There are others besides fishermen to whom the frozen surface of Otsego Lake offers the means of pleasure and occupation. In some seasons the freezing of the lake occurs within a few hours, after a great and sudden fall in temperature, during a night of calm and intense cold. At such times, before snow has fallen upon the surface, the lake presents a scene of splendor. The ice is quite transparent, and has the effect of a great sheet of glass spread out amid the hills. This offers a perfect surface for skating, and attracts not only the boys and girls of the village, but a large number of their elders. The lake grows lively with the gracefully gliding promenade of skaters, with here and there a group playing at hockey, while others disport themselves at "crack the whip." The friction of so many gliding feet imparts to the frozen surface a low and weirdly humming sound, and the droning note is echoed by the hills, until the valley resounds with monotonous music. There are times when the lake is so well frozen that skaters traverse the entire length. In some seasons ice-boats have been used, slanting from end to end of the lake with prodigious speed. As the winter advances and the ice grows stronger, driving upon the lake becomes common, and horse-races upon the ice have sometimes been included among the winter sports. At about five miles above the foot of the lake, and extending across it from shore to shore, a large fissure in the ice usually appears during the winter. This fissure is sometimes so wide that a team cannot cross it, and many years ago a span of horses was accidentally driven into it. The crevice in the ice has caused much speculation. The lake is narrow at the place where the crack appears, and the fissure is supposed to be created by expansion from the north and from the south, causing the ice to rise several feet in gable-like form until the ridge cracks, for fragments of ice are found on each side of the crevice.[125] The tremendous forces exerted by the expansion of the freezing lake cry aloud on still winter nights, whenever, after a period of thawing weather, the mercury suddenly drops to a point far below zero. On such nights, while the trees of the surrounding forest here and there begin to be so penetrated with the fierce cold that they crack like rifle-shots, the ice-bound lake sets up an unearthly groaning, and the cavernous sound of its bellowing echoes dismally over the sleeping village, like the trumpetings of some huge leviathan in agony. Cooperstown has a winter harvest-time, in January or February, when ice is cut from the lake for the summer supply. This industry occupies a large force of men, with plows, saws, hooks, crowbars, horses and bob-sleds, for several weeks. The ice taken from Otsego Lake, from ten to twenty inches thick, according to the severity of the winter, is always pure as mountain dew, and clear as crystal.