"You may go down with this party," said Mr. George, "and then you can come up and take care of Rosie while I go down with our guide."
So Rollo and Josie followed the two young men down. Mr. George watched them from above. They went down very easily, for the sand was soft, and the track turned this way and that, so as to avoid the steepest places. The black lava covered the whole floor of the crater, and Mr. George and Rosie supposed that those who had gone down would be able only to go to the edge of it; but, to their great surprise, they found that the guide, as soon as he reached it, stepped upon it, and walked boldly out, followed by the young men and by Rollo and Josie, like a party of boys walking out upon the ice on a pond.
"Why, uncle George!" exclaimed Rosie, "they are walking over the lava. Why don't they sink in?"
"I cannot imagine," said Mr. George. "I supposed it was soft."
In fact, it was soft; that is, it was soft enough to flow if it had been on a slope, but yet it was hard enough to walk upon. A current of lava, when it is coming down the mountain side, can often be walked upon while it is still in motion. Its fluidity at the best is very imperfect, and its motion is very slow. The lava which Rollo was upon in the floor of the crater, though pretty nearly cool and hard on the surface, was hot below. Rollo could see the redness of the heat in the holes and crevices. Probably, if a heavy stone were laid upon the bed of lava, it would gradually have sunk into it. And yet persons could walk over it without any difficulty.
Rollo and Josie followed the young men over the lava until they came so near the cone in the centre that if they were to advance farther they would be in danger of having the lava which was thrown up from it fall upon their heads. Here they found some boys, who belonged to the mountain, engaged in getting out small pieces of the lava, where it was hot and soft, and pressing coins into it, to sell to the people above. Rollo and Josie bought some of these specimens of the boys, and put them hot in their pockets.
While the boys were thus near the cone in the centre of the crater, they were sometimes lost to view from Mr. George and Rosie, on account of the puffs of vapor which the wind blew over them. Rosie was very much afraid whenever this happened. She thought that Josie and Rollo were lost; but Mr. George assured her that there was no danger.
"I should think there would be a great deal of danger," said she.
"So should I," said Mr. George, "of my own judgment. But I do not go by my own judgment in such cases."