Coarse- to fine-grained gneiss and quartzite; well-foliated and banded to massive; locally cataclastic; ranges from pelitic schist that contains abundant sillimanite to gneisses of probable igneous origin. All rocks are well foliated, and dominant foliation is folded. Protolith may include both Paleozoic and Precambrian sedimentary and igneous rocks (Weber and others, 1978). Unit is widespread throughout out the Yukon-Tanana Upland and the included meta-plutonic rocks may be equivalent to the Pelly Gneiss in Yukon, Canada. Also includes gray, medium-grained, mylonitic, quartzofeldspathic biotite-sillimanite gneiss that forms core of a gneiss dome in the central Big Delta quadrangle (Dusel-Bacon and Foster, 1983). Several U/Pb zircon ages have been determined on this unit, and Mississippian to Devonian crystallization ages are common for the metaigneous rocks within this unit and within unit |ymi (Aleinikoff and Nokleberg, 1985; Aleinikoff and others, 1986). Day and others (2003), Dusel-Bacon and Williams (2009), Aleinikoff and Nokleberg (1985) all indicate that inheritance of zircon grains is common. Detrital zircon analyses by Aleinikoff and others (1984, 1986) and Dusel-Bacon and Williams (2009) from quartzite in the unit yielded Proterozoic and Archean zircons