It looked, at first, like a small bunch of black dots high up on the steep slope before them. But before it could be reached, the glacier must be crossed. It was a river, indeed, but not like most other rivers in the world. It was a river of solid ice! When it first came in sight, it seemed like a broad, smooth sheet. Carl was a little bit disappointed. He turned to his uncle, and said: "I don't see anything wonderful or dangerous in a glacier, I'm sure." "Wait till you get a little nearer," was the answer. "It is not as easy to cross it as it at first seems." "Why does it stay a river of ice all the time, uncle? I should think it would melt in the summer-time, and be like other rivers," Carl went on. "High up in the mountains the snow stays all the year round. You know that?" "O, yes, Uncle Fritz." "Very well, then. The mass gets heavier and heavier, and much of it is gradually changed into ice." "Yes, I know that, too." "The great weight makes it begin to slide down. It comes very slowly, of course,--so slowly that it does not seem to move at all. But it does move, and brings with it rocks and trees and whatever is in its way." "I see now why it is called a _river_ of ice, uncle. But it doesn't move as fast in the winter as in the summer, does it?" "O, no, it can hardly be said to move at all during the coldest months of the year. In the summer-time, however, it moves much faster than it seems to do. I have been crossing a glacier more than once when I was suddenly startled by a tremendous noise. It would seem like the roar of thunder; but as the sky was clear, it was certainly not thunder. It was a sound made by the glacier itself as it passed over uneven ground. It is very likely that deep cracks opened in the ice at the same time, making a noise like an explosion. "But here we are, my dear, on the edge of the ice river. Don't you think now that it is a wonderful sight?" "Yes, indeed. How beautiful the colour is! It is such a lovely blue. But dear me! look at this mass of rocks all along the edge. The glacier is a giant, isn't it, to make these great stones prisoners and bring them along in its course? They look strong and ugly, yet they are helpless in its clutches. It isn't easy walking over them, either, is it?" After some hard climbing they found themselves on the glacier. It was not smooth, as Carl had at first thought, but was often cut into deep furrows or piled into rough masses. "Look out, now, Carl. We must cross that deep chasm ahead of us very carefully. It is wider than it looks. Here! Follow me." Fritz led the way to a place where the chasm was narrow enough for him to spring across with the aid of his mountain staff. Carl followed, while Fritz reached over from the other side and seized the boy as he landed. Carl laughed. He wasn't the least bit frightened.