Finally, however, Challenger, bent upon proving some point which Summerlee had contested, thrust his head over the rock and nearly brought destruction upon us all.
In an instant the nearest male gave a shrill, whistling cry, and flapped its twenty-foot span of leathery wings as it soared up into the air.
The females and young ones huddled together beside the water, while the whole circle of sentinels rose one after the other and sailed off into the sky.
It was a wonderful sight to see at least a hundred creatures of such enormous size and hideous appearance all swooping like swallows with swift, shearing wing-strokes above us; but soon we realized that it was not one on which we could afford to linger.
At first the great brutes flew round in a huge ring, as if to make sure what the exact extent of the danger might be.
Then, the flight grew lower and the circle narrower, until they were whizzing round and round us, the dry, rustling flap of their huge slate-colored wings filling the air with a volume of sound that made me think of Hendon aerodrome upon a race day.
"Make for the wood and keep together," cried Lord John, clubbing his rifle. "The brutes mean mischief."
The moment we attempted to retreat the circle closed in upon us, until the tips of the wings of those nearest to us nearly touched our faces.
We beat at them with the stocks of our guns, but there was nothing solid or vulnerable to strike.
Then suddenly out of the whizzing, slate-colored circle a long neck shot out, and a fierce beak made a thrust at us.
Another and another followed.
Summerlee gave a cry and put his hand to his face, from which the blood was streaming.
I felt a prod at the back of my neck, and turned dizzy with the shock.
Challenger fell, and as I stooped to pick him up I was again struck from behind and dropped on the top of him.
At the same instant I heard the crash of Lord John's elephant-gun, and, looking up, saw one of the creatures with a broken wing struggling upon the ground, spitting and gurgling at us with a wide-opened beak and blood-shot, goggled eyes, like some devil in a medieval picture.
Its comrades had flown higher at the sudden sound, and were circling above our heads.
"Now," cried Lord John, "now for our lives!"
We staggered through the brushwood, and even as we reached the trees the harpies were on us again.
Summerlee was knocked down, but we tore him up and rushed among the trunks.
Once there we were safe, for those huge wings had no space for their sweep beneath the branches.
As we limped homewards, sadly mauled and discomfited, we saw them for a long time flying at a great height against the deep blue sky above our heads, soaring round and round, no bigger than wood-pigeons, with their eyes no doubt still following our progress.
At last, however, as we reached the thicker woods they gave up the chase, and we saw them no more.
"A most interesting and convincing experience," said Challenger, as we halted beside the brook and he bathed a swollen knee.
"We are exceptionally well informed, Summerlee, as to the habits of the enraged pterodactyl."
Summerlee was wiping the blood from a cut in his forehead, while I was tying up a nasty stab in the muscle of the neck.
Lord John had the shoulder of his coat torn away, but the creature's teeth had only grazed the flesh.
"It is worth noting," Challenger continued, "that our young friend has received an undoubted stab, while Lord John's coat could only have been torn by a bite.
In my own case, I was beaten about the head by their wings, so we have had a remarkable exhibition of their various methods of offence."
"It has been touch and go for our lives," said Lord John, gravely, "and I could not think of a more rotten sort of death than to be outed by such filthy vermin.
I was sorry to fire my rifle, but, by Jove! there was no great choice."
"We should not be here if you hadn't," said I, with conviction.
"It may do no harm," said he.
"Among these woods there must be many loud cracks from splitting or falling trees which would be just like the sound of a gun.
But now, if you are of my opinion, we have had thrills enough for one day, and had best get back to the surgical box at the camp for some carbolic.
Who knows what venom these beasts may have in their hideous jaws?"
But surely no men ever had just such a day since the world began.
Some fresh surprise was ever in store for us.
When, following the course of our brook, we at last reached our glade and saw the thorny barricade of our camp, we thought that our adventures were at an end.
But we had something more to think of before we could rest.
The gate of Fort Challenger had been untouched, the walls were unbroken, and yet it had been visited by some strange and powerful creature in our absence.
No foot-mark showed a trace of its nature, and only the overhanging branch of the enormous ginko tree suggested how it might have come and gone; but of its malevolent strength there was ample evidence in the condition of our stores.
They were strewn at random all over the ground, and one tin of meat had been crushed into pieces so as to extract the contents.
A case of cartridges had been shattered into matchwood, and one of the brass shells lay shredded into pieces beside it.
Again the feeling of vague horror came upon our souls, and we gazed round with frightened eyes at the dark shadows which lay around us, in all of which some fearsome shape might be lurking.
How good it was when we were hailed by the voice of Zambo, and, going to the edge of the plateau, saw him sitting grinning at us upon the top of the opposite pinnacle.
"All well, Massa Challenger, all well!" he cried.
"Me stay here.
You always find me when you want."
His honest black face, and the immense view before us, which carried us half-way back to the affluent of the Amazon, helped us to remember that we really were upon this earth in the twentieth century, and had not by some magic been conveyed to some raw planet in its earliest and wildest state.