While some of the old grist mills still perform their time-honored task to the music of purling mill streams, the vast majority have vanished, or stand as crumbling landmarks of another generation. Yet in their day they were indispensable to life and labor. The memory of them will always be as green as the moss that clung to the dripping paddles of the great water wheels. [Illustration: When the mill was not in operation, the water was deflected from the water wheel, as shown in this view of a mill near Bristol, Tenn.] The Covered Bridge [Illustration: For many years the covered bridge was a familiar part of the country scene in America. This bridge still stands in the White Mountains, New Hampshire, with Mt. Liberty in the background. Photo by Winston Pote from A. Devaney, Inc., New York.] Like many other supplanted or vanishing features of early American life, the covered bridge is enshrined in song, legend and story. It has been a prize subject for etchers and painters. Innumerable post cards bearing the picture of some famous bridge crowd the mail pouches, especially in the New England States. Just as the railroad sounded the doom of the Conestoga wagon, the Concord coach and the narrow inland canal, so did the automobile end the larger era of the covered bridge. The motorist wanted a steel, iron or concrete ground-hold for his car when he dashed across a river. Although the old bridges were built for good, solid wear, and sometimes a lot of tear as well, they could not stand up against the speedster. They were built for slow traffic. In the old days, teams were obliged to proceed at a walk, under penalty of a fine ranging from $2.00 to $5.00. The motor car, however, had stout allies in bridge destruction in fire, flood, and changes in highway routes. Many of the oldest and best known of the covered bridges were destroyed by fire or high water. Although the covered bridge, as we know it, is distinctly an American institution, it did not originate in this country. There is a record of a roofed bridge built over the Euphrates in Babylon in 783 B.C. The Tiber at Rome was crossed by several covered bridges. The best known structure of this type in Europe is across an arm of Lake Lucerne in Switzerland. It has a steep, arched roof, is built entirely of timber, and is used only by pedestrians.