He scrambled out and the two boys made their way back to dry ground. "How are you going to get dry?" asked Charley. "I don't want to make a fire unless it is absolutely necessary."
"Never mind about me. I'll dry off soon enough. Let's find their dam."
They made their way toward the run and soon discovered the dam. It was a great pile of branches, stones, moss, grass, mud, bark, etc., that had been built across the stream and extended for rods on either side. It looked very solid, yet the water did not pour over it, but filtered through it.
"Think of all the work it took to make that," cried Lew. "Why, every stick in it had to be gnawed down and floated here, and all the bark and grass and roots had to be pulled and brought here and the stones collected. And say! How in the world do you suppose they ever handled those stones? And how do you suppose they ever anchored the stuff when they began building? I should think the current would have swept everything away at first. That's a pretty swift stream."
"I read that they start their dams with saplings, which they anchor across the current with stones. They are much like squirrels, you know, and can use their fore paws about as well as we can use our hands. I suppose the stones lose weight by displacing water, but if I hadn't seen these rocks, I'd never have believed that such big stones could be handled by animals no larger than beavers."
"See here," said Lew. "These willow branches must have taken root, for they seem to be growing right up out of the top of the dam. And there's a birch that's surely growing. You know the branches of some trees will root if you put them in water, especially willows. Why, if they continue to grow and take more root, there'll be a hedge of living trees right across this brook. The dam will become so dense that it will back up a great quantity of water. I reckon this bottom will just naturally turn into a swamp after a time."
"Now that's interesting," suggested Charley. "You know the Bible tells us the world was made in six days; but it seems to me it isn't finished yet. Every rain washes down soil from the hills and helps to fill up the valleys and the river-bottoms, and the floods scour out the watercourses and carry earth and stones down to the ocean. And here we see a piece of land that used to be fine, dry bottom, now becoming a swamp. It looks to me as though the earth is changing every day."
They examined the dam more critically. "It's two hundred feet wide if it's an inch," said Lew, "though the brook isn't more than fifteen or twenty. You see, it extends on each side of the brook to land that is a little higher than the level of the stream bank. That's what makes this big head of water. At the least there are several acres of it."
"There's one thing that we haven't seen yet," added Charley, "and that's their houses. They ought to be some distance above the dam."
"I wonder if those are beaver lodges," said Lew, pointing to some bulky heaps of brush at a little distance up-stream.