Summerlee had lain down and slept upon the sand, but we others roamed round the edge of the water, seeking to learn something more of this strange country. Twice we found pits of blue clay, such as we had already seen in the swamp of the pterodactyls. These were old volcanic vents, and for some reason excited the greatest interest in Lord John. What attracted Challenger, on the other hand, was a bubbling, gurgling mud geyser, where some strange gas formed great bursting bubbles upon the surface. He thrust a hollow reed into it and cried out with delight like a schoolboy when he was able, on touching it with a lighted match, to cause a sharp explosion and a blue flame at the far end of the tube. Still more pleased was he when, inverting a leathern pouch over the end of the reed, and so filling it with the gas, he was able to send it soaring up into the air.