Millions of years ago, clays that accumulated on the ocean floor compressed into shale. When the ocean floor uplifted to form the Taconic Mountains, heat and pressure metamorphosed the shale into much harder slate. Lake Bomoseen nestles in a valley surrounded by some of the lower hills on the western side of the range. The Taconics are the slate-producing region of Vermont, and the area's history parallels the rise and fall of Vermont's slate industry.