Hardness, in this context, is a complex articulation of several factors, essentially a measure of how resistant rock is to various kinds of permanent shape change when a compressive force is applied to it.
42.
The escarpment and screes are made up of hard wearing Borrowdale Volcanics rock, however there are areas of less resistant rock which have been eroded and this has led to deep gullies in the cliff face.
43.
The very resistant rocks of the Lower Greensand, in particular the Hythe Beds, have produced prominent escarpments that form an arc around the northern edge of the Low Weald, running parallel to and just south of the chalk escarpment of the North Downs.
44.
The national park preserves rainforest and eucalypt forests in the cliff-lined headwaters of rivers and creeks flowing to the Gold Coast, in particular the Nerang River on the plateau's west and Little Nerang River to the east, both of which have eroded away less resistant rock.
