As one descended the slope the woods became thinner, and bushes, with occasional high trees, took the place of the forest.  I could make good progress, therefore, and I could see without being seen.  I passed close to the pterodactyl swamp, and as I did so, with a dry, crisp, leathery rattle of wings, one of these great creatures—­it was twenty feet at least from tip to tip—­rose up from somewhere near me and soared into the air.  As it passed across the face of the moon the light shone clearly through the membranous wings, and it looked like a flying skeleton against the white, tropical radiance.  I crouched low among the bushes, for I knew from past experience that with a single cry the creature could bring a hundred of its loathsome mates about my ears.  It was not until it had settled again that I dared to steal onwards upon my journey.

The night had been exceedingly still, but as I advanced I became conscious of a low, rumbling sound, a continuous murmur, somewhere in front of me.  This grew louder as I proceeded, until at last it was clearly quite close to me.  When I stood still the sound was constant, so that it seemed to come from some stationary cause.  It was like a boiling kettle or the bubbling of some great pot.  Soon I came upon the source of it, for in the center of a small clearing I found a lake—­or a pool, rather, for it was not larger than the basin of the Trafalgar Square fountain—­of some black, pitch-like stuff, the surface of which rose and fell in great blisters of bursting gas.  The air above it was shimmering with heat, and the ground round was so hot that I could hardly bear to lay my hand on it.  It was clear that the great volcanic outburst which had raised this strange plateau so many years ago had not yet entirely spent its forces.  Blackened rocks and mounds of lava I had already seen everywhere peeping out from amid the luxuriant vegetation which draped them, but this asphalt pool in the jungle was the first sign that we had of actual existing activity on the slopes of the ancient crater.  I had no time to examine it further for I had need to hurry if I were to be back in camp in the morning.

It was a fearsome walk, and one which will be with me so long as memory holds.  In the great moonlight clearings I slunk along among the shadows on the margin.  In the jungle I crept forward, stopping with a beating heart whenever I heard, as I often did, the crash of breaking branches as some wild beast went past.  Now and then great shadows loomed up for an instant and were gone—­great, silent shadows which seemed to prowl upon padded feet.  How often I stopped with the intention of returning, and yet every time my pride conquered my fear, and sent me on again until my object should be attained.

At last (my watch showed that it was one in the morning) I saw the gleam of water amid the openings of the jungle, and ten minutes later I was among the reeds upon the borders of the central lake.  I was exceedingly dry, so I lay down and took a long draught of its waters, which were fresh and cold.  There was a broad pathway with many tracks upon it at the spot which I had found, so that it was clearly one of the drinking-places of the animals.  Close to the water’s edge there was a huge isolated block of lava.  Up this I climbed, and, lying on the top, I had an excellent view in every direction.