Another stream was passed rising out of a boggy patch of ground, and here footprints were plentiful, but they were only those of birds that had been down to drink.
Onward again, and to ascend a steep precipitous slope right before them they had to descend into a dank, dark, gloomy-looking gorge, whose vegetation was scarce, and yet the place seemed to grow hotter as they went down.
A peculiar whistling sound came now from before them, and they stopped to listen, with the day evidently growing hotter, for down in the gorge there was not a breath of air; while as they listened the whistling grew louder and was accompanied by another in a different key, the two producing a curious dissonant sound for a few minutes, increasing rapidly, and then ceased, to be followed by absolute silence, and then a dull sound followed as if something had burst.
“Steam—a hot spring, I should say,” exclaimed the captain, going cautiously forward, parting the low growth as he went.
His progress became slower, and at the end of a minute he stopped and stepped cautiously back.
“Not safe,” he said; “my feet were sinking in. We must go farther round.”
He led the way, and they forced their way through the sickly-looking bushes till they came all at once upon a glistening patch of whitish-looking mud some thirty or forty yards round, and above which the atmosphere seemed to be quivering, if it were not so much clear steam rising in the air.
Here they found the cause of the noise, for as they approached there was a tiny jet of steam issuing from one side near the dense growth of a peculiar grass, and when this had been whistling for about a minute, another jet burst out on the other side, whistling in the different key, while in the middle of the mud-pool there was a quivering and rifting of the surface, followed by the formation of a huge bubble, which kept on rising up larger and larger till it was a big globe of quite two feet high, when it suddenly burst with a peculiar sound, as if someone had said the word Beff! in a low whisper.
This occurred several times before they went on, having vainly searched the borders of the mud-pool for footmarks; and at the end of another few hundred yards loud hissing and shrieking noises led them to another pool, but, far from being so quiescent as that which they had left behind, this was all in commotion. The hot shining mud was bubbling furiously, rising in mud bladders, which were incessantly rising and dancing all over the surface, while one in the middle, larger than the rest, rose and burst with a loud puff.
Very little steam was visible, and though here too the edge of the pool was examined, there was not even the footprint of a bird.