Skirting the hither side of the pond to near its head, he crossed the little meadow and the canal, and reached the brook again about fifty yards beyond. Here he found it flowing swift and narrow, over a rocky bottom, between high banks; and this was its character for nearly half a mile, as he judged. Then, emerging once more upon lower ground, he came upon a small dam. This structure was not much over eighteen inches in height, and the pond above it, small and shallow, showed no signs of being occupied. There was no beaver house to be seen, either in the water or on shore; and the water did not seem to be anywhere more than a foot and a half in depth. As he puzzled over this--for he did not think the beavers were likely to build a dam for nothing--he observed a second and much larger dam far away across the head of the pond.
Hastening to investigate this upper dam, he found it fully three feet high, and very massive. Above it was a narrow but deep pond, between comparatively steep shores; and along these shores he counted three low-roofed houses. Out in the middle of the pond there was not one dwelling; and he came presently to the conclusion that here, between the narrow banks, the current would be heavy in time of freshet. The lower dam, pretty obviously, was intended to reinforce the upper, by backing a foot and a half of water against it and taking off just that much of the pressure. He decided that the reason for locating the three houses along the shore was that the steep bank afforded special facilities for shore burrows.
The explorer's fever being now hot upon him, the Boy could not stay to examine this pond minutely. He pressed on up-stream with breathless eagerness, thrilling with expectation of what the next turn might reveal. As a matter of fact, the next turn revealed nothing--nor the next, nor yet the next. But as the stream was full of turns in this portion of its course, that was not greatly discouraging.
About a quarter of a mile, however, above the head of the narrow pond, the ardent explorer came upon a level of sparse alder swamp. Here he found the stream just beginning to spread over its low banks. The cause of this spreading was a partial obstruction in mid-channel--what looked, at first glance, like an accidental accumulation of brush and stones and mud. A second look, however, and his heart jumped with excitement and delight. Here was the beginning of a new pond, here were the foundations of a new dam. He would be able to see what few indeed of the students of the wilderness had had the opportunity to watch--the actual process by which these wilderness engineers achieved their great work.