Ridge Hill Shelf
Encyclopedia
The Ridge Hill Shelf is a landform that forms part of the foothills of the Darling Scarp
, a low escarpment that runs parallel with the west coast in southwest Western Australia
. It was formed by coastal erosion of the scarp in the Pleistocene
, when the sea level was higher, and the scarp located further west than at present. The action of coastal forces produced sand dunes that subsequently lithified into eolianite
, and eroded the ironstone
of the scarp, resulting in an iron-rich sandstone with a laterite
cap. The iron gives the sandstone a dull purple-brown colour; depending on the extent of iron-enrichment, the sandstone may appear predominantly yellow, predominantly purple-brown, or a mottled combination of the two.
The shelf is about 250 feet (76.2 m) high on average, and is therefore well-drained. It is largely vegetation by a forest of Eucalyptus marginata (Jarrah) and Corymbia calophylla
(Marri), with an understorey of Banksia
, Casuarina fraseriana and Xylomelum occidentale
(Woody Pear).
Some publications identify the Ridge Hill Shelf with the foothills of the scarp, but this is incorrect. The foothills are about 15 kilometres wide, and largely continuous, whereas the Ridge Hill Shelf is no more than 3 kilometres wide and highly discontinuous.
Darling Scarp
The Darling Scarp, also referred to as the Darling Range or Darling Ranges, is a low escarpment running north-south to the east of the Swan Coastal Plain and Perth, Western Australia...
, a low escarpment that runs parallel with the west coast in southwest Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. It was formed by coastal erosion of the scarp in the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, when the sea level was higher, and the scarp located further west than at present. The action of coastal forces produced sand dunes that subsequently lithified into eolianite
Eolianite
Eolianite or aeolianite is any rock formed by the lithification of sediment deposited by aeolian processes; that is, the wind. In common use, however, the term refers specifically to the most common form of eolianite: coastal limestone consisting of carbonate sediment of shallow marine biogenic...
, and eroded the ironstone
Ironstone
Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical repacement, that contains a substantial proportion of an iron compound from which iron either can be or once was smelted commercially. This term is customarily restricted to hard coarsely...
of the scarp, resulting in an iron-rich sandstone with a laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
cap. The iron gives the sandstone a dull purple-brown colour; depending on the extent of iron-enrichment, the sandstone may appear predominantly yellow, predominantly purple-brown, or a mottled combination of the two.
The shelf is about 250 feet (76.2 m) high on average, and is therefore well-drained. It is largely vegetation by a forest of Eucalyptus marginata (Jarrah) and Corymbia calophylla
Corymbia calophylla
Corymbia calophylla is a bloodwood native to Western Australia. Common names include Marri and Port Gregory Gum, and a long standing usage has been Red Gum due to the red gum effusions often found on trunks.It is distinctive among bloodwoods for its very large buds and fruit Corymbia calophylla...
(Marri), with an understorey of Banksia
Banksia
Banksia is a genus of around 170 species in the plant family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes and fruiting "cones" and heads. When it comes to size, banksias range from prostrate woody shrubs to trees up...
, Casuarina fraseriana and Xylomelum occidentale
Xylomelum occidentale
Xylomelum occidentale, commonly known as the western woody pear, is a tree species in the family Proteaceae. It is endemic to Western Australia. It was first described by Robert Brown in 1830. The species name is derived from the Latin adjective occidentalis "western"....
(Woody Pear).
Some publications identify the Ridge Hill Shelf with the foothills of the scarp, but this is incorrect. The foothills are about 15 kilometres wide, and largely continuous, whereas the Ridge Hill Shelf is no more than 3 kilometres wide and highly discontinuous.