in the plain are usually red and yellow in texture. The sclerophyll woodlands are situated on a nutrient-poor alluvium deposited by the Nepean River from sandstone and shale bedrock in the Blue Mountains. Despite this, they support a tremendous regional biodiversity. Cleared and used first for agriculture and then for urban development, most of the ecological communities that originally flourished on the plain are now considered endangered. Geology Formed about 80 million years ago, the Cumberland Plain consists of not exactly flat plains; overall it is a low-lying area, largely over shale and labile sandstone, which derives its recognition largely by comparison with the surrounding uplands of harder quartzose Sydney sandstone. Relative to the surrounding higher sandstone lands, Hornsby and Blue Mountains Plateaux, it was an early matter of debate in Sydney physiographic circles as to whether the Cumberland Plain had gone down, or the surrounding plateaux had been raised up. Despite much study, especially along the western side at the Lapstone monocline, this complex matter is still not fully understood. There are volcanic rocks from low hills in the shale landscapes. Swamps and lagoons are existent on the floodplain of the Nepean River. The Wianamatta Plain, with many undulating hills of Wianamatta Group shales and sandstones, bounded by the Woronora and Illawarra Plateaus to the south, the Blue Mountains Plateau to the west and the Hornsby Plateau to the north/northeast. At the front of the Blue Mountains Plateau runs the Lapstone Structural Complex, which forms the western edge of the Cumberland Basin and Cumberland Plain. This is a north-south trending collection of reverse faults and monoclinal folds which extends generally north south for over . At the opposite side of the Cumberland Plain the Hornsby Plateau is fronted by the Hornsby Warp. That warp is topographically subtle in comparison to the Lapstone Structural Complex, and it is a feature which is poorly defined and inadequately defined in literature. The Prospect dolerite intrusion in western Sydney is the largest assemblage of igneous rock in the Plain. The oval-shaped ridge was made many millions of years ago when volcanic material from the Earth's core actuated upwards and then sideways. Slow erosion of the overlying layers of sedimentary rock by the flow of rainwater have eventually laid bare the edges of the volcanic and metamorphic rocks of the intrusion. The western suburbs lie on the relatively flat, lowly elevated parts of the