The rest of the way down the mountain was easy tramping.

The path soon led by the end of the great Upper Wetterhorn Glacier, and the Overall Boys begged their father to let them explore it.

"All right," said their father. "Just step into this small car and we will go on an exploring trip."

Before the boys knew what was happening, the tiny square car rose from the ground and began moving slowly upward, following the steep slope of the mountain.

"Oh, Jack, where are we going?" cried Joe. "This car is built bottom side up. The wheels are on the top of it, instead of on the bottom."

"That's so!" exclaimed Jack. "We are hanging in the air on a cable. It is lifting us right up the mountain side. And look away up there! Another car just like this one is coming down. My! Do you suppose we shall go as high as that?"

"I hope so," said Joe. "But see what is below us. It is the glacier! Look at the great cracks in it. Do you hear that noise, Jack? It sounds like thunder."

"I guess it is only another crack bursting open," said Jack. "This hot sun makes the glacier move faster, and so it cracks open."

Up, up, climbed the car, right over the glacier, until it came to a wild goat's path on a narrow shelf of the mountain, more than twelve hundred feet above the starting point.

Here it slipped into a small station, and everybody stepped out. Other people took their places, and then the car moved slowly downward, leaving the boys on the steep mountain side.

"My! That was great!" cried Jack. "Now what are we going to do?"

"We are going to walk across the glacier, aren't we, father?" said Joe.

"Of course we are. We have come up here to explore it, you know," said their father.

And they did explore 'way across the great ice river. In many places they had to walk very carefully, or they would have fallen into one of the deep cracks, but at last they came safely to the other side. There was no car on this side of the glacier to carry them down the mountain, but there were long ladders to help them over the very hardest and steepest places.

They had to climb over great ridges of rocks, which the glacier had torn away from the higher mountains years and years before. These rocks had been brought slowly down on the ice, and dropped along the sides and end of the glacier.

At last the party came to the place where the sun and the warm winds changed the glacier from a river of ice to a river of water.

"Well, boys," said their father, "we have had a look at the outside of the glacier; now let us take a look at the inside of it." So a man threw warm blankets over their shoulders, and they entered a long, narrow passage through a hole in the ice wall.

This passage led into a beautiful, blue ice room. The floor was ice, the walls were ice, and the ceiling was ice. There was no lamp in the room, and yet it was not dark.

"Isn't it beautiful!" cried Joe. "Think of it, we are in the center of a great ice river. There is nothing but ice all around us."

"I know it," said Jack. "I am sure the glaciers are the most wonderful things in Switzerland, but I have stayed inside of this one as long as I want to. I should rather be tramping."