The plan was greeted enthusiastically and after the fellows at the other end of the pool had been told about it, they rushed out and dressed quite as quickly as the rest. Then they hiked back to camp and put the matter before the Scout-Master, who readily assented to the trip, and, as Jack had foreseen, was very glad to go along. After a little more than an hour’s tramp Jack held up his hand in caution.

“You’ve got to be careful now, Scouts,” he said. “They’re wary old fellows and the least thing disturbs them. If they once suspect that we are anywhere near, it’s good-night with us. Those big, bright eyes will see us all right but we won’t catch a glimpse of them. Now’s the time for you Scouts to show what you know of woodcraft and follow me as silently as a band of Indians.”

Thus cautioned, the boys fell in behind Jack and, carefully avoiding stepping upon twigs or speaking above a whisper, soon reached the dam. They were on the banks of a mountain stream that wound its way through the woods until at the point where they stood it was perhaps a hundred feet in width. Just below them the progress of the stream had been checked by what seemed at first sight a narrow bridge extending from one bank to the other. This was about three feet wide and perfectly smooth.

As Jack whispered to Dick, who was the nearest, this was made just wide enough so that the beavers in going to and fro could pass each other in comfort.

It evidently grew a great deal thicker as it approached the surface of the water and at the lowest part was probably ten or twelve feet thick. As the current was not especially strong, this served effectually to make an almost unrippled pond such as the beavers love. It was not exactly straight across but bent in slightly on the side that pointed up stream so that at the center it was decidedly curved.

This, as Jack further whispered, was to break the force of the current and shunt it off gradually to each side of the dam.

It was the same principle that in a racing automobile gives the cigar-like point to the machine so as to act as a wedge going into the wind and lessening by that much its resistance. The base of the dam was formed by young saplings and branches of trees that had been cut by the beavers’ teeth and planted as piles. Between these they had woven blades of grass and strips of bark so as to hold the branches straight and form a foundation for the mason work that was coming next. For the wise little creatures knew perfectly well the force of the current, and were determined to make a good job while they were at it. They had made mortar from the gravel and clay on the bank of the stream, using their broad, flat tails as a trowel for mixing. They must have had to travel to and fro thousands of times before they completed the work and built around their temporary outlines of plaited branches the solid wall of masonry. They knew enough also not to make it top-heavy, and so gradually sloped it from the bottom to the top, making it more compact by slapping it with their tails until at last it stood almost like a wall of granite. They watched over the dam day and night. No Hollander was ever more careful to prevent a leak in the dikes than they were to keep their dam perfectly solid. They knew that a little carelessness at the start might spoil the work of years.

While the boys were looking open-eyed at this specimen of the beavers’ work, Jack suddenly whispered, “’Sh, here they come! Now keep perfectly still, boys, and you will see something worth while.”

From one of the mound-like houses up the stream a large beaver came out, slowly looking around him with infinite caution before he left the safety of his home. He was about two feet long in addition to a flat oval tail that made his total length nearly three feet. His nose was blunt, his ears small, and his eyes wonderfully soft and intelligent. He carefully scanned the banks and the surface of the stream, and, satisfied at length, paddled slowly toward the dam. Something in its appearance must have alarmed him, for suddenly he lifted his tail and struck it several times against the side of the dam. At the sound, as though it were a signal, two or three other beavers emerged from their houses and rapidly joined him. They swam toward a point on the farther side, where the boys, now that their attention was attracted to it, could see that a little stream was trickling through and falling to the lower level of the creek beyond.

In an instant all was activity, although there was no confusion. They acted as though they were perfectly disciplined and each knew just what he had to do. Two of them swam to the farther bank, climbed up and began to tear with their sharp teeth at some slender saplings. It was astonishing to see how quickly they had gnawed their way through and how adroitly they moved to one side when it fell. These they dragged to the edge of the bank, plunged into the water, holding an end in their teeth, and swam quickly toward the threatened point. Then two or three of them got together and pushed the young branches in among the others. One of them in the meantime had taken up his position on the bank and was rapidly making mortar, doing it as skillfully as the most experienced mason, pounding the clay and mud and stones together until it reached an even consistency and at times flirting water upon it with his tail. Then gathering up as much as he could carry between his two front paws and chin and with head held well out of the water he swam to the others, just as Jack had said, using his hind feet alone. There he dropped his load and returned for another.