Figure 6.22a. Tobacco Root Mountains, Montana, USA. Metamorphosed mafic dikes and sills (MMDS) that have intruded quartzofeldspathic gneisses of the Pony–Middle Mountain Metamorphic Suite are visible as nearly horizontal bands in a cliff face in the central Tobacco Root Mountains. The middle of the three prominent MMDS in the photo thins dramatically, as if caught in the act of intrusion, even though the MMDS are now garnet amphibolites. Zoom and pan with your mouse are enabled. John Brady photo.