour in the cavern, with its supply of air, revived us; and then we sat up and asked ourselves:  “What for?”

“And all that brings us—­to this,” said Harry, with a sweeping gesture round the cavern.

“At least, it is a better tomb,” I retorted.  “And it was a good fight.  We still have something in us.  Desiree, a good man was lost in you.”

Harry rose to his feet.

“I’m going to look round,” he announced.  “We’ve got to do something.  Gad, and it took us a month to build that raft!”

“The vanity of human endeavor,” said I, loosening the strap round my shoulders and dropping my bundle to the ground.  “Wait a minute; I’m going with you.  Are you coming, Desiree?”

But she was too tired to rise to her feet, and we left her behind, arranging what few skins we had as well as possible to protect her from the hard rock.

“Rest your weary bones,” said Harry, stooping to kiss her.  “There’s meat here if you want it.  We’ll be back soon.”

So we left her, with her white body stretched out at its full length on the rude mat.

Bearing off to the left, we soon discovered that we would have no difficulty to leave the cavern; we had only to choose our way.  There was scarcely any wall at all, so broken was it by lanes and passages leading in all directions.