"We must look out here, son," said Hugh; "we may strike bad places anywhere and must go carefully."
Presently they were stopped by a ditch two or three feet wide, in which a few inches of water seemed to stand. Hugh stepped across it, finding the bank on the other side firm enough, and Jack jumped after him.
"This," said Hugh, "is one of those ditches that I was telling you about that the beaver dig to float their feed down to their ponds. If we could follow it back to the brush we would find that the willows all along it had been cut off."
A little beyond this they came to a place where the water was deeper and where the mud under the water was soft, and here they stopped and turning up the stream, followed as nearly as they could the edge of the old pond. Standing in the grass, out where the water was deeper, Hugh pointed out a number of little mounds overgrown with grass and low willows, which he told Jack were old and long-deserted beaver houses. "If we could get out to them," he said, "we should find under that brush a solid foundation of sticks and mud. Those houses will last for a long time, for as the sticks are kept wet all the time they don't rot, but just become water-soaked and will last pretty nearly forever."
The grass, the mud and water, and the frequent detours they had to make made their progress up stream slow, but at length they came to a grass-grown wall a foot or two higher than the rest of the ground, and when he saw that, Hugh gave an exclamation of satisfaction.
"Now," he said, "I think we'll have better going. This, you see, is an old dam, and the chances are we can get on it and cross the stream, and on the other side, where the bottom is narrower, we shall have better going." It turned out just as he had said. The dam, though soft in places, was generally so firm that they could walk along on it pretty comfortably. Over toward its further end it was partly broken down and the water of the stream trickled over and through it for a width of about twenty feet, but by carefully feeling their way and at every step testing the dam with their feet, they managed to cross the running water, and from there to the other side of the valley the dam was firm.
On this west side of the stream the moist bottom was much narrower and they presently found themselves on firm ground, and started to walk briskly up the creek.
"All this work here," said Hugh, "is very old, and I haven't seen any sign of beaver being here for a long time. We'll go up stream as far as we can, but we must cross to the other side before it gets night. We'd be pretty badly off if we were caught in this beaver swamp after dark. We'd sure have to spend the night here. I wouldn't be much surprised if we found that we had to move camp and go up further toward the head of the stream. The beaver have certainly left this part of it."
They hurried on, and for a mile or two nothing was said. The sun was hot and the rubber boots which both wore seemed clumsy and heavy. Jack felt pretty tired but he said nothing of this to Hugh. Presently, from the dry upland where they were walking they could see ahead of them a pond, and then, a little later, the dam which held back its waters.
"There," said Hugh, "that looks to me like fresh work. Don't you see there in that dam some green leaves sticking up? That looks as if the dam had been lately mended; so lately that the twigs and brush used in repairing it have not yet died and lost their leaves."