An intrusion of igneous rock which spreads along bedding planes in a nearly horizontal sheet. Sills are mostly concave, and can be fed from dykes, or the steep climbing portions of deeper sills. Both sills and dykes can provide magma to overlying volcanic fissures, and sills can feed shallow laccoliths (Thomson (2006) Bull. Volc. 66, 4).
Subjects: Earth Sciences and Geography.