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Sydney sandstone is the common name for Sydney Basin Hawkesbury Sandstone, historically known as Yellowblock, is a sedimentary rock named after the Hawkesbury River north of Sydney, where this sandstone is particularly common. It forms the bedrock for much of the region of Sydney, Australia. Well known for its durable quality, it is the reason many Aboriginal rock carvings and drawings in the area still exist. As a highly favoured building material, especially preferred during the city's early years—from the late 1790s to the 1890s—its use, particularly in public buildings, gives the city its distinctive appearance. The stone is notable for its geological characteristics; its relationship to Sydney's vegetation and topography; the history of the quarries that worked it; and the quality of the buildings and sculptures constructed from it. This bedrock gives the city some of its 'personality' by dint of its meteorological, horticultural, aesthetic and historical impact. One author describes Sydney's sandstone as "a kind of base note, an ever-present reminder of its Georgian beginnings and more ancient past."〔Falconer 2010 p.3〕 ==Geology, vegetation, topography== (詳細はTriassic Period〔Fairley, 2000 p. 19〕 and is the caprock which controls the erosion and scarp retreat of the Illawarra escarpment. Six kilometres of sandstone and shale lie under Sydney. In Sydney sandstone, the ripple marks from the ancient river that brought the grains of sand are distinctive and easily seen, telling geologists that the sand comes from rocks formed between 500 to 700 million years ago far to the south. This means that the highest part of the visible lines almost always faces approximately south.〔Flannery, Tim, "Introduction: The sandstone city" in Flannery 1999 p8-9〕 It is a very porous stone and acts as a giant filter. It is composed of very pure silica grains and a small amount of the iron mineral siderite in varying proportions, bound with a clay matrix.〔Flannery, Tim; 'The Stone', in Deirmendjian, 2002.〕 It oxidises to the warm yellow-brown colour that is notable in the buildings which are constructed of it. The sand was washed from Broken Hill, and laid down in a bed that is about 200 metres thick. Currents washed through it, leaching out most of the minerals and leaving a very poor rock that made an insipid soil. They washed out channels in some places, while in others, the currents formed sand banks that show a characteristic current bedding or cross-bedding that can often be seen in cuttings. 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. From the beginnings of the colony in 1788, settlers and convicts had to work with the stone, using it for building and trying to grow crops on the soil over it. The sandstone had a negative effect on farming because it underlay most of the available flat land at a very shallow depth. In the late 19th century, it was thought that the sandstone might contain gold. Some efforts were made at the University to test this idea. Reporting on them in 1892, Professor Liversidge said "The Hawkesbury sandstone and Waianamatta shale was, of course, derived from older and probably gold-bearing rocks hence it was not unreasonable to expect to find gold in them." The sandstone is the basis of the nutrient-poor soils found in Sydney that developed over millennia and 'came to nurture a brilliant and immensely diverse array of plants'.〔Karskens 2010, p23〕 It is, for example, the "heartland of those most characteristic of Australian trees, the eucalypts". As plants cannot afford to lose leaves to herbivores when nutrients are scarce so they defend their foliage with toxins. In eucalypts, these toxins give the bush its distinctive smell.〔Flannery, Tim, "Introduction: The sandstone city" in Flannery 1999 p15〕 Sandstone escarpments box in the Sydney area on three sides: to the west the Blue Mountains, and to the north and south, the Hornsby and Woronora plateaux'.〔Karskens 2010 p19〕 These escarpments, avoided by the early settlers, kept Sydney in its bounds and some people still regard the spatial boundaries of the city in these terms. Other rock types found in Sydney include Narrabeen shale and the younger Wianamatta shale and Mittagong formation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sydney sandstone」の詳細全文を読む スポンサード リンク
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