Subvolcanic rocks include diabase (also known as dolerite) and porphyry. Around Launceston, igneous rocks were intruded into Cainozoic sediments forming dolerite and monzonite. The breccia matrix is mud, and the stones consist of basalt, dolerite, and gabbro. They are formed of trachyte, dolerite and basalt. Igneous intrusions of dolerite, felsite, lamprophyre and diorite of Palaeozoic age are encountered in places. Gneisses, volcanics and metasediments are intruded by granites, granodiorites and a suite of dolerite dykes. In the batholiths there are quartz-feldspar porphyry and dolerite dykes. The pebbles are mostly quartzite, but include dolerite and agate. Karoo Koppies hills are capped by hard, erosion-resistant dolerite sills. The material is predominantly coarse grained picrite with olivine-dolerite and dolerite. There was a wide volcanic dyke made of dolerite, two metres tall from the Jurassic. Sediments are up to 500 meters thick, with the lowest layers consisting of dolerite boulders. Many dolerite dykes also have been reported from this area. The rock, known as dolerite, used to be quarried and used for road construction. There is also an area of dolerite intrusions.