Once there came a loud boom, like a cannon. The boom was followed by a crash, and the crash by a long, loud rumbling noise, which gradually died away.
"Oh, Gretel, what was that?" cried Joe. "I believe it was an earthquake."
One of the mountain alps they crossed
"Oh, no! That was not an earthquake," said Gretel, laughing. "That was a piece of the glacier breaking off. It must have had a long fall before it found a place where it could stop."
"I am glad it couldn't fall in this direction," said Jack. "I thought I wanted to take a walk on a glacier, but I am not so sure about it now."
"Oh, yes, you must!" said Gretel. "It is lots of fun. I have been up to that glacier twice with father. There are great cracks in it, so deep you can hardly see the bottom of them. It is perfectly safe to go with father. He often takes Americans up there."
"Well, I think I should rather take a walk on some other glacier. I am afraid this one is going to pieces," said Joe.
"No, it isn't!" said Gretel, laughing at Joe again. "The glacier melts and moves a little every summer, but a great deal of fresh snow falls on it every winter. I guess it will last as long as the mountains do."