Granite, gabbro, and an intervening hornfels occur in the Carrock Fell area, northwestern England. The gabbro and hornfels have been thermally metamorphosed by the granite, and all three have been hydrothermally altered by quartz veins. Complete alteration is found only within a few feet of the vein contacts, but in each type of rock the end product is essentially the same, a quartz-muscovite greisenlike rock carrying pyrite and arsenopyrite. Tourmaline and fluorite are practically absent. It is concluded that the alteration has not gone to completion. It is also noted that activity indicative of high temperature is noticeably absent.