Lit-par-lit gneiss is a common wallrock of the uraniferous pegmatite dikes at the Bicroft mine and nearby. It is developed mainly from pelitic gneiss, but also from amphibolite. The pelitic gneiss contains sillimanite, garnet, biotite, cordierite and quartz, and shows evidence of much shearing during and after garnet formation. The lit-par-lit gneiss consists of granitic and pelitic layers. The latter is devoid of quartz, rich in biotite, and has corundum in part pseudomorphous after sillimanite. Petrographic and chemical data suggest that this gneiss is formed by metamorphic differentiation accompanied by addition of alkalis and some calcium.