Biotite schist and gneiss
Gneiss, schist & quartzite. Paleoproterozoic, about 2,500 to 1,600 million years old. 1 crag on this site has its map point on it.
What the map says
Conspicuously banded rock marked by alternating layers of contrasting composition that probably reflect original sedimentary layering, as well as effects of metamorphic segregation and partial melting. This unit is typical of the highest grade metamorphic terranes, where coarse sillimanite is common and partial-melt textures are widespread. Dark-gray to black, medium- to coarse-grained layers are rich in biotite, sillimanite, and magnetite, and locally contain high-grade cordierite and (or) garnet (Gable and Sims, 1969; Cole, 1977, 2004b). Irregular quartzofeldspathic layers, bordered by selvages rich in biotite, sillimanite, and oxide minerals, formed in place in the rock during partial melting at the peak of metamorphism. Unit is subdivided as follows in areas of more detailed mapping and (or) better exposure (Cole, 1977; Braddock and Cole, 1990) Lithology: schist, gneiss.
1:100,000 sheet: Workman and others, 2018, U.S. Geological Survey Scientific Investigations Map 3399 (1 crag). A contact line at that scale is about 100 m wide on the ground.
Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.