Vermont is a land of compression and sutures as well as marble and slate. (more below)
Created by Andrew Alden from the U.S. Geological Survey's Geologic Map of the United States, 1974, by Philip King and Helen Beikman (fair use policy)
Click the map for a larger version
Vermont's geologic structure parallels the Appalachian chain, which runs from Alabama to Newfoundland. Its oldest rocks, of Precambrian age (brown), are in the Green Mountains. To its west, starting with the orange band of Cambrian rocks, is a belt of sedimentary rocks that formed near shore on the western shore of the ancient Iapetus Ocean. In the southwest is a large sheet of rocks that were thrusted over this belt from the east during the Taconian orogeny some 450 million years ago, when an island arc arrived from the east.
The thin purple strip running up the center of Vermont marks the boundary between two terranes or microplates, a former subduction zone. The body of rocks to the east formed on a separate continent across the Iapetus Ocean, which closed for good during the Devonian about 400 million years ago.
Vermont produces granite, marble and slate from these various rocks as well as talc and soapstone from its metamorphosed lavas. The quality of its stone makes Vermont a producer of dimension stone out of proportion to its size.
More about Vermont Geology
More Vermont resources on About.com:
Vermont Geography, State Symbols & Facts
Vermont National Parks
Vermont State Parks, Winter
Vermont State Parks, Spring
Fall Foliage Camping
Vermont Attractions and Sightseeing