original meaning, and are often quaint or endearing descriptions (e.g. 'Paradise'). History Physical history The island was adjoined to the mainland of Australia until the end of the last glacial period about 11,700 years ago. Much of the island is composed of Jurassic dolerite intrusions (the upwelling of magma) through other rock types, sometimes forming large columnar joints. Tasmania has the world's largest areas of dolerite, with many distinctive mountains and cliffs formed from this rock type. The central plateau and the southeast portions of the island are mostly dolerites. Mount Wellington above Hobart is a good example, showing distinct columns known as the Organ Pipes. In the southern midlands as far south as Hobart, the dolerite is underlaid by sandstone and similar sedimentary stones. In the southwest, Precambrian quartzites were formed from very ancient sea sediments and form strikingly sharp ridges and ranges, such as Federation Peak or Frenchmans Cap. In the northeast and east, continental granites can be seen, such as at Freycinet, similar to coastal granites on mainland Australia. In the northwest and west, mineral-rich volcanic rock can be seen at Mount Read near Rosebery, or at Mount Lyell near Queenstown. Also present in the south and northwest is limestone with caves. The quartzite and dolerite areas in the higher mountains show evidence of glaciation, and much of Australia's glaciated landscape is found on the Central Plateau and the Southwest. Cradle Mountain, another dolerite peak, for example, was a nunatak. The combination of these different rock types contributes to scenery which is distinct from any other region of the world. In the far southwest corner of the state, the geology is almost wholly quartzite, which gives the mountains the false impression of having snow-capped peaks year round. Aboriginal people Evidence indicates the presence of Aboriginal people in Tasmania about 42,000 years ago. Rising sea levels cut Tasmania off from mainland Australia about 10,000 years ago and by the time of European contact, the Aboriginal people in Tasmania had nine major nations or ethnic groups. At the time of the British occupation and colonisation in 1803, the indigenous population was estimated at between 3,000 and 10,000. Historian Lyndall Ryan's analysis of population studies led her to conclude that there were about 7,000 spread throughout the island's nine nations; Nicholas Clements, citing research by N.J.B. Plomley and Rhys Jones, settled on a figure of 3,000 to 4,000. They engaged