- Bunter (geology)
Bunter beds are
sandstone deposits containing rounded pebbles, such as can notably be found inWarwickshire ,Cheshire ,Staffordshire ,Nottinghamshire ,Devon andDorset inEngland . They are thought to be alluvial deposits and, judging from the rounding of the mainlyquartzite pebbles, to have resulted from prolonged transportation in a large and turbulent river, resulting in powerful abrasion. The deposits in the EnglishMidlands are thought to have been transported in this way Northwards fromBrittany ,France . This supposed river has been called the "Budleighensis", after the Devon village ofBudleigh Salterton , a site where such deposits were discovered. The depositions took place in theTriassic period. Some newer conglomerates, e.g. in Warwickshire, near Ryton are thought to have arisen from the Southward transportation of older deposits by ice flows, in theIce Age .The
pebble s, also calledcobble s, which can be used asgravel , as ballast or ascobblestone s, are mainly milky-white quartzite but can vary in colour and composition, including some that are hard, reddish-coloured sandstone. The sandstone in which these pebbles are deposited can be used for building or as an aggregate forcement orconcrete .The name "Bunter" derives from the German term "Buntsandstein", "bunt" meaning "variegated", referring to the colour of the sandstone deposit, which varies from reddish to greenish. This sandstone is widespread across central Europe, notably the
Black Forest andOdenwald inGermany .The sandstone can be hard enough for building, yet easy enough to "work", resulting in
bridge s,castle s,cathedral s and churches constructed of reddish sandstone, throughout the relevant areas ofEurope (e.g. Germany,Luxembourg ,Switzerland ,Alsace inFrance ,Denmark ,Poland ).The land under which these beds lie is generally very well drained, creating heathlike conditions. Because of the drainage, the soil tends to be of low fertility. A notable area in Britain, which has these characteristics, is
Cannock Chase , a designatedArea of Outstanding Natural Beauty (AONB).The long
shingle tombolo ofChesil Beach in Dorset and the raised beach of Portland, Dorset are partly composed of Bunter pebbles. As yet, no fully satisfactory and universally accepted geological explanation has been formulated to explain their precise origin and mode of transport, as each proposed theory has its difficulties.
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