High Quality Content by WIKIPEDIA articles! A layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions typically are many kilometers in area covering from around 100 km2 to over 50,000 km2 and several hundred meters to over a kilometer in thickness. While most are Archean to Proterozoic in age (for example, the Paleoproterozoic Bushveld complex) they may be any age such as the Cenozoic Skaergaard intrusion of east Greenland. Although most are ultramafic to mafic in composition, the Ilimaussaq complex of Greenland is an alkalic intrusion.