- People & Economy
- Nature & Environment
- Heritage & Recreation
- Issues in the Basin
Over 500 million years ago, long before the present day Atlantic, the shoreline and tropical waters of the Iapetus Ocean, once existed in what is now the Champlain Basin. Evidence for this ancient ocean includes sedimentary rocks such as sandstone and limestone, and marine fossils, such as the Chazy Reef in Isle La Motte, Vermont, the world’s oldest known reef to contain coral.
Over 400 million years ago the tectonic plates shifted the Iapetus Ocean closed. The sedimentary rocks of the shoreline and continental shelf were folded and faulted to form the Green Mountains, part of the Appalachian Mountain chain. The great stresses of mountain building altered the older sedimentary rocks by heat and pressure into metamorphic rocks such as schist, marble and slate. The huge compressive stresses of mountain building also caused portions of the earth’s crust to break and move as large fault blocks. The sedimentary rocks of western Vermont and the Taconic Mountains are examples of these large fault blocks, where younger rocks have been pushed up and over metamorphosed continental shelf rocks beneath.
The Adirondack Mountains are a unique dome formation, which started to emerge approximately 150 million years ago. As the dome rose over time, successively older rock layers were eroded away, exposing on today’s surface rocks that formed deep within the crust more than one billion years ago. One of the predominant rock types is anorthosite, an unusual rock on earth’s crust but which is found on the Moon. Recent surveys suggest that the Adirondacks may still be rising faster than the rate of erosion.