Adirondack Rocks

The Adirondack Mountains are part of an ancient belt of rocks which were formed over a billion years ago. Hard to imagine, yet evidenced by the known creation and accumulation of the various types of rock found in the area.

Originally, the rocks of the southeastern Adirondacks were primarily sedimentary rocks layered with volcanic rock, and the oldest recognized rocks are within a group of inter-layered sandstones, limestones, shales, and volcanics. It is known that the major continents were once mostly covered by the shallow seas, and this area of ancient rocks is no exception. It is believed that the waters were clear, shallow, and warm, not unlike that of the Caribbean, for the next rocks to be deposited were limestones which were free of the sand and silt common to dirty waters occurring during land erosion. Limestones are formed in only 2 ways; either by the chemical precipitation of calcium carbonate from warm sea water, or by the accumulation of shell material from marine organisms.

On top of the limestone are formed shales and siltstones which are up to 1200 feet thick. The layered rocks found above these are believed to be accumulations of airborne volcanic ash and dust. Next is a varied group of sedimentary rocks, many of which contain large quantities of garnet, sillimanite and graphite. Above this group is the relatively thick marble which contains thin beds of quartzite.

It is important to remember in exploring the Adirondacks, that the rocks have undergone constant change over a billion years, and continue to be subject to the forces of nature. The rocks seen today will no doubt be very different in years to come.