Sill (geology)

In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock. A sill is a concordant intrusive sheet, meaning that it does not cut across preexisting rock beds. Stacking of sills builds a sill complex^[1] and a large magma chamber at high magma flux.^[2] In contrast, a dike is a discordant intrusive sheet, which does cut across older rocks.