Adirondack Mountains

The rocks of the Adirondacks, almost without exception, are metamorphic. They have been subjected to high temperatures and pressures at depths of up to 30 km in the earth's crust. Most of the rocks in the Northwest Lowlands are metasedimentary or metavolcanic and have a complex history.  The Adirondack mountains consist primarily of metamorphic rocks, mainly gneiss, surrounding a central core of intrusive igneous rocks, most notably anorthosite, in the high peaks region. The Adirondack Lowlands contains a diverse range of meta-igneous and meta-sedimentary rocks. The oldest lithologic unit is the Lower Marble formation consisting of calc-silicates, quartzites, gneisses, and tourmalinites. The Popple Hill gneiss composed of metamorphosed mudstones, slates, sandstones, and volcanogenic sequences overlies the lower marble.