Sill

In geology, a sill is a sheet like body of intruded rock that has forced its way between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the foliation of metamorphic rock. A sill is a concordant intrusion, meaning it does not cut across the existing rock layers, unlike a dike, which is discordant and does cut across them. Where sills stack on top of each other under high magma flux they can build up into a sill complex feeding a large magma chamber.