When geologists study rocks, they usually try to recognize similar kinds of rocks in different places, in order to relate the history of one place to that of another. A layer of relatively homogenous rock that can be recognized across a reasonable distance (for example, 10-20 miles) may be called a formation. Formations are sometimes gathered into groups or subdivided into members. Formations, groups and members are usually given names that relate to the places where they are best exposed.

Stone steps wind a path up the gorge at Enfield Glen in Treman State Park.