There are times when the dam has sprung a leak and must be repaired on the inside beneath the ice. Early thaws and spring freshets sometimes wreck a dam beyond repair, or do extensive damage to the house or dam at the time when beaver enemies are likely to be at their leanest. The house and dam are sometimes ruined when the streams are so low and icy that it is not safe for beaver to go about. I know of two colonies that were crushed out of existence by snow-slides. The dam is on rare occasions broken by late spring ice-jams. Sometimes the ice-cakes pile up on the dam and raise the water in the pond to such a height that it rises in the house and drives the beaver forth. A few beaver houses that are situated in places where the ice or spring floods may raise the water much above normal level are shaped to meet this trouble. The house is built higher and the room internally is twice the usual height. Thus there is space for the beaver to build a "platform bed" on the floor and thus raise themselves a foot or more above the common level. Despite all pains, floods sometimes drive beaver to the housetops. By laying up supplies, and by the help of artificial pond, canal, and house, the beaver is able to spend his winter without hunger and with comfort and far greater safety than his neighbors. The winds may blow and blinding snow or flying limbs may endanger those outside; snow may bury the forage of bird and deer, and make the movement of beasts of prey slow and difficult; the cold may freeze and freeze and strew the wilds with lean and frozen forms; but the beaver beneath ice and snow shelter serenely spends the days with comfort and safety. The winter, with its days long or short, never comes to an end, however, quite early enough to suit the beaver. They emerge from the pond at the earliest moment that frozen conditions will allow. If their subway is choked with ice, and food becomes exhausted, they will sometimes bore holes through the base of the dam. Apparently, too, holes of this kind are bored through, or a section cut through the dam to the bottom, for the purpose of completely draining the pond. As this appears to be most often done with ponds that are full of stagnant water, or water almost stagnant, this draining may be a part of the beaver's sanitary work,--done for the purpose of getting filth and stale water out and also that the sour bottom may be sterilized by sun and wind. Conditions determine the length of time before the dam is repaired and the pond refilled. In some cases this is done after the lapse of a few weeks and in others not until autumn. Ponds that have large pure streams running through them do not need this emptying, but occasionally they accidentally have it. Most beaver colonies are deserted in summer, and fall thus into temporary decline.