Intrusion 1 : A body of igneous rock that invades older rock. The invading rock may be a plastic solid or magma that pushes its way into the older rock
National Park Service, U.S. Department of the Interior, Geologic Resources Division, Natural Resource Program Center, Wolf Trap National Park for the Performing Arts, Geologic Resource Evaluation Report, Natural Resource Report NPS/NRPC/GRD/NRR 2008/041, Technical Geologic Terms, Denver, Colorado, USA 2008. http://www.nature.nps.gov/geology/inventory/public ations/reports/wotr_gre_rpt_view.pdf, (ND/ Lndsld - Amer) {923}