approaches the Hornsby Plateau. The grassy woodlands contain eucalyptus trees which are usually in open woodlands that have sclerophyllous shrubs and sparse grass in the understory, reminiscent of Mediterranean forests. It has been calculated that around 98,000 hectares of native vegetation remains in the Sydney metropolitan area, about half of what is likely to have been existing at the time of European arrival. The endemic flora is home to a variety of bird, insect, reptile and mammal species, which are conspicuous in urban areas. Introduced birds such as the house sparrow, common myna and feral pigeon are ubiquitous in the CBD areas of Sydney. Possums, bandicoots, rabbits, feral cats, lizards, snakes and frogs may also be present in the urban environment, albeit seldom in city centres. Geology The Sydney area lies on Triassic shales and sandstones with low rolling hills and wide valleys in a rain shadow area. Sydney sprawls over two major regions: the Cumberland Plain, a relatively flat region lying to the west of Sydney Harbour, and the Hornsby Plateau, a plateau north of the Harbour rising to 200 metres and dissected by steep valleys. Sydney's native plant species are predominantly eucalyptus trees, and its soils are usually red and yellow in texture. At a time in the past, monocline formed to the west of Sydney. The monocline is a sloping bend that raises the sandstone well above where it is expected to be seen, and this is why the whole of the visible top of the Blue Mountains is made of sandstone. Sandstone slopes in the Sydney area are on three sides: to the west the Blue Mountains, and to the north and south, the Hornsby and Woronora plateau. The centre of the Sydney basin is located beneath Fairfield. Bringelly Shale and Minchinbury Sandstone are often seen in the greater western parts of Sydney, which are part of the Wianamatta Shale group. The Prospect dolerite intrusion in Pemulwuy is the largest assemblage of igneous rock in Sydney. The oval-shaped ridge was made many millions of years ago when volcanic material from the Earth's upper mantle moved upwards and then sideways. Swamps and lagoons are existent on the floodplain of the Nepean River, one being Bents Basin, which is also a recreational area. Parramatta River drains a large area of Sydney's western suburbs. With 5,005,400 inhabitants (as of 2016) and an urban population density of 2037 people per